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DT Tech Cam Test - IQ250 vs IQ260 vs IQ280
- Thread starter dougpeterson
- Start date
dougpeterson
Workshop Member
Torger, you're "discovering" an issue that has been previously discussed on this forum and is even mentioned in the test article I wrote that this thread is about: color fidelity suffers with large movements. This is not new - it was first meaningful with the Aptus II 12 about four years ago and came to broad prominence with the IQ180 when users noticed they could get color casts so severe you couldn't restore high fidelity color.
I'm not being defensive. We both agree that loss of color fidelity occurs at some point in the movement range and that it occurs earlier in the image circle than with a 260. I'm just saying I've thoroughly evaluated the images and I don't share your pessimism about how early it occurs.
This was designed to be a worst case scenario full of bright vivid colors which would show the real world impact of any loss of color fidelity. And to my eye they show that the 250, combined with Rodenstock lenses allow a good amount of movement before quality suffers. Less than the 260 for sure, but more than enough to make a 250 a compelling option to consider for a tech camera user. Obviously anyone considering such a system should do their own testing and look out for color fidelity (which is mentioned in my article) as well as light falloff, artifacts, and noise.
I'm not being defensive. We both agree that loss of color fidelity occurs at some point in the movement range and that it occurs earlier in the image circle than with a 260. I'm just saying I've thoroughly evaluated the images and I don't share your pessimism about how early it occurs.
This was designed to be a worst case scenario full of bright vivid colors which would show the real world impact of any loss of color fidelity. And to my eye they show that the 250, combined with Rodenstock lenses allow a good amount of movement before quality suffers. Less than the 260 for sure, but more than enough to make a 250 a compelling option to consider for a tech camera user. Obviously anyone considering such a system should do their own testing and look out for color fidelity (which is mentioned in my article) as well as light falloff, artifacts, and noise.
Yes I've known about those color fidelity issues, but I thought this was mainly a dynamic range issue, ie too much signal loss so you can't recover properly. This can also happen, but the IQ250 loses no more than 4 stops of its large dynamic range towards the edge, and that's without center filter. The IQ180 had some micro lens issues too if I remember correctly.
As far as I can recall the term "pixel crosstalk" or "color crosstalk" was never used so the model I had in my head, and I guess most others too, is that it was all about color casts not becoming too extreme. Color crosstalk is not a difficult term to explain to a layman, it's actually simpler to understand and show in one picture than why color cast occurs. So I find it remarkable that color crosstalk term is not used if dealers have been aware about it for so long. Especially since it's a different phenomenom from color cast and it cannot be corrected with LCC.
With this sensor we (probably) start to get crosstalk before we've lost even as much as a stop in vignetting and maybe as little as 5mm shift. It's a different mix than before. In other words, the picture looks perfectly okay in terms of sharpness and structure and the LCC shot may look kind of fine, but colors are not right. Knowing that the color channels become mixed makes you look upon the problem in a different way.
Again, I think it would not be too much to require from a seller of at $35k back to inform potential customers that this sensor is designed with a critical crosstalk angle X, and these XYZ lenses fit this design criteria, these XYZ do not to the IC edge but you can use it up to X mm, and if color fidelity can be compromised you can stretch it a bit more -- but then you are on your own.
Maybe the P30+ had similar properties, I don't know, but noone really suggested that it would be used with wide angle tech cam lenses. Now there is suggestion that the IQ250 can work, and then I think one can expect a bit better information about this issue. I don't think it's fair to push the testing to the customer, the customer may not be an expert on color fidelity issues, may not even have the best color eyesight, but still want to be able to produce accurate colors from the camera system.
A gradual increase in noise (caused by corrected color cast) is quite easy to evaluate and find if it's acceptable or not. But a gradual decrease in color accuracy and saturation (caused by crosstalk) is much harder. Therefore I would like to have support from proper targeted tests/measurements concerning those aspects. Maybe I'm alone on that, I don't know, but crosstalk do worry me more than color cast.
As far as I can recall the term "pixel crosstalk" or "color crosstalk" was never used so the model I had in my head, and I guess most others too, is that it was all about color casts not becoming too extreme. Color crosstalk is not a difficult term to explain to a layman, it's actually simpler to understand and show in one picture than why color cast occurs. So I find it remarkable that color crosstalk term is not used if dealers have been aware about it for so long. Especially since it's a different phenomenom from color cast and it cannot be corrected with LCC.
With this sensor we (probably) start to get crosstalk before we've lost even as much as a stop in vignetting and maybe as little as 5mm shift. It's a different mix than before. In other words, the picture looks perfectly okay in terms of sharpness and structure and the LCC shot may look kind of fine, but colors are not right. Knowing that the color channels become mixed makes you look upon the problem in a different way.
Again, I think it would not be too much to require from a seller of at $35k back to inform potential customers that this sensor is designed with a critical crosstalk angle X, and these XYZ lenses fit this design criteria, these XYZ do not to the IC edge but you can use it up to X mm, and if color fidelity can be compromised you can stretch it a bit more -- but then you are on your own.
Maybe the P30+ had similar properties, I don't know, but noone really suggested that it would be used with wide angle tech cam lenses. Now there is suggestion that the IQ250 can work, and then I think one can expect a bit better information about this issue. I don't think it's fair to push the testing to the customer, the customer may not be an expert on color fidelity issues, may not even have the best color eyesight, but still want to be able to produce accurate colors from the camera system.
A gradual increase in noise (caused by corrected color cast) is quite easy to evaluate and find if it's acceptable or not. But a gradual decrease in color accuracy and saturation (caused by crosstalk) is much harder. Therefore I would like to have support from proper targeted tests/measurements concerning those aspects. Maybe I'm alone on that, I don't know, but crosstalk do worry me more than color cast.
Notwithstanding the fact that I've been pretty impressed with many aspects of what I've seen so far of the 250, I do think it's worth highlighting the (sure, maybe it's obvious) point re the bolded bit (if it is to be taken verbatim).
If you're looking to shift to get the top of something in shot (very typical in architectural shots of course), there's a double whammy with the 250.
You need to shift more than the 260 because of the cropped sensor, and you can't shift as much as you can with the 260.
dougpeterson
Workshop Member
I was actually meaning to refer to final-subject position. If I wanted to be more generous to the 250 (and be more marketing oriented) I could talk about maximum allowed rise/fall, but as you point out this would be a bit disingenuous as the 250 has to be risen several mm before it's seeing what a 260 would see with no rise. But yes, someone interested in choosing between the two backs for tech cam use will definitely want to download the composite test files which clearly show how far each back can go into a specific area of the subject with a given lens and how much rise/shift that translates to.
I've looked a bit more on the files, and I've become even more sure that the green channel separation is a crosstalk indicator.
If you have the sensor in horizontal orientation and shift left, you don't get the same separation of greens. Why? Probably because the sensor has some horizontal wiring between pixel row pairs which photons hit instead of crossing over to the next pixel. If we shift left though this wiring does not become a barrier and we get a more evenly distributed crosstalk, but we still have it of course. Due to this phenomenom you will probably get a slightly different color result depedning on which orientation you have the sensor, and you'll more likely to see demosaicing mazing artifacts if you shift up the sensor horizontally rather than vertically.
When raw analyzing the LCC shots of the IQ260 from the 32HR there's no significant separation of greens anywere in the image, from which I assume that there's no crosstalk and thus likely that the whole image surface has proper color reproduction, which also seems reasonable as the Digaron-W 32 was designed when 6um CCD sensors existed on the market.
If you have the sensor in horizontal orientation and shift left, you don't get the same separation of greens. Why? Probably because the sensor has some horizontal wiring between pixel row pairs which photons hit instead of crossing over to the next pixel. If we shift left though this wiring does not become a barrier and we get a more evenly distributed crosstalk, but we still have it of course. Due to this phenomenom you will probably get a slightly different color result depedning on which orientation you have the sensor, and you'll more likely to see demosaicing mazing artifacts if you shift up the sensor horizontally rather than vertically.
When raw analyzing the LCC shots of the IQ260 from the 32HR there's no significant separation of greens anywere in the image, from which I assume that there's no crosstalk and thus likely that the whole image surface has proper color reproduction, which also seems reasonable as the Digaron-W 32 was designed when 6um CCD sensors existed on the market.
Oh, while out running I figured out the mystery why the green separation is different on the LCC shot compared to the main image. This is because it's a directional crosstalk phenomenom.
For exampe we may have leaks from blue to green and green to red, but not as much from green to blue and red to green, depending on the direction of the shift and orientation of the sensor. This means that a particular shift and sensor orientation will have a particular crosstalk, and that crosstalk will cause larger effect for some colors and smaller for others.
The LCC shot is made with some light source diffused through a white card, which will lead to one particular crosstalk distribution which is different from if the sensor sees say a clear blue color in the same position.
Maybe my explanation is not too easy to follow, but anyway the result is that depending on shift and orientation of the sensor the color fidelity will be affected in different ways. If you're lucky the scene you're shooting won't contain the colors that are affected the most.
Due to the complexity of the effects of crosstalk, ie that you can get different results depending on scene content and composition, it's not wise to draw conclusions that "it's good enough" from one test. The right way is of course to not use the sensor with shifts that introduce crosstalk.
I only need to look at LCC raw files to make a good estimate where crosstalk begins (which is where greens start to separate), and for the IQ250 with 32HR it starts around 40mm IC, ie the corners of the unshifted image is slighthly affected. You need certain strength before color differences start become visible (and as said, how colors are affected is hard to predict), but you need to be inside that to be safe.
So if color fidelity is important to you, the 32HR + IQ250 is not a great combination for you. The only reason I see the IQ250 to be suggested for this type of combination is live view. If the IQ250 did not have live view noone would think it would be a good idea to push crosstalk limits and hope for the best.
For professionals that need consistent results with tech wides the IQ260 must still be the recommendation over the IQ250 at all times.
I've attached an image that maybe helps to show my concern about the color fidelity. It shows how similar IQ250 and IQ260 are in the center of the image (as they should be assuming a sane profile has been used), and how quickly the colors start to separate quite significantly. It might partly be a white balance issue in the processing (it's from the example jpegs, not my own processing), but turning a green dress into blue without an otherwise severe cast is likely not a white balance issue alone, and there is documented crosstalk there, as I also show in a magnification of the green channels directly from the raw file which shows the horizontal lines due to separation (ie a crosstalk artifact).
The dress color change from green to blue in the painting may look extreme, but I don't think it is from a crosstalk perspective. Muted colors (ie a high and similar content from all three RGB channels) is more likely to change hue due to a crosstalk phenomenom (as you only need a small change to make the balance tip over to a different hue) than saturated colors which probably is just going to look a bit desaturated. But it will as said depend on the sensor orientation too as that decides in which direction the crosstalk flows. If the same painting had been shot with the sensor in vertical position I'm quite sure the color would be yet another. Probably different if you attach the back horizontal but upside down too.
Maybe I am the last person to know about this phenomenom and this is just old news. But as the last one I can sure tell you that if I had tested the system with the knowledge I had say one year ago, I could have missed this, you need to know that you should look for color, and not just be blinded by the fantastic sharpness and lack of noise, and the liveview of course. I hope the potential buyers that rent for testing know more about crosstalk than I did.
For exampe we may have leaks from blue to green and green to red, but not as much from green to blue and red to green, depending on the direction of the shift and orientation of the sensor. This means that a particular shift and sensor orientation will have a particular crosstalk, and that crosstalk will cause larger effect for some colors and smaller for others.
The LCC shot is made with some light source diffused through a white card, which will lead to one particular crosstalk distribution which is different from if the sensor sees say a clear blue color in the same position.
Maybe my explanation is not too easy to follow, but anyway the result is that depending on shift and orientation of the sensor the color fidelity will be affected in different ways. If you're lucky the scene you're shooting won't contain the colors that are affected the most.
Due to the complexity of the effects of crosstalk, ie that you can get different results depending on scene content and composition, it's not wise to draw conclusions that "it's good enough" from one test. The right way is of course to not use the sensor with shifts that introduce crosstalk.
I only need to look at LCC raw files to make a good estimate where crosstalk begins (which is where greens start to separate), and for the IQ250 with 32HR it starts around 40mm IC, ie the corners of the unshifted image is slighthly affected. You need certain strength before color differences start become visible (and as said, how colors are affected is hard to predict), but you need to be inside that to be safe.
So if color fidelity is important to you, the 32HR + IQ250 is not a great combination for you. The only reason I see the IQ250 to be suggested for this type of combination is live view. If the IQ250 did not have live view noone would think it would be a good idea to push crosstalk limits and hope for the best.
For professionals that need consistent results with tech wides the IQ260 must still be the recommendation over the IQ250 at all times.
I've attached an image that maybe helps to show my concern about the color fidelity. It shows how similar IQ250 and IQ260 are in the center of the image (as they should be assuming a sane profile has been used), and how quickly the colors start to separate quite significantly. It might partly be a white balance issue in the processing (it's from the example jpegs, not my own processing), but turning a green dress into blue without an otherwise severe cast is likely not a white balance issue alone, and there is documented crosstalk there, as I also show in a magnification of the green channels directly from the raw file which shows the horizontal lines due to separation (ie a crosstalk artifact).
The dress color change from green to blue in the painting may look extreme, but I don't think it is from a crosstalk perspective. Muted colors (ie a high and similar content from all three RGB channels) is more likely to change hue due to a crosstalk phenomenom (as you only need a small change to make the balance tip over to a different hue) than saturated colors which probably is just going to look a bit desaturated. But it will as said depend on the sensor orientation too as that decides in which direction the crosstalk flows. If the same painting had been shot with the sensor in vertical position I'm quite sure the color would be yet another. Probably different if you attach the back horizontal but upside down too.
Maybe I am the last person to know about this phenomenom and this is just old news. But as the last one I can sure tell you that if I had tested the system with the knowledge I had say one year ago, I could have missed this, you need to know that you should look for color, and not just be blinded by the fantastic sharpness and lack of noise, and the liveview of course. I hope the potential buyers that rent for testing know more about crosstalk than I did.
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Till your last post it was pretty clear to me, that you are some kind of crazy scientist that lost his mind in numbers and other dimensions. It wasn't easy for me to get any content out of your first gazillion word posting which seemed to never had an end... and I was scared that I would end up in an alternative timeline, if I would continue reading your posts. So I stopped.
But that last crop cleared things up a lot for me.
A picture... worth a thousand words.
Thanks Torger!
To me, this looks like big bad news.
But that last crop cleared things up a lot for me.
A picture... worth a thousand words.
Thanks Torger!
To me, this looks like big bad news.
Here's another picture which shows where I took out the crop of the painting (the green rectangle). Note that it's just outside the unshifted frame. I reattached the original crop comparison image for reference.
The picture also shows the whole IQ250 and IQ260 32HR stitched images side by side so you can see that in the center area of the lens the color rendition is very similar, and outside you start to get quite different colors, due to crosstalk occurring on the IQ250, while the IQ260 provides the whole image circle free from crosstalk.
Note how quickly the IQ250 color fidelity fails vertically while it handles quite okay sideways, this is extra clear on the right side of the image where you get a sudden color shift/desaturation in the large painting on the right wall, almost a sharp edge. This is because the different crosstalk behaviour vertically vs horizontally on the sensor. I'm not sure if horizontal crosstalk is less or if it's just more evenly distributed hurting those particular colors in the image less. More thorough testing in lab conditions would be required to figure that out. I think though that if we put a color checker just outside to the left or right of the unshifted frame we would see a color shift, just not as large as we do vertically.
Currently the DT page states 80mm usable image circle for color images for the IQ250/32HR combination. I do not agree with that. From my test results presented here I'd say that the guaranteed circle for color fidelity is no more than 40mm (supported by my measurements of crosstalk in the LCC shot), and the area with reasonable amount of crosstalk to only produce slight color shifts is not a circle, it's an oval related to the sensor orientation, which is about ~40mm high and ~55mm wide for horizontal orientation. You're free to make your own interpretations.
I hope I've presented enough material so any user trying out this combination or others know what to look out for.
The picture also shows the whole IQ250 and IQ260 32HR stitched images side by side so you can see that in the center area of the lens the color rendition is very similar, and outside you start to get quite different colors, due to crosstalk occurring on the IQ250, while the IQ260 provides the whole image circle free from crosstalk.
Note how quickly the IQ250 color fidelity fails vertically while it handles quite okay sideways, this is extra clear on the right side of the image where you get a sudden color shift/desaturation in the large painting on the right wall, almost a sharp edge. This is because the different crosstalk behaviour vertically vs horizontally on the sensor. I'm not sure if horizontal crosstalk is less or if it's just more evenly distributed hurting those particular colors in the image less. More thorough testing in lab conditions would be required to figure that out. I think though that if we put a color checker just outside to the left or right of the unshifted frame we would see a color shift, just not as large as we do vertically.
Currently the DT page states 80mm usable image circle for color images for the IQ250/32HR combination. I do not agree with that. From my test results presented here I'd say that the guaranteed circle for color fidelity is no more than 40mm (supported by my measurements of crosstalk in the LCC shot), and the area with reasonable amount of crosstalk to only produce slight color shifts is not a circle, it's an oval related to the sensor orientation, which is about ~40mm high and ~55mm wide for horizontal orientation. You're free to make your own interpretations.
I hope I've presented enough material so any user trying out this combination or others know what to look out for.
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Short answer: as the wide angle lenses for the D800 and even the mirrorless A7r have stronger retrofocus designs than the Rodenstock wides you don't get issues with crosstalk even if the sensors have as narrow critical crosstalk angle as the IQ250 sensor (which they probably have).
Long answer:
CMOS sensors have traditionally not very wide angular response at all. When manufacturers do brag about it they say like "wow we have 20 degrees unlike 10 we had before!", while the medium format CCD sensors have typically 40 degrees or so (with a few exceptions). The reason for that is as far as I understand mainly the larger pixel size (which relatively speaking puts the photodiode closer to the color filter) and a different design target, eg you rather put a light shield in there and reduce the fill factor than make a very limited critical crosstalk angle.
In the 135 systems including mirrorless you use different lens designs which are stronger retrofocus so the light comes in closer to perpendicular.
The 32HR is indeed a retrofocus lens, but noway as much as the 135 mirrorless wide angles. The DSLRs are even more retrofocus of course due to the extra flange distance dictated by the mirror box, so the D800 sensor have even less reason than the A7r to have a high critical crosstalk angle.
Probably it's not too hard for Sony to reduce the crosstalk with the current sensor, just put up some walls between pixels, it will however reduce the fill factor a bit and lower quantum efficiency, ie you get a lower base ISO and worse ISO performance. For a tech cam that would be no problem. But this sensor is not designed for that, simple as that, and then it's smarter to skip those walls and just use lenses which delivers the light closer to perpendicular. On the DF+ there's no issue.
In other words I don't think this CMOS sensor is much worse than any other typical CMOS sensor in production, a high critical crosstalk angle has simply not been a design target so far.
The disadvantage with retrofocus design is that it's harder to make sharp lenses with large image circles with low distortion. Ie, it's a disadvantage for tech camera needs. However, an advantage of retrofocus design is that you can more easily have wider aperture and less vignetting, great for high ISO shooting, so the retrofocus design found in 135 systems is not only to adapt for sensors, it's to adapt for the needs found in the all-around 135 format. So for all CMOS applications so far there's been no value in compromising fill factor to increase critical crosstalk angle.
New CMOS designs are coming however which will put the photodiode closer to the color filter, so you get a higher critical crosstalk angle (and less color cast) "for free". Hopefully these type of designs will find it's way to medium format sooner rather than later.
Below an example from Fuji/Panasonic new vs old design which was presented in July 2013:
note that they brag about improvement to 60 degrees here, but using the way to measure I've done (ie measure from perpendicular) it means only 30 degrees, ie less than say a P45+ have. This is for a very small pixel size though as new CMOS technology comes first to mobile phones and compacts, with a larger pixel size the angle would increase.
Sony have their own variants, backside illumination and stacked CMOS which produce similar results. None of these technologies have yet come to a 135 full-frame though, and it needs to come there before it can come to MF.
Arca-Swiss should release a Sony bellows for their Arca-Swiss MF-two. Then someone could test the A7r sensor with Rodenstock wides, but as far as I know noone has yet presented any such results. I assume that the A7r will show similar problems when shifted as I would guess the pixel design is the same.
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dougpeterson
Workshop Member
Here is a comparison of torger's crop of the composite *JPG* (in which I made some effort to match white balance on each frame, but was doing several hundred files of processing and was not perfect at - it's also, to be fair, hard to white balance stitched tech camera shots).
In his crop of the JPG the color sure looks pretty bad. With proper white balance applied not so much (though to be clear - absolutely there is a difference in color and some additional work to achieve white balance and localized good color - download the raws and play with them yourself).
Again - we both agree there are issues with color fidelity when you excessively shift the IQ250. We just disagree where it is a practical hinderance to photographic use, vs just a scientific curiosity. We also agree that anyone looking to make the investment in a DB for a tech camera should be aware of these issues (hence the entire reason for our spending several days testing and making the raw files available) - though I also think the end user should do their own testing (I realize from your point of view in a country/market where it's very hard to do such testing this seems like a large ask - bear in mind for most of our customers here in the US it's a phone call away from arranging).
I have to leave it at that. I have other tests to process, evaluate, and share.
In his crop of the JPG the color sure looks pretty bad. With proper white balance applied not so much (though to be clear - absolutely there is a difference in color and some additional work to achieve white balance and localized good color - download the raws and play with them yourself).
Again - we both agree there are issues with color fidelity when you excessively shift the IQ250. We just disagree where it is a practical hinderance to photographic use, vs just a scientific curiosity. We also agree that anyone looking to make the investment in a DB for a tech camera should be aware of these issues (hence the entire reason for our spending several days testing and making the raw files available) - though I also think the end user should do their own testing (I realize from your point of view in a country/market where it's very hard to do such testing this seems like a large ask - bear in mind for most of our customers here in the US it's a phone call away from arranging).
I have to leave it at that. I have other tests to process, evaluate, and share.
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Not a big deal to change wb to match the colors in the the corners...
But how do the centers of these shots look, do they match in color also?
Nope?
Move on to the next one.
I can't get my head around this either. Surely changing WB to "fix" the issue that torger highlighted would just cause problems elsewhere in the frame?
It's a shame that Doug has moved onto other tests, because this would appear to be a pretty critical one to evaluate properly for those customers who consider colour accuracy to be of critical importance. Hopefully someone else here can spare the time to look into it to validate (or otherwise) Doug's conclusions that this is just a scientific curiosity.
(From torger's analysis, we are not talking about "excessive" shifts here. We're talking about issues that would occur without any shifting whatsoever.)
The greens still suffer quite a bit even after Doug's rework (much appreciated) on the 250 example green dress.
Reds and yellows look good.
Hopefully someone will be able to test the 250 in a outdoor environment when spring gets here and all the leaves are green again with some moderate shifts.
Paul C
Reds and yellows look good.
Hopefully someone will be able to test the 250 in a outdoor environment when spring gets here and all the leaves are green again with some moderate shifts.
Paul C
It is pretty obvious that the IQ250 is not ideal for tech wide angle lenses specially when stitching for critical use but produces good quality results. If you want high quality results with tech wides the best all around back seems to be the IQ260 and then the IQ160 or 180 or 280.
That said the IQ250 should work great with an fps type unit and a SLR lens like the 24mm TSE-II and of course superb with any of the MF SLR platforms.
That said the IQ250 should work great with an fps type unit and a SLR lens like the 24mm TSE-II and of course superb with any of the MF SLR platforms.
Short story: Doug and I have different views on how a high end system like this should be evaluated and recommended, and therefore we end up with vastly different results. The reader is free to make up their own minds of which approach that's better. I still prefer my approach, but I bet some agree with Doug too and will be happy using the IQ250 with tech wides despite its liminations.
Long story:
My approach to this is that MF users in general is crazy about all aspects of image quality and that includes color fidelity. See how much D800 gets bashed for its inferior color. That IQ250 then should have some free pass to fall short in color fidelity while the DSLRs don't get any slack at all I feel is very biased way to look at it, and that's not my way of doing it, my loyalty is with the buyers of photographic equipment. Another advantage of MF that is very often emphasized is the less amount of color post-processing requried, which also is an aspect to take into account.
Note that my analysis of the IQ250 files is an ongoing process, at some point I will try to produce the best results I can from these files, but I have not yet come to this step in the process. My current step in the process is analyzing how the sensor performs, and here I see a clear crosstalk problem, problems which are not seen with the traditionally recommended CCD+tech wide combinations. I think that is important to note. I get the sense that because this IQ250 has live view and that is great for tech cams, we're so excited by that so we're kind of letting go the very high quality standards we had before. Noone was recommending the P30+ with tech wides, as there were much better alternatives.
With selective color adjustments crosstalk problems can be worked around to some extent, but I still feel that it's highly unwise to build a tech cam system with lenses that produce crosstalk on the sensor, and I would not recommend such a system to a high end user, even if you can with post-processing hacks equalize the color. With post-processing hacks like this you reduce the the tonality performance, and with selective needs you end up with hours in color-tuning in post-processing, and what MF is supposed to do is minimize that kind of work. If you stitch and need to apply a different white balance and tonality settings on the different segments to make them match, that's not what I call a well-behaved system.
There's one thing if you mainly use the back for your DF+ and occassionally use it on a tech camera, and an entirely different thing if you're a professional interior photographer and intend to use the back for wide angle photography in production. I'm thinking about the latter.
As far as I can see Doug and I have a different view on how a system should be recommended. In my process scientific measurements is an important component. The thing with gradual degradations of performance and subject-dependent and even orientation-dependent issues, like the crosstalk phenomenom is, is that it's easy to get into situations when it works kind of fine for one subject, and you get much worse performance in another situation. Things like reduced tonality performance is also hard to detect, but you would not be thrilled if you knew your $35K back got its tonality reduced to Canon-like performance
.
Therefore I think it's good to support the field testing with scientific measurements that makes a clear definition where this system provides stable performance. As far as I've come with this I can say that the crosstalk-free and thus stable performance region of the IQ250+32HR combination is an image circle of about 40mm. Sure you can get okay color performance outside with mild crosstalk, the degradation is gradual and subject-dependent and you can hide the effect with post-processing, but a sensor+lens combination where the sensor has to work beyond its critical crosstalk angle and thus get color crosstalk is broken by design, and I still maintain that those should not be combined in a high end system for production use. Anyone is free to disagree with me on that. I just want to be clear what my performance targets are.
Doug seems to me to have a more end-result-based approach to the problem. If results from a few real scenes look good to the eye after post-processing then it's fine and the system can be recommended. It's a practical "real photography" approach. I understand that Doug is a bit angry with me that I have used his raw files to present my measurement-based results (which is an ongoing process) which are much less optimistic about the IQ250+tech wides than the "real photography" test cases he has done. I'm very sorry for that. It's not my intention to make someone angry or misuse anyone's raw files or so, I just thought that my expertise in dealing with raw data would be appreciated by potential buyers in this forum.
In any case, I still don't think that the "real photography" way of testing a high end system like this is sufficient. It's surely a key aspect, but not sufficient. I've already mentioned why: with the real photography tests you can miss gradual degradation performance issues that can be easily seen with measurements and or just looking at spec sheets if we had them. I simply do not think it is okay to present a combination to the user which has crosstalk so close to the center, especially to users that like the MF backs for their superior tonality and color performance.
With good contacts in Phase One and in Rodenstock (which I don't personally have) it should hopefully be easy to find out the critical crosstalk angle of the sensor and the angular design of the Rodenstocks, so it would be easy to find out which system that work by design and which that do not. I think that when selling a $35K back with a $7K lens to the customer has a right to know these things.
I took the words in the original post for real: "Go crazy guys. Ask questions. Tear the files apart. Find the good. Find the bad. Let me know what you think of my effective image circle evaluations". That is exactly what I have done here, and I'm sorry I don't agree with Doug's conclusions, my image circle is considerably smaller, but I just can't change them on the basis of the results I have so far and the definition of how high performing MF systems should work. My main question is what the critical crosstalk angle of this sensor actually is according to Sony, and what the design target of the Digarons is in this aspect. Is that too hard to find out? I think it is a highly relevant question.
I will surely try to see how far one can go into crosstalk space and still get okay results, I'm just not there yet. But I see that as some kind of hack which you need to use if you happen to end up with a poor sensor + lens combination, not something that you should recommend to users. In general you can with smart software algorithms hide away serious performance issues of a system, you can never restore it in full but make it a lot better, I do this a lot myself, but I think the user has a right to know about something as serious as crosstalk, because then we are in guesstimate space. In a theoretical noise-free system color cast can be 100% recovered. Crosstalk cannot.
Long story:
My approach to this is that MF users in general is crazy about all aspects of image quality and that includes color fidelity. See how much D800 gets bashed for its inferior color. That IQ250 then should have some free pass to fall short in color fidelity while the DSLRs don't get any slack at all I feel is very biased way to look at it, and that's not my way of doing it, my loyalty is with the buyers of photographic equipment. Another advantage of MF that is very often emphasized is the less amount of color post-processing requried, which also is an aspect to take into account.
Note that my analysis of the IQ250 files is an ongoing process, at some point I will try to produce the best results I can from these files, but I have not yet come to this step in the process. My current step in the process is analyzing how the sensor performs, and here I see a clear crosstalk problem, problems which are not seen with the traditionally recommended CCD+tech wide combinations. I think that is important to note. I get the sense that because this IQ250 has live view and that is great for tech cams, we're so excited by that so we're kind of letting go the very high quality standards we had before. Noone was recommending the P30+ with tech wides, as there were much better alternatives.
With selective color adjustments crosstalk problems can be worked around to some extent, but I still feel that it's highly unwise to build a tech cam system with lenses that produce crosstalk on the sensor, and I would not recommend such a system to a high end user, even if you can with post-processing hacks equalize the color. With post-processing hacks like this you reduce the the tonality performance, and with selective needs you end up with hours in color-tuning in post-processing, and what MF is supposed to do is minimize that kind of work. If you stitch and need to apply a different white balance and tonality settings on the different segments to make them match, that's not what I call a well-behaved system.
There's one thing if you mainly use the back for your DF+ and occassionally use it on a tech camera, and an entirely different thing if you're a professional interior photographer and intend to use the back for wide angle photography in production. I'm thinking about the latter.
As far as I can see Doug and I have a different view on how a system should be recommended. In my process scientific measurements is an important component. The thing with gradual degradations of performance and subject-dependent and even orientation-dependent issues, like the crosstalk phenomenom is, is that it's easy to get into situations when it works kind of fine for one subject, and you get much worse performance in another situation. Things like reduced tonality performance is also hard to detect, but you would not be thrilled if you knew your $35K back got its tonality reduced to Canon-like performance
.Therefore I think it's good to support the field testing with scientific measurements that makes a clear definition where this system provides stable performance. As far as I've come with this I can say that the crosstalk-free and thus stable performance region of the IQ250+32HR combination is an image circle of about 40mm. Sure you can get okay color performance outside with mild crosstalk, the degradation is gradual and subject-dependent and you can hide the effect with post-processing, but a sensor+lens combination where the sensor has to work beyond its critical crosstalk angle and thus get color crosstalk is broken by design, and I still maintain that those should not be combined in a high end system for production use. Anyone is free to disagree with me on that. I just want to be clear what my performance targets are.
Doug seems to me to have a more end-result-based approach to the problem. If results from a few real scenes look good to the eye after post-processing then it's fine and the system can be recommended. It's a practical "real photography" approach. I understand that Doug is a bit angry with me that I have used his raw files to present my measurement-based results (which is an ongoing process) which are much less optimistic about the IQ250+tech wides than the "real photography" test cases he has done. I'm very sorry for that. It's not my intention to make someone angry or misuse anyone's raw files or so, I just thought that my expertise in dealing with raw data would be appreciated by potential buyers in this forum.
In any case, I still don't think that the "real photography" way of testing a high end system like this is sufficient. It's surely a key aspect, but not sufficient. I've already mentioned why: with the real photography tests you can miss gradual degradation performance issues that can be easily seen with measurements and or just looking at spec sheets if we had them. I simply do not think it is okay to present a combination to the user which has crosstalk so close to the center, especially to users that like the MF backs for their superior tonality and color performance.
With good contacts in Phase One and in Rodenstock (which I don't personally have) it should hopefully be easy to find out the critical crosstalk angle of the sensor and the angular design of the Rodenstocks, so it would be easy to find out which system that work by design and which that do not. I think that when selling a $35K back with a $7K lens to the customer has a right to know these things.
I took the words in the original post for real: "Go crazy guys. Ask questions. Tear the files apart. Find the good. Find the bad. Let me know what you think of my effective image circle evaluations". That is exactly what I have done here, and I'm sorry I don't agree with Doug's conclusions, my image circle is considerably smaller, but I just can't change them on the basis of the results I have so far and the definition of how high performing MF systems should work. My main question is what the critical crosstalk angle of this sensor actually is according to Sony, and what the design target of the Digarons is in this aspect. Is that too hard to find out? I think it is a highly relevant question.
I will surely try to see how far one can go into crosstalk space and still get okay results, I'm just not there yet. But I see that as some kind of hack which you need to use if you happen to end up with a poor sensor + lens combination, not something that you should recommend to users. In general you can with smart software algorithms hide away serious performance issues of a system, you can never restore it in full but make it a lot better, I do this a lot myself, but I think the user has a right to know about something as serious as crosstalk, because then we are in guesstimate space. In a theoretical noise-free system color cast can be 100% recovered. Crosstalk cannot.
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I sometimes complain about MFDB manufacturers not caring enough about tech camera users. I know that too is not a popular opinion among some dealers. Ok, fine, agree to disagree.
I think this is another sign of it. If P1 had a clear interest in tech cams would do the simple thing to check the data sheet of the Sony and the data sheet of the Rodenstock and Schneiders and make those numbers available to dealers so they could be formed into good lens recommendations. Guesswork from what C1 algorithms can hide in some situations I do not think is a serious take on the problem. I'm sure many dealers won't agree on that, but I think I'm free to have that view and actually I think mine should be considered less controversial if you look at it from a buyer's perspective.
When you design a camera system you make sure sensor and lens play together in concert. The Rodenstock wides have been designed with certain sensor properties in mind, probably what is found on the the 6um CCD sensors. The Rodenstock designers have known the critical crosstalk angle of these sensors and adapted their optical design to that. Sure there's color cast, but that's reversible unlike crosstalk.
When you then sell a new back with radically different sensor properties the original design criterias can break, and that is what's happening with the IQ250. If I had been a dealer I would find it very difficult to suggest a lens+sensor combination which I knew broke the design criterias and require software algorithm guesswork to hide. As said, while colorcast is 100% reversible (with the exception of a bit DR loss of course) crosstalk is not.
The reason I write these long explaining posts of my position now is that it has come to my attention that my pessimistic view on the IQ250 with tech wides is by some seen as unfair, even to the point that some get angry. I maintain that my points are both valid and fair, but sure for someone that think live view is more worth than color fidelity fine at the high end, go ahead use it with these combinations. My recommendation is however to pick the IQ260, IQ160, Credo 60, P65+ or any other 6um Dalsa sensor technology to use with these wides. Furthermore based on my results I do not think it's a good idea to upgrade P40+ or IQ140 (44x33 6um Dalsa CCD) to IQ250 if you are a tech cam wide angle user that actually use shift or tilt.
By actually having the IQ250 back and a lens lineup I could make much better tests and come with more nuanced conclusions. I would still use measurement-based test as an important aspect of testing, and I would still not recommend to use the sensor in crosstalk mode as it compromises the fine color rendition properties. But I could make a much better assessment of exactly how bad crosstalk will hurt your colors and complicate your post-processing needs, if someone still would like to push its limits. But I would point on an image circle diagram which show "no crosstalk inside this circle" and say "outside this border, you're on your own". The supposedly superior CFA design doesn't count when colors are mixed. I think that matters to users.
As co-author of Lumariver HDR and RawTherapee where I specialize on various algorithms I know a thing or two about raw processing. I'm also myself a tech cam user which shoot landscape on a recreational basis. This makes me a bit emotional about this subject, I have quite strong ideas on what makes up a well-behaved system, and what's fair to fix/hide in post-processing and not, and what the customer has the right to know about the substantial amount of money that goes into these systems. To me it's a big difference between color cast and crosstalk. Reversible vs not reversible. And it doesn't end there, green separation which is a crosstalk side effect makes the back sensitive to particular LCC and demosaicing strategies. I would not be surprised if Lightroom makes a much worse job on this particular back than C1. I think it's a bad idea(tm) to make a high end system dependent on advanced guesstimate algorithms. Therefore I think what's the "crosstalk-free image circle" is a very central piece of information.
I have a somewhat faint memory of that there were rushed tech cam upgrades from P65+ to IQ180, and they did not all turn out too well, as the IQ180 has much more wide angle issues than the P65+ and IQ160. Did the dealers give proper information to the customers about that before upgrade was sold? It would be sad to see people rush from IQ140 to IQ250 and be semi-disappointed in the longer term when it's clear that it actually doesn't perform as well as it seemed in the first tests with the favourite wides. Presenting the actual crosstalk free image circles where performance can be guaranteed would avoid that situation.
I think this is another sign of it. If P1 had a clear interest in tech cams would do the simple thing to check the data sheet of the Sony and the data sheet of the Rodenstock and Schneiders and make those numbers available to dealers so they could be formed into good lens recommendations. Guesswork from what C1 algorithms can hide in some situations I do not think is a serious take on the problem. I'm sure many dealers won't agree on that, but I think I'm free to have that view and actually I think mine should be considered less controversial if you look at it from a buyer's perspective.
When you design a camera system you make sure sensor and lens play together in concert. The Rodenstock wides have been designed with certain sensor properties in mind, probably what is found on the the 6um CCD sensors. The Rodenstock designers have known the critical crosstalk angle of these sensors and adapted their optical design to that. Sure there's color cast, but that's reversible unlike crosstalk.
When you then sell a new back with radically different sensor properties the original design criterias can break, and that is what's happening with the IQ250. If I had been a dealer I would find it very difficult to suggest a lens+sensor combination which I knew broke the design criterias and require software algorithm guesswork to hide. As said, while colorcast is 100% reversible (with the exception of a bit DR loss of course) crosstalk is not.
The reason I write these long explaining posts of my position now is that it has come to my attention that my pessimistic view on the IQ250 with tech wides is by some seen as unfair, even to the point that some get angry. I maintain that my points are both valid and fair, but sure for someone that think live view is more worth than color fidelity fine at the high end, go ahead use it with these combinations. My recommendation is however to pick the IQ260, IQ160, Credo 60, P65+ or any other 6um Dalsa sensor technology to use with these wides. Furthermore based on my results I do not think it's a good idea to upgrade P40+ or IQ140 (44x33 6um Dalsa CCD) to IQ250 if you are a tech cam wide angle user that actually use shift or tilt.
By actually having the IQ250 back and a lens lineup I could make much better tests and come with more nuanced conclusions. I would still use measurement-based test as an important aspect of testing, and I would still not recommend to use the sensor in crosstalk mode as it compromises the fine color rendition properties. But I could make a much better assessment of exactly how bad crosstalk will hurt your colors and complicate your post-processing needs, if someone still would like to push its limits. But I would point on an image circle diagram which show "no crosstalk inside this circle" and say "outside this border, you're on your own". The supposedly superior CFA design doesn't count when colors are mixed. I think that matters to users.
As co-author of Lumariver HDR and RawTherapee where I specialize on various algorithms I know a thing or two about raw processing. I'm also myself a tech cam user which shoot landscape on a recreational basis. This makes me a bit emotional about this subject, I have quite strong ideas on what makes up a well-behaved system, and what's fair to fix/hide in post-processing and not, and what the customer has the right to know about the substantial amount of money that goes into these systems. To me it's a big difference between color cast and crosstalk. Reversible vs not reversible. And it doesn't end there, green separation which is a crosstalk side effect makes the back sensitive to particular LCC and demosaicing strategies. I would not be surprised if Lightroom makes a much worse job on this particular back than C1. I think it's a bad idea(tm) to make a high end system dependent on advanced guesstimate algorithms. Therefore I think what's the "crosstalk-free image circle" is a very central piece of information.
I have a somewhat faint memory of that there were rushed tech cam upgrades from P65+ to IQ180, and they did not all turn out too well, as the IQ180 has much more wide angle issues than the P65+ and IQ160. Did the dealers give proper information to the customers about that before upgrade was sold? It would be sad to see people rush from IQ140 to IQ250 and be semi-disappointed in the longer term when it's clear that it actually doesn't perform as well as it seemed in the first tests with the favourite wides. Presenting the actual crosstalk free image circles where performance can be guaranteed would avoid that situation.
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AreBee
Member
Torger,
You have nothing whatsoever to apologise for. Your posts on the adverse effect of crosstalk on the IQ250 have been presented in an unbiased way. No fair minded reader - especially those of us familiar with your posting history on GetDPI and LuLa - could arrive at any conclusion other than that.
As you rightly point out, Doug invited others to "Go crazy guys. Ask questions. Tear the files apart. Find the good. Find the bad. Let me know what you think of my effective image circle evaluations". Therefore, Doug has no grounds on which to complain, though he understandably can be forgiven for not appreciating to learn of bad news.
There is nothing wrong in principle with a real-world point of view. However, to hold a real-world point of view is to accept an end result despite other effects, adverse or otherwise, which may exist. A person ignorant of the facts is unable to hold a real-world point of view.
Far from being criticised for reporting about crosstalk, in my view you are to be commended. For my part, many thanks for bringing to my attention what I agree is an important issue.
Kind regards,
You have nothing whatsoever to apologise for. Your posts on the adverse effect of crosstalk on the IQ250 have been presented in an unbiased way. No fair minded reader - especially those of us familiar with your posting history on GetDPI and LuLa - could arrive at any conclusion other than that.
As you rightly point out, Doug invited others to "Go crazy guys. Ask questions. Tear the files apart. Find the good. Find the bad. Let me know what you think of my effective image circle evaluations". Therefore, Doug has no grounds on which to complain, though he understandably can be forgiven for not appreciating to learn of bad news.
There is nothing wrong in principle with a real-world point of view. However, to hold a real-world point of view is to accept an end result despite other effects, adverse or otherwise, which may exist. A person ignorant of the facts is unable to hold a real-world point of view.
Far from being criticised for reporting about crosstalk, in my view you are to be commended. For my part, many thanks for bringing to my attention what I agree is an important issue.
Kind regards,