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Thread: Credo 50 Review coming

  1. #51
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    Re: Credo 50 Review coming

    That CMOS sensor has super-good DR never seen before in medium format which means that it can suffer quite some vignetting before it becomes a problem, so in a way it's less dependent on center filters. This also means that it can recover better than other backs from severe color casts. When color cast is severe there's a crosstalk component too though, which does affect color fidelity. In practical photography that's generally quite mild though.

  2. #52
    Administrator, Instructor Guy Mancuso's Avatar
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    Re: Credo 50 Review coming

    Quote Originally Posted by Pemihan View Post
    I'm pretty sure there is no center filter for the 40HR.
    I don't think there is either but there is for the 28 and 32 roadie. I had the 28 myself. Nice nice lens
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  3. #53
    Administrator, Instructor Guy Mancuso's Avatar
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    Re: Credo 50 Review coming

    Quote Originally Posted by torger View Post
    That CMOS sensor has super-good DR never seen before in medium format which means that it can suffer quite some vignetting before it becomes a problem, so in a way it's less dependent on center filters. This also means that it can recover better than other backs from severe color casts. When color cast is severe there's a crosstalk component too though, which does affect color fidelity. In practical photography that's generally quite mild though.
    Guess we need to try a find that limit.

    I do think most folks shooting tech most likely have what I have on hand.
    Photography is all about experimentation and without it you will never learn art.

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  4. #54
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    Re: Credo 50 Review coming

    It would be highly desirable to see more testing with this back comibned with the Digaron-S 28 and Digaron-W 32 sometime in the future :-). I think most (but not all) will be happy with the Digaron-W 40 performance, but many won't be happy if that is the widest lens they can use.

    From Doug's tests it seems Digaron-W 32 pushes it further, but still it can be good enough for many, and we don't know about the Digaron-S 28. It's not necessesarily worse than the Digaron-W 32 as you can make a lens more retrofocus to compensate the wider angle.

    As I mentioned in a few posts back I think it's a real possibility that this CMOS back is the back for some wide angle shooters, but not yet for all. Need to balance my possibly negative-looking take on the back -- it's certainly not game over yet for the wide angle shooter. We just know that there are issues and they're still not so well-documented, and as long as this is the case it's good to be a bit cautious. For example if you think the Digaron-W 40 results look great but you plan later on to buy a Digaron-S 28, you should not "put in basket" before you actually get to see how the 28 performs too.
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  5. #55
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    Re: Credo 50 Review coming

    Looking at Doug's 32 HR raw files I think one can get better results than I initially thought. I have not actually myself done a stitch of those files but only looked at the finished stitch made by someone at DT. Now I brought up a couple of the raw files in C1 and took a look. Few may be aware but this sensor has offset microlenses (or more correctly offset photo diodes) towards the sides so it can handle wide angles better. This assumes that the lens is centered though. It still helps when the lens is off center -- up to a certain point -- past that it suddenly breaks and you get very bad performance.

    I've attached examples of 32 HR crop located at the upper part of an horizontal image shifted up 13mm. As you see the left 100% crop looks fine (possibly desaturated, don't know that, but if so not with much) while the right one look terrible, even with failed demosaicing artifacts. This is the same place on the image circle, but in the second case the sensor has been shifted more up. In the left the offset microlenses helps the sensor, in the right it breaks because the sensor is shifted too far up.

    Thanks to the offset microlenses the back will probably perform quite well within a moderate shift range, but will suddenly break if shifted too far. The tricky part is that a fixed part of the scene that looked good with a lower amount of shift can start looking bad when you shift some more. This is a new effect, as none of the CCDs employ offset microlenses.

    I think that whoever that did the DT example stitch did not know about this effect and may not have made an ideal stitch, ie some parts of the picture contains segments of a sensor shifted to far when you could have got a better render at that particular place in the image circle with the sensor in a different position. With optimal technique you could make it perform better.

    It needs some figuring out what this technique should be and which guidelines to give. This sensor + wide angles is not the easiest to review... but I think if you handle everything carefully and never "overshift" it is possible that you can use both the 32HR and the 28HR with good results, perhaps not with reproduction-quality color fidelity but certainly fine for less demanding applications. It takes more testing to give any good answers.

    For reference, this image illustrates offset microlenses concept:
    Last edited by torger; 30th September 2014 at 03:32.

  6. #56
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    Re: Credo 50 Review coming

    Guy, about the three-stitch image you posted;

    Due to the offset microlenses - you probably get the best stitching result if you use as much as possible of the center image (where offset microlenses will work best in helping improve the result), and for the left image you should use as little as possible of the right half (as there the microlens offset will counter-act the incoming light angle), and for the right image as little as possible from the left half for the same reason. Maybe it's already stitched that way, but anyway good to know.

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    Re: Credo 50 Review coming

    Quote Originally Posted by Pemihan View Post
    I'm pretty sure there is no center filter for the 40HR.
    There is no Rodenstock CF. However Heliopan made a series of CF filters and the P/N 706751 works very well with the 40mm Rod.

    67/86mm 1.5 stops. Schot glass optically very good.

    Appears now to be discontinued but there are a few probably still floating around.

    On the 40mm this filter does help on shifts of 12mm or more. Much less noise in the shifted sides with a CCD back.

    Paul

  8. #58
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    Re: Credo 50 Review coming

    Here's an illustration to show a bit clearer. For optimal result as much as possible of the red center frame should be used, and minimize the use of the overlapping segments of the green and blue frame. This makes the best use of the sensor's microlens offset.

    Examining the overlapping segment, for example the one outlined in yellow, can be interesting. In a perfect system the colors would be exactly the same for both images, at least after white-balancing after a common point. I think the C1 LCC application can cause some white balance shift, so it may not match directly after LCC apply.

    The sky seems to pick up some magenta cast towards the left side, I don't know if that's natural (depending on the sun's position the sky may not be 100% even) or if it's an artifact. Could be as simple as a white balance mismatch.

    I know from previous testing that the sensor present very different color cast not only horizontal vs vertical but also if you turn the back upside down. This should be visible in your LCC shots. If the sensor behaves perfectly symmetrical the LCC shot from the green frame (left) should be the same as a mirrored blue frame (right), but I'm quite sure that's not the case, instead it will be more towards red on one side (the left?) and more towards blue on the other.

    If the magenta cast of the left side sky indeed is a crosstalk artifact that effect may explain why it's not the same on the right side, on the left side you may get a bit more red/magenta, and on the right side a bit more blue/cyan.

    There's a whole lot of speculation here though... I hope you'll share raw files at some point

    The image does look great and natural. But say if the actual sky at the scene was indeed solid blue left to right and now it's not, is that an acceptable result? The greyer greens on the leftmost tree does not look unnatural, but if they in actuality was as green as the center bush, is that an acceptable result? For some it will, for others it will not. In the best case the greyer greens and the magenta left really was the look of the original scene, and that would be a lovely result. Unfortunately it's hard to nail down this for sure without lab-style testing, I have some results pointing towards that it should work, and others that are less positive. I don't really know what to think myself.

    I think that the greyer greens and magenta can either be natural or just a white balance error, and if so I think the HR40 will make most users satisfied. And after taking another look at Doug's library test on HR 32 in C1 and making a stitch "microlens-offset-aware" I'm a bit more optimistic.

    Personally I would however not get the back without lab-style testing with the full range of wide angles I have in mind, I would just hate it if I'd been shooting a year and then realize that wait a minute, I have color shift in many of my shifted images that I just did not notice at first. I know MF users generally dislike lab tests, but for things like slight color shifts and desaturation which this is about it's much more reliable to make a lab test than shooting live scenes. A simple lab test would be to shoot a color checker in center, and then move the camera and shift around and shoot the exact same setup in various shift combinations, then overlay and look for differences. Then you would know what kind of color shifts and desaturations we're looking at for which colors, and then one can go on shooting live scenes and relate to what we saw in the lab. If I was a dealer I would do it first thing, the whole issue is so complex (the offset microlens thing doesn't make it easier) that I don't think it's really fair to say to a potential buyer "make your own real-world tests and make up your mind", because it's so easy to make mistakes of the kind that you don't really notice anything when you do your casual tests but then over time you notice that maybe there's something with the color not doing so well.

    This thread shows how such a color-checker lab test can look (for a different back / lens combination):
    http://www.getdpi.com/forum/medium-f...y-results.html
    (unfortunately the early crosstalk cancellation algorithm demonstrated in that thread did not work out for the kind of crosstalk we see in this CMOS, but maybe I'll make another attempt...)
    Last edited by torger; 30th September 2014 at 05:39.

  9. #59
    Administrator, Instructor Guy Mancuso's Avatar
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    Re: Credo 50 Review coming

    Folks Im working on the review . i know you see it on the forum Its locked for now until I get more data up but downloads are there and i hate working alone. LOL
    Photography is all about experimentation and without it you will never learn art.

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    Re: Credo 50 Review coming

    Thanks Guy.
    A question though, is the straight non stitched shot taken with the 40mm HR with fall of the back? Just trying to gauge how it might suit my purposes, as I never stitch but want and need to perform perspective correction in camera. I'd need a 32 HR to cover my work though. Any thoughts on how that lens would perform compared to the 40 HR?
    Thanks again for your time and effort on this.
    TJV

  11. #61
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    Re: Credo 50 Review coming

    I've taken a quick look on the tech HR40 raws. Thanks for sharing.

    I think it looks quite good. There is crosstalk going on, as one can measure in green channel separation in the LCC shots (if there is no crosstalk green1 and green2 are the same). This separation can also be seen as demosaicing mazing when using more sensitive demosaicers than the one in C1. Haven't yet checked in C1 but I know that mosaicer is robust so I would be suprised if I find any mazing artifacts at this level.

    One can see the asymmetric behavior of the sensor, the left shift LCC has a different color scale than the corresponding right shift. If symmetric behavior is desired one can turn the back upside down on the left shift for example. It might be the case that the right shift has a bit less issues, ie a tiny little better result could have been had if turning the back upside down on the left shift.

    So how much is color affected? A color checker test would be needed to make really sure, but from the paint on the buildings in the examples and grass etc I'd say that there is desaturation but a very low amount. It would probably not be acceptable for reproduction photography, but for any normal landscape or architectural photography I think most users would be satisfied. Of the sky I'm not sure if it's a shift or if it's natural. I suspect that the fitness center magnenta left could have been different (ie bluer) if the back was turned upside down when shooting that segment.

    Can the sensor be shifted more than 15mm? From Doug's library test we know that at 30mm there is total breakdown, but I have not seen any test files examining the range between 15 and 30mm. My guess is that 15mm is as far as you'd want to go.

    How will the 32HR perform? Need to test to make sure, probably a little bit less good but not by much. Speculating now - perhaps 12mm shift would yield a similar result as 15mm on the HR40.

    Do we have the full picture? No, to really document color stability of this system with asymmetrical behavior you'd need to make a lab test. Personally I'd want to do that before investing in this type of system so I get a full understanding of its color performance as I'm quite picky about color and lack of other crosstalk-related artifacts, but I understand that not everyone is that.

    Would I recommend using the Credo 50 with the HR40? No, not really, but at the same time I'd say that many will be satisfied so I think some people will go this way and I think that is an okay decision, real-world post-processed result will be fine almost always. If buying into it with open eyes I cannot say it would be a bad decision, color and tonality is just one of many measures.

    Note that some of my skepticism is that I'm an engineer, and as such I just don't think it's sane design for a system to push the sensor into operation in an area which it's not designed for and patching up with a robust demosaicer, it's also obvious that the great technology advances in both fine tonality and DR is compromised in the shifted areas, moreso than we're used to. I think having to use LCC is bad enough, and at some point I think is pushed too far than is sane, and this sensor lens combination is such a case. I can't however deny that thanks to the huge DR of this sensor and the stable C1 demosaicer the real world results you can have look pretty good.

  12. #62
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    Re: Credo 50 Review coming

    Looking at the LCCs in rawdigger you lose about 2.6 stops to the side and about 2.8 stops to the corner. The green channels that are equal in center separate 20 - 30% at the shifted sides/cornes.

    You can't translate green separation to amount of crosstalk straight away as it depends on the color of light shining on the LCC and a bunch of other factors, but as a comparison a IQ260 shifted to hard vignetting on the 32HR has <3% green channel separation, ie negligible crosstalk (horizontal orientation, it's about 5% vertical, ie still low). There are worse examples though, the Credo40 shifted to the edge in vertical orientation on an SK28 is kind of a worst case and that has 80% separation (totally black and white in that case). The Hasselblad 50 megapixel Kodak CCD backs keeps the separation at 5% even with the SK28 close to the edge.

    When there's so much leaks between pixels that a neighboring green pixel can differ as much as 20 - 30% you can't of course expect perfect tonality and color, and not perfect demosaicing either as this difference between green neighbours can be converted into false detail. How far from perfect? Well, good real-world results can still be had, you don't need to have the best product concerning tonality to make good images. You just need to be aware what you compromise.

    A shifted lens of course always means compromise, you get less sharpness and the increased vignetting means you get more noise. The desaturation and reduced tonality followed by crosstalk can be seen as just another of these, and depending on how you see it you may not think that it is any worse than vignetting is and you don't need to give it much attention. While I don't agree for a number of reasons I think it's a reasonable point of view you can have as a pragmatic photographer.

    To compare with something we know from the past, a HR40 on the Credo 50 is about the same type of compromise concerning color and tonality as an SK35 on an P65+/IQ160/IQ260 (although the latter is a bit better at rise/fall in horizontal orientation). That is a fully usable combination in real-world scenarios within limits, but they were not really made to match. If you were satisfied with the SK35 performance on the Dalsa-based 60 megapixel backs you're probably going to be satisfied with the HR40 on the Credo50.
    Last edited by torger; 1st October 2014 at 03:26.

  13. #63
    Senior Member ErikKaffehr's Avatar
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    Re: Credo 50 Review coming

    Hi Guy,

    I checked out some of the raw files in capture One.

    Regarding ISO I cannot say that much. I mostly shoot 50 ISO on both my P45+ and the Sony Alpha 99.

    What I noticed is that there is a marked fall off in sharpness in the corners and edges on the Mamiya 55LS.

    The technical camera image is impressively sharp.

    Thanks for the review, job well done, and thanks for posting the raw images!

    Best regards
    Erik

    Quote Originally Posted by Guy Mancuso View Post
    Folks Im working on the review . i know you see it on the forum Its locked for now until I get more data up but downloads are there and i hate working alone. LOL

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