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IQ4 150 help working out how to get to a reliable histogram please.

Greg Haag

Well-known member
I am trying to get to a point where I trust the histogram on the back of the camera for accurate exposure. I have taken 2 pictures, the first is where the RGB histogram appears to be pushed to the right without clipping, the second is 2/3 of a stop under that. I have included a shot of the back of the IQ with histogram as well as the histogram from Capture One. I set the exposure warning in Capture One to 254. Also, I may not understand how to properly use the RAW histogram, but it appears of no value to me from an accuracy standpoint. Any guidance from others with the IQ4 would be greatly appreciated.
Thanks in advance!
Greg

IQ4 150 Cambo 1600 Rodenstock 90

Normal
Normal Histogram.jpg

Minus 2/3 stop
Histogram minus two thirds stop.jpg
 

pegelli

Well-known member
I think judging burned out channels in a raw converter for any camera is a lost cause, there's too many things going on below the hood that areas that appear non blown can actually be blown and vice-versa. The only program I trust for these kind of accurate determinations is rawdigger, there's a 30 day free evaluation and the simple version to just look at raw histograms for all 4 channels is not very expensive.

The next step would be to shoot a relatively high contrast scene (like the example you showed) with 1/3 EV steps and compare the camera histogram with what you see in rawdigger to make a judgement where the camera histogram needs to be in order to avoid blown channels.

Pls. note this is "generic" advice for digital sensors in general, I have no experience with MF or digital backs.
 

Greg Haag

Well-known member
I think judging burned out channels in a raw converter for any camera is a lost cause, there's too many things going on below the hood that areas that appear non blown can actually be blown and vice-versa. The only program I trust for these kind of accurate determinations is rawdigger, there's a 30 day free evaluation and the simple version to just look at raw histograms for all 4 channels is not very expensive.

The next step would be to shoot a relatively high contrast scene (like the example you showed) with 1/3 EV steps and compare the camera histogram with what you see in rawdigger to make a judgement where the camera histogram needs to be in order to avoid blown channels.

Pls. note this is "generic" advice for digital sensors in general, I have no experience with MF or digital backs.
Thank you! I would be great if you could then use those findings to re-calibrate the histogram on the camera.
 

pegelli

Well-known member
That would indeed be great, on my cameras you can do that to some extent by adjusting contrast (since the only option is a JPG histogram) but it's a "crutch" and also not very accurate.

Don't know about the phase one backs, looking at your images I'm also wondering how the raw histogram works, because I don't seem to see blown out channels. Maybe the first thing you can do is examine the two files you showed here in rawdigger and see if that program shows you any blown channels, easy to see in the histogram view of the four channels (Red, Blue and two Greens)
 

Greg Haag

Well-known member
That would indeed be great, on my cameras you can do that to some extent by adjusting contrast (since the only option is a JPG histogram) but it's a "crutch" and also not very accurate.

Don't know about the phase one backs, looking at your images I'm also wondering how the raw histogram works, because I don't seem to see blown out channels. Maybe the first thing you can do is examine the two files you showed here in rawdigger and see if that program shows you any blown channels, easy to see in the histogram view of the four channels (Red, Blue and two Greens)
Pieter, hopefully I have done this properly, but here are the histograms of the two images from RawDigger.

Normal histogram based on in camera RGB Histogram
Normal.jpg

2/3 under based on camera RGB Histogram
Under two thirds.jpg
 

pegelli

Well-known member
The way it looks to me is that indeed on the first image the two green channels are blown out (a peak at 64000), while the blue and red channels seem OK. So your camera histogram was too far to the left.

On the second image all channels are OK (no spike at 64000) so the fact you see blown channels in C1 is an artifact of some C1 (default) conversion settings and working with the sliders in C1 should result in a good image without any colour cast in the highlights.

Another way to quickly check for blown channels is in the main screen of rawdigger and checking the box "OvExp" on the top ribbon under "Display"
The blown channels will then be highlighted in your image, and by using the lowest radio button you can do that for every individual channel.

Hope this helps.
 

docholliday

Active member
I never use a histogram on any camera, digital (or film scanned) to judge exposure or range. I also don't use EVF for any reason. I may use LV for composition, but that's only for set buiilds and composition. There's just too many variances that can affect it such as if the image is generated from the raw data, an internal JPG, or some other arbritrary method of creation. There's also the issue of the subject matter that can affect what the "proper" histogram should be. I also don't ever judge an image exposure on any camera screen as that too has a lot of variance and no standard to calibrate to (screen brightness, environment brightness, LCD gamut/range, etc).

I actually use the histogram on my IQ so little that it's moved to the bottom of the list of tools. The Exposure Zone, Level, and Focus are the 3 items that come up first with the blown highlights display and Settings next. When the backs aren't on a SLR body, I use a handheld spot meter to establish exposure and range.

For example, a complete whiteout snowstorm with a tree to the right of frame exposed with everything to the right, as one think's it should, would be completely blown out as snow isn't pure 253/254 white. The opposite would be a dark scene, like nighttime or dark room with a TV on, which you may have nothing to the right. A scene with a shiny red satin dress may have spots that *are* supposed to be blown out (highlights of the shimmer), so in that case, the histogram would/should show a spike in the red channel. I've also had black fabric with brighteners that reflected excessive blue so a histogram showing even exposure for each color would be wrong, as the blue channel should be higher than the rest (and since it's black fabric filling the frame, where's the histogram supposed to fall?)

For any new camera, I always spend a few weeks calibrating the camera to my handheld meters so I can trust the spot metering, adjusting the meter bias to compensate. On one of my H bodies, I have a -1/3 bias and another is +/- 0. With my H5 and IQ, the meter is set to +1/3. Then, there's a page in the Wildi "The Hasselblad Manual" that shows colors and how much to bias when metering for that color. I've memorized that so I can bias my meter as needed during the initial metering for the shot. I always treat digital shooting like I was metering to expose for 4x5 or 8x10 sheet film *slides*. I spent so much time learning that process that I rarely ever blew a slide, so the same technique works for digital.

Once in C1, I rarely have to adjust exposure on any shot (unless I screwed up and pointed the spot at the wrong place). The most I ever tweak is +/- 0.5 stops and if I'm "exposing to the right", I'll pull the highlights back a touch to get detail levels where I want it. If there's need to be sure of a pure white or slightly under (like snow highlights), I'll put one of the color readouts in the darkest areas of the highlight and start to pull highlights until it moves to 252 or so. It's pretty much like the application technique of the Zone system to color slide exposure.

The other thing about ETTR that most people neglect to talk about is that the highlights *are* expected to be slightly blown in the captured image - to ensure that there's data recorded. In post, it's expected to pull back those highlights to get proper exposure since pulling highlights doesn't generate noise where pushing shadows would produce noise.
 
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Greg Haag

Well-known member
I never use a histogram on any camera, digital (or film scanned) to judge exposure or range. I also don't use EVF for any reason. I may use LV for composition, but that's only for set buiilds and composition. There's just too many variances that can affect it such as if the image is generated from the raw data, an internal JPG, or some other arbritrary method of creation. There's also the issue of the subject matter that can affect what the "proper" histogram should be. I also don't ever judge an image exposure on any camera screen as that too has a lot of variance and no standard to calibrate to (screen brightness, environment brightness, LCD gamut/range, etc).

I actually use the histogram on my IQ so little that it's moved to the bottom of the list of tools. The Exposure Zone, Level, and Focus are the 3 items that come up first with the blown highlights display and Settings next.

A complete whiteout snowstorm with a tree to the right of frame exposed with everything to the right, as one think's it should, would be completely blown out as snow isn't pure 253/254 white. The opposite would be a dark scene, like nighttime or dark room with a TV on, which you may have nothing to the right. A scene with a shiny red satin dress may have spots that *are* supposed to be blown out (highlights of the shimmer), so in that case, the histogram would/should show a spike in the red channel. I've also had black fabric with brighteners that reflected excessive blue so a histogram showing even exposure for each color would be wrong, as the blue channel should be higher than the rest (and since it's black fabric filling the frame, where's the histogram supposed to fall?)

For any new camera, I always spend a few weeks calibrating the camera to my handheld meters so I can trust the spot metering, adjusting the meter bias to compensate. On one of my H bodies, I have a -1/3 bias and another is +/- 0. With my H5 and IQ, the meter is set to +1/3. Then, there's a page in the Wildi "The Hasselblad Manual" that shows colors and how much to bias when metering for that color. I've memorized that so I can bias my meter as needed during the initial metering for the shot. I always treat digital shooting like I was metering to expose for 4x5 or 8x10 sheet film *slides*. I spent so much time learning that process that I rarely ever blew a slide, so the same technique works for digital.

Once in C1, I rarely have to adjust exposure on any shot (unless I screwed up and pointed the spot at the wrong place). The most I ever tweak is +/- 0.5 stops and if I'm "exposing to the right", I'll pull the highlights back a touch to get detail levels where I want it. If there's need to be sure of a pure white or slightly under (like snow highlights), I'll put one of the color readouts in the darkest areas of the highlight and start to pull highlights until it moves to 252 or so. It's pretty much like the application technique of the Zone system to color slide exposure.

The other thing about ETTR that most people neglect to talk about is that the highlights *are* expected to be slightly blown in the captured image - to ensure that there's data recorded. In post, it's expected to pull back those highlights to get proper exposure since pulling highlights doesn't generate noise where pushing shadows would produce noise.
Thank you! Interesting that you should mention light meter, I went so far yesterday as to put one in my shopping cart but did not order it. I grew up using various Sekonics but when googling it seemed like the only discussions I found were with people shooting film. I will reconsider the light meter. If you were ordering one today is there a particular meter you would buy?
Thanks,
Greg
 

Ray Harrison

Active member
@Greg Haag I'll chime in - I have both the Sekonic L-478 and L-858 (the former has 5 degree reflected spot meter, the latter has a 1 degree spot and a few other bells and whistles and both are nice incident meters as well, of course. While I don't use a meter 100% of the time, I always have one with me for challenging scenes. Others may have their favorites, of course. And of course, I'd recommend the L-858 highly.
 
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docholliday

Active member
I have the L-558 (Pocketwizard) and the L-758DR (Pocketwizard) as well as an old L-328 (see below). I also have the C-700 color meter (I don't use gray cards/Colorcheckers as much anymore with this).

If I was buying a new one...it'd definitely be the L-858 with the new pretty display, USB calibration, and sensor range cal stuff. It depends if you need the spot function or not. I use the 1° spot a lot when I'm shooting LF or if I have a troublesome scene I need to check tonal values in (Zone system stuff). I even use the spot in studio to spot check strobe lighting on tiny specific areas. It also allows you to "calibrate" the meter to your sensor response...though I have yet to see anybody do it.

The L-478 is great if you don't need a real spot (5° is pretty much useless for a spot). I know a few people using it, as well as the ol' trusty L-328F. I got so used to the 328 that it's my "reference" meter I calibrate the other meters to. That 328 went around the world with me back in the 503CW days and I'm so used to it's quirks (I have the little 5° spot attachement for it) that I know what to expect.

Most "old schoolers" will have some really archaic meter sitting around that you'd ask "why do you still have that piece of crap?!". It's usually because they lived with it so long they know exactly what it does.

The nice thing about having a good meter, learning it, and getting used to it is that no matter what camera you have or upgrade to, you'll get perfect exposure the first shot each time. When I occasionally teach new photographers (I hate teaching), I make it a habit to either 1) tape over their display with a large piece of gaffers or 2) paint over their display with liquid latex. It forces them to have no feedback on their shots and then I work on getting them to learn *and trust* their meters (no matter if it's an in-camera meter or a handheld).
 
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vjbelle

Well-known member
This has also been a nagging question of mine and for me its really hit and miss. However I do recall a post by either Doug Peterson or CI that was emphatic about being able to recover anything that wasn't clipped. So for me if I don't see clipping or if the RAW portion of the exposure tool isn't pushed too far to the right I feel I'm OK and almost always it turns out that way. It would be helpful if there was some in depth documentation but it is nowhere to be found.

I find if anything that I am always underexposing slightly which is OK with me..... I also find that the horizontal exposure indicator is of little use. Each scene is also a little different in how the tool works. Practice, practice......

Why don't you see if you can 'completely' recover anything overexposed in you first image?

Victor B.
 

vjbelle

Well-known member
Greg..... I just took a shot from my front door with a tough scene..... lots of snow - which is rarity here. I adjusted so that I was just below clipping. The raw histogram was not all the way to the right but fairly far to the right. The horizontal exposure bar showed about 1 stop overexposure but there was no clipping. The image show just a hint of white on the DB Zone exposure overlay. When I brought it into C1 nothing was clipped. If you want I could make the file available to you. Could be that our two backs don't match for exposure.....

Victor B.
 
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Greg Haag

Well-known member
Thank you Victor! Short of getting a light meter, which I am seriously considering, it appears for me if I push the RGB histogram to the right then back off 2/3 stop of a stop I am generally just short of clipping. I am not sure what to make of my RAW histogram? I have searched everywhere I can think of for information regarding IQ4 and histograms but so far no luck.
 

vjbelle

Well-known member
Clipping is just to bottom of the exposure display. If there is no clipping then the image should be exposed so that anything 'should' be recoverable in C1.

Don't buy a light meter.... a waste of money and another thing to carry around. This will all work for you....

If in doubt, as I am accustomed to, take a couple of shots +-....

Will be in Death Valley end of Feb...... Maybe we can meet.......

Victor B.
 

jng

Well-known member
Hi Greg,

I finally took a closer look at your original post on my computer (vs. my iPad) and can now see the back's histogram more clearly... I generally tether to Capture One in the field and learned to ignore or at least not take too seriously the histogram output on my IQ back(s). With my old IQ3 100, as you have observed I also found that the back's histogram was shifted quite a bit to the left compared to what I was seeing in Capture One on my computer. Of course even the latter's histogram will be affected by color balance and ICC profile, but I think it's a more accurate representation of the data. Your comparisons between the C1 and Rawdigger outputs would seem to confirm this, at least in broad strokes. If I'm in a situation where I think I'm coming close to blowing out the highlights, I don't trust the histogram but rather use the cursor to scan across the image to read out Lab values as this allows me to isolate a smaller area that might not show up in the histogram; I might adjust the exposure if I find anything of interest registering above 95 in luminance, just to be safe. I've only had the chance to take my new IQ4 150 for a quick spin but my impression - again confirmed by your posting - is that the histogram is behaving similarly as on my old IQ3 100.

John

P.S. This thread got me thinking about my Pentax Spotmeters. I managed to find where I stashed at least one of them (the sleek little digital one, the other is the older Spotmeter V), but not sure where I hid the batteries. These were great tools for me back when I was shooting film. I'm surprised that others here haven't mentioned them in this context...
 

Ray Harrison

Active member
Instead of spending my day on my "day job", I've started down this rabbit hole (thanks Greg :)). I did a few experiments with the IQ4/Cambo combo with X-Shutter. I spend most of my time in manual mode and often manually meter when I use the Cambo. It tends to get me where I want very quickly and with a great level of control. Sometimes though I do use the raw histogram/clipping bars and so took my own challenging scene at ISO 50, f16 and letting shutter speed float - bright white wall (metered at 1/125s). shadow area, and an area that metered around 1/30 - 1/60 and bright blue sky, which I did not meter. I manually exposed at 1/80 which worked well as my baseline. Then I tried the following:

(1) "Auto exposure" - maybe I don't understand how it is supposed to work but that was rubbish - over exposed by 2+ stops. Surely I was doing something wrong there.

(2) The ETTR lab feature - it chose 1/100 of a second - again, not sure if I had it set correctly (no real docs) or if it is even supposed to work on this particular setup - but unlike the XF, it does do something and it was close, though I wouldn't call what it did "exposing to the right" - quite the opposite. When I've tested this in the past, it will mostly ETTL and maybe 1 or 2 times out of 10 actually ETTR - seems to be very scene specific but not sure of the exact elements that make it work.

(3) Live view, Manual exposure - just used the raw histogram, clipping indicators and not the RGB histogram. The shutter speed before the raw histogram showed any clipping was 1/80 of a second, what I'd chosen above. 1/60 showed some clipping both in the raw histo and the clipping indicators but did not clip in C1 (other than a warning on a few small areas).

For me, in this scene, using live view, manual exposure, raw histogram got me closest (other than metering the scene manually). I'll poke around on it with some other scenes later.

Cheers,
Ray
 

Greg Haag

Well-known member
Hi Greg,

I finally took a closer look at your original post on my computer (vs. my iPad) and can now see the back's histogram more clearly... I generally tether to Capture One in the field and learned to ignore or at least not take too seriously the histogram output on my IQ back(s). With my old IQ3 100, as you have observed I also found that the back's histogram was shifted quite a bit to the left compared to what I was seeing in Capture One on my computer. Of course even the latter's histogram will be affected by color balance and ICC profile, but I think it's a more accurate representation of the data. Your comparisons between the C1 and Rawdigger outputs would seem to confirm this, at least in broad strokes. If I'm in a situation where I think I'm coming close to blowing out the highlights, I don't trust the histogram but rather use the cursor to scan across the image to read out Lab values as this allows me to isolate a smaller area that might not show up in the histogram; I might adjust the exposure if I find anything of interest registering above 95 in luminance, just to be safe. I've only had the chance to take my new IQ4 150 for a quick spin but my impression - again confirmed by your posting - is that the histogram is behaving similarly as on my old IQ3 100.

John

P.S. This thread got me thinking about my Pentax Spotmeters. I managed to find where I stashed at least one of them (the sleek little digital one, the other is the older Spotmeter V), but not sure where I hid the batteries. These were great tools for me back when I was shooting film. I'm surprised that others here haven't mentioned them in this context...
Thanks John! I love shooting tethered, but have resisted due to the additional 4lbs or so in my backpack but maybe I should reconsider.
 

Greg Haag

Well-known member
Instead of spending my day on my "day job", I've started down this rabbit hole (thanks Greg :)). I did a few experiments with the IQ4/Cambo combo with X-Shutter. I spend most of my time in manual mode and often manually meter when I use the Cambo. It tends to get me where I want very quickly and with a great level of control. Sometimes though I do use the raw histogram/clipping bars and so took my own challenging scene at ISO 50, f16 and letting shutter speed float - bright white wall (metered at 1/125s). shadow area, and an area that metered around 1/30 - 1/60 and bright blue sky, which I did not meter. I manually exposed at 1/80 which worked well as my baseline. Then I tried the following:

(1) "Auto exposure" - maybe I don't understand how it is supposed to work but that was rubbish - over exposed by 2+ stops. Surely I was doing something wrong there.

(2) The ETTR lab feature - it chose 1/100 of a second - again, not sure if I had it set correctly (no real docs) or if it is even supposed to work on this particular setup - but unlike the XF, it does do something and it was close, though I wouldn't call what it did "exposing to the right" - quite the opposite. When I've tested this in the past, it will mostly ETTL and maybe 1 or 2 times out of 10 actually ETTR - seems to be very scene specific but not sure of the exact elements that make it work.

(3) Live view, Manual exposure - just used the raw histogram, clipping indicators and not the RGB histogram. The shutter speed before the raw histogram showed any clipping was 1/80 of a second, what I'd chosen above. 1/60 showed some clipping both in the raw histo and the clipping indicators but did not clip in C1 (other than a warning on a few small areas).

For me, in this scene, using live view, manual exposure, raw histogram got me closest (other than metering the scene manually). I'll poke around on it with some other scenes later.

Cheers,
Ray
Ray, I am sorry I distracted you from work, but thank you for taking the time and sharing! I am uncertain what to make of my RAW histogram, it is so far off it almost seems like either it is not functioning properly or somehow I have have something set wrong. I will keep exploring.
 

Greg Haag

Well-known member
Clipping is just to bottom of the exposure display. If there is no clipping then the image should be exposed so that anything 'should' be recoverable in C1.

Don't buy a light meter.... a waste of money and another thing to carry around. This will all work for you....

If in doubt, as I am accustomed to, take a couple of shots +-....

Will be in Death Valley end of Feb...... Maybe we can meet.......

Victor B.
Victor, I sent you a PM with my cell phone and schedule, it would be great to visit if our schedules match up!
 

Ray Harrison

Active member
Ray, I am sorry I distracted you from work, but thank you for taking the time and sharing! I am uncertain what to make of my RAW histogram, it is so far off it almost seems like either it is not functioning properly or somehow I have have something set wrong. I will keep exploring.
What happens if you ignore the RGB histogram entirely and push the exposure using the raw histogram until just before highlight clipping indicators / actual clipping happens in the same/similar scene? The raw histogram (in theory) should be an indicator of "headroom" - if the RGB is showing clipping but the raw histogram doesn't, it should mean that you still have recoverable highlights and you should be able to push just that bit more if you wanted. Lots of "shoulds".
 
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