under/overexposure

Questions, comments and suggestions regarding Phase One P+ series and P series digital camera backs.

under/overexposure

Postby Joris1 » Sat Dec 03, 2005 8:50 pm

Can anyone say something sensible on the following:

I have heard people say that it is better to slightly overexpose rather than underexpose when shooting digitally.
Sometimes when the contrast of a subject is too high (or would be too high for film anyway) one must choose between the lesser of two evils, and then rescue details from the reserves that the RAW image has.

My feeling is that it there more retrievable detail in the shadows (at the cost of more noise) than in the highlights.
Whenever I apply a negative exposure correction the highlights go funny, and I get effects that look like banding.

I used to always underexpose my negative film slightly, and by habit continue to do the same on the P25.

Am I overlooking something smart in C1?
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Postby damienlovegrove » Sun Dec 04, 2005 12:06 am

Well unlike you I always used to overexpose my negatives by about half a stop and cut the dev time by about 15%.

On the P25 at 400 ISO I am generous with exposure. I nearly allways use exposure compensation on the H1. For pictures without sky or large areas of highlight I tend to aim to get info well into the right section of the histogram. This results in me using a small amount of negative exposure compensation in C1. I combine this with a mid tone levels adjustment. The result is a set of slightly flat images with low noise in the shadows and the highlights well in control. I usually then set the contrast for each element of the image seperately in Photoshop using curves before dropping down to 8 bit. This gives me a system similar to hand printing using split grading. If you don't want a Photoshop stage then use the CC control to set the desired contrast.

With 100 ISO (in the studio) I get the exposure spot on with all controls at their centre marks. I adjust the contrast with the lighting. If I am after an effect like a washed out bleached look I set up the first image by hand then set C1 to use the settings as the default for subsequent captures.

The exposure tool has it's own characteristics. It is not linear. If you 'push' the exposure it ramps the highlights so that they tend towards white but never quite get there. Similar to using the curves by pushing up a point 3/4 of the way up the slope on RGB. The levels control right hand slider is linear and will clip your highlights at will. The centre slider is like a gamma control that does not effect the highlight or lowlights and is very useful indeed.

I can understand contours in the highlights with quickproof but I've never had them in 16 bit output unless of course I have clipped the highlights too hard in exposure. In this instance a subtle INCREASE with the exposure tool can be forgiving if used with a slight drop in contrast. It renders a high key arty look.

The answer is to be generous with exposure but keep your highlights in the picture. I've shot 21,000 frames on my P25 at weddings in every light imaginable usually with a white dress and a black suit in the same frame so extremes are critical for me. I spent days getting a system of exposure that was full proof and it is very important to set the brightness of your P25 screen to match your computer. I took a frame, downloaded it and put the CF card back in the P25. I then looked at the frame in C1 with the settings as default and matched the P25 brightness to give a similar representation of highlight and shadow detail. Forget about the midtones because the gamma of the P25 screen is totally different to a CRT or TFT computer screen. You might be tempted to make the P25 screen brighter as it will seem dull. But if you do this then you will start underexposing, so beware.

I hope this helps.

Damien.
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over/under

Postby Joris1 » Sun Dec 04, 2005 3:29 pm

Damien,

Thanks for a very detailed answer.
I guess I´ll have to take some time to run a set of experiments to see how I can get the best ouf of my raw images in C1 - I suspect I don´t know half the subtleties. All is fine in the studio, it´s just outdoor photography and burnt-out skies I am scared of. I always keep the camera at 50ASA (no people, so exposure speed is rarely an issue).
I don´t trust the monitor image at any brightness (there are only three settings anyway), but I do check the histogram.
You are saying that you´re not worried when the whites go over the right edge?

So much to learn....
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Postby Stefan1 » Sun Dec 04, 2005 5:37 pm

Hi Damien,

great tips for me to start with my new P25.
Thanks !
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Postby damienlovegrove » Sun Dec 04, 2005 5:46 pm

50 iso high and contrast scenes need careful exposure. You have several options:

1) If you are not capturing a moment in time and are tripod mounted take two exposures one for the shadows and one for the highlights. combine them later by processing them both to the same dimentions in C1 and open both in Photoshop. Drag one image on top of the other using the move tool and with the shift key held down. They will snap into perfect register. Then create a mask on the top layer and paint in the mask to let the bottom layer through where needed.

2) Or take one well exposed capture and switch C1 film curve setting to Linear. This will give the best contrast to your sky. set the exposure as required for the sky and process the image. Then switch the film curve to film or film extra shadow, set the exposure for the midtones and shadows and process again. Combine the 2 images as described above in option 1. This is how Ansel Adams would do it today I'm sure! It's a similar approach to two bath processing of negs.

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linear film curve

Postby Joris1 » Fri Dec 09, 2005 5:42 am

Damien,

The linear film curve trick sounds plausible - thanks.
I'll try it out as soon as I can.
I have on occasion processed the same file twice, once for highlights and once for shadows, rather than to make double exposures. When it's the same image, obviously register is perfect. With colour film I often made 2 exposures, but lining up two scans was always a nightmare. Sometimes I would control the conrast with push and pull processing (which is as far as the zone system would go in colour).

But I had never seen the use of the linear film curve - perhaps it'll work out...

Re: film grain for skin: I add (very subtle) grain to ALL images. It doesn't show up in offset printing, but portfolio prints get a more \"photographic\" look, and it adds some texture to burnt-out highlights.
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Postby pmirror » Sun Dec 11, 2005 5:13 pm

Thank you for sharing Damien. Nice trick. I'll try it later :)
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