ISO v contrast

Even with fast lenses, contrast lowers as the ISO increases - how best to overcome this and correct the outcome?

<p>Simple -- only use ISO 800+ when you HAVE to. Always be aware of your ISO. Aim for 100 or 200 all the time unless you need a faster shutter speed. Auto ISO is something I abhor.</p>

<p>Your mileage will probably vary -- but still, very high ISO on modern EOS (1600 and higher) bodies delivers <strong>excellent IQ</strong> regardless. What's to complain about?</p>

<p>Turn off auto iso, I hate the "feature". Do test shots and manually select the iso, take control and post processing issues are mitigated. When you have to shoot higher iso make sure you expose to the right, underexposed high iso images are the worst to process.</p>

<p>Ditto, to Scott and Ken. ISO is a factor you can override on every DSLR unit Canon makes. If you shoot at the lowest <em>practical</em> ISO, you'll always maximize the potential DR of the resulting image. Frankly, given the awe inspiring performance of current sensors, it has become something I change almost as often as the aperture.</p>

 

There are two reasons why contrast drops when ISO increases. First, higher ISO means lower dynamic range, which means range of brightnesses that the camera can capture decreases. That leads to lower global contrast. Second, higher ISO means more noise and noise reduces contrast. That leads to lower local contrast.<br><br>

 

If you can't overcome this problem in the natural way (by shooting at lower ISO), post-processing offers a large variety of ways and tools to make the contrast of the image almost anything you'd like it to be.

<p>Yet again, use only the "advanced" modes P, Tv, Av, M.<br>

Then, choose the ISO <strong><em>you</em></strong> want and get the most effective lens hood you can get to cut down on extraneous light bumping around inside the lens. At higher ISOs, I think, such reflections that would be minor at low ISOs, are 'sensed' more.<br>

Finally, in post-processing, push up Contrast. ;)</p>

<p>Although I agree that auto-ISO is typically not the best idea, it does depend what you are shooting and how the light is changing. We shoot auto racing weekends, and in those conditions you don't always have the time to pre-set everything, especially with races under the lights and 24-hour races. There you just focus on shutter speed and composition, and let the camera handle ISO, and maybe even aperture, although I tend to try to manage that depending on the DOF we're aiming for. So, no "rule" is for every situation.</p>

<p>When I shot auto racing with film I managed to preset the iso. I shoot live music now with very changeable stage lighting but have still never found the need to rely on auto iso.</p>

<p>Whilst variable iso does have some merit it is like all automisation, it only works for you if you understand what it is doing when it is doing it, I would venture to suggest auto iso has given people more unnecessarily bad shots than saved once in a lifetime opportunities, what it can do is drum in the unthinking attitude of "the camera will sort it out" that invariably ends up resulting in the question as posted.</p>

<p>If you have to rely on auto iso then at the very least take control of it and program in the range you are happy for it to use, if you can't process a shot that was taken at 3200 iso then there is no point in taking it, set the range limit for 1600, shoot it at 1600 and learn to pan, or get a faster lens, or use lights, or whatever.</p>

<p>@Scott - I agree that in the film days we worked differently - usually I had a couple of cameras with different ISO (or, if you're old enough, ASA) ratings to be able to handle changing scenes. The option now to have all of that in one camera is a good thing - and I often go with the notion that the camera will sort it out in a race environment (but not usually in other places). What I'm more focused on is the ability to have a wide range of shutter settings, to quickly switch from a series of "freeze" shots to a long pan on the same camera without a bunch of fuss, in the same light without doing anything except working with shutter speeds, and perhaps apertures if you're close enough for that need. I know what ISO I'm likely getting into - it doesn't take long to know when the camera is going to head to 3200 to get a shot, and I can decide if that's acceptable without fiddling with it.</p>

David,

 

I would confidently put you in the category for whom "it only works for you if you understand what it is doing when it is

doing it", my point was more for those that don't have that experience and hands on knowledge, for them auto iso can be

an image quality sapping negative that can be a surprise if they don't realize what it is doing. Like so many other features,

used correctly it can be a fantastic help, but when used inappropriately it can be counter productive.

 

And yes, I surely do remember ASA :-)

<p>Wow this is all confusing. I always thought the higher the ISO, the higher the contrast having nothing to do with the range of dMax but having to do with how steep the curve is from pure black to pure white. Higher ISO- higher sensitivity to light, steeper curve between light and dark = higher contrast.The practical look is less grades of tone between white and black, more blocky shadows, more halted whites. If instead you are talking about a higher range of contrast i.e. extended contrast curve than what you all are saying makes more sense to me. But am I all confused is it me. or is this thread misusing terms?</p>

<p>Barry - there seems to be some disagreement in the various forums one reads. One school of thought is that for a given scene, shooting at low and high ISO's will not change the apparent contrast if other settings are adjusted to match. Elsewhere I read individuals saying that it does make a difference, with higher ISOs resulting in less contrast, and that is compared to the idea of shooting ISO 50 film as a conscious choice over ISO 400 (for example) where the ISO 50 provided noticeably higher contrast. The argument seems to be about whether those results were affected by specific film emulsions, and of course you don't have that impact with a sensor. It's not one of those things I've tested specifically, but I'm thinking I need to do that based on this discussion. I use higher ISO as a way to get more shutter speed and DOF; but perhaps the notion of contrast would make a difference too.</p>

<p>I really think people are saying higher contrast, when they mean higher range of contrast.. Well, in school anyways, lower contrast meant more grays, less blacks and whites, meaning not a deep black black or white white with more stops of gray scale between true black and true white. High contrast meant fewer available stops of grey between full white and full black, but easier to get true black and true white, such as slide film tended to have. High Iso pulled the scale up, but the curve between bull black and full white is steeper, i.e. fewer shades of grey between full black and full white.<br>

Another way of saying it is high contrast is like moving the sliders on your levels or curves adjustments in you histograms in from the ends. Also called constriction, No?<br>

Here's an example from film shot at 1600 but pulled processed to 1200. Why? Because in film, this allows the blacks to come up and get some tone while restricting the development of white so the whites don't get so overpowering like you see with reflections and lights in windows etc. <img src="http://farm3.staticflickr.com/2325/2015898932_4919229b32_o.jpg" alt="" /> Here is digital at 2000 ISO, though because of the lighting situation may not be best exampleI think it shows higher, not lower contrast. i.e., lot of black, lights strong, and very little in between</p><div></div>

<p>Hey, if my terms or understanding is wrong. please let me know because It means I've been operating under some false premises for quite while...YIKES.</p>

<p>David, one thing I do know for sure, if you are measuring a middle grey let say a number 21/2 and filtered grey in darkroom terms, and then develop the same neg with 0 - 5 contrast filters, the middle grey will be the same on all of the prints. I know because we had assignments on this so I've done empirically. The rest of the contrast will go from extremely low "0" to extremely high "5". Especially easy to see if you use a well exposed negative to begin with. So the contrast of the middle grey will stay the same, but everything else will either broaden (lower contrast) or restrict (higher contrast) It seems here that people are talking in reverse. </p>

<p>Barry - I think you may be right about the definition of contrast, vs. a range and the conversation here. Here's a shot from a race this spring, where I knew it was going to require high ISO (2000); but I expected a low-contrast perspective (or what I call that) and I think it meets your criteria about broader range. I certainly could add contrast in post-processing to get a more "dramatic" look but I wanted that race-track waking-up feeling that this contrast gave. So now I'm questioning whether the basic notion of high ISO forcing a low-contrast look is the right question.</p>

<p>I think the OP's question was whether high ISO forced a low-contrast look - and that would meet your definition I think. But you've thought more about this than I have, clearly.</p><div></div>

<p>just as important, dynamic range decreases the higher the ISO. I too like to stick to the lowest possible ISO, rather than bump it up one or two stops and not have to worry about technique.</p>

<blockquote>

<p>Turn off auto iso, I hate the "feature".</p>

 

</blockquote>

<p>I have the opposite opinion. My 5D2 is in auto-ISO mode 95% of the time. I love it. The camera always selects the lowest practical ISO and is, in effect, only doing what I would normally have to do myself anyway. Not only does it take focal length into account, it also takes image stabilisation into consideration and even works with extenders attached. In changing light conditions it enables you to keep shooting at the highest possible image quality without having to fiddle around.I only wish it was a bit more customisable so you could set upper and lower limits. Naturally the feature is fairly useless if you are using a tripod.</p>