Too push or not to push, that is the question.

[Fast Glass]

If I push the exposure, say two stops,on a camera with a better SNR (signal to noise ratio), and use a higher ISOon a camera with a worst SNR.With the best software for the job. Which would have abetter result?


Your thoughts would be greatly appreciated.


John.

[HiFiGuy1]

I have wondered this to myself before, as well. Curious if Daniel or someone will answer this in-depth, but in a way that we mere mortals will understand.


And in a somewhat related question, I wonder how catastrophic it is to under-expose a couple of steps to get a stable shot in a last ditch effort when my ISO 1600 of my 40D will not get the job done.... Is it correctable in post enough that I wouldn't know the difference from a properly exposed shot, or will it be obviously inferior? I know, getting a shot at all is better than not taking it because it isn't perfectly exposed, but I am curious how detrimental it is do what I am asking about. Dynamic range, noise, etc.

[Daniel Browning]

If I push the exposure, say two stops,on a camera with a better SNR (signal to noise ratio), and use a higher ISOon a camera with a worst SNR.With the best software for the job. Which would have abetter result?

SNR is not one single thing. It changes based on the ISO setting (among other things). For a given exposure, some cameras have very poor SNR at low ISO, but get much better at high ISO. (The 5D2 has *10 times* less read noise at ISO 1600 than ISO 100).


If you take just a single camera (not two), then what's important to know is this: for a given exposure, how much is noise improved by increasing ISO instead of using post? On the 5D2, going from ISO 100 to 200 is far, far better than +1 in post. 200 to 400 is quite a bit better than +1 in post. 400 to 800 is somewhat better than +1. 800 to 1600 is only slightly better. 1600 to 3200 is imperceptible. So there is never a reason to use ISO 3200, because doing ISO 1600 +1 EC in post will give you the same noise but more highlight headroom. Going from 800 to 1600 is a more difficult choice. The noise is somewhat better than doing it in post, but you lose a full stop of highlights. I often choose 800 for that reason, but I wont hesitate to use ISO 1600 if noise is more important than highlights.

[twistedphrame]

so I'm a tad confused now, I always worked off the assumption that lower the iso the less visible noise, is this somehow different from read noise?





would it be correct to assume what you mean is switching iso from say 2^x * 100 to 2^(x+1) *100 will add less noise than changing exposure in post (this difference dropping off after a certain ISO range is reached)?





sorry for the powers of 2, I just like math.

[Daniel Browning]

so I'm a tad confused now, I always worked off the assumption that lower the iso the less visible noise, is this somehow different from read noise?

The reason why we normally think about low ISO having less noise is because we assume one of two things:

• The exposure will change with ISO (low ISO = bright exposure, high ISO = dim exposure)
• The low ISO shot will be darker

But in the case of this thread, neither of those are true. When the exposure (i.e. f-number, shutter, etc.) is the same on both, and the brightness is the same on both (one from ISO setting, the other from pushing in post), then the high ISO has less noise than the low ISO.

would it be correct to assume what you mean is switching iso from say 2^x * 100 to 2^(x+1) *100 will add less noise than changing exposure in post (this difference dropping off after a certain ISO range is reached)?

Precisely. But keep in mind that it's only valid when you don't change exposure and ISO at the same time. Just ISO. If you reduce exposure at the same time you increase ISO, then the reduction in exposure will cause a lot of noise. (Far greater an increase than the decrease from ISO.)

[twistedphrame]

<span style="font-size: small; font-family: Times New Roman;"]ok, got it, thanks Daniel

[Fast Glass]

Thanks Daniel for the info.


Here is my predicament. I was all-aboard on the 7D.But lately I was looking ultra-wides, and now I really want one! But my buget limits me to the $1800 price range and no farther. So naturally I looked at the 50D and the T1i. But something else caught my fancy, the SIGMA 12-24MM! The 12mm perspective on a full-frame is awesome! So I took at the Canon EOS 1ds. But it only goes to ISO 1,280.Would I get resonable results if I pushed it to say an equivelant ISO of 12,800? How would it compare the the 50D/T1i? I know what you said about regular ISO's, but how about expanded ISO's? On the DXO website the 1ds is supposed to have better noise than the 50D/T1i. Here is the link http://www.dxomark.com/index.php/eng/Image-Quality-Database/Compare-cameras/(appareil1)/190%7C0/(appareil2)/267%7C0/(appareil3)/319%7C0/(onglet)/0/(brand)/Canon/(brand2)/Canon/(brand3)/Canon.


Thanks Daniel in advance!


John.

[Daniel Browning]

So I look at the Canon EOS 1ds. But it only goes to ISO 1,280.Would I get resonable results if I pushed it to say an equivelant ISO of 12,800?

Most people would not consider the results reasonable.

How would it compare the the 50D/T1i?

If you're even thinking of ISO 12,800, you should run, don't walk, to the nearest 7D. It's far better than the 50D/T1i. Or, consider waiting until the 60D or 550D comes out, I expect them to have the same low light performance as the 7D.


In any case, my guess is that the 50D would be superior to the 1Ds at ISO 12,800, but I could not be certain without seeing 1Ds raw files (A 6.5-year old camera) to check for pattern noise.


The 7D would blow it away when both are pushed to ISO 12,800.

On the DXO website the 1ds is supposed to have better noise than the 50D/T1i.

First, let's talk about what the DXO "low light ISO" metric means:
<p style="padding-left: 30px;"]"The Low-Light ISO metric indicates the highest ISO sensitivity to
which your camera can be set while maintaining a high quality,
low-noise image (based on a Signal-to-Noise-Ratio [SNR] of 30dB, a
dynamic range of 9EVs and a color depth of 18bits). As cameras improve,
the highest ISO setting to produce 30dB, 9EVs, 18bits images will
continuously increase, making this scale open. The Low-Light ISO metric
is of primary importance in photojournalism, sports and action
photography."


That's a very high standard of quality. According to that standard, they rate the 50D at just ISO 700. If you have a similar standard of quality, and you never go above ISO 800 on the 50D, then yes, the 1Ds will be superior.


But if you find the 50D results at ISO 1600, 3200, or higher to be usable in some circumstances, then you can't rely on the DXO "low light ISO" number, because it changes everything.


That DXO number does not apply to your situation.
<div id="txt_rank_lln" style="display: block;"] </div>

[Fast Glass]

Thanks so much Daniel!


Based on your advice I will not get the 1ds. I still really want a ultra-wide and I guess the 50D is a much resonable option. Or just get the 7D and save for a long time and get the 10-22mm.


Thanks again,


John.

[Sheiky]

What about a Tamron 10-24..??? It lacks the usm, but I doubt you'll need it with this lens. And it's half the price and still getting very nice pictures.... BTW a polarizer on these vocal lengths really rocks!





http://www.dpreview.com/lensreviews/tamron_10-24_3p5-5p6_n15/