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Author Topic: Optimum ISO?  (Read 7050 times)
JohnKoerner
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« Reply #20 on: November 08, 2010, 06:49:18 AM »
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i only use 160/320/640 etc on my MkII. and never use 100 you get pattern noise at 100 but not at 160.   that's why those dxo charts are not the whole story as they never take into account the native iso.


I am curious if there is such a graph for the 7D.

For most of my (admittedly brief) experience shooting DSLR I have tried to stick to ISO 100 religiously. (I shoot predominantly macro.)

Lately, I have had the opportunity to review multiple images from various nature photographers, many of which were truly stunning, and almost none of them were shot at ISO 100 ... but instead were shot @ ISOs 400 and 800.

I have found that, shooting at these higher ISOs has removed the need for flash in most of my images and also allows me to use a faster shutter speed. As such, I almost never shoot at ISO 100 any longer. It is interesting to me that (for the 5DII) the ISOs 160, 320, 640 are the preferred ISOs as well as being successive doubles of each other.

So I am curious to know if there was such a patten with the 7D.

Thanks for any input,

Jack




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bjanes
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« Reply #21 on: November 08, 2010, 07:46:53 AM »
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Most digital cameras don't have an optimum ISO setting. Instead, they have two.

At one ISO setting—usually the very lowest, typically ISO 50/18°, ISO 80/20°, or ISO 100/21°, in some cameras called 'pull'—the digital noise is at its optimum. i. e. lowest. At some other ISO setting—usually one or two stops above the lowest, typically ISO 160/23° or ISO 200/24°, in some cameras the lowest that's not marked 'pull'—the dynamic range is at its optimum, i. e. widest. These two optima usually don't coincide. Exceptions to this rule may exist, in particular at very large or very small sensor formats.

I would like to see data and analysis supporting these two optima. The best DR and SNR will be obtained when the sensor is at saturation. From my experience with Nikon D3, whose base ISO is 200, an ISO of 100 is available, but this is merely overexposure. If you use the same exposure (f/stop and shutter speed), the raw files at the two ISOs are the same. The electronic amplification is the same for these ISOs.  The DXO measured ISOs are the same for the camera set ISOs of 100 and 200, consistent with this observation. DXO shows the same situation for the Canon 5D Mark II. Unfortunately, DXO does not measure the DR and SNR for these overexposure modes.

Roger Clark's data for the Canon 1D do show that the lowest ISO, 50, does have higher signal-to-noise ratios than ISO 100, but at the expense of lower dynamic range and danger of saturating highlights. An ISO of about 75 would be a better match to the sensor range and would not sacrifice dynamic range. Unfortunately, ISO 75 is not available. I take this to mean that the sensor saturation would occur at an ISO of 75.

Regards,

Bill
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01af
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« Reply #22 on: November 08, 2010, 08:47:03 AM »
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The best DR and SNR will be obtained when the sensor is at saturation.

If the sensor is at saturation then dynamic range is zero.


From my experience with Nikon D3, whose base ISO is 200/24°, an ISO of 100/21° is available, but this is merely overexposure.

Sure. That's why it reduces both noise and dynamic range. So for that camera, ISO 100/21° is the optimum for low noise; ISO 200/24° (most likely) is the optimum for dynamic range.
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David Sutton
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« Reply #23 on: November 08, 2010, 12:36:27 PM »
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Did you experiment with livemode in these cases? I was under the impression that livemode actually was slightly superior to MLU in terms of shake in recent Canon DSLRs.

-h
Yes, I believe so too. But the times I've used it I've found it sometimes inconvenient to implement (standing around in the freezing cold waiting for the right moment to fire the shutter).
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bjanes
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« Reply #24 on: November 08, 2010, 04:39:44 PM »
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If the sensor is at saturation then dynamic range is zero.


Sure. That's why it reduces both noise and dynamic range. So for that camera, ISO 100/21° is the optimum for low noise; ISO 200/24° (most likely) is the optimum for dynamic range.


By at saturation, I mean that the highlights are at saturation or just below it, that is fully exposed to the right. This will produce maximum DR. You are incorrect on your second point. Overexposing will blow the highlights. The shadows will have a better SNR. What you gain at the low end, you lose at the high end.

Regards,

Bill
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daws
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« Reply #25 on: November 08, 2010, 08:10:54 PM »
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I've also got the Canon TS-E 24mm f/3.5L II Tilt-Shift coming with the 5D MkII. I'm very excited to use these tools.
Jeff, with that camera and lens combination and your best shooting techniques, you're going to quickly be making some amazing images. My advice is to early on get into as many extremities of light and shadow as you can, and push the 5DII and TS-E 24II as far as you can, in every way you can think of. Shoot as much as your batteries can sustain and your cards can hold (wait until the sweet reality of "no film costs" filters down to gut level!). Then get those RAW files up on your monitor and see what is beautiful, what is fixable and what is discardable. By refining the beautiful and repairing the fixable, you'll soon gain confidence in the combination of the your gear's abilities and your skill at using today's software to produce quality work from less-than-optimum conditions.
- Daws
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ErikKaffehr
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« Reply #26 on: November 08, 2010, 11:29:12 PM »
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Hi,

These are the DxO graphs for Canon 7D, 60D and Nikon D300s.

Two graphs, one showing DR vs. ISO and the other showing SNR (Signal Noise Ratio) vs. ISO.

Nikon uses a Sony chip, with massively parallel on chip AD-converters. The near linear DR vs. ISO is typical of that solution, it seems.

Best regards
Erik


I am curious if there is such a graph for the 7D.

For most of my (admittedly brief) experience shooting DSLR I have tried to stick to ISO 100 religiously. (I shoot predominantly macro.)

Lately, I have had the opportunity to review multiple images from various nature photographers, many of which were truly stunning, and almost none of them were shot at ISO 100 ... but instead were shot @ ISOs 400 and 800.

I have found that, shooting at these higher ISOs has removed the need for flash in most of my images and also allows me to use a faster shutter speed. As such, I almost never shoot at ISO 100 any longer. It is interesting to me that (for the 5DII) the ISOs 160, 320, 640 are the preferred ISOs as well as being successive doubles of each other.

So I am curious to know if there was such a patten with the 7D.

Thanks for any input,

Jack




.
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01af
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« Reply #27 on: November 09, 2010, 03:00:10 AM »
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You are incorrect on your second point.

No, I'm not.


Overexposing will blow the highlights. The shadows will have a better SNR. What you gain at the low end, you lose at the high end.

That is exactly what I keep saying. The highlights will get blown only if there are any highlights to blow in the first place. If there aren't any then nothing will get blown. So in situations where you can get away with the reduced dynamic range at the highlight end, you may take advantage of the improved (i. e. reduced) shadow and mid-tone noise. That's why the ISO 100/21° setting exists. It does make sense, sometimes—even if some fail to understand it.

So—the optimum for noise is not the optimum for dynamic range, and the optimum for dynamic range is not the optimum for noise. So we have two optima ... or even three if we take other aspects into consideration (the third being the setting that is optimal for actually getting the image—after all, you don't always shot at ISO 100/21° or ISO 200/24°, do you?).
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JohnKoerner
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« Reply #28 on: November 09, 2010, 06:45:35 AM »
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Hi,
These are the DxO graphs for Canon 7D, 60D and Nikon D300s.
Two graphs, one showing DR vs. ISO and the other showing SNR (Signal Noise Ratio) vs. ISO.
Nikon uses a Sony chip, with massively parallel on chip AD-converters. The near linear DR vs. ISO is typical of that solution, it seems.
Best regards
Erik


Thanks for taking the time to post these graphs Erik. They're a little different from the previous graph.

Am I reading them right to conclude that the 7D has overall slightly-better DR at most ISOs, but overall slightly more noise also?

Jack




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bjanes
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« Reply #29 on: November 09, 2010, 06:59:24 AM »
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No, I'm not.


That is exactly what I keep saying. The highlights will get blown only if there are any highlights to blow in the first place. If there aren't any then nothing will get blown. So in situations where you can get away with the reduced dynamic range at the highlight end, you may take advantage of the improved (i. e. reduced) shadow and mid-tone noise. That's why the ISO 100/21° setting exists. It does make sense, sometimes—even if some fail to understand it.

So—the optimum for noise is not the optimum for dynamic range, and the optimum for dynamic range is not the optimum for noise. So we have two optima ... or even three if we take other aspects into consideration (the third being the setting that is optimal for actually getting the image—after all, you don't always shot at ISO 100/21° or ISO 200/24°, do you?).

More experienced photographers practice ETTR (exposure to the right). If the highlights have headroom, one gives more exposure. You could use ISO 100 for this purpose, but one stop more exposure might not be the appropriate value to use. Leave the ISO setting at ISO 200 and employ ETTR.

Personally, I never shoot at ISO 100 (LO 1) with the D3. For a given exposure (f/stop and shutter speed) one gets the same results as shown in the graph below. What evidence do you have for your confused theories?

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Jeff Welker
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« Reply #30 on: November 09, 2010, 07:22:32 AM »
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Jeff, with that camera and lens combination and your best shooting techniques, you're going to quickly be making some amazing images. My advice is to early on get into as many extremities of light and shadow as you can, and push the 5DII and TS-E 24II as far as you can, in every way you can think of. Shoot as much as your batteries can sustain and your cards can hold (wait until the sweet reality of "no film costs" filters down to gut level!). Then get those RAW files up on your monitor and see what is beautiful, what is fixable and what is discardable. By refining the beautiful and repairing the fixable, you'll soon gain confidence in the combination of the your gear's abilities and your skill at using today's software to produce quality work from less-than-optimum conditions.
- Daws

Hey Daws;

Thanks for comments and encouragement. Getting familiar with this new equipment will be great fun and most instructive.

Take care.
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01af
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« Reply #31 on: November 11, 2010, 01:26:26 AM »
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More experienced photographers practice ETTR (exposure to the right). If the highlights have headroom, one gives more exposure. You could use ISO 100/21° for this purpose ...

Exactly. So why are you argueing against me? Obviously you don't understand your own statements. It does absolutely not make any difference, technically, whether you set your light meter to ISO 200/24° and, ignoring the metering, over-expose deliberately by one stop on your own devices, or set your light meter to ISO 100/21° and let it control the exposure automatically. In both cases you're effectively using ISO 100/21°, in both cases you're sacrificing dynamic range, and in both cases you're getting less shadow noise. So what's your problem?


What evidence do you have for your confused theories?

To the confused, everything appears confused.
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douglasf13
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« Reply #32 on: November 11, 2010, 04:03:42 PM »
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Andrey (author of RPP) talks a lot about how ETTR isn't generally necessary in newer cameras, and exposing midtones more than a stop or so can affect color.
http://forum.getdpi.com/forum/showthread.php?t=7885
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Daniel Browning
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« Reply #33 on: November 11, 2010, 04:09:26 PM »
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exposing midtones more than a stop or so can affect color.

Increased flare (veiling or otherwise) from ETTR may change color, but aside from that I can't think of anything else that would affect color aside from a braindamaged raw converter (unfortunately many of them are/were).
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--Daniel
bjanes
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« Reply #34 on: November 11, 2010, 08:16:31 PM »
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Exactly. So why are you argueing against me? Obviously you don't understand your own statements. It does absolutely not make any difference, technically, whether you set your light meter to ISO 200/24° and, ignoring the metering, over-expose deliberately by one stop on your own devices, or set your light meter to ISO 100/21° and let it control the exposure automatically. In both cases you're effectively using ISO 100/21°, in both cases you're sacrificing dynamic range, and in both cases you're getting less shadow noise. So what's your problem?

I do understand my own statements, but you apparently don't. One thing you are missing. When one increases the ISO of a camera such as the D3 over base two things are done: 1) the metering causes less exposure to be given and 2) the amplifier gain is increased so that the full scale of the ADC is used. For example, if you raise the ISO set on the camera to 400 from the base of 200, only half as much exposure is given and amplification is doubled so that the the raw data values are recorded at the same level as before.

If you set the camera to Lo1 (ISO 100), the metering changes but the amplification does not. There is no need to change the ISO. Merely expose to the right. There is only one optimum ISO for the D3, contrary to your assertions. I don't know how Canon handles this situation, but I suspect that it is the same as with the D3 (according to the DXO ISO data). Rather than confuse the op with your double talk about two optima, I would merely advise him to shoot at base ISO and expose to the right.

If a higher ISO is needed due to shutter speed or f/stop considerations, as pointed out by the DigitalDog earlier in this thread, one should be aware of the characteristics of the camera as explained by Emil Martinec. Often, one can increase exposure in the raw converter and preserve highlight headroom. However, the histogram would not be to the right. It is the number of photons collected and not the appearance of the histogram that is important. That is one thing that Michael does not point out in his essay.

Regards,

Bill
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Daniel Browning
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« Reply #35 on: November 11, 2010, 08:21:43 PM »
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I don't know how Canon handles this situation.

Exact same, with few exceptions. The "Lo" ISO (ISO 50 on Canon) changes only metering and metadata. One of the exceptions was the original 5D, which implemented Lo ISO with irreversible gain in-camera -- they've since fixed that braindamage (only to make room for new and more innovative ways to design the camera wrong, like the angular response and 1/3 stop digital pushes).
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--Daniel
bjanes
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« Reply #36 on: November 11, 2010, 08:35:05 PM »
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These are the DxO graphs for Canon 7D, 60D and Nikon D300s.

Two graphs, one showing DR vs. ISO and the other showing SNR (Signal Noise Ratio) vs. ISO.

Nikon uses a Sony chip, with massively parallel on chip AD-converters. The near linear DR vs. ISO is typical of that solution, it seems.

Erik. The DR graphs you post are instructive. The lower slope to the left of the DR curve for the Canon means that the camera is not using the full range of the sensor. This is usually to to the electronics and ADC. Read noise increases at low ISO. With ideal electronics, one would lose a stop of DR for each doubling of ISO as Emil Martinec explains here.

The SNR plots at 18% are in the range where photon shot noise is predominant and read noise is less important.

Regards,

Bill
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ErikKaffehr
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« Reply #37 on: November 11, 2010, 09:34:39 PM »
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Yes, that was the idea...

And thank you for your very good explanation.

Best regards
Erik


Erik. The DR graphs you post are instructive.

....
Regards,

Bill
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