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Thread started 09 Apr 2009 (Thursday) 18:11
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What is the best "standard ISO" for the 5D MkII?

 
Pekka
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Apr 11, 2009 16:12 |  #61

When you shoot one stop lower than "proper" exposure (i.e. with ISO 1600 vs. 3200 rest being the same) the data stored to RAW file will not be the same as you would get with proper exposure (with 3200 in this case) no matter what method is used (sensor native ISO or interpolation). So when you push +1 in RAW conversion the end result can never be the same, even when you know the camera does 1600 and 3200 by computing from same sensor data.

Exposure is a "window" to range of light (bits). If you shift that window in post you will lose some.


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Panopeeper
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Apr 11, 2009 17:18 |  #62

Pekka wrote in post #7711069 (external link)
When you shoot one stop lower than "proper" exposure (i.e. with ISO 1600 vs. 3200 rest being the same) the data stored to RAW file will not be the same as you would get with proper exposure (with 3200 in this case) no matter what method is used (sensor native ISO or interpolation). So when you push +1 in RAW conversion the end result can never be the same, even when you know the camera does 1600 and 3200 by computing from same sensor data.

A side note: if you shoot with ISO 1600, the exposure is higher than with 3200, assumed the same metering.

The exposure is shutter and aperture; ISO is not part of the exposure. This distinction may appear to some as pedantary, but it is not. The amount of captured light does not depend on the ISO selection, and the ISO setting does not make up fully for the light.

Anyway, back to the subject: if you make a shot with the top real ISO and push in in raw processing by 1 EV, the result is almost the same as with the next step (fake ISO) with the same exposure. The fake ISO menas namely pushing the intensity before the raw data gets recorded.

However, there is an important difference, which is against the in-camera pushing, and here your

by boosting exposure you will cut highlights

becomes relevant: boosting the intensity (note: not the exposure, for that is gone when you press the button) in camera is indiscriminate. It pushes out the highest stop, whatever it might be. Everything in the range of the top stop of the highlights gets blown. On the other hand, pushing the intensity in raw processing is controllable:

- you can increase the intensity in general but reduce it in the highlights ("recovery" in ACR),

- you can increase the intensity only in the shadows ("fill ight" in ACR),

- you can increase only the mid-range ("brightness" in ACR),

or any combination of these functions; other raw processors offer the same functions under different labels.

Now, the next stage is, that most cameras "overstep their engineering boundaries". For example the 5DMkII offerst "true" ISO of 3200. However, as measurements prove, it offers NO advantage compared to 1600. ISO 3200 with the 5DMkII is not better than a fake ISO. If you calculate the loss of highlights (a full stop), then it is clear: there is no reason to use 3200 with the 5DMkII except for the brighter preview on the LCD.

The fractional ISO steps of the 5DMkII are all fakes; as such, they are useless for raw shooters. The speciality of the 5DMkII is, that the full stop + 1/3 EV ISO steps are horrendeous fakes; they cause lots of damage [I]in return for nothing[I] (not only the view finder can be used as an excuse).

[SIZE=2]The studySource of Noise (external link), particularly the last set of captures demonstrate just this aspect. namely that increasing the ISO from 1600 to 3200 with the 5DMkII brings nothing but reduction of the dynamic range.


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Pekka
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Apr 11, 2009 17:43 |  #63

Panopeeper wrote in post #7711335 (external link)
A side note: if you shoot with ISO 1600, the exposure is higher than with 3200, assumed the same metering.

The exposure is shutter and aperture; ISO is not part of the exposure. This distinction may appear to some as pedantary, but it is not. The amount of captured light does not depend on the ISO selection, and the ISO setting does not make up fully for the light.

Exposure can not happen without storage media, whether it is film, plate or sensor. So sensitivity of the media is always a factor in exposure. I experience this daily :) I'm not going to fight it, though - if you like to understand ISO in the way you presented then that's ok, too :)

Anyway, back to the subject: if you make a shot with the top real ISO and push in in raw processing by 1 EV, the result is almost the same as with the next step (fake ISO) with the same exposure. The fake ISO menas namely pushing the intensity before the raw data gets recorded.

[SIZE=2]The studySource of Noise (external link), particularly the last set of captures demonstrate just this aspect. namely that increasing the ISO from 1600 to 3200 with the 5DMkII brings nothing but reduction of the dynamic range.

If you take a shot with ISO 3200, then keep all same but take shots with 2500, 2000, 1600 and so on you will soon make all shadow detail disappear. Some scenes (like a gray card) may tolerate it and behave as you described but in real life shooting there is simply no reason to shoot ISO 1600 if you should use 2500. This is what just try to say. Even if some ISO's are "better" than other technically, they should be used properly in getting right exposure for capturing the scene.


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Panopeeper
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Apr 11, 2009 18:45 |  #64

Pekka wrote in post #7711491 (external link)
Exposure can not happen without storage media, whether it is film, plate or sensor. So sensitivity of the media is always a factor in exposure

1. This has nothing to do with ISO.

2. The concept of "exposure" is nothing new, I have not invented it. It does not include the "sensitivity", no matter if it is chemistry or analog electronics or digital manipulation.

If you take a shot with ISO 3200, then keep all same but take shots with 2500, 2000, 1600 and so on you will soon make all shadow detail disappear

This is a concept, not a generic truth. If we stick to the 5D2, it is true regarding ISO 200 to 100, 400 to 200, 800 to 400 and even 1600 to 800. However, it is not true when comparing 3200 with 1600, or going higher.

This is proven in the paper I linked to above.


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Apr 11, 2009 18:55 |  #65

Your points 1&2 above make no sense at all.
How can you say that the media's "ISO" or ASA speed has no bearing on the exposure you chose?

Go back a page , this is what was said;

Pekka wrote in post #7708932 (external link)
You change ISO when you get too low/high shutter speed with selected aperture. Aperture is the the decision that matters most, it "defines" the photo. To make sure you have required shutter speed for the shot you change ISO as much as needed. Forget fear for big numbers and noise charts, make use of them all. Don't let numbers drive your decisions.

Of course the speed of the film or sensor effects our exposure settings, Just as the strength of the light source does. Are you going to say that the available light is also not a part of the exposure equation?
No we can't dial down the sun, but we do agree it's presence impacts the exposure.

So does media sensitivity.


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Panopeeper
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Apr 11, 2009 19:17 |  #66

CyberDyneSystems wrote in post #7711784 (external link)
Your points 1&2 above make no sense at all.
How can you say that the media's "ISO" or ASA speed has no bearing on the exposure you chose?

1. The ISO setting is a factor in the selection of exposure, but it is not a component of the exposure.

Pekka included ISO in exposure. No, ISO as a function has nothing to do with the exposure. The exposure is illumination of the media, determined by the aperture and the shutter time, NOT by the ISO selection.

2. The sensor captures the light (photons) and stores it in form of electric charge. That charge gets converted in digital data at a later stage, and that is, when the ISO setting becomes effective.

A given sensor does not have different sensitivities, but it may have different conversions of the electric charge in digital values; this is known as ISO setting.

Understanding the above is particularly important when the subject is "fake ISO", i.e. when the above process (from capturing the light to creating digital values) does not change by some settings. In such cases the ISO setting is plainly an adjustment of the raw data in an early stage; such adjustments can be done better in raw processing.

The subject of the previous discussion is just this: ISO settings, which are nothing more but such adjustment done too early, indiscriminately.


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Apr 11, 2009 19:40 |  #67

Im not buying the question and im not buying the answers... could be that its 2.30 in the morning :) The guy just wanted to know what the standard iso is... :) you are killing me with graphs... :) If you got the camera just go out and shoot and see which is better for you. I doubt that the next time OP goes out on a shoot his job is on the line, (then he would not have asked), compare 100 to 400 to 800 etc... yesterday i was shooting 800 and the guy next to me 6400... different cameras, different lenses, and different end results. Honestly I cant see an answer to this? :)


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Pekka
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Apr 11, 2009 20:26 |  #68

Panopeeper wrote in post #7711747 (external link)
1. This has nothing to do with ISO.

2. The concept of "exposure" is nothing new, I have not invented it. It does not include the "sensitivity", no matter if it is chemistry or analog electronics or digital manipulation.

When you really start taking photographs you can not ignore ISO from equation.

I don't know who wrote it, but Wikipedia says it:

"In photography, exposure is the total amount of light allowed to fall on the photographic medium (photographic film or image sensor) during the process of taking a photograph."

Media sensitivity is an integral part in controlling how much light actually sticks :)

This is a concept, not a generic truth. If we stick to the 5D2, it is true regarding ISO 200 to 100, 400 to 200, 800 to 400 and even 1600 to 800. However, it is not true when comparing 3200 with 1600, or going higher.

This is proven in the paper I linked to above.

Ok, I just take photos, not use calculators. If I take a shot that produces darker and darker frame it shows shadows becoming value zero which means no data, hence no recovery possible. Have you tried that? That is why a fact "ISO 1600 and ISO 3200 are same inside camera" is moot. You need to STORE the information, that process is "exposure".

Can you please show some photos that prove that a shot taken with 1/50 2.8 ISO 800 and pushed 3 stops will look just like a proper exposure taken with 1/50 2.8 ISO 3200?


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Daniel ­ Browning
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Apr 11, 2009 20:46 |  #69

Pekka wrote in post #7712129 (external link)
I don't know who wrote it, but Wikipedia says it:

"In photography, exposure is the total amount of light allowed to fall on the photographic medium (photographic film or image sensor) during the process of taking a photograph."

Media sensitivity is an integral part in controlling how much light actually sticks :)

Pekka, there's an important difference between light falling on something and light sticking to something. Only the former is correctly related to "exposure".

f/5.6, 1/250, and ISO 400 looks like it is getting more light than f/5.6 1/250 and ISO 100, so the "apparent" exposure is different; however, the exposure is the same because the light intensity falling on the sensor is the same.

Pekka wrote in post #7712129 (external link)
When you really start taking photographs you can not ignore ISO from equation.

First of all, there are many things you "can't ignore", but that doesn't make them part of the definition of the word "exposure". You "can't ignore" highlight headroom, read noise, and many other factors that affect the settings and optimal exposure, but that doesn't make them part of the exposure.

in any case, on many cameras, you can ignore ISO, because they have the same amount of read noise at ISO 50 as they do at ISO 6400. It literally makes no difference what the ISO is set to at the time of taking the photo: the pictures will come out the same from the raw converter when digital gain is applied. Only the *exposure* (light intensity falling on the sensor) will affect the image.

It's only JPEG shooters and cameras with read noise that varies by ISO (gain) setting that makes it necessary for us to be careful with how the ISO is set.

Hope that helps,
--Daniel


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Apr 11, 2009 21:00 |  #70

Without digging too deep into the potential fray, I would say that it depends a great deal on perspective. If you're of an engineering mind, the correct definition of exposure is the quantity of light that actually occurs. Aperture and time control how much total light energy gets to the sensor. I really can't argue with that from a definitive standpoint.

On the other hand, from the perspective of the photographer, you look at exposure from the perspective of how bright that slide, negative, or RAW image file is. One would expect that aperture and shutter speed are two factors. And ISO (or sensor sensitivity, or amplification) is the third factor in that equation. Perhaps post-processing should be a fourth factor. That's fine, but I would expect that a properly exposed image at ISO 3200 would have cleaner shadows than a "pushed" image taken at ISO 1600 and brought up 1 stop in post-processing.

I'm certainly getting some ideas as to what kinds of tests I might want to perform on the 5D2. :)


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Panopeeper
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Apr 11, 2009 22:49 |  #71

Pekka wrote in post #7712129 (external link)
If I take a shot that produces darker and darker frame it shows shadows becoming value zero which means no data, hence no recovery possible

Switching from 1600 to 3200 with the 5D2 does not help on those shadows.

That is why a fact "ISO 1600 and ISO 3200 are same inside camera" is moot. You need to STORE the information, that process is "exposure"

What you are saying is, that adjusting the intensity in raw processing has no effect on the outcome. Do you really think this is so?

Can you please show some photos that prove that a shot taken with 1/50 2.8 ISO 800 and pushed 3 stops will look just like a proper exposure taken with 1/50 2.8 ISO 3200?

This is your example, not mine. I have not stated that ISO 800 pushed two (not three) stops equals to ISO 3200, for ISO 1600 is an effective step.

I stated that ISO 1600 and ISO 3200 produce identical results, i.e. the pushing is a perfect make-up for the higher ISO setting.

However, if you like the example with three stops pushing, then take ISO 1600 and 12800; they would be the same.

In fact, the even higher ISO steps, i.e. 6400 and above with the 5D2 are nothing but "pushing" before writing the raw file.

Following are selections from the red raw channel, ISO 1600, 3200 and 6400. The pixel intensities are roughly one stop apart: 8.78 EV, 7.88 EV and 6.73 EV from saturation (these were the closest ones I found in those shots). This means, that roughly the same amount of light has been captured on these areas (but the increased ISO boosted the pixel values).

Now, look at the noise: 45.7%, 47.2% and 43.4% - roughly the same. Look at the appearance: the noise looks the same.

This means, that increasing the ISO higher than 1600 does not reduce the noise any more (even though ISO 3200 is not a numerical derivative of 1600).

However, look at the forth one: that is with ISO 800. The intensity is 9.91 EV from saturation, i.e. roughly the same amount of light captured as in the other samples, but the noise is 59.8%, much higher than at 1600; the appearance too shows, that the noise is worse here.

This shows, that ISO 1600 does reduce the noise. Therefor I am not suggesting that ISO 800 pushed by 1 EV is the same as ISO 1600.

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Apr 11, 2009 22:58 |  #72

Daniel Browning wrote in post #7712224 (external link)
on many cameras, you can ignore ISO, because they have the same amount of read noise at ISO 50 as they do at ISO 6400

The majority of MFDBs do not have different native ISOs (though they never go higher than 1600).

These cameras demonstrate, that "storing" the pushed values is irrelevant; the ISO setting is only meta-information for the raw processor. In fact, this is a smarter solution than what the DSLRs are doing, for the camera does not cause clipping by applying the pseudo-ISO; the raw processor can do that more intelligently.

Hasselblad announced for a short while ago, that one of their MFDBs will now support ISO 1600. This without any hardware upgrading. Owners of those expensive tools seldom bother for technicalities, and some were outraged when I posted that this is eye-wash. Then in a separate paper appeared, that Hasselblad is doing this because the enhanced noise reduction in raw processing allows for the extra pushing.

So much to ISO vs reality.


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Apr 12, 2009 07:17 |  #73

Interesting comparison, Gabor. The test images, as shown, do point towards what you are saying.

I will experiment with my own 5D2 as time permits to see if this is repeatable. In particular, I'd like to see comparisons in situations with a greater diversity of brightness and color.

I will also look at them when I'm back home since the monitor on my laptop isn't all that accurate.


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Apr 12, 2009 08:39 |  #74

Gabor, you obviously approach things like engineer and mathematician. That's fine. But analyzing color swatches is only part of the whole picture. I'll try to be very clear what my point is:

You seem to talk about noise alone, I talk about whole image, a photograph.

You shoot a subject with 1/200 1.2 ISO 3200. The subject has high dynamic range and you capture it with this exposure so that all intensities are contained in histogram, you have shadow detail and highlight detail.

Now, you say you get same result if you shot it with 1/200 1.2 ISO 1600 and push it one stop in post. No. Noise might be the same, histogram will not be, color will not be. What happens is when you essentially underexpose the frame by reducing sensor sensitivity (or whatever emulation makes it tick) the left side of histogram is lost for good, shadow detail has not been captured . Not matter how you push it in RAW converter you can not make those zeros come alive again.

Daniel said:
"in any case, on many cameras, you can ignore ISO, because they have the same amount of read noise at ISO 50 as they do at ISO 6400. It literally makes no difference what the ISO is set to at the time of taking the photo: the pictures will come out the same from the raw converter when digital gain is applied. Only the *exposure* (light intensity falling on the sensor) will affect the image."

You see things from camera's sensor point of view. In practical photography you must capture range of light into a usable file. Shooting ISO 50 and pushing 5 stops does not give you a usable ISO 1600 equivalent file no matter how sensor or theory has it. Just try it if you don't believe it.

And yes, the difference in us using terms like exposure is exactly like Tom said in https://photography-on-the.net …hp?p=7712297&po​stcount=70 . When you ask a photographer "what was the exposure" you can not avoid taking into account the effect of ISO, really. If I'd give advice "shoot in this venue with these lights with 3.5 1/250, any ISO you like because it won't matter" I'd hear about it later!


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Apr 12, 2009 08:51 |  #75

Is there such a thing as the best standard ISO? I would think the very lowest one (waiting for an engineer to rebute that). 400 is a happy medium, but definitely not a one size fits all.


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What is the best "standard ISO" for the 5D MkII?
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