ISO Question

[Dennis Connell]

In the ID series Canon bodies, particularly 1DMKIIn, is it to better stick with the "standard" ISO's 100,200,400,800 or is it OK to use the in between ISO's 125,160,250,320,500,640 to get the best IQ ?

Dennis

[Dan Brown]

IMHO, 1/2 stops are good enough for exposure increments. As for shutterspeeds, I might resort to the 1/3rd stop increments to squeeze as much as possible out of the top speed for a given situation. I have set my Nikon D300 for 1/2 stops for both ISO and SS.

[Axel Hildebrandt]

If by better you mean as little noise as possible then sticking with standard values is a good idea, above ISO 800 there is no advantage anymore, though.

[Roger Clark]

Hello Dennis
BPN member Emil Martinec has studied this question:
http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p2.html#read_vs_iso

Result: there is a small increase in read noise at intermediate ISOs but read noise is only significant about 10 stops of more below sensor saturation. Even in deep shadows, photon noise and fixed pattern noise would be greater and tend to mask any effects of the amplifier noise at intermediate ISOs. A greater concern to me would be less control/knowledge of when the sensor saturates. I usually use only the factors of 2 ISO: 100, 200. 400, 800 etc.

Roger

[Dennis Connell]

Thanks for those replys !
"Birdphotographers.net" is the go to site to get the info, that is for certain.

The study Roger directed me to is just what I was looking for, thank you !

Taken from Emil Martinics' study :

"On the other hand, if shooting raw, it makes little sense to use the extended ISO's since they are simply mathematical manipulations of the raw data post-capture, and their main effect is to throw away one or more stops of highlight headroom as the doubling, quadrupling etc of the raw values pushes more and more of them beyond the maximum recordable value of 4095 for 12-bit, or 16383 for 14-bit data. Setting the highest analog ISO amplification keeps the headroom, and one can always do as much additional software amplification as is needed afterward during raw conversion."

Good Shooting,
Dennis

[Axel Hildebrandt]

It is important to mention that this applies to Canon cameras only, the intermediate ISOs in Nikon are 'real' ISOs that are hardware-implemented and there is no reason not to use them.

[Doug Brown]

I don't hesistate to use the intermediate ISOs on the 1D Mark III.

[Roger Clark]

Dennis,
While I agree with Emil on the math and the effects, there is one practical thing one should consider if needed extended ISO: image preview. If you need the speed, e.g. to freeze action, and you limit ISO, to say 1600, then you are underexposing and it is more difficult to preview the image to see what you are getting. I rarely go above iso 1600 (and never for deep sky astrophotos for exactly the reason Emil states). But for a low light action situation, I'll sometimes go to the high ISO to preview what I am getting, then back off on the ISO and underexpose, then fix it in post processing. But for more static subjects, I'll use the lowest ISO and increase exposure time as much as I can as that gives an image with better signal-to-noise ratio.

Roger

[Emil Martinec]

In the ID series Canon bodies, particularly 1DMKIIn, is it to better stick with the "standard" ISO's 100,200,400,800 or is it OK to use the in between ISO's 125,160,250,320,500,640 to get the best IQ ?

Dennis

There was a discussion of this issue at NSN some time ago:
http://www.naturescapes.net/phpBB3/v...p?f=2&t=139621

The upshot is that the in-between ISO's offer very little on 1 series Canons. For the details see my posts in the linked thread.

Note also, that the extended ISO's (eg 6400 or above) are a bit different than intermediate ISO's on the 1 series. While the in-between ISO's such as 125,160,250,320,500,640 on these bodies are implemented (poorly, IMO) as hardware amplifications, the high ISO extension is implemented in software post-capture, by multiplying the RAW data by a numerical factor, something that could equally well be done in competent RAW converter software, so there is no improvement in the data. In fact, the data is degraded by throwing away highlight headroom.

The xxD series Canons are different than the 1 series; in-between ISO's are implemented as software multiplications, just like the high ISO extension. Again the consequences for photography are explained in the linked thread.

Finally, all these arcane issues are specific to Canon's implementation of ISO; Nikon does it differently (and better, IMO) and there are no drawbacks to using in-between ISO's on Nikon.

I use the Custom Function that restricts ISO to "full stop" values 100-200-400-800 etc, on both my 1D3 and 40D, and underexpose by 1/3-2/3 stop if I need the shutter speed or DOF.

[Dennis Connell]

Thanks Emil, for the the link to the previous discussion on this topic.

There was a discussion of this issue at NSN some time ago:
http://www.naturescapes.net/phpBB3/v...p?f=2&t=139621

This info is what I was looking for. I found this all very interesting and hope others did as well.:)

Good shooting,
Dennis