disadvantages to ISO expansion?

Having just finished searching for the answer to this question on the web and within forum. (doesn't mean its not there, I just did not find it)

Does anyone know why I would not want to just turn on the ISO expansion and leave it on?

With my 10D I never liked anything above ISO 400 and would only go to ISO 800 on rare occasions. ISO 1600+ was useless to me in my opinion so I did not bother with ISO expansion on my 10D, on the flip side with my 1DsMkII the ISO 3200 looks a bit better then ISO 800 on my 10D, so there will be times when I may use it.

Since Canon felt the need to put it in a optional category, I would presume there was a reason for this.

Any one know the reason?

Thanks,

I just read something about that the other week but I can't remember where (that's old age showing through right there ). Anyway, from what I can recall, it had something to do with either some of the color at the highest ISO not being accurate or the tone sensitivity not being consistent throughout the exposure range. I guess Canon makes you go out of your way to select the 3200 ISO setting to make sure that that's what you want to do and are not setting it accidentally.

I'll see if I can find that info for you when I get a chance.

in the 20d manual it says that some people feel that 3200 is unexceptable therefore when you turn on the expansion to be warned about the excessive noise levels.

That's really strange - I find ISO 800 very usable with my 10D, and even shots at ISO 1600 are quite usable once I run them through the RAW converter with noise reduction option turned on. The key to low noise is to expose to the right - that way the image has fewer dark areas in which the noise is the worst. See this photo for example - it was shot at ISO 800 (100% full resolution, straight from the camera, no post-processing), and being properly exposed is shows almost no noise, except in the most dark areas (which can be easily removed in post-processing) :

http://www.pbase.com …s/image/3611420​6/original

ISO 3200 is quite noisy with 10D, but it's better to get a noisy shot than not get the shot at all - that was the reason to include ISO 3200 in this camera, I believe. I used ISO 3200 in a few occasions - and had to convert the images to B&W every time, it was the only way to get usable pictures due to heavy color noise. In B&W it looked more like high-sensitivity film grain.

On my 10D, I might be able to accidently run the ISO up to high, but not on my 1DsMkII, it takes two fingers for that trick, bit hard to do accidently.

I believe the 20D answer, but that is a stupid reason and especially if applied to the 1Ds series. Although I don't think they would design it just to remind people you will get high noise that would be obvious. Then again...

Olegis,
You have to take into account I am a former Imagery analyst and a bit overly picky as to image quality. I tend to leave my cameras on ISO 100 and only change when absolutely needed because I can't get the shot any other way.

There is also a chance that my 10D is noisier then yours for some reason.

I tend to crop my images as much as 50% at times, which also tends to make noise more noticable and I like to be able to print upto 13x19" prints which adds another layer to the quality factor, so any noise is usually bad, but sometimes I have to live with it. Examples being like when I take IR shots of people as they can hold still for 4-6 seconds, but not 15-30 seconds, so I need to up the ISO a bit to get the shot, since I need a bring the aperture down to compensate for my adjustment for the IR focus point.

Overall however,
on my D60 I found ISO 100 good, 400 acceptable, 800+ not unless desperate.
on my 10D I found ISO 100-200 good, 800 marginal, 1600+ not unless desperate.
on my 1DsMkII I find ISO 50-400 good, 800 decent, 1600 acceptable, 3200 marginal.

This is just my opinion for my style of photography and what I want out of my pictures. If needed I can get a perfectly good picture from ISO 3200 on my 10D, I just won't like it.

I have allways left expansion on.

When I want or need 3200 ISO I do not want to have to go fiddling in custom functions to get the setting.

There is no reason not to leave "expansion" turned on unless you have a reason to never use the expanded settings... Heck there are times I drop to ISO 50 when I have a fast lens wide open in strong light.

Its set off by default so that you don't accidently set it when you didn't mean to. I have done that in the past and I find that 3200 ISO is a bit too grainy for my liking.

As far as I can tell, it doesn't really have a 3200 mode, it just adjusts something else to simulate it.

Alan

From what I've heard, the 10D achieves ISO 3200 by underexposing ISO 1600 by stop and doubling the values that come out of the A/D converter. Therefore, if you shoot RAW, you can avoid ISO 3200 and use ISO 1600 with -1 EC. I suspect that the 20D operates the same way.

I got a response from Canon (I usually don't when I can't find it on my own)

The rep stated that it causes a longer processing time when on as the only disadvantage.

"Dear Mr. Dolan,

Thank you for your response.

The only real disadvantage to ISO expansion would be the longer
processing time.

Unfortunately, the spectral range is not published information."

Someday I will bother to take the time to stop next door (figuratively) and visit NASA Langley Research Center (since I drive through it to get to/from work) and hook up with the guys that have the equipment and find out for myself what the spectral respose of the sensor is, since Canon seems to not want to part with the information, even after the camera is released.

I can understand them not wanting to before it is released, but not after.

At least they answered one of my two questions, Better then I expected.