Let's talk about ISOs

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mumrar

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Matt
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Hi. I own a Canon 450D, and have progressed through to this my 3rd gen consumer Canon DSLR.

The pictures I get are exactly what I want, but there are two situations where I just wish the ISO was more useful. Firstly I'm annoyed with the 'full stop' ISO increments, versus the 1/3 stop of more expensive cameras. This is purely a firmware issue, in telling the electronics how to use the parts at it's disposable. It seems especially bad when wanting a fraction more shutter speed. Say I'm getting 1/320s on ISO 400 and need a tad more, 1/640s is excessive and comes with a noise penalty. Overcast especially seems to hover between 'ISO 400-800 weather' as I call it.

Secondly I like doing pans and zoom blurs of things that are moving, mostly road vehicles and trains. If you want to do this in sunshine, when things look nicer, then you have to shoot at ISO 100 and f/11 or worse for the right shutter speeds, or for more blur in daytime using a tripod, start to use ND filters. Would it not be better to just have a set of lower ISOs starting at for example ISO 6 ad still be able to do a shot at f/3.5 like you would if you were freezing the action?
 
mumrar said:
Hi. I own a Canon 450D, and have progressed through to this my 3rd gen consumer Canon DSLR.

The pictures I get are exactly what I want, but there are two situations where I just wish the ISO was more useful. Firstly I'm annoyed with the 'full stop' ISO increments, versus the 1/3 stop of more expensive cameras. This is purely a firmware issue, in telling the electronics how to use the parts at it's disposable. It seems especially bad when wanting a fraction more shutter speed. Say I'm getting 1/320s on ISO 400 and need a tad more, 1/640s is excessive and comes with a noise penalty. Overcast especially seems to hover between 'ISO 400-800 weather' as I call it.

Secondly I like doing pans and zoom blurs of things that are moving, mostly road vehicles and trains. If you want to do this in sunshine, when things look nicer, then you have to shoot at ISO 100 and f/11 or worse for the right shutter speeds, or for more blur in daytime using a tripod, start to use ND filters. Would it not be better to just have a set of lower ISOs starting at for example ISO 6 ad still be able to do a shot at f/3.5 like you would if you were freezing the action?
Click to expand...

Know what you mean about ISO I used to use the inbetween ones on my 40D
320 and 640 were very useful but the 550D cam only do whole steps 200,400,800 ect
 
mumrar said:
Would it not be better to just have a set of lower ISOs starting at for example ISO 6 and still be able to do a shot at f/3.5 like you would if you were freezing the action?
Click to expand...

Not sure you'd be happy when ISO 100 was then hitting the noise limit.
 
Since ISO is just the camera adjusting gain at the software level, there is little benefit to "in between" ISO values, its just a different value in the scaling algorithm - you aren't magically going to somehow get less noise than if you had 1-stop interval values. If ISO 800 is too noisy for you, I'd suggest either getting better noise reduction software (LR3 etc) or a more modern camera with a better sensro... oh - you are shooting RAW, aren't you...

The same problem applies when going down - an artifical "extended low" iso simply means the camera is throwing perfectly good information away and will give you a drastically reduced dynamic range. ND filters are the only solution once your f-stop is higher than you want. Sorry.
 
I actually have my cameras (which have the 1/3 iso ability) set to change in full stops anyway. When i need a higher frame rate, a massive percentage of the time only a stops worth at minimum is any use. It's also quicker and easier to set and can be done with confidence while looking through the viewfinder.

Did you know that pretty much all canon cameras (except the 1D series i think) intermediate isos can be either more noisy or have less dynamic range than the full stop iso above it? It's because the intermediate isos are obtained by either using the iso below that and boosting (and so making more noise) or using the iso above and rolling back the exposure. That's another reason i don't bother with the intermediates (though to a lesser extent).
 
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