Simple 'ISO Range' question.

Bluie

Bluie

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Martin
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Hey everyone!

I'm still new to this whole photography business, and this is my first ever post, so be gentle =)

I'm just wondering exactly what is meant when they say an ISO range is, for example, 200 - 3200, but 'expandable' to 100 - 6400. I ask this as I mainly try to shoot in ISO 200, and no lower, as I'm almost 'put off' as it were, into using the 'expanded' section of the ISO range. (I'm not sure why either!)

Really, my question is... If the 'Low 1' setting on my ISO is equivalent to ISO 100, why is not ISO 100? =)

Hope this makes sense and thanks in advance!
 
The camera sensor can't actually be set as low as 100, 200 is it's base ISO. The ISO 100 setting takes an overexposed shot with the sensor at 200 then reduces the exposure of the output file by a stop (be it raw or JPG) so you've taken an exposure one stop longer (or wider aperture) than at ISO 200. So you get less noise in the shadow areas at the sacrifice of dynamic range in the highlights.
Personally I'd use this setting only if you're taking long exposures and want to lengthen them more or want to use bright apertures for shallow DoF in bright light (which might max out the shutter speed at ISO 200 so 100 could let you shoot a stop brighter).

Same with the 6400 setting only reversed, it takes the shot underexposed at 3200 then brightens it a stop on the output file. It lets you use a stop dimmer aperture or a stop faster shutter speed but the noise level will increase even more and dynamic range in the shadows is sacrificed.

I'd stick to the normal ISO range unless the situation demands an extreme :).
 
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Squishy! Your my hero =)

I wasn't sure if any of what I was saying made sense, but you've answered it perfectly.

Thanks a lot! An amazing reply to my first post here! Looks like I'll be sticking around.
 
Worth bearing in mind with these "made up" ISOs that they can be more prone to noise.

My 7D has 1/3 stop ISOs available so rather than just the normal 100, 200, 400, 800, 1600, 3200, 6400, there are values in between where the camera processors make up what they think it should be (it's a lot more complicated than that but you should get the idea ;) )

They can work OK but from what I've read on here, it's best to avoid if poosible.

Having said that, I would think there'd be less problem using ISO100 than ISO6400.
 
Thanks Russ, I think I'll take your advice and just avoid if possible! 200 - 6400 is still plenty for me =)
 
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