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Old Jun 14, 2010, 12:34 AM   #1
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Default Auto ISO

I'm wondering if anyone ever uses Auto ISO? I'm curious as to if it's useful in any situation - or never.

I shoot mostly always in M or A mode. I've never used it, though have started playing with it just to see what it does. One thing I noticed it did was set ISO to 200 in extremely bright outdoor sunlight. Strange.

I would worry that it would self adjust to some ridiculously high ISO high noise setting in low light. Maybe not the best place for this then...so why is it even there?
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Old Jun 14, 2010, 5:30 AM   #2
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As a general rule, Auto ISO tries to insure that your shutter speed is 1/35mm equivalent focal length or faster. In other words, it's just trying to insure the shutter speed is fast enough to reduce the potential for blur caused by camera shake. It's not really smart enough to take subject type into consideration (are you shooting a still versus moving subject), and of course, it doesn't know if you're using a tripod.

Since camera shake is magnified as focal lengths get longer, the "rule of thumb" for reducing blur from camera shake is 1/focal length (and you should use the 35mm equivalent focal length). If you're using camera with an APS-C size sensor, you'd want to multiply the actual focal length by 1.5x. So, if you're shooting with a 300mm lens (same angle of view you'd have using a 450mm lens on a 35mm camera), the camera is probably going to try and keep shutter speeds at around 1/500 second using Auto ISO.

Quote:
One thing I noticed it did was set ISO to 200 in extremely bright outdoor sunlight. Strange.
You didn't mention the model you're using. But, note that with some camera models (for example, the Sony A700), the base ISO is ISO 200. With that camera, using ISO 100 will degrade image quality in comparison, reducing Dynamic Range, because it works by over exposing the image, then "pulling" it during processing (reducing the values associated with each pixel so that it appears to be properly exposed) in order to simulate an ISO speed that's lower than ISO 200. So, you can more easily blow highlights trying to use ISO 100.

I use Auto ISO from time to time when outdoors in changing lighting (for example, starting out early in the morning before the sun comes up much when it may use a higher ISO speed setting to help prevent blur; then drop to a lower ISO speed as the sun comes up more and the lighting gets brighter).

Note that it doesn't take Stabilization into consideration (the last time I ran tests anyway). So, it may lean towards a faster shutter speed than needed. But, that's not a bad thing (depending on how high the ISO speed is), since faster shutter speeds can help get sharper photos, especially if wind blowing foliage is a factor in dimmer lighting.
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Old Jun 14, 2010, 6:02 AM   #3
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BTW, here is some discussion on the rule of thumb for preventing blur from camera shake, and if that rule should be changed for higher resolution cameras.

http://forums.steves-digicams.com/ge...n-cameras.html
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Old Jun 14, 2010, 8:56 AM   #4
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Thank you - interesting that it's intent is to help with camera shake above any other purpose. I guess this sort of makes sense, though I never would have thought of that - believing proper exposure and less noise being most important.

I shoot both the Sony A850 and A700 FWIW - in this last case , trying "AI" I was using the 850.

I would think that using Auto ISO indoors in low light would be unwise considering all of this - as it would try to jack the ISO to keep a faster shutter, resulting in noisier images (the enemy of low light digital photography).

Something to play with, probably just not for any time I'm doing a shoot where I know what ISO I really want/need. Thanks again!
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Old Jun 14, 2010, 8:57 AM   #5
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Quote:
Originally Posted by JimC View Post
BTW, here is some discussion on the rule of thumb for preventing blur from camera shake, and if that rule should be changed for higher resolution cameras.

http://forums.steves-digicams.com/ge...n-cameras.html
Also an interesting discussion, thanks!
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Old Jun 14, 2010, 9:10 AM   #6
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Originally Posted by CaliGal View Post
I would think that using Auto ISO indoors in low light would be unwise considering all of this - as it would try to jack the ISO to keep a faster shutter, resulting in noisier images (the enemy of low light digital photography).
Well... sometimes a bit of noise can be better than a blurry photo if your shutter speeds are too slow. ;-)

Most of the time, in more controlled lighting conditions (i.e., indoor shooting), I'll set ISO speed manually. But, in changing lighting outdoors when I'm shooting stationary versus moving subjects, sometimes I'll switch to Auto ISO instead using a model like my A700 (as it's more tolerant of higher ISO speeds compared to many cameras and I'd prefer the faster shutter speeds).

BTW, if you haven't tried it yet, you may want to upgrade to the latest Sony IDC version 3.2 for raw conversion. I was impressed at how well it worked using Auto Noise Reduction with the A850's files.

See this post for more details:

http://forums.steves-digicams.com/so...-sr-3-2-a.html

Of course, all of the RAW converters are making progress with Noise Reduction Algorithms anymore (newer versions of DxO Optics Pro, Adobe Lightroom 3.0, Bibble Pro 5.1, etc.). But, I was quite surprised at how much progress Sony has made in this area with it's latest converter.

If you get a chance, please try to post more often, as we don't have a lot of Sony dSLR owners sharing images here yet.

I'm a Sony shooter myself.

By the way, Welcome to the Forums.
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Old Jun 14, 2010, 10:39 AM   #7
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Thanks Jim - again much appreciated. I'm already hooked on Lightroom and with the new NR in V3, it's a real winner! It would take a lot for me to change camps on RAW processors and input workflow software at this point.

The Sony software has never been very good, although yes better in the latest rev. The interface is horribly clunky still and miles behind LR in functionality.

Remote control is not working for the A850 currently, though I have managed to use it to pass through tethered shooting to Lightroom 3b anyway. It works for my needs on that level.

I will try to visit the forums here again - thank you!
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