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Old Dec 3, 2004, 9:57 AM   #1
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I'm at that stage where I'm really starting to experiment with different settings on my A75. I have a general question concerning taking outdoor shots with good lighting. Is there any reason one might choose to use a higher ISO setting when there is ample ambient lighting? I usually use ISO 50 on all my shots, indoor and out. But with the amount of noise created with higher ISOs, 200 and 400, does anyone even use these settings at all with lower end digicams? Thanks.

Sam
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Old Dec 3, 2004, 10:45 AM   #2
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As a general rule you always want to use the lowest ISO setting you can - even if you were using an SLR. So, if you have enough light to shoot with the aperture and shutter speed you want there is no reason to 'bump up' the ISO. Typically people will only shoot at higher ISO because they can't get the shutter speed or aperture they want. An example would be a photograph of a moving target. You may have excellent light for a 1/250 shot at your cameras widest aperture on a given day but for action shots 1/250 may not be fast enough. In order to get 1/500 you would have to bump up your ISO (say from 100 to 200). So if you're happy with the f-stop and shutter speed, leave the ISO as low as you can.
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Old Dec 3, 2004, 10:08 PM   #3
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i agree with john 100%

listen to him...
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Old Dec 3, 2004, 10:26 PM   #4
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Yup, as low an ISO as possible is the way to go.

The way to look at your photos to see if you have too low an ISO is to look for "blur". That can be movement (shake - your movement, or subject movement) or it can be lack of depth of field - only subjects at a certain range of distances are sharp. If you see those, you are likely to want a higher ISO to get a faster shutter speed to better freeze motion or a smaller aperature (higer f/number) for more depth of field.
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Old Dec 3, 2004, 10:53 PM   #5
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Thanks John for your excellent explanation. I guess I should think of ISO speeds as "gain" and stick with the lowest possible that will create the exposure I want via my optical controls, shutter speed and lens speed.

Bill, I'll look for unwanted blur and adjust my ISO speed incrementally. Thanks for the reply guys.

Sam
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Old Dec 4, 2004, 8:44 AM   #6
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i agree with Bill and the group, the lower ISO the better, i never up the ISO when shooting and instead change aperture and shutter speed, EV level, WB, etc, even in low light conditions, in fact i rarely ever use a flash, but compensate with the flexibility in my SLR and have never really noticed a bad shot by doing this.
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Old Dec 5, 2004, 3:18 AM   #7
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The posters above recommending ISO be left on the lowest possible- well, IMHO the only reason to suggest that is to minimise visible noise. If the noise characteristics were the same at say ISO100 as it is at ISO800, I'd use 800 anyday! Higher sensitivity equates to more shooting options with regards to aperture and shutter speed selection.

But at the moment, technological limitations and the laws of physics dictate higher image noise with the selection of higher ISOs.
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Old Dec 5, 2004, 8:31 AM   #8
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Onyx wrote:
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... the only reason to suggest that is to minimise visible noise. If the noise characteristics were the same at say ISO100 as it is at ISO800, I'd use 800 anyday! ...
and if pigs had wings :idea:

Onyx is right: noise is the only reason I can think of using low ISO - a VERY good reason. The use of your image comes into play in this sense. If you are shooting images that will only be used as low resolution (web), smallish amounts of noise are not noticable compared to the JPEG artifacts that result from required compression.

Every rule in photography has at least one exception. Except this rule, of course.
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Old Dec 5, 2004, 10:06 AM   #9
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Onyx wrote:
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The posters above recommending ISO be left on the lowest possible- well, IMHO the only reason to suggest that is to minimise visible noise. If the noise characteristics were the same at say ISO100 as it is at ISO800, I'd use 800 anyday! Higher sensitivity equates to more shooting options with regards to aperture and shutter speed selection.

But at the moment, technological limitations and the laws of physics dictate higher image noise with the selection of higher ISOs.
Most of the time, that's true. But, if you wanted to deliberately use slower shutter speeds for effect (for example, panning the camerawith a subject moving at higher speeds, where you want to see the background blurred to exaggerate motion), you may not be able to get slow enough shutter speeds at higher ISO speeds, even with the lens stopped all the way down.Many consumer models won't go smaller than f/8 (and some will have softer photos from diffraction at this aperture setting).

Inbrighter conditions, at ISO 800, you'd exceed the fastest available shutter speed in many models, too -- even stopped all the way down to their smallest available aperture. So, even if ISO 800 was noise free, you'd still need to use lower ISO speeds in many conditions with many cameras.

For example, in very bright outdoor conditions, with an EV of 16, at ISO 800, you'd need a shutter speed of 1/8000 second for proper exposure at f/8 (the smallest aperture available on many consumer models). Unfortunately, the fastest available shutter speed on many is around 1/1000 second.

Now, on a DSLR model with a lens you could stop down to f/22, it wouldn't be a problem (but you'll probably get softer photos using an aperture this small with many lenses).

Also, even with a DSLR, you may want to shoot at larger apertures for a shallow depth of field to help your subject stand out from backgrounds. So, this would cause you to exceed the fastest available shutter speeds on many models in better light if you couldn't reduce ISO speed below 800.

Noise free ISO 800 would be very nice. But, I'd still want a way to set it lower. I'd hate to need to stack Neutral Density Filters just to get slower shutter speeds when I needed them.
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Old Dec 5, 2004, 10:37 AM   #10
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Going back to Spark's original post, he's using a Canon A75. We have one of these as well as an EOS 20D. The A75 is a nice little easy to carry camera with a small sensor. It doesn't offer the same ISO range as the DSLR and noise becomes a problem as ISO is increased.

I'd suggest keeping the ISO as low as you can, increasing it as necessary only to get those shots you simply can't capture at the lowest ISO values because of lighting or subject movement. As noise becomes evident, consider software to mitigate the problem.
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