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12-09-2009, 09:23 PM   #1
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Which is worse for noise? Long Exposure or High ISO

All things being equal, would it be better to raise ISO or exposure time to shoot in the dark?

12-09-2009, 11:26 PM   #2
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shooting in the dark

Here are my thoughts:

1) from a noise only point of view, a long exposure at a low iso will usually be better than a high iso shot. It will not only look cleaner but will also have a better dynamic range.

2) However, you may only be able to adopt this low iso approach and the resulting long exposure if you have a tripod and/or its a static subject where motion blur won't be a problem.

Often the motivation of raising iso is one of necessity to either get a faster shutter speed e.g. shooting sports inside or getting more depth of field. In these cases you often don't have another option.

I apologize in advance if you know all this already.

Oliver
12-09-2009, 11:40 PM   #3
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hey you don't have to apologize for being considerate. Thank you for the info. I actually just got a 25 dollar cheapo tripod from amazon and was wondering about this question. I see what you're saying make total sense, for fast shutter speed, use iso. For slow shutter speed, use exposure.

Thanks

ps - so im to understand high iso and longer exposure gives same amount of noise everything else being equal

Last edited by boodiespost; 12-09-2009 at 11:48 PM.
12-10-2009, 01:08 AM   #4
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Noise is caused by higher ISO. Exposure will cause noise as a side effect of under exposure (ie not long enough) and that noise will be created if you try and compensate for the under exposure in PP.

12-10-2009, 01:35 AM   #5
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Unfortunately, this hasn't held for the K20D.
The CCD sensors have enabled clean low ISO long exposure captures, but the K20D (from my experience) has fallen short of giving good long exposure results - despite exposure not being pushed in PP.
Don't know about the K-7, but the K-x has been impressive in this regard - they must have got it right with that CMOS sensor...
12-10-2009, 03:34 AM   #6
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So far as the physics is concerned, long exposure always gives lower noise than increased ISO, in proportion to the square root of ISO.

One exception is when the heat generated by the camera's electronics adds too much extra noise during a long exposure (but this is usually for really long exposures and often plagues astrophotographers.)

Dave in Iowa
12-10-2009, 05:20 AM   #7
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I asked that same question a couple of days ago. Here's the link so you can see the responses I've received.

https://www.pentaxforums.com/forums/everything-else/82248-iso-question.html
12-10-2009, 07:57 AM   #8
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QuoteOriginally posted by boodiespost Quote
All things being equal, would it be better to raise ISO or exposure time to shoot in the dark?
All things being equal, if you already have a DSLR, why don't you just try it for yourself and see?
That way you'll know for sure.
And who knows, you might learn some other useful tidbit of information along the way.

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