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04-13-2011, 09:00 AM   #1
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Low ISO

Hello, I am pretty much still a total noob and wish to ask a noobish question about ISO; I hope this is the right place.

I read the thread

https://www.pentaxforums.com/forums/general-photography/72868-iso-ranges-low-...ease-look.html

but that did not answer this question exactly.



So, question: I just read this blog post

Saving the World One Pixel at a Time Blog Archive Expanded ISO Settings: Why I don’t like’em

and though it is about other camera's it got me wondering about my camera. I have a K200D and when there is light, I shoot at ISO 100 mostly. This article got me wondering if, like the Nikon's discussed, the K200D might be better off at ISO 200. Is it possible that 200 is the standard and going to 100 is actually some modification and not going to get better images?

Not that I am that great of a photographer that needs super results, just wanting to use the camera as it was meant to be used, when possible.

Thanks

04-13-2011, 10:40 AM   #2
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The short answer is, you're fine at ISO 100.

The longer answer starts with post #3 in the thread you quoted:

QuoteOriginally posted by Marc Sabatella Quote
A sensor has one and only one "native" ISO - that is, it only actually collects photon at one given rate. All higher ISO's above that are created by amplifying the results collected at the native ISO. The more amplification, the more noise. A lower native ISO means more amplification is required to get to, say, ISO 1600. Meaning it's likely to be noisier at ISO 1600 than an otherwise-similar sensor with a higher native ISO.

And there's no good way to "de-amplify" the results collected at native ISO in order to simulate lower ISO. A shutter speed slow enough to get a good exposure at ISO 25 would clip at the native ISO of 100 or 200. I gather some cameras have implemented some sort of magic to get around this, but it's probably more work than it's worth given that a ND filter solves the problem nicely.
The Nikon D300s mentioned in the second link does have that magic trick. Here's a qoute from the dpreview.com review:

"The base sensitivity of the sensor used in the D300S is ISO200. There is also a Lo 1.0 mode that attempts to mimic ISO 100 but it's effectively just ISO 200 over-exposed by a stop. The result is that the sensor becomes saturated and clips to white quite easily, limiting that mode's dynamic range. For most applications, you'd be better off buying a neutral density filter if you need slower shutter speeds than ISO 200 will allow."

Your camera does not do this, so ISO 100 really is ISO 100. Both cameras also have a confusingly similar feature to cram more information into JPEG files. Pentax calls it D-Range and Nikon, Active D-lighting. Some magic is applied to JPEG processing with that setting too. It has no effect if you shoot RAW.

Although the highly technical camera review sites can overemphasize small number differences into giant problems, it's worth reading the review for details like this.

Oddly enough, I briefly met both these guys at the same moment.
04-13-2011, 10:46 AM   #3
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Thanks One More Dave, it helps. I shall carry on at 100. I did enjoy reading both the blog post and the thread here about ISO, just was not sure I was getting it.

thanks again

j
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