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12-01-2008, 09:41 AM   #1
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ISO400 with a K20D

id like to hear some thoughts from other K20D users

but it seems to me like the K20D takes a dive around the ISO400 mark in dynamic range and an awfully lot of noise seems to creep up in the entire picture, esp in the shadows

start going up to 800+ and it seems to get better, not worse, only hitting a ceiling at around 1600.

thoughts?

12-02-2008, 01:35 AM   #2
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Ive shot at different iso settings at times and don't really find a problem.
Ive used 400 a bit and find it ok. Could it be different on different cameras.
12-02-2008, 04:12 AM   #3
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I've been happy up to ISO 800 and ISO 1600 is usable. I have not noticed any problem or difference in ISO 400 versus ISO 800. There is less noise in ISO 400 than in ISO 800 as it should be.

Sounds odd!
12-02-2008, 04:31 AM   #4
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It seems to be by design, but try taking a look at your NR settings. As shown here Pentax K20D Review: 18. Photographic tests (Noise): Digital Photography Review, noise pretty much takes a big jump between 400 and 800 and leveling off a bit once you hit 800 and the NR really kicks in. Jumping to the next page there Pentax K20D Review: 19. Photographic tests (Noise): Digital Photography Review, you can see just how much of an effect the NR has at ISO's above 800.

12-02-2008, 07:07 AM   #5
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QuoteOriginally posted by Gooshin Quote
id like to hear some thoughts from other K20D users

but it seems to me like the K20D takes a dive around the ISO400 mark in dynamic range and an awfully lot of noise seems to creep up in the entire picture, esp in the shadows

start going up to 800+ and it seems to get better, not worse, only hitting a ceiling at around 1600.

thoughts?
Theorically, by each stop of sensitivity you gain, you loose one stop of dynamic range.

On dpreview.com forums some people have calculated that starting at iso 1600, Pentax is applying a bit of NR to raw files. But certainly not at 400. And I presume you're talking about raw.
12-02-2008, 07:44 AM   #6
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yes i'm shooting raw,

basicaly let meput it this way, it seems i would rather shoot ISO 800 than 400

again this is in no way scientific, just a general observation.
12-02-2008, 08:11 AM   #7
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I thought the K20D was supposed to be very good at ISO up to, or beyond 800...

on the other hand, I attend on occasion another board which is non-brand specific and this issue of ISO 400 in particular being a strange speed and yielding noise levels or characteristics quite different than even at up to 800...most owners were Canon and Nikon and they reported similar results...400 is preferred less than even 800 at times.

Jason
12-02-2008, 09:12 AM   #8
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ISO800 on the K20D certainly has a distinct grain pattern: tight, compact and quite celluloid-like. I like it as well. And I have found for those situations where you want to get rid of it, you can do so easily in most PP programs.

12-02-2008, 09:17 AM   #9
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QuoteOriginally posted by Gooshin Quote
yes i'm shooting raw,

basicaly let meput it this way, it seems i would rather shoot ISO 800 than 400

again this is in no way scientific, just a general observation.
Perhaps you could post some pics to demonstrate this problem...
12-02-2008, 09:21 AM   #10
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QuoteOriginally posted by kunik Quote
Perhaps you could post some pics to demonstrate this problem...
thats why i said its not scientific

the problem could very well be simply wrong exposure.
12-02-2008, 11:43 AM   #11
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definitely could be due to incorrect exposure. on my k20d one stop is the difference between an unuseable image or a perfectly clean one, even up at high ISOs... I usueally end up compensating a couple of clicks up just to avoid the noise
12-02-2008, 02:31 PM   #12
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QuoteOriginally posted by Gooshin Quote
thats why i said its not scientific

the problem could very well be simply wrong exposure.
I know what you're talking about, noticed the same thing, but I think it's
incorrect exposure.

For example, all the shots in This Thread were taken at ISO 400,
and I think the DR is good, colors sparking and I see minimal noise.

However, in poorer lighting situations where it's a temptation to underexpose,
ISO 800 gives similar results as ISO 400. Just something I've noticed.

Here's some lower-light snapshots I took just now at both ISO 400 & 800:

(all these are 77ltd wide open)

ISO 400 & ISO 800:

ISO 400 crop:

ISO 800 crop:


ISO 400 & 800:

ISO 400 tight crop:

ISO 800 tight crop:


ISO 400 & 800:

ISO 400 tight crop:

ISO 800 tight crop:


And here's just a nice ISO 400 shot using a willing model:


crop:
12-02-2008, 03:47 PM   #13
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The difference in that cereal-box-logo photo is pretty dramatic, but I notice that the plane of focus in the blue-block crops changed a bit between the 400 and 800 shots. Are you sure the box in the ISO 400 cereal-box crop is focused the same as the 800 shot? If not, how were those processed? It looks as if there's heavy NR being applied to the 400 crop but not to the 800 crop so much.
12-02-2008, 04:28 PM   #14
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QuoteOriginally posted by er1kksen Quote
The difference in that cereal-box-logo photo is pretty dramatic, but I notice that the plane of focus in the blue-block crops changed a bit between the 400 and 800 shots. Are you sure the box in the ISO 400 cereal-box crop is focused the same as the 800 shot? If not, how were those processed? It looks as if there's heavy NR being applied to the 400 crop but not to the 800 crop so much.
Those are just jpeg's out of the camera, and I think the ISO 800 shot on the
cereal box was more in focus, or had less handshake because of faster shutter.

And yes, they're handheld between 1/15sec & 1/90sec, and the camera position
is slightly different between shots (no tripod). Mainly wanted to show noise, not focus,
etc.


.
12-03-2008, 04:13 AM   #15
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Hiya folks! Just a newbie here trying to understand ISO. After reading this thread, what would be the general advice for someone like me? Use ISO 400 or 800 in low light situations.

Thank so much!
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