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05-02-2008, 10:56 PM   #1
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K20 Vpn? :(

Is this the dreaded "VPN", on my new K20d?

If so... is there anything I can do about it - ie. get pentax to fix it, or..?


this was 1600iso and converted to B&W / levels changed to make it more obvious, but it was noticable in the raw image




05-03-2008, 06:51 AM   #2
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QuoteOriginally posted by ennoia Quote
Is this the dreaded "VPN", on my new K20d?

If so... is there anything I can do about it - ie. get pentax to fix it, or..?


this was 1600iso and converted to B&W / levels changed to make it more obvious, but it was noticable in the raw image


No! It's the dreaded HPN!

Scanlines can sometimes be visible in dark parts of some K20D shots although I didn't notice it under ISO 3200.

It's obvious at ISO 6400 though in shadows.

If it is of any reassurance, the 30D and 5D also show these artifacts at ISO 3200 and sometimes 1600.
05-03-2008, 07:17 AM   #3
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QuoteOriginally posted by ennoia Quote
this was 1600iso and converted to B&W / levels changed to make it more obvious, but it was noticable in the raw image
That is the key to the problem: "to make it more obvious". Every camera can show vertical/horizontal banding or some sort of pattern noise at any ISO if enhanced enough. Trust me, I have tried several cameras (Pentax DS, K10D, Nikon D50, D40, Canon Rebel, 20D, 30D) and if you severely underexpose and then "recover" by pumping up brightness with levels or exposure controls in RAW converters you will ALWAYS get banding or pattern noise.

Why is all this? Because the noise is always there at all ISOs and readout electronics always introduces some sort or pattern noise. It is just a question or signal to noise (S/N) ratio: if your RAW capture (12-bit = 4096 levels) has noise averaging at 50 and highlights at 3000 you are good. You won't need to enhance anything and noise stays where it should be: under the radar. However, if you underexpose and your highlights average drops to 300 you will need to boost levels by 10 times (assuming linear boost) to reach acceptable highlights (say that 3000 was good). However, your noise goes up as well by 10X up to 500 and you are beginning to see it, along with all irregularities in electronics, readout noise, thermal noise, electromagnetic interference and what not.

Remember though that with higher ISO you have decreased S/N by default and more accurate exposure is even more important than with lower ISO. This is because the noise is constant but with high ISO exposure threshold gets lowered and signal amplified latter, which will include noise amplification as well.

So if you want to maximize S/N ratio always make sure to properly expose.
05-03-2008, 09:20 AM   #4
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yeah, well it was pretty obvious - ie, unprintable, unmodified...

It was a test shot - one of the "Yay new camera, click-click-click" shots - high iso in a badly lit kitchen though - i've never seen anything like this in my previous (and only other) DSLR, the Fuji S5


I will definitly shoot more real shots and see if it still occurs before worrying about it, but figured I'd see if anyone else was seeing anything like this at 1600 with the k20

05-03-2008, 09:31 AM   #5
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Did you "test" the Fuji S5 under identical conditions? It looks to me like you set the camera up to fail. You've set a high ISO, and then taken a big chunk of the visible spectrum away from the sensor. Why you would expect perfect results under these conditions is a better question than is there something wrong with your camera.
05-03-2008, 01:10 PM   #6
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i didn't "test" the Fuji but i owned it for a year and shot in similar conditions - i wasnt really testing the K20 either, it was just a quick snapshot while unboxing the camera

i didn't expect perfect results, i expected it to be noisy, I just didn't expect to see a pattern of vertical noise - this is new to me, other than the Fuji (which didnt exihbit patterns of noise like that,maybe just cause it was their honeycomb ccd?) my only cameras have been film, so i'm still newish to this whole thing

No need to be defensive, i'm not trolling or upset or anything- I'm just curious if this is expected/normal behaviour for high iso noise. So far I'm very happy with the k20d (And 35mm limited)!
05-04-2008, 07:29 PM   #7
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It's almost impossible to compare cameras this way because they all have different noise reduction algorithms. The Fuji Super CCD technology is quite a bit ahead of the curve as well. The K20 does have adjustable high ISO noise reduction available in menuville. Play with that a bit until you hit on a compromise that you like for your shooting conditions.
Remember that the more noise reduction you choose, the more fine detail gets wiped out as well.
05-22-2008, 09:10 PM   #8
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Just a followup, Pentax Canada got back to me pretty quickly, but by the time they did I had done a bunch of tests, tried everything I could... I can't get it to happen again. Even when setting conditions intentionally to try to make it happen, It simply won't occur!

I can only assume it was caused by interference from something, or something else.. Who knows!

I'm just glad it's gone

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