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08-16-2009, 12:51 PM   #1
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K20D banding / long exposure

I was out testing some long exposures today, and right from the first test shot I noticed weird banding that had never appeared before:



I thought "oh no, i hope the sensor isn't bust", so I packed up and went home. I told my dad and showed him the picture. I then told him that I had my back to a bright sun then he suddenly clicked and said "ahhhh, that's probably light getting in through the viewfinder". I did another 30 second exposure test and the banding wasn't there, but there was no bright sun behind me.

Has anyone else had problems like this? Is there an official Pentax viewfinder cover I can get hold of? Any tips and tricks? I don't often use long exposures, I'm just starting to try them out.

Oh, and I know my sensor has blotches on it - I had it cleaned today to remove the hair and the splats.

08-16-2009, 12:59 PM   #2
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Well my K20D came with the viewfinder cover. It's a tiny piece of black plastic which is easily lost if one is not careful when tearing the stuff out from the retail package Anyway, I have never experienced such phenomenom with k20d's viewfinder exposed to the sun behind my back.

By the way, that is way cool photo. Shame that these bandings, whatever they be, ruined it
08-16-2009, 01:02 PM   #3
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That's definitely a sensor issue. Nothing that has to do with light through the viewfinder because the camera isn't designed like that.
08-16-2009, 01:13 PM   #4
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Are you sure?

I've done several tests since that shot and there have been no problems.

08-16-2009, 01:17 PM   #5
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It is definitely because the viewfinder was not covered. I believe the manual mentions that this can happen when the viewfinder isn't covered, but I don't have mine handy right now so I can't check. I know I've read from a reliable source somewhere, if not the manual, that the K20D as well as most other DSLRs need to have the viewfinder covered when the camera is on a tripod in a bright setting.
08-16-2009, 01:33 PM   #6
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Cheers guys, I've just gone and done a quick test (with a rubbish picture or two) and found the following:

30 seconds, f/4, B+W ten stop.



30 seconds, f/4 B + W ten stop - this time shining a torch into the viewfinder for a few seconds.



Not a scientific test by any means, but it exhibits exactly the same banding when I shine a torch into the viewfinder in the same fashion that the bright sun was shining behind me on my long exposure seascape.

Definitely light into the viewfinder then.
08-16-2009, 02:12 PM   #7
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You've answered your question Big G, and is a good lesson for those who think they've got dud sensors...
08-16-2009, 02:16 PM   #8
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Yeah it wasn't confirmed until I just did a final test there, definitely worth noting if you're doing long exposures!

08-16-2009, 02:27 PM   #9
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Interesting thread, now we for sure why the nice people at Pentax include the viewfinder blind.
08-16-2009, 03:00 PM   #10
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It's also so light coming in the viewfinder doens't mess with exposures when metering on a tripod with your head elsewhere. It hadn't occured to me it could also have the effect seen here - that's a new one on me. But a very convincing demonstration!

BTW, before seeing that, I was going to guess some sort of flare that had to do with a momentary reflection - from a passing airplane, say. Because it definitely looked optical, not electronic. But I never would have suspected the viewfinder - kudos to your dad!
08-16-2009, 03:24 PM   #11
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Yeah my dad is a long time amateur photographer, lots of experience, he got me into Pentax as he gave me his old *ist DS .
08-16-2009, 04:16 PM   #12
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QuoteOriginally posted by kerrowdown Quote
Interesting thread, now we for sure why the nice people at Pentax include the viewfinder blind.

Yes the viewfinder blind is a must for long exposures >1/4 sec in dark IMO. I was taking some pics on my tripod and I noticed blueish spots oval in shape and faint like UFOS or something, on almost all pics and at different locations. I knew light could affect the pic but there was no light behind me, but...

there was light in my ear. I had a blue-tooth in my ear and it flashed a blue light every 10 seconds or so yep
08-16-2009, 06:53 PM   #13
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QuoteOriginally posted by jamesm007 Quote
there was light in my ear. I had a blue-tooth in my ear and it flashed a blue light every 10 seconds or so yep
LOL. Now that's funny. It's funny how people just throw that viewfinder cover away too
08-16-2009, 09:34 PM   #14
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QuoteOriginally posted by kenyee Quote
LOL. Now that's funny. It's funny how people just throw that viewfinder cover away too
Mine sits on my ME Super when I don't need it for my K20D.
06-04-2010, 08:22 AM   #15
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I have gone through two already, the plastic pieces can easily come off. Since I do mostly tripod shooting, I pretty much keep it on at all times and just lift it to look through, so it does get used. When my first one broke, I called Pentax to get a replacement, but had a heck of a time getting someone who actually knew what I was asking for. They kept on trying to give me the eyepiece attachment with the rubber around it for normal shooting. Luckily I found someone and they actually sent it to me for free. I now see it is available online, for a pricey 10.00.

It is a must if you do night shooting or use an infrared filter. To get the best shots on a tripod I would recommend always using one. There is always light around to seep in through the viewfinder. In the future I hope they will make an option to have a blinder to cover the eyepiece automatically, inside the camera. I believe some higher end cameras have this capability.

If anyone is interested, here is where you can purchase one if you lost yours or it breaks like mine. This one does only indicate through k10d, but it is my understanding it is the same for the k20d. The product is called, Pentax eyepiece blind "M":

http://www.pentaxwebstore.com/product_detail.asp?T1=PTX+31011&trk_src_ss=PTXGBASEWEBMACSS%7CSEO%7CGB%7C
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