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05-04-2013, 02:08 AM   #1
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Photodetector issue on k5

Dear All-

I was trying my hand a star-trails on the k5. To minimize noise, I kept the ISO at 80, switched on NR at long exposures, and took 30 sec exposures. I see something weird. Each image.. has a central ring of luminous "haze". It can't be the lighting.. since the haze is consistently at the center of the image and I have tried at two different times, with very different lighting conditions. Could it be that my k5 is faulty.. it's pretty new. Also.. do you expect such results... as seen in the final one.. or am I missing something critical here.

One suspicion I have is that of the UV filter I have left on. Though the best test would be to take it off and retake.. just want to hear you guys first.. since the nights are cold!

Thanks!

Saumendra

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05-04-2013, 02:50 AM   #2
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UV filter is one more glass that can and will genarate problems such as abarations and flaers on image. IMHO UV filters are scam.
05-04-2013, 02:56 AM   #3
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It seems to be a type of ghosting.
it can indeed be the UV filter if not it could be internal reflection inside the lens or refelction of the sensor against the rear element of the lens.
If it isn't a digital lens the later could very well be the case, lenses for digital have a special coating to prevent that.
05-04-2013, 02:57 AM - 1 Like   #4
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QuoteOriginally posted by i83N Quote
IMHO UV filters are scam.
For film and lenses made before 1940 it isn't

05-04-2013, 05:29 AM   #5
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By the way it could be some moister trapped between lens and filter.
05-04-2013, 05:36 AM - 1 Like   #6
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One more thought - condensation mist. Many astronomers use a heating element on the front optics - many people cannot even detect such heaters are working, but they keep the front element at the surrounding ambient temperature. Here is a simplfied explanation... Whereas the sun sends IR at us in the daytime, the night sky sucks it away. If you use a lens you can focus the sun's IR and actually burn things, at night this same lens is sending focused IR skyward and it actually cools more than the ambient air temperature. A surface colder than the surrounding air will cause condensation. The condensation is heavier at the center of the lens because that is where light transmission is most direct and therefore coldest.
05-04-2013, 08:07 AM - 1 Like   #7
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UV filters will wreck images with a dslr, also with such a long exposure you should try covering the viewfinder.
I'm also curious as to why the tree is so red.
05-04-2013, 08:33 AM   #8
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QuoteOriginally posted by chromo Quote
UV filters will wreck images with a dslr, also with such a long exposure you should try covering the viewfinder.
I'm also curious as to why the tree is so red.
EXIF data shows manual white balance and manual metering ... my guess is there was a sodium vapor street light somewhere in the area, or a nearby home with incandescent light. As for the viewfinder blind, a viewfinder exposed to backlight risks throwing off exposure metering. Once metering is done, this is no longer a risk .... so it doesn't matter at all if you use manual exposure, and once the mirror is up you have an internal blind in place.

05-04-2013, 08:49 AM   #9
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QuoteOriginally posted by JimJohnson Quote
EXIF data shows manual white balance and manual metering ... my guess is there was a sodium vapor street light somewhere in the area, or a nearby home with incandescent light. As for the viewfinder blind, a viewfinder exposed to backlight risks throwing off exposure metering. Once metering is done, this is no longer a risk .... so it doesn't matter at all if you use manual exposure, and once the mirror is up you have an internal blind in place.
I think I have seen elsewhere on the forum that the mirror seal is not perfect on every camera, and some light can leak into the mirror box during very long exposures. I cannot remember the thread, but it was within the last couple of months, and was referring to astrophotography.
05-04-2013, 09:06 AM   #10
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QuoteOriginally posted by Canada_Rockies Quote
I think I have seen elsewhere on the forum that the mirror seal is not perfect on every camera, and some light can leak into the mirror box during very long exposures. I cannot remember the thread, but it was within the last couple of months, and was referring to astrophotography.
For that matter, the light seal of the Pentax ME viewfinder blind (still the official part for all current Pentax dSLRs) isn't very good. But once the mirror is up I would expect that any flare caused by light from the viewfinder would be bounced evenly around the baffles in the mirror box and not be concentrated in the center of the image as shown in the examples. This leads me to think the distortion is coming through the lens and not the viewfinder. I'll bow out at this point, stop guessing and let the light physics pros weigh in.
05-04-2013, 08:23 PM   #11
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Very insightful feedback from everyone, thanks a ton..! Really appreciate all the time you too out for it.

I shall be taking precautions this time.. against condensation, removing the UV filter.. and seeing the results again. I did have the viewfinder blind on.. so perhaps it may not have been tight shut. There was a strong light source at the back of the camera.. so I'd not be surprised that it's the culprit. The lens is a DA lens so I hope it's a genuine copy.

Anyhow.. hope to come up with something better soon..!

Saumendra
05-04-2013, 10:20 PM   #12
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QuoteOriginally posted by saumendra Quote
Though the best test would be to take it off and retake..
My money just now is on the UV filter being the culprit, but we'll all know soon after the retake.
05-04-2013, 11:15 PM   #13
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QuoteOriginally posted by kerrowdown Quote
My money just now is on the UV filter being the culprit, but we'll all know soon after the retake.
I'll +1 that. It seems that especially for low light photos, UV filters are nothing but trouble. Wasn't there a thread around here a few weeks ago with a very very similar situation?

After using UV filters religiously for protecting the front elements of my Zuiko's for a decade, I discovered that not a single of the protective UV filters had gotten a scratch or a nick - I simply did away with them and haven't been happier. And none of my Zuiko's or Pentax lenses have gotten any nicks or scratches either (a hood beats an UV filter in both optical benefits and protective abilities any day).
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