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12-21-2009, 11:03 PM   #1
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yellow streaking

I started using an A 50mm 1.7 today and some pictures had a yellow band while most were fine. What can be the cause? Is the lens bad?

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12-21-2009, 11:36 PM   #2
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I'm betting this was shot under fluorescent lighting. Fluorescent lighting, unlike halogen or tungsten, flickers on/off at the mains frequency (usually 50 or 60Hz); technically, it operates at twice the mains frequency. Someone correct me if I'm wrong, but most Pentax DSLRs are synced at 60Hz. Therefore, if your mains power operates at 50Hz or just slightly off 60Hz, the fluorescent bulb will flickr slightly out of sync with the camera's shutter. As a result, you will get bars of discoloration when the out-of-sync lighting conditions changed while the sensor was capturing that part of the image.

Hope that makes sense.

- Jason
12-21-2009, 11:43 PM   #3
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Wow! Yes it was fluorescent light. That was really informative...I was freaking out. Thanks!
12-21-2009, 11:44 PM   #4
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I'd second that

Looks like fluorescent light. Try slower shutter speed, like 1/30s.

Fluorescent bulbs do not emit in the spectrum simultaneously - they oscillate through the spectrum, and with high enough shutter, you can catch the transition.

12-22-2009, 10:04 AM   #5
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Check this series shot with my K20. Ignore the fact that the AF couldn't keep up, that wasn't the purpose.
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12-22-2009, 02:44 PM   #6
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QuoteOriginally posted by Wheatfield Quote
Check this series shot with my K20. Ignore the fact that the AF couldn't keep up, that wasn't the purpose.
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That's an amazing sequence, and a great reminder to set the colour balance.
12-22-2009, 04:57 PM   #7
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QuoteOriginally posted by Lloydy Quote
That's an amazing sequence, and a great reminder to set the colour balance.
White balance wouldn't have helped. That sequence was shot RAW. The colour was all over the place because I was catching the florescent lights out of phase.
12-22-2009, 08:10 PM   #8
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I've noticed this before with my K-7 and K-x... a orange/yellow tint at the bottom or top edge of the frame. Nice to know there's an explanation.

12-23-2009, 03:13 PM   #9
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QuoteOriginally posted by Wheatfield Quote
White balance wouldn't have helped. That sequence was shot RAW. The colour was all over the place because I was catching the florescent lights out of phase.
wouldn't the colour temp of the lights remain constant enough to not record the shift / flicker from the phase fluctuation if the camera was set for flourescent light?
12-24-2009, 06:54 AM   #10
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QuoteOriginally posted by Lloydy Quote
wouldn't the colour temp of the lights remain constant enough to not record the shift / flicker from the phase fluctuation if the camera was set for flourescent light?
no.

.........
12-25-2009, 05:17 AM   #11
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Very interesting! Another lesson learnt.
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