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12-28-2014, 09:57 PM   #1
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Is this the rolling shutter problem?

I was messing around with some macro shots and noticed some banding that's obvious in the background but is also exhibited in the subject. Is this an example of the rolling shutter? Photo was taken with a Pentax Q7 using a Super-Takumar 50mm f/1.4 + extension tube No. 1 + Fotodiox M42-to-Q adapter. Shutter speed is 1/2000, ISO 100, f/11. Lighting is with 2 23W 5000K compact fluorescent bulbs.




Last edited by murrelet; 12-29-2014 at 02:45 AM. Reason: fixed image link
12-28-2014, 10:17 PM   #2
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12-29-2014, 02:46 AM   #3
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QuoteOriginally posted by Steve.Ledger Quote
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Should be fixed.
12-29-2014, 03:39 AM   #4
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Looks rather like the interference bars you get in video from flourescent tube lighting when FPS matches the flouro's frequency..
Can't say as I've ever seen it in stills though.

12-29-2014, 05:32 AM   #5
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QuoteOriginally posted by Steve.Ledger Quote
Looks rather like the interference bars you get in video from flourescent tube lighting when FPS matches the flouro's frequency..
Can't say as I've ever seen it in stills though.
Funny you should mention that. I was taking test shots today (FA 31 + Q) and I came across that phenomenon. I went into the Q forum to see if someone else had encountered such a thing before. It freaked me out because I thought something was wrong with the lens or the Q, but your explanation seems reasonable.
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12-29-2014, 10:39 AM   #6
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I've seen that effect ON THE SCREEN when using liveview w/ fast lenses (only seems to happen at faster than f/2-ish) and CF lighting while composing on the K-01, but not in the actual taken images. But of course that's a mechanical shutter. So at 1/2000s on the Q using the electronic shutter, yeah that's a possibility. Using a different type of light would probably get rid of it...
12-29-2014, 10:54 AM   #7
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QuoteOriginally posted by Steve.Ledger Quote
Looks rather like the interference bars you get in video from flourescent tube lighting when FPS matches the flouro's frequency..
Can't say as I've ever seen it in stills though.
I'll have to think this through. Makes sense, but shouldn't 1/2000 be fast enough? I think I need a better understanding of the physics.
12-29-2014, 11:14 AM   #8
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QuoteOriginally posted by murrelet Quote
I'll have to think this through. Makes sense, but shouldn't 1/2000 be fast enough? I think I need a better understanding of the physics.
It is the rolling shutter in combo with the phase of the lights. It still takes 1/13s to take your image even with a "shutter speed" of 1/2000s. It wouldn't happen with a mechanical shutter.

12-29-2014, 11:23 AM   #9
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QuoteOriginally posted by murrelet Quote
I'll have to think this through. Makes sense, but shouldn't 1/2000 be fast enough? I think I need a better understanding of the physics.
(Yes, vonBaloney beat me to it, but putting it several different ways might be helpful.)

1/2000 is the exposure time of an individual pixel, but not all pixels are exposed at the same time when using the electronic shutter. The image is scanned top to bottom (or maybe it was the other way around). They say the whole image takes 1/13 seconds to scan, but I think it's actually faster. It seems to be about 1/8 of the cycle time of your light source.

If you take many shots and stack them the effect should disappear.
12-29-2014, 11:34 AM   #10
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QuoteOriginally posted by vonBaloney Quote
It is the rolling shutter in combo with the phase of the lights. It still takes 1/13s to take your image even with a "shutter speed" of 1/2000s. It wouldn't happen with a mechanical shutter.
Actually it does also happen with a mechanical shutter. Unless you have an iris shutter a vertically travelling shutter is no different than a rolling shutter.

If you use the Q with one of its own lenses and internal iris shutter,mor the pentax q-K adaptor, you will get this
12-29-2014, 01:26 PM   #11
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QuoteOriginally posted by Lowell Goudge Quote
Actually it does also happen with a mechanical shutter. Unless you have an iris shutter a vertically travelling shutter is no different than a rolling shutter.
Well, not quite true -- with mechanical shutter all lines on the sensor are exposed at once, or at least within that 1/2000s, whereas with electronic shutter it always takes 1/13s to get through all the lines. The difference is that with mechanical shutter it downloads the data off the sensor after whole sensor has been exposed while with electronic shutter it "exposes" a row for 1/2000s, downloads the data for just that row, moves onto the next row, etc. This is the bottleneck that causes the 1/13s thing.

In any case I've never seen the effect on a still image with a mechanical shutter and using those kinds of lights was my standard for ebay shots (of which I do a alot) for a long time (I use flash now). I did see it on the screen, but never in the images themselves. It is possible maybe with certain shutter speeds? But I've not seen it...
12-29-2014, 02:41 PM   #12
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Take a shot of a flourescent tube on an angle at a slow shutter speed, the Color changes as a function of when the first and second curtain move, relative to where in a cycle the arc in the tube is, the prosphour coating changes color over time

This has been posted many times
12-29-2014, 02:51 PM   #13
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QuoteOriginally posted by drougge Quote
(Yes, vonBaloney beat me to it, but putting it several different ways might be helpful.)

1/2000 is the exposure time of an individual pixel, but not all pixels are exposed at the same time when using the electronic shutter. The image is scanned top to bottom (or maybe it was the other way around). They say the whole image takes 1/13 seconds to scan, but I think it's actually faster. It seems to be about 1/8 of the cycle time of your light source.

If you take many shots and stack them the effect should disappear.
This is all very helpful! Just to make sure I'm understanding...

The lighter bands are being scanned while the fluorescent light output is high and the darker bands are being scanned while the light output is low. The 1/2000 exposure time is fast enough to "stop" the variable light output.

So, if I forced a slower exposure time, perhaps using an ND filter, could that help ensure the overall light output hitting each pixel is consistent?
12-29-2014, 03:03 PM   #14
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QuoteOriginally posted by Lowell Goudge Quote
Take a shot of a flourescent tube on an angle at a slow shutter speed, the Color changes as a function of when the first and second curtain move, relative to where in a cycle the arc in the tube is, the prosphour coating changes color over time

This has been posted many times
Well, of the tube. But I have a million shots taken under such lamps -- they don't have banding like is shown here.
12-29-2014, 03:45 PM   #15
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QuoteOriginally posted by murrelet Quote
I was messing around with some macro shots and noticed some banding that's obvious in the background but is also exhibited in the subject. Is this an example of the rolling shutter? Photo was taken with a Pentax Q7 using a Super-Takumar 50mm f/1.4 + extension tube No. 1 + Fotodiox M42-to-Q adapter. Shutter speed is 1/2000, ISO 100, f/11. Lighting is with 2 23W 5000K compact fluorescent bulbs.
This is off topic to your original question, but

Is that The Little Mermaid wielding two ninja swords?
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