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02-12-2017, 11:00 PM   #1
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Banding with Q-S1 ?

Hi,

I'm having one hell of a time figuring out why I'm having banding issues with my Q-S1.

Here are two pictures of my washer + dryer, both using the 02 lens at 11mm, 1/500, ISO 12800, f/4.

The only difference is the clean one is using the normal shutter, and the one with banding is using the electronic shutter.

Taken in the evening (no sunlight) and lighting is a mix of incandescent (main room lighting) & LED (bleeding in from adjacent room).

Flickering compensation: 60 hz. (I'm in Canada)

Now, I understand that lighting pulses at 60 hz and that LEDs also pulse. However, what I don't get (at all) is how this would have such an effect -- UNLESS not all pixels of the Q's sensor absorb lighting at the same time?

And even if that was the case, why would I get a clean image with the leaf shutter?

And why would I still see this effect at all shutter speeds past 1/60, but starting to be more noticeable past 1/200 ?

And why would I see the same number of bands, regardless of shutter speeds ?


I'm really confused and wondering if the Q is defective.

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02-12-2017, 11:31 PM - 1 Like   #2
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Similar effect to the old TV photos with the scanning electron gun not being picked up, the electronic shutter scans a line at a time, similar to the old westerns with the wheels rolling backwards or propellor blades being bent with the electronic shutter.
02-12-2017, 11:42 PM   #3
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Thanks, but again, why would I see the same number of bands regardless of shutter speed?

And why do I see no banding with the leaf shutter?
02-13-2017, 12:27 AM - 3 Likes   #4
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That's because the sensor readout speed is fixed regardless of exposure duration, i.e. the lines are scanned at the same speed regardless of how long they have been exposed. We can deduce the sensor readout speed from the maximum flash sync speed, which is 1/13 s for the Q series. This is much slower than the AC switching frequency, causing the very prominent bands in the second photo.

The leaf shutter is global, meaning the exposure begins and ends at exactly the same time at every point on the sensor. Readout (which still scans the sensor line by line) doesn't begin until the physical shutter is fully closed.

The flicker reduction setting serves only to match the frame rate to the AC switching frequency so that the rear monitor (and recorded video) does not flicker.

Focal plane shutters also "scan" the sensor, but much faster, e.g. 1/180 s for the K-3, so AC flicker is less conspicuous since the sensor is "swept" in one third of a cycle.

02-13-2017, 07:03 AM   #5
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QuoteOriginally posted by dr_justice Quote
However, what I don't get (at all) is how this would have such an effect -- UNLESS not all pixels of the Q's sensor absorb lighting at the same time?
^^^ THIS^^^^

With an electronic shutter, the successive rows of pixels are exposed at different times. The total delay between the exposure of the top and bottom rows of the sensor is usually related to the max frame rate of the camera and can be quite long. If the electronic shutter time is short, some of the rows of pixels will be collecting light whilst the light source is in the low or off part of it's flicker cycle. You can even get oscillating bands of color with LED and CFLs due to the different spectra of the driving emissions of the light and the various color phosphors that continue to glow for a short time while the main light is flickering on and off rapidly.

There's nothing wrong with your Q.
02-13-2017, 07:40 AM   #6
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Wow. Ok.

Then, if the sensor can only be fully read at 1/13, one scanline at a time, then by the same reasoning very fast-moving objects won't really be frozen at very high shutter speeds, or at least, if the image is not blurry, will be distorted in shape.

I'll try to snap a picture of a rotating ceiling fan at its highest speed, with the shutter's highest e-shutter speed and see what comes out.
02-13-2017, 09:21 AM   #7
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QuoteOriginally posted by dr_justice Quote
I'll try to snap a picture of a rotating ceiling fan at its highest speed, with the shutter's highest e-shutter speed and see what comes out.
You'll get the same effect seen on YouTube videos taken with GoPros of propeller-driven aircraft, where the blades seem to either not move, bend, or detach from the hub depending on perspective and prop speed.
02-13-2017, 05:25 PM   #8
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Thank you, after much research and this thread, I now completely understand what's going on. You guys rock.

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