Quote:
Originally Posted by multiweb
My guess would be a USB cable running close to a power cable with a pulse. Like a dew heater. Some EL panels flicker as well when you lower the voltage to dim them and that can cause banding in the same fashion.
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Are you suggesting the USB cable is affecting the power cable running to the light box and making it flicker, or the power cable affecting the USB from the camera, creating the banding?
Quote:
Originally Posted by JA
I think it may have something to do with LED flicker being picked up by the imaging system. It may be that pulse width modulation is used in the dimming circuit of the lamp or there is AC in its power supply. To the human eye with its relatively slow response the light may appear continuous and appears as always ON, but if recorded with video or a suitably short exposure you may, if I'm correct see the truth of a changing illumination pattern, some rows on, others off then changing....possibly. Why others may not see this phenomenon would depend on the nature of the LED source and camera type and exposure. Try increasing the exposure duration in steps say: your initial setting, then 2x, then 4x, then 8x.... what differences do you see? If you see a more integrated or whole pattern as you increase the exposure duration that is a sure sign of what I suggested. You could also use an incandescent light source with white diffuser or t-shirt to verify that its the LED light source which is the issue due to its inherent flicker/fast response compared with the pedestrian speed of an incandescent source. If that shows no change (lines still present) then it's a camera issue or interaction
Best
JA
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I feel like this is the most likely culprit.
I have tried two different ways of dimming the box, one being the inbuilt function of the ASIair (which I believe is PWM) and also the dimmer that came with the light box. The included dimmer is of the variable resistance variety, I am no electrical engineer, but I don't believe that it's the same as PWM, correct?
I was using the automatic exposure function for flats on the ASIair and was varying the exposure time using the dimmer. I will experiment today with more precise exposure differences and see what happens.
Flat frames taken with the sky and t-shirt as well as using an white screen on an iPad do not replicate the banding.