Banding/strobing issues with LED lights (Hydra 26's)

Chris Wells · Jul 25, 2018

ajm83 said:
Depends which way round he physically had the camera during the shot (unless I'm missing a shot which is showing banding in both directions?)

OP side shot was vertical and the front shot was horizontal.

Ah, just got it. always vertical on phone....related to sensor

Chris Wells · Jul 25, 2018

i_declare_bankruptcy said:
Vertical and horizontal is just due to how the sensor reads. They're actually always 'vertical' on the cellphone (only images I supplied in this thread) -- one is short portrait and then one is shot landscape, hence the difference in orientation. The banding itself is not actually changing orientation -- I just changed the camera's orientation.

Edit: Dang you beat me ajm83

Vertical makes more sense.

ajm83 · Jul 25, 2018

Chris Wells said:
Vertical makes more sense.

Well, copy the image, go into MS Paint and rotate it 90 degrees. That's all the camera has done. The sensor still physically reads the same direction, it's just the resulting image gets flipped.

i_declare_bankruptcy · Jul 25, 2018

I think he meant vertical makes more sense as in the sensor reads L->R T->B. Since the sensor is oriented in landscape (like any camera sensor), holding the phone vertically would thus produce vertical bands.

Chris Wells · Jul 25, 2018

i_declare_bankruptcy said:
I think he meant vertical makes more sense as in the sensor reads L->R T->B. Since the sensor is oriented in landscape (like any camera sensor), holding the phone vertically would thus produce vertical bands.

I did mean that.

I might be wrong, but I would still think the vertical bands would be emanating like a cone from each individual PWM generated led. Very interesting tho.
Following along regardless.

Keep us updated.

i_declare_bankruptcy · Jul 25, 2018

Chris Wells said:
I did mean that.

I might be wrong, but I would still think the vertical bands would be emanating like a cone from each individual PWM generated led. Very interesting tho.
Following along regardless.

Keep us updated.

What do you mean a cone? I'm curious. Could you draw a picture?

The bands make sense to me (if PWM) because the sensor reads out line "chunks" (typically) in some top to bottom fashion. I believe the line "chunks" are read at a speed much faster than the PWM flicker but the whole sensor itself is read at a speed slower than the flicker rate. Therefore you get some chunks with full signal and some without. At least that's my best guess.

TheEngineer · Jul 25, 2018

Here’s what banding due to color separation from surface motion looks like. See the sand? Just adding for reference.

Chris Wells · Jul 25, 2018

I was thinking a cone like this and bands would follow the shape. I am just an Electrical Engineer with no lighting experience, so I can be way off on the lighting.

Chris Wells · Jul 25, 2018

TheEngineer said:
Here’s what banding due to color separation from surface motion looks like. See the sand? Just adding for reference.

I was seeing that when I was playing around with my color percentages.

TheEngineer · Jul 25, 2018

Chris Wells said:
I am just an Electrical Engineer

JUST!? No sir. You are an engineer! I’m also a EE and ME.

i_declare_bankruptcy · Jul 25, 2018

I'm a Software Engineer

So I really have no business here lol.

Thanks for adding the banding picture with the disco effect -- I think the more info we can get in here the better we can help the next confused person lol.

ReefLEDLights · Jul 25, 2018

When LEDs are dimmed via PWM they cycle on and off at a lower rate... or Frames Per Second.

Think of those pics or films of a helicopter with the blades simply still... Might be your camera...Not 100% Sure.

I do know that the lights you are using are rather weak in intensity especially at the low setting you are using.

Try some pics with a stronger light say a simple Cool White with a Cree CXA 2530 LED. This will allow you a smaller aperture for greater depth of field... Of course depending on your software you may have to digitally adjust the colour balance...

Or you can try dialing the lights up just for the pics...

Bill

i_declare_bankruptcy · Jul 26, 2018

Edit: Reminder that I'm using the Hydra Gen 1's

Hey everyone. Unfortunately I've confirmed the hypothesis that the PWM function is causing the banding.

I conducted many tests with shutter speed and light intensity % and anything shy of 100% causes shot-breaking banding at a shutter speed above 1/200s.

I guess each channel has a PWM function (so you can control each channel differently) which probably doesn't help the issue! Regardless, running even one channel (all others at 0%) and dimming to 99% produces the same banding issue with no improvement.

It appears I'm SOL here with my lighting choice and my camera choice. Two very expensive things. I didn't choose my camera for reef tank imaging but dang I have no way of taking pictures or video now without changing my lights

I'm thinking Hydra HD users don't have this issue because the lights are engineered differently OR because nobody has used my imaging hardware with their setup. The latter I believe would be a rare case. This is almost just as much about my camera as it is the lighting although I'd argue just about any mirrorless camera (whether it's your phone or a $3000 Sony) will have this issue with PWM banding due to the way they work.

Sigh.