Is this a thing? LED lighting affecting focus?

Cheese Scientist

Cheese Scientist

Suspended / Banned
Messages
584
Name
Amanda
Edit My Images
Yes
Sorry about this - I think that if this is explicable then I probably won't understand it, but it's probably not explicable...

Anyhoo...
I've found that when taking pics under specific LED sort of theatre lighting that the camera doesn't seem to focus properly and I noticed that when on a high shutter speed, it looks like that lighting flickers (dark/light stripe).
I haven't noticed this issue onter other lighting conditions.
Is this a thing?
 
Cheese Scientist said:
Sorry about this - I think that if this is explicable then I probably won't understand it, but it's probably not explicable...

Anyhoo...
I've found that when taking pics under specific LED sort of theatre lighting that the camera doesn't seem to focus properly and I noticed that when on a high shutter speed, it looks like that lighting flickers (dark/light stripe).
I haven't noticed this issue onter other lighting conditions.
Is this a thing?
Click to expand...
There's some flicker certainly, though less noticeable than with CFL.
I've not heard any other reports about the focus though, I'd have thought that'd take a bigger shift away from the continuous spectrum, but I'm no expert.

Theoretically it's perfectly feasible (remember the IR markings on your old lenses), different parts of the spectrum have a focus shift. But as above I wouldn't expect an LED to be that far off. Though @HoppyUK or @Garry Edwards might be able to cast some light.
 
I've noticed the same exact thing, that's why I mainly shoot available light with a little addition of flash through a 20cm diffusor, to get a nice catchlight in the eyes and the yellowish background. I'm typically shooting TTL -0,7ev and I'm happy with the results..
 
I've been shooting bands at festivals and gigs that use led lighting and have never experienced this.
Do you have a sample picture?
 
Dino f said:
I've been shooting bands at festivals and gigs that use led lighting and have never experienced this.
Click to expand...
•



The banding is always there but easier to see on plain
surfaces.

As stage lights, they use less energy, generate far less
heat and are, in a public area, a safety factor.

Better suited for video use a with a proper diffuser than
photography… SS oblige!
 
a sample would help.

Various issues

at high shutter speed, you will get variations. LEDs often use PWM dimming - meaning they're flashed on and off very fast, at different rates to dim them, so you can get variations and 'phasing' there.

some autofocus sensors are poor with some wavelengths, especially blue and red LEDs - they give out a very narrow spectrum of light unlike tungsten

camera sensors are particularly bad with the red and blue LEDs too, so purple is sometimes near unbearable. Make sure to nail your exposure, as you can't really take them up or down in post without it all going to hell, especially around the lights themselves
 
The light tends to be really pink/purple on some parts of the stage so maybe the red/blue thing is the issue?
Thanks for the thought about using a flash but it's usually not possible.
I don't use high shutter speeds - it was just a one off where I noticed a flicker.
Thanks guys - sample here 100% crop (or thereabouts) 24mm, 1/250, 1,600. Not the worst example but I've already deleted those.
 

Attachments

  • 2016-06-24 Dead Ringers1000.jpg
    2016-06-24 Dead Ringers1000.jpg
    203 KB · Views: 58
A random thought.I know various LED colours are engineered to be different brightnesses so our eyes perceive them as looking the same (for example Blue LEDS are actually emitting much more light). I'm not sure how, bit maybe that could be causing the issue
 
do you mean the lines in the background? cos no idea what that is if it isn't several separate lights / one patterned light
 
Cheese Scientist said:
What really is confusing me is why it's happening with some lenses and not others.
Click to expand...
I don't have a deep enough technical knowledge to answer your question, but based purely on experience, this does seem to be a bit of a problem with the cheaper LED lighting, which is very poor.
Unless we go into the depths of Quantum Physics (which says that light consists of particles as well as waves) then light is just waves, and as soon as some physical event occurs that interferes with those waves, strange things are bound to occur. And a camera lens interferes with the waves, and different lenses, with different constructions, interfere in different ways and to different degrees. Sometimes, this interference may or may not be affected by the lens coatings, which also vary, so it would be very strange if you didn't get different effects with different lenses.
 
Cheese Scientist said:
What really is confusing me is why it's happening with some lenses and not others.
Click to expand...
wow, ok, yeah, no idea, though I suspect that that might be a red herring due to timings and camera changes and when it was and wasn't being used or something? The whole effect confuses me to be honest, very very strange
 
Can't see as I'm on my phone atm, but what are the exif details on this shot.
 
Cheese Scientist said:
His face isn't sharp (the blue lines are curtains behind him)
Click to expand...
Ok, thanks.
You haven't given clear/full shooting/EXIF info so it's a little difficult to figure but, looking at your posted crop it looks quite noisy so I presume ISO was relatively high, which would go some way to explaining the softness of detail - especially if this is in fact a 100% crop.
You say that shutter speed was 1/250. Fine. But was he moving quickly? Turning around perhaps? If so that might be another factor in the lack of sharpness here.
Did you need to push the exposure much from RAW or JPEG? That wouldn't help either.
Also, I don't see your camera model, and some are worse and give softer results at higher ISOs than others, of course.
To be honest, without more info or example shots it's difficult to tell. This could simply be down to high ISO and/or subject movement and, if that's the reason, it doesn't look that terrible for a 100% crop to me.
 
There is no reason for the light source itself to affect PDAF. Autofocus uses separate images from separate areas of the objective lens and compares them for "phase" (contrast). The most probable answer is that the lighting is causing a lack of contrast in the scene.

But a poorly corrected lens (i.e. exhibits stronger CA) will have more issues with specific colors.
 
Last edited:
You must log in or register to reply here.
Back
Top