how to use gels to balance flash with ambient

ShawWellPete

ShawWellPete

Suspended / Banned
Messages
3,699
Name
Pete
Edit My Images
Yes
I took some photos at a quiz night recently which was in a school sports hall. The light was (I think) tungsten so I gelled my flash with a CTO gel and was hoping to get a good balance between ambient and fill light. I had varied success as you can see here...


DSC_6478.jpg


DSC_6442.jpg


DSC_6441.jpg


Any tips on choosing the best colour matched gel for ambient light? or any other tips for balancing flash with ambient?

apart from the obvious...

DSC_6550.jpg
 
ShawWellPete said:
I took a photo of the white basket ball board with the white balance set to flash and it looked orange, so I though an orange gel on my flash would correct it. Am I barking up the wrong tree?
Click to expand...

Wouldn't that make it even more orange?

I would have thought a light green would correct it.


Steve.
 
They look like fluorescent to me as well, but they could be "warm" or "daylight" or maybe something else.

As I understand it, the problem with fluorescent lights is that the colour alters as the mains supply does its 50Hz cycle. If you want to average out the colour so that you get consistent colour from one shot to the next you need a shutter speed of 1/50, 1/25, 1/12 etc. in order to pick up one or more full cycles of the mains. This could be a problem for freezing shake/blur if you have a high proportion of ambient light in the mix. If you use higher shutter speeds you will randomly pick up different slices of the variable colour from the lamps, so matching temperature will not be easy at higher shutter speeds.

Probably your best bet is to bounce the flash off the ceiling, which looks a little warm, but not too far from "neutral" and then you should end up with a blended mix of flash + ambient that should average out to not give you too much of a problem. I'd shoot raw and fine tune WB in post, probably using a white shirt or similar for reference and then adjusting by eye to achieve the most pleasing look overall.

If you are bothered you might gel the flash to bring the temperature down a little, but I don't think you would want to go all the way to CTO. Some people use a green gel to match fluorescent, but if the lights are "warm" you would probably need to go further than that. Maybe 1/4 CTO would be about right. Unfortunately I have not tried balancing with fluorescent lights so I have no personal experience of the best solution.
 
ShawWellPete said:
I thought the idea was to use the same colour light as the background and then use the correct WB to correct both of them.

:thinking:



:lol:

thanks for you help
Click to expand...

You're welcome :lol:

Yes, what I meant was, you are employing the right solution (matching the ambient) but thems look remarkably like fluo... hence the wrong tree ;)

Reading it back it looked like I was being unhelpful :bonk:
 
Flash In The Pan said:
Clickity :)
Click to expand...

incapete said:
Ever wonder if we should just replace the whole Flash section of the forum with a link to Strobist? :lol:
Click to expand...

:)

I did read that before the event, it was the reason I gelled the flash. I got a lot of variations though. I guess it was due to the different balance betweek flash and ambient light for different shots and as tdodd says maybe down to the frequency of the lighting.

tdodd, thanks for the comments by the way :thumbs:
 
Good post from Tim :thumbs:

I thought I'd do some test shots to see how bad it gets using too high a shutter speed. I knew it changed things a bit, but wow! it was scary bad!!! :eek:
Regular kitchen strip lights.

I was getting variations in both colour and exposure at anything faster than 1/30sec, but 1/30sec was consistently fine. At 1/125sec the variations frame to frame were quite marked and by 1/250sec effectively unusably bad. Every frame was dramatically different with both colour and exposure all over the place.

To see how bad I could make it I shot at 1/2000sec. Colour varied wildly from orange to green, and (because of the way the focal plane shutter works) in some frames I was getting orange at the top and green at the bottom of the same frame. Exposure variation was up to 1.5 stops.
 
HoppyUK said:
Good post from Tim :thumbs:

I thought I'd do some test shots to see how bad it gets using too high a shutter speed. I knew it changed things a bit, but wow! it was scary bad!!! :eek:
Regular kitchen strip lights.

I was getting variations in both colour and exposure at anything faster than 1/30sec, but 1/30sec was consistently fine. At 1/125sec the variations frame to frame were quite marked and by 1/250sec effectively unusably bad. Every frame was dramatically different with both colour and exposure all over the place.

To see how bad I could make it I shot at 1/2000sec. Colour varied wildly from orange to green, and (because of the way the focal plane shutter works) in some frames I was getting orange at the top and green at the bottom of the same frame. Exposure variation was up to 1.5 stops.
Click to expand...

Interesting stuff, thanks.
 
ShawWellPete said:
Interesting stuff, thanks.
Click to expand...

I was shocked TBH. I guess I've never shot at high shutter speeds in flourescent light before, which I guess is not that surprising, but anyway.

Thinking about the theory, I believe these things flicker at 50 cycles per second don't they? But the action of the focal plane shutter is going to slice that up into different bits of different cycles which complicates things (and will also vary a bit between camera models).

It would be nice to think that shooting at 1/50sec would give you exactly one clean cycle, but it doesn't work like that. I was getting slight variation at that speed, acceptable if you're stuck, but the more full cycles you can get obviously the better.

Don't some of these tubes cycle at 100cps? How does it work with those super-bright flourescent bulbs used in budget studio lighting kits?
 
50 is mains so most use that or 25 (half wave stuff) again some use 100, generally variations on 50Hz

its the same as for shooting tv/pc screens you want a shutter of the refresh rate or lower so the images look good
 
david1701 said:
50 is mains so most use that or 25 (half wave stuff) again some use 100, generally variations on 50Hz
Click to expand...

Yes, mains frequency is 50Hz but light will be output on positive and negative swings so it is effectively 100Hz.

So in theory, a speed faster than 1/100 would only have the shutter open for part of the waveform and it would likely be a different part each time.

HoppyUK said:
Don't some of these tubes cycle at 100cps?
Click to expand...

Cycles Per Second. A much nicer unit than Hertz!

HoppyUK said:
I was getting variations in both colour and exposure at anything faster than 1/30sec
Click to expand...

Perhaps they give out different colour depending on the polarity of the voltage. This would need a shutter firing circuit synchronised to the mains to prove and I'm not interested enough to do that but it may explain why you were still getting variance up to 1/30.



Steve.
 
Nobody know what happens with those great big flourscent studio bulbs? If they behave anything like my kitchen lights, it'll be chaos.

On the other hand, do they get around this problem by using three or four different bulbs, both to increase the light ouput and effectively nullify the cycling problem? If they are all connected to the same mains supply, won't they all cycle in sync, so the problem is still there? :thinking:
 
HoppyUK said:
Nobody know what happens with those great big flourscent studio bulbs? If they behave anything like my kitchen lights, it'll be chaos.

On the other hand, do they get around this problem by using three or four different bulbs, both to increase the light ouput and effectively nullify the cycling problem? If they are all connected to the same mains supply, won't they all cycle in sync, so the problem is still there? :thinking:
Click to expand...

they could shift em out of phase with each other, or use a 3 phase supply and split it
 
david1701 said:
they could shift em out of phase with each other, or use a 3 phase supply and split it
Click to expand...

Cheers David. I guess they've got that covered then. Catastrophe narrowly averted :)
 
Fluorescent lights normally operate at twice the supply frequency (so 100Hz), but can start to flicker at main's frequency just before they kick the bucket. The good news is most new buildings (and many replacement strip lights) use high-frequency lighting (it's more energy efficient and better for reading) which cycle @ 20+kHz.

Try getting your shutter speed to match that!

Should make things a little easier.
--
Starabo
 
starabo said:
Fluorescent lights normally operate at twice the supply frequency (so 100Hz), but can start to flicker at main's frequency just before they kick the bucket. The good news is most new buildings (and many replacement strip lights) use high-frequency lighting (it's more energy efficient and better for reading) which cycle @ 20+kHz.

Try getting your shutter speed to match that!

Should make things a little easier.
--
Starabo
Click to expand...

Clearly, my kitchen under-lights are on their last legs! Quite likely. I notice that when I renew one of the tubes it is brighter and a bit less yellow.

That's 20,000 times per second :eek: Really? If so, then it must be effectively continuous light as the gas will continue to glow between cycles.

Or at least, from oscilloscope traces I've seen of high-speed flash strobing at 40kHz, there is very little dip in light output between pulses, for this reason.
 
You must log in or register to reply here.
Back
Top