Metering problems when flash reflects in mirrors & windows

mattbaume · Jul 9, 2013

I'm sure we've all experienced this problem: when firing a flash straight on into something reflective (mirrors, windows, tiled walls), the bright reflection of the flash "tricks" the metering system into underexposing the picture.

So, what are your ways of dealing with this? I'm interested to hear your techniques.

Obviously, the simplest way is to avoid shooting directly into something reflective, or position the subject to block the reflection, or move the flash way off-camera so its reflection is out of frame. But what about when that's not possible? (For example, I sometimes shoot at a nightclub in LA that has wraparound mirrors on all the walls -- which is both tacky and challenging!) I've read that Sony has an ADI mode that compensates for reflective surfaces, but I'm shooting on Canon.

The best solution I've found is to switch the flash out of ETTL mode and into full manual. Experiment a bit to find the flash setting that works for that environment -- often around 1/16 or so -- and then stick to that. But of course, that only works if I maintain a consistent distance between flash and subject. This technique also produces unpredictable results when shooting people with very different skin tones.

As I'm typing this, it occurs to me that I might also be able to use FEL to find the right setting, rather than experiment.

Any tips from folks who've dealt with the same issue?

tirediron · Jul 9, 2013

The best solution is to shoot manual flash and set exposure using a flash meter. If you're dealing with widely varying skin tones then you may need to shoot a trial shot to confirm, but a good flash meter will be your best friend. TTL is pretty much no one's friend.

cgipson1 · Jul 9, 2013

Manual flash! Consistent and accurate. Learn it.. and you can control different distances with your aperture! (look up guide number)

http://www.amazon.com/Light-Science...92616&sr=1-1&keywords=light+science+and+magic

Big Mike · Jul 9, 2013

Yes, the issue is cased by the TTL metering...so the solution is to use manual flash. And depending on the model of flash you have, it shouldn't really take much fiddling around. Most modern flashes have a distance scale (when you put them into manual), so all you have to do is adjust your settings (Aperture, ISO & flash power) until the distance from flash to subject, matches what is on the distance scale.

Another option is to change the angle of the light, which can be done either by moving the flash off camera, or simply by bouncing the flash off of a suitable surface. Again, manual flash mode can be beneficial.

Of course, it's not just the metering problems caused by reflective surfaces....but also that those reflections probably don't look good in the photo. So changing the angle is likely your best option...but sometimes (depending on what you're shooting) it will be hard or impossible to completely avoid those reflections.

Light: Science and Magic: An Introduction to Photographic Lighting: Amazon.ca: Steven Biver, Paul Fuqua, Fil Hunter: Books

Mike_E · Jul 9, 2013

Learn to bounce your flash. Use manual as stated.

A flash meter is somewhat helpful- extremely helpful if you get the flash off camera.

Proper exposure is proper exposure no matter the color or how varied the tones are within the shot. The exception to this is if your shadows don't have enough detail to suit you. As Dean Collins used to say: True tonality only comes from the subject being properly exposed. At the expense of going off the subject (and not to be argumentative- just informative) dark skinned people should be lit so that you get detail from their highlights and light skinned people so that their detail is from shadow- also from Dean Collins. This is one of the main reasons that to shoot people properly you need your light to be mobile in regards to your camera, iow off camera.

pixmedic · Jul 9, 2013

Im on my phone at work, but if you dig up my wedding pic thread, i shot in front of an aquarium in almost no light. Used a sb700 facing the ceiling with a large bounce card facing IN FRONT of the flash. It gave me enough light to expose the picture and the bounce card in front kept the light from reflecting in the glass.

mattbaume · Jul 9, 2013

Hey thanks folks -- this is all really helpful. I'd never really looked at the distance scale on my flashes (a 430EXII and 580EXII) but after just a little fiddling around I can see just how useful it is. Obviously, it'll take some practice before I develop a good instinct for what settings all work well together, but I'm off to a good start now. Thanks again!

mattbaume · Jul 9, 2013

pixmedic said:
Im on my phone at work, but if you dig up my wedding pic thread, i shot in front of an aquarium in almost no light. Used a sb700 facing the ceiling with a large bounce card facing IN FRONT of the flash. It gave me enough light to expose the picture and the bounce card in front kept the light from reflecting in the glass.

Here it is: http://www.thephotoforum.com/forum/people-photography/330127-one-weekend-wedding.html

That looks fantastic. So, you're essentially using the ceiling as your light source, right? Blocking the hotspot with a card is brilliant.

pixmedic · Jul 9, 2013

That was shot in a tunnel in the aquarium. The only lighting besides the lights IN the aquarium were one blue and one purple spotlight. There is no way to get even a halfway decent exposure without flash. However, if you flash straight on, even diffused, you will get a lot of glare. Place a large bounce card in front of an upwards facing flash, and that pic is the result. I was pleased. So was the wedding party.

Gavjenks · Jul 9, 2013

You don't have to rely on intuition or anything, by the way. There are readily available flash exposure tables (depending on the guide number of your flash, otherwise I would link you directly to one) that tell you aperture/ISO/distance combinations that should give a roughly correct exposure (of the portion of the scene at that distance). Print one off and carry it with you for now.

If bouncing off of a flat object at an optimal bounce angle, just estimate the added distance as a traced ray from you to bounce point to subject. If bouncing off a non optimal angle, up the exposure beyond what the table says by a bit, depending on how oblique the angle of the surface is from what it would ideally be.

If shooting through diffusers, apply compensating numbers that you calculate ahead of time at home for that diffuser and that flash.