Red Eye and Flash/Lens Distance

bvy · Oct 10, 2015

Red eye is an issue when the flash is "too close" to the lens. Is there any rule for how close is too close? I figure subject distance figures into the equation. I'll be shooting in a dark theater this week, subject three to four feet from my TLR, flash is on a clamp about six inches from the lens. Thanks.

Peltigera · Oct 10, 2015

Red eye is caused by the flash being too close to the subject and close to the lens/subject axis. You need a flashgun that will do a pre-flash as that will cause the subject's pupils to close up.

Sirius Glass · Oct 10, 2015

Besides or instead of preflash just raise the flash mounting point a few inches or 5 cm to 10 cm.

bvy · Oct 10, 2015

Here's what I'm working with...

Sent from my iPhone using Tapatalk

Gerald C Koch · Oct 10, 2015

Red-eye is caused by light being reflected from the retina of the eye. It has relatively nothing to do with distance. You will see it in group shots as well close-ups. It has to do with the position of the flash relative to a person's retinas. To prevent it move the flash away from the lens so that they are not on the same axis.

RobC · Oct 10, 2015

use b+w film. Problem solved.

bvy · Oct 10, 2015

RobC said:
use b+w film. Problem solved.

Ha! Actually, I am tonight. But the costumes are so colorful (it's an opera) that I want at least a few shots in color...

M Carter · Oct 10, 2015

Gerald C Koch said:
Red-eye is caused by light being reflected from the retina of the eye. It has relatively nothing to do with distance. You will see it in group shots as well close-ups. It has to do with the position of the flash relative to a person's retinas. To prevent it move the flash away from the lens so that they are not on the same axis.

Exactly correct - you can get red eye from quite a distance. Though your pic looks like you could be OK (do a test??)

By the way, this cheap diffuser is the best I've ever used. I'm not much for on-camera flash, but when I need to, I use one of these. Softer look than the "Fong" things (though it is a bit bigger). Great use of twenty bucks!

Mainecoonmaniac · Oct 10, 2015

I think the closer the flash is to the lens axis, the greater chance of red-eye.

RobC · Oct 10, 2015

bvy said:
Ha! Actually, I am tonight. But the costumes are so colorful (it's an opera) that I want at least a few shots in color...

It will only be a problem (I think) if they are looking fairly straight into camera. As already suggested a flash unit with pre-flash to close their pupil will help too. If they have bright spot lamps on them their pupils may already be closed down quite small.

Mainecoonmaniac · Oct 10, 2015

My wife is an optometrist and she told me that red-eye can be a diagnositic tool.

http://www.eyecancermd.org/retinoblastoma/diagnosis.html

MattKing · Oct 10, 2015

Children are much more susceptible, because the lens in their eye is relatively larger, and generally less cloudy.

If you can move your light source farther from the optical axis of the lens, it will definitely reduce the effect.

Sirius Glass · Oct 10, 2015

APUGuser19 said:
B&W film does NOT stop red-eye. Instead you get the same thing, but it's white.

Yes, in fact the retina produces unnatural looking glowing eyes.

Mainecoonmaniac · Oct 10, 2015

Don't know if they sell them anymore, but some photo stores had red-eye pens. It's just a green pen for color prints.

wiltw · Oct 11, 2015

I dare say that the offset distance -- the measurement of flash lens to lens axis -- DOES NOT MATTER!

Because what DOES matter is the ANGLE formed between the subject's eyes and the flash lens to lens axis! What works for 5" offset at subject Distance X might NOT work to avoid redeye at subject Distance 3X, for example.

Ian C · Oct 11, 2015

This is discussed in the Wikipedia article Red-Eye Effect.

Under the heading Photography techniques for prevention and removal the recommendation is to separate the flash head and lens axis by at least 1/20th the camera-to-subject distance.

Thats an angular separation of about 2.9°.

https://en.wikipedia.org/wiki/Red-eye_effect

Peltigera · Oct 11, 2015

wiltw said:
I dare say that the offset distance -- the measurement of flash lens to lens axis -- DOES NOT MATTER!

Because what DOES matter is the ANGLE formed between the subject's eyes and the flash lens to lens axis! What works for 5" offset at subject Distance X might NOT work to avoid redeye at subject Distance 3X, for example.

As it is not easy to measure angles while taking photographs, the offset distance is related to the angle and much easier to measure. Increasing the flash/lens offset as much as possible will reduce red-eye as much as possible in a real world activity even if not perfectly in a laboratory. You also get better modelling to boot.

John Koehrer · Oct 11, 2015

wiltw said:
I dare say that the offset distance -- the measurement of flash lens to lens axis -- DOES NOT MATTER!

Because what DOES matter is the ANGLE formed between the subject's eyes and the flash lens to lens axis! What works for 5" offset at subject Distance X might NOT work to avoid redeye at subject Distance 3X, for example.

Geez, most amateur shoe mount flash don't have either the offset or the range to make a difference.
With the amateurs the easiest solution was to get the flash off the camera.

Keep in mind with those users it's very difficult for them to understand or see depth of field or f stops let alone trying to
describe angular limitations. So for a general EASY explanation. Move the flash or raise the ambient light level.

cliveh · Oct 11, 2015

Just selotape a bit of tracing paper over the flash and you wont have the problem.

Red Eye and Flash/Lens Distance

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