Red Eye in individuals.

Hi all,

As I mentioned in a previous post, I took a load of pictures of people picking up their silverware at Saturday's Darts Presentation evening. I'm just going though them and doing a little touching up here and there, and I've noticed that the same people are getting red eye?? I know the hows and whys of red eye, and it's only a few seconds work to select and desaturate the red/magenta pixels, but I was wondering; are certain people more susceptable to red eye than others?

Is it perhaps that they may have been blinking on preflash, and so don't get the iris reduced sufficiently; or that people with certain coloured eyes (hazel for instance, where there is a certain amount of red anyway, and the sensor enhances it more???) are more likely to suffer.

Just a thought, and I know that it's probably out there on the interweb thingy, but it might be useful to someone else here, if it was discussed.

Cheers

Liam

only 2 factors cause red eye.
A) lack if melonin- albinoism (I'd like to figure out how the albino in the davinchi code could've been driving at night or shooting people, as all albinos are vision severely impared to clinically blind as a result of the condition).
b) flash bouncing off the retina back to the lens.....long lenses plus low light, flash too close to the lens.

Liam,
The red eye is the reflection off the retina at the back of the eye, so it has nothing to do with the iris colour on the front.
You need a couple of things for red eye -
1) An open pupil - this often happens in subdued lighting. If the person's pupil response is slow, their pupil may not close up in time.
2) A direct flash-to-lens angle. The wireless flash on the *ist-D is a great help in reducing this (when you turn off the popup in the custom menu). Increasing the flash to lens distance reduces the risk of getting a "direct hit" on the retina.

There could be more to it, but that's what I know at the moment
Matt

Anatomy of the eye (at least, the bits contributing to redeye in your pics).

The iris is what gives our eyes their colour. The pupil ( the black part in the centre of the iris) is the variable opening (aperture) that regulates the amount of light that enters the eye. The retina is the innermost coating at the back of the eye (much like the film in a camera) and contains light sensitive nerve endings which feed into the optic nerve and onto the brain for interpretation. The retina is kept enriched with blood, which leads me to . . .

Redeye in photo's is red light (blood coloured) reflected from the retina of a subjects eye, not the iris. The colour of the eyes has no influence over whether a subject produces more or less redeye, but the size of their pupil, or aperture, under any given lighting condition has a huge effect.

The built-in flash of any modern camera is generally much too close to the lens resulting in a very narrow reflectance path. A flash attached to a cameras hot shoe can also be too close to the lens as to produce redeye, depending on the flash/lens to subject distance. The further away the subject, the more likely you will get redeye'd pics.

To stand a better chance of eliminating redeye at its source, ie when the scene is captured on film or by digital sensor, you need to increase the reflectance angle by increasing the flash to lens distance either by hand holding the flash or at least have it mounted on a flash bracket or hot shoe grip.

The redeye reduction system of modern cameras, consisting of one or more short pre-flashes is designed to fool the subjects pupil into behaving as if more light is generally available thus closing it down briefly creating a smaller aperture.

If you are taking a group shot where their attention is on you and yourcamera, you could hold up a white card or something similar a few inches or so from the camera on the opposite side to the flashgun and tell your subjects to look at the object you are holding rather than directly into the lens. The resulting pic will still look as if they are looking at the camera but their eyes will have moved enough to reduce the possibility of redeye. This of course does not work for impromptu pics at darts matches.

I suspect the ones more prone to redeye were the ones who'd had the most to drink! Alcohol slows the reflexes, and that must surely also affect the speed at which the pupil reacts to the anti-redeye pre-flash, so you'd be more likely to get redeye with those that had had a tipple.

Just a guess, perhaps someone would like to conduct an experiment?

Dan

This isn't quite true. Yes all people that suffer from albinism have vision problems and some have visual acuity that classifies them as legally blind but some have vision good enough for them to be able to drive (and presumably shoot) The simplest way that I have heard the visual problems albino's experience described, which I guess we will all be able to relate to, is that what they see is a low resolution image.
The reason why some but by no means all albino's have red or pink eyes is that light can reflect not just through the pupil but through the iris as well due to it's lack of pigmentation. For many albinos however their visual problems are far more complex as they often have varying degrees of nystagmus (involuntary movement of the eye back and forth) and strabismus (the eyes don't fixate and track together)

The more logical explanation as why some people suffered more from red eye at your darts match would be that there is a direct correlation between the number of pints consumed and the dilation of ones pupils and their ability to react to sudden changes. I would hazard a guess that the people with persistent red eyes will also be the ones holding an empty or nearly empty glass in most of the pictures!

Now seems an opportune time to go and crack open my last can of Caffrey’s that I brought back from the UK at Christmas, to see if my theory works! Cheers!

Steve

PS. The bit about albinism comes about from the work I’m involved in here in Cameroon and from which I take my moniker – if your interested take a look at http://www.promhandicam.org/23800/index.html

It would seem that Daniel and I are thinking along similar lines - albeit slightly blurry ones that won't keep still

promhandicam said:

I just had a look. Very Interesting.

more accurate for me to have said many instead of all right?

My information comes from having met an albino a long time ago when i was in fostercare. His eyes were pale blue. I remeber something about scar tissue in the retinas and cornia.

You'd know more than me though....I got twenty odd years to fog my memory from that experiance.

Hi all,

thanks for all the info. The one pint too many explanation fits nicely. As you are probably aware, most dart players like a little something to stiffen their resolve..

Except for the 6 year old son of one of the players, who consistently had red eye, this seems a sound reason.

Sorry, I'd better be off to work now,

Cheers

Liam

We all started some time although maybe 6 is a bit on the young side.
Just don't tell his mum about your suspicions otherwise the poor lad won't be able to sit down for a week!

Don,

Yes you are right – many albinos have disabling visual problems but albinism is a very complex condition. For example for some albinos it is only their eyes that are affected – they can have dark hair and skin that tans.

A colleague of mine who is an ophthalmologist did try and explain to me on one occasion what exactly it that causes visual impairment in albinos. If I remember correctly it is that they have fewer rods and cones which are the actual photoreceptors in the retina, and they also have abnormal development of the fovea.

In an eye there are around 120 million rods, which are responsible for black and white vision and are very sensitive to low light. Cones on the other hand are responsible for colour vision and are not so sensitive and there are only around 6 million of them. In general rods are found in the periphery of the retina with cones being concentrated towards the centre – the fovea. The area surrounding the fovea is the macula where most of the cones are concentrated. This explains why in AMD (Age related Macula Degeneration) people loose the ability to read and can be registered blind but often have fairly good night vision. This distribution of rods and cones also explains why to see a faint star you cannot look directly at it, but must look slightly to the side.

To get back to photography I guess you could use the analogy that albinos have to view the world through the equivalent of a camera phone set at low resolution where as the rest of us are blessed with the equivalent of a couple of istD’s !

Steve

Interesting info.

Given the rod/cone count of the eye one can assume then that when we have digital sensors of 128MP or so, we will have something akin to the resolution of the human eye. I wonder how far we are away from that ?

I played cricket against an albino west indian chap many years ago. Blessed with the same facial features and tight wavy hair of a west indian except his skin was a very light pinkish brown colour, almost blonde hair, and blue eyes. I can testify that, at that time (30 years ago), there was nothing wrong with his sight as he was an exceptionally good bowler and batsman, and what a sense of humour. If any of you out there plays cricket and has never played against an all west indian side, you have no idea of what you are missing. Don't expect to hit the ball too much, you'll be too busy laughing. Great fun.