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12-16-2007, 12:41 AM   #1
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Red eye on K10D

This question probably has a very obvious answer but I am perplexed and need some help. Recently I was shooting indoors using the DA 50-200 mm lens during a Christmas party. I wasn't too close to the subjects I was shooting and for some reason some of those subjects would get the red eye. I was just wondering why this is the case. I had the flash mode on for "red eye + flash" but there was still red eye. I am thinking that with the built in flash only being useful for 4m or less, the red eye reduction isn't effective? I was probably at least 10m away from where I was sitting to where I was shooting. TIA

12-16-2007, 03:26 AM   #2
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Red-eye is the result of visible light falling on the backside of the eye through the iris. What you're actually seeing is the retina with blood vessels. An on-camera flash can easily light up the area of the retina visible in the resulting image, causing the phenomenon commonly referred to as red-eye. The flash unit's red-eye reduction mode is an attempt to reduce the visible area of the retina by causing the iris to close as much as possible, but will not work every time for various reasons. The only certain solution is to cause the light to fall on the retina somewhere outside the area visible in the resulting image. This means using an external flash unit held or mounted further away from the camera.

By the way, the angle of the light, not distance from the subject, is the primary factor here. Of course, when you're further away from the subject, the eye itself is less visible, hence any red-eye is also less visible. However, if you zoom in on that subject from any distance away (enlarging the eye in the final image), red-eye will again be an issue to deal with.

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12-16-2007, 03:35 AM   #3
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Expanding on Stewart's post, if I may.....The closer the source of light to the lens, the greater the chance of red-eye. And on any camera it is always the built-in flash which manages to be closer than anything else. Any flash at all mounted on the hotshoe is going to do a better job of reducing red-eye than the best built-in flash. It's just a matter or angles.
12-16-2007, 11:21 AM   #4
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Thank you for your replies. I was wondering whether distance was an issue because the photos that I take that are closer to the subject, ie using the kit lens never had a problem with red eye and the built in flash.

12-16-2007, 04:30 PM   #5
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QuoteOriginally posted by weaponx525 Quote
Thank you for your replies. I was wondering whether distance was an issue because the photos that I take that are closer to the subject, ie using the kit lens never had a problem with red eye and the built in flash.
The further you are from the subject, the closer the flash is to the center of the pupil, and the more likely you will get red eye.
12-17-2007, 07:55 AM   #6
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QuoteOriginally posted by weaponx525 Quote
Thank you for your replies. I was wondering whether distance was an issue because the photos that I take that are closer to the subject, ie using the kit lens never had a problem with red eye and the built in flash.
Again, it is all about the angles.

Imagine an eyeball looking straight into your lens from 5 meters away and an eyeball looking into your lens from 1 meter away. Since the lens-to-flash distance remains the same on both, that means there is a greater angle between the eyeball and flash at the shorter distance, hence less chance of red-eye.

In either case, moving the flash farther from the lens-eyeball axis will improve things. In its simplest form, that can be just using a hotshoe mounted flash instead of the built-in flash. Doing things like bouncing the flash off the ceiling instead of firing it straight into your subjects eyeballs will practically guarantee zero red-eye.

Wherever that strong light goes in, it is going to reflect off the retina (picking up red from the blood vessels in the process) and come right back out. Imagine aiming a BB gun straight at a steel wall a few feet away and pulling the trigger. You're going to catch a BB right between the eyes for your trouble. That's the same thing the light from the built-in flash is doing. Now imagine holding the BB gun a few inches higher and aimed at the same spot. The BB is going to ricochet all the same, but it's going to come back and pop you in the throat or chest. In other words....that red-eye ricochet is still going to come out somewhere....you just have to make it so it doesn't fly straight back into your lens. The more straight-on that line is, the more it's going to hit your lens.

I hope that made sense.
12-17-2007, 04:22 PM   #7
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I also find some people seem to have a predisposition to red eye, blondes in particular.
12-17-2007, 04:50 PM   #8
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QuoteOriginally posted by Arpe Quote
I also find some people seem to have a predisposition to red eye, blondes in particular.
Yep, it has to do w/ blue/green eyes actually. Easier to hit the blood in the veins in the back and reflect back
e.g., I almost never get redeye w/ my F30, but tried photographing a blond (green eyes) for the first time this weekend and couldn't photoshop it out :-P

12-17-2007, 07:15 PM   #9
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QuoteOriginally posted by Arpe Quote
I also find some people seem to have a predisposition to red eye, blondes in particular.
I was doing headshots for a friend and she had the worst case of redeye I had ever seen. Every picture no matter where I placed the flash (off camera) she had red eye. It was quite surprising.
12-17-2007, 07:30 PM   #10
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Red eye is also easy to fix in photoshop or many programs.
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