Getting To Know Your Digital Camera

[freeztar]

Good answer, thanks.

But it raises another question, perhaps beyond the scope of this thread...

Why do dilated pupils cause "red eye"?

[alexander]

tomorrow, wait, already today, i will work on some shots for you guys with my moms point and shoot to show what the settings i was discussing do for your picture

for now Q, nice explanation, that is exactly why they do that. Generally this is not a large problem for the pros as they will work in well lit areas, but it can be, in which case, it is generally a matter of angle, if red eyes show up, you would reposition light, perhaps soften it, bounce it, and/or ask the subject to focus on another spot. Sometimes you have to reposition the camera too, but that is how pros will take care of red eye (like lens flares from glasses actually) (occasionally some PS work may be needed

[LaurieAG]

Hi Freeztar,

Originally Posted by freeztar

Why do dilated pupils cause "red eye"?

Good Question and a good example of how the image capture mechanism works in Digital and Film cameras compared with our own eyes.

Theory of color

At low light levels, cones cease to function. Cones respond to different wavelengths of light

There are red, green and blue cones that act as color receptors in the eye and the red cones are probably the last ones to cease functioning in low light. Other animals have different numbers of cones with many missing the red cones so they display a different color (or combination of colors) when their eyes are dilated and their images are captured.

[Qfwfq]

Originally Posted by alexander

Generally this is not a large problem for the pros as they will work in well lit areas

Yup. certainly the flash is for impromptu photography, when lighting isn't taken car of better. The problem is of course when we want people to watch the lens so that they are looking at the viewer of the resulting photo, the flash being near the lens for practical reasons.

In any case the flash is only any use for very short ranges of a subject, like 3 or at the most 4 metres. You see so many people using it when it is totally out of place. It should only be used when both necessary and effective. I hardly use it and once I missed a good shot, when I could have exploited the very last one of the spool (back in prehistory) in my girl's little automatic compact. I always found it annoying because I had to remember to set it to no flash every time I switched it on; that time I forgot and I couldn't repeat! It was hopelessly underexposed.

[jab2]

Originally Posted by freeztar

Why do dilated pupils cause "red eye"?

Due to the many blood vessels in the retina, it will display a red colour when illuminated. If the iris is wide enough and the flash/lens axis is of very small angle and strong enough, one can actually see this red colour displayed as "red eyes" in a picture. This effect is not normally visible as normal illumination (sun, roof lighting etc) is never from a source that shines horizontally and would thus not reach the retina in the back of the eye. The one cure for “red eyes” is to force the iris to contract by giving a pre-flash, thus forcing an reflectance angle that is smaller than that between the flash and lens axis as described by Alexander. This however have the disadvantage that people react to the pre-flash and might have "lost" their “pose” by the time the exposure is made. A much better solution is to move the flash off-camera, (only possible with high end cameras) thus increasing the flash/lens angle outside the cone of reflection of the retina through the iris. This have an added advantage that the resulting photo will have much more depth and natural looks as the off-camera flash will cast slight oblique shadows due to the greater flash/lens angle. This is particularly true for faces. In normal on-camera flash one get a very flat looking photo as the flash do not cast visible shadows due to narrow angle.

[jab2]

Originally Posted by alexander

Anyways, another use of the strobe is to freeze subjects. A standard flash, like an sb800, on 1/16th power will produce a flash of light lasting about 1/11,000th of a sec. This will properly expose the subject it is facing, fixating it in the shot at that instance. This ofcourse meaning that if you are shooting in dark conditions, at say 1/80th shutter speed, you still have around 274/22,000 of a second before your shutter closes

Much easier to describe than to do.

Back in the early 80's I bought Stephen Dalton's book: Caught in Motion: High Speed Nature Photography.

The book is a real treasure of information on using strobes to freeze motion in the natural world. It is full of diagrams on setup and has some really amazing photos.

Leopard frog diving I remember from the book as well as Swallow drinking. I also remember another unique photo of a swallow as it contorted itself mid-flight to squeeze through a rather narrow gap above a barndoor.

I only found Stephen's website while researching for this reply, but do not think it does his work justice at all, at least not from the experience I had reading that book. I'll have to dig it up again and enjoy it once more.

[alexander]

Originally Posted by Qfwfq

Yup. certainly the flash is for impromptu photography, when lighting isn't taken car of better. The problem is of course when we want people to watch the lens so that they are looking at the viewer of the resulting photo, the flash being near the lens for practical reasons.

In any case the flash is only any use for very short ranges of a subject, like 3 or at the most 4 metres. You see so many people using it when it is totally out of place. It should only be used when both necessary and effective. I hardly use it and once I missed a good shot, when I could have exploited the very last one of the spool (back in prehistory) in my girl's little automatic compact. I always found it annoying because I had to remember to set it to no flash every time I switched it on; that time I forgot and I couldn't repeat! It was hopelessly underexposed.

Flash has a lot of uses, and can be used much farther away then 3-4 meters, it all depends what it is that you are shooting and how you are using flash. If you are speaking strictly about on camera flash, then yes, generally it is used close up, take that flash off camera and your flashes, while will likely be within 5 meters of the subject, will take on objectives that most sane people don't like to think about

for example this before-mentioned photo here: http://www.flickr.com/photos/davidhobby/3250091189/sizes/l/ there are 3 flashes used to light up this photo (but you couldn't really tell now, could you ), there is a strobe to the right, that looks soft, so probably with a soft box, probably at a fair power to light up the right side of the body, there is a strobe hidden behind him, knowing David, probably bare, set very low, to backlight the subject and separate him from the background. And there is a green-gelled strobe on the left of the photo, lighting the subject's right shoulder with some green light it looks...

I know it looks like your average photo, but there is a lot of thought put into it to make the light look natural, and yet light the subject just enough

Here are some of my fav shots of his, shots i used and still use to learn more about photo myself


http://www.flickr.com/photos/davidhobby/3311616091/in/set-72157614396346749/
http://www.flickr.com/photos/davidhobby/176516763/in/set-72157603549501638/
http://www.flickr.com/photos/davidhobby/3349749823/sizes/l/
http://www.flickr.com/photos/davidhobby/2776002397/sizes/l/
http://www.flickr.com/photos/davidhobby/2594689052/sizes/l/
http://www.flickr.com/photos/davidhobby/2503065839/sizes/l/
http://www.flickr.com/photos/davidhobby/491513344/sizes/l/
http://www.flickr.com/photos/davidhobby/420038884/sizes/l/
http://www.flickr.com/photos/davidhobby/143215686/sizes/o/

Yes high speed is indeed easier said then done, you are absolutely right jab, infact that sound like something fun to do today, i'll attempt a high speed shot of something (i'll figure out what eventually )

[Qfwfq]

Originally Posted by alexander

If you are speaking strictly about on camera flash, then yes, generally it is used close up

Well of course.