in regards to photography of all kinds, be it motion picture, or digital, something about apertures in regards to exposure has always bugged me... you see, the aperture doesn't magically disappear when exposing whatever you may be exposing. It has to open from the center to the outer limit, and then close fby going from the outer limit to the center again. Now, wouldn't one then expect the exposure of ANY photography, film, slide, censor, to be bright in the center and gradually lose exposure when reaching the outer edges? I understand that it is all done PSYCHO fast... but in an age where it isn't uncommon to see 1/8000 of a second exposures, I'm left to wonder how fast can it possibly be, and how come I don't see any difference really... Am I not looking hard enough? I know cameras don't open exactly from center to the outer edge, the paerture tends to be built of 3 or 4 piece the retract on their own, and then go back to form a nice black wall... but still, they do have to retract, and that would mean the center gets more exposure than the outer edges.... I'm kinda lookin at misha and wolfsnap for answers here, but nay input would be cool.

forgive the typos, I have gas.

The case of this is that it does occur BUT most people do NOT use film fast enough to record it. Also when it does occur the rest of the film is exposed to such a great degree it would be hard to notice the difference in exposure changes from the center as opposed to the edges. Think of it this way. You decide to stare at the sun fot 1/16 of a second lets say. At the same time you look at the sun a person shines a flashlight into you eye for 1/128 of a second. Will you notice the flashlight? Probably not. What if the flashlight were open for twice as long? Same thing. 4 times...ect. Basically it is a a typical problem of systematic reading which is so "swamped" or overpowered by the actual reading the background reading does not exist. One way you could attempt to see this effect is to open the shutter and photograph a comply black room or subject while using slide film ( To avoid the same effect as exposing the paper ). But then you would still have to use VERY fast film and probably perform iris opening many times. Now for a fun question if one photographs things during the summer when things are hotter how much does the exposure time change? ( I bet Kodak and the other film companies have performed this experiment several times!! ) =:-) Bsteph

k, merci bri.

Huh?

Ummm...if I am understanding this question correctly; I think the answer to the question is that the camera stops the apeture down to whatever you set before it ever opens the shutter. So, lets say you set it for 1/2000 at f/16. Simplified would go something like: 1) Press shutter button 2) Apeture closes from wide open to f/16 3) Mirror flips up (2 and 3 may happen simultaneously) 4) Shutter opens and closes in 1/2000sec exposing film 5) Apeture opens back up to wide open Was that the question? -=>Donald

Well that sounds like a good answer! That is how it happens in most cameras.....if like you said that was the question..... ......still scratching my head at bstephs reply..... what does heat have to do with anything?

now that'd make sense as well... i assume something similar would happen for non slrs. the temperature of the film might have repercussions in regards to all sorts of part of the exposure i'd think as well, though likely nothing noticeable I'd imagine, these guys have had plenty of time to get their film making processes down pat.

...hmm...scratches body part... If I understood the question, Don gave the right answer, at least for focal plane shutter SLR's. The lens is already stopped down before the little slits go winging their way across the film plane. Now, for in the lens shutters, hmm... Again, the aperature is steady before the shutter opens. But the shutter blades are like sphincters, [hows your gas, BTW?]. I think bsteph must be close. There 'prolly is a small amount of different exposure across the whole frame, but not enough to make any difference compared to the total time the shutter is open. Can't follow the temperature argument myself, but I think exposure does change a small amount with temperature.

I am still trying to see where I mentioned "heat". I did use the word "degre" but I was using it in place of amount. That is to say I wrote "Also when it does occur the rest of the film is exposed to such a great DEGREE it would be hard to notice the difference in exposure changes from the center as opposed to the edges." I could have written "Also when it does occur the rest of the film is exposed to such a great AMOUNT it would be hard to notice the difference in exposure changes from the center as opposed to the edges." Sorry all. But when you ask an analytical chemist a question like that...That is the kind of answer you likely to get. If one gives an explanation. Would you have perfered the answer "There is a difference across the exposed film but the background is buried in the nominal exposure". I can provide some not so fancy graphs and - or spectra to prove my point. But I thought my flashlight analogy was pretty good. Sigh. Didn't everyone here have to take a science class in highschool? Bsteph

Public schools (in the States). Sure, there is science and math. Just don't mention Darwin, pi == 3, and keep an open mind about the possibility that moon landing was staged on Hollywood set.

Well, someone had to say it. (",)