sulhan said:Hieee.....
FYI......its basically a position encoder.....which is plated onto the lens barrel. SO for specific discrete position there is a encoded signal/combination obtained from this position encoder and this translate to a distance...."data" which may be send from the lens IC chip to the body.
rgds,
me
YSLee said:Zerstorer's got it. There are two common formulas, the first is Gaussian, which I think we covered in secondary school, and it goes like this:
ST1100 said:Put another way, we're answering the wrong question. loupgarou's question is how the camera/lens achieves focus in the first place, since the camera's vision is monocular and unable to tri-angulate.
VADER said:actually...the camera relies on the CCD sensors located on the camera to focus. Light goes through the lens and is reflected by the sub-mirror to the CCD sensors located below the mirrorbox.once infomation is caculated by the processor the AF drive motor will work the coupler to rotate the focusing lens group.....circuit-board on the lens serve to tell the camera what focal length is used....
YSLee said:Zerstorer's got it. There are two common formulas, the first is Gaussian, which I think we covered in secondary school, and it goes like this:
1/focal length = 1/distance to object from lens + 1/distance to image from lens
Newtonian formula is as follows:
(distance to object from lens - focal length) * (distance to object from image - focal length) = focal length ^ 2
These formulas are used by the processors in the lens and camera to derive the distance.
StreetShooter said:Well, actually, nobody knows how it all works. According to some people, it's alien technology which we exchanged for some human bodies (all volunteers, apparently). There's even a movie about it.
Anyway, some of us tried to reverse engineer the autofocus technology:
http://electronics.howstuffworks.com/autofocus.htm
loupgarou said:isn't the doppler effect about moving objects? ie: a radar gun uses the doppler effect to calculating the speed of a moving object. ie: you literally need to shoot a beam and time it when it comes back to you.
if I'm not wrong, photographic lenses are passive, with the exception of the AF assist beams/pre flashes, they don't emit anything.
TME said:I'm trying to follow this so am I right to say then that if the focus is right, then the rest of the stuff falls in place?
Cos it would seem from justarius that the different points of focus (however the camera may define it in its internal processor) is related to different subject distances. So when the SLR (using phase change detection) to determine that the subject is in focus, it automatically assigns a distance that has been pre-programmed into the camera. Is that how it is done? Justarius did I quote u correctly? If I didn't sorry....
How do film distance to lens (would that be the front or rear of lens?) and focal length play a part in determining the subject distance? :dunno: