A formula to decide which size tele lens to use?
Mar 15, 2018 15:12:26 #
That's goal line to goal line on a football field, but your goal end seats will be some 10 yards further away.
Manglesphoto wrote:
I have a question for you. Have you ever viewed a person at a MEASURED 100 yds with the naked eye?
Mar 15, 2018 15:39:27 #
This formulation works because subject distances greatly exceed the focal length. The exact formula is
(size of subject)/(size on sensor) = (subject distance)/(focal length) - 1 . When subject distance greatly exceed focal length, the 1 may be dropped with trivial loss of precise accuracy.
(size of subject)/(size on sensor) = (subject distance)/(focal length) - 1 . When subject distance greatly exceed focal length, the 1 may be dropped with trivial loss of precise accuracy.
blackest wrote:
the basic equation might be fairly straight forwar... (show quote)
Mar 15, 2018 16:35:37 #
itsnoelb
Loc: Edgewater, FL. Originally: FLINT. MI.
One day, fiddling around, I shot the car next block over just....to see. Either a T1i, or my 7D and a 100-400 Canon L. Tripod, wireless remote, mirror lockup, calm wind, no straps on body. Its just over 400'. GPS software says 422. I could read the expiration tag of the license plate( 1 inch by 1.5 inch) clearly on the best shot at 400mm. And at least 100% crop. But, c'mon, the practicality of such a shot....and reliable results are.....unpredictable unless condition are darn near perfect.
Sidebar, I got sharper photo'x more consistly with my T1i and the 400 than my 7D and the 400. Just saying.
Sidebar, I got sharper photo'x more consistly with my T1i and the 400 than my 7D and the 400. Just saying.
Mar 15, 2018 17:39:06 #
John_F wrote:
This formulation works because subject distances greatly exceed the focal length. The exact formula is
(size of subject)/(size on sensor) = (subject distance)/(focal length) - 1 . When subject distance greatly exceed focal length, the 1 may be dropped with trivial loss of precise accuracy.
(size of subject)/(size on sensor) = (subject distance)/(focal length) - 1 . When subject distance greatly exceed focal length, the 1 may be dropped with trivial loss of precise accuracy.
i'm not sure how that equation works
with size on sensor in mm/ focal length mm = subject size (feet /meters/ yards) / subject distance ( feet /meters/yards) the units cancel
your equation is some what different.
Mar 15, 2018 20:48:55 #
My equation came from the image magnification formula and the other is the lens formula. See my earlier post in this thread. Or refer to any Physics of Optics book.
blackest wrote:
i'm not sure how that equation works
with size on sensor in mm/ focal length mm = subject size (feet /meters/ yards) / subject distance ( feet /meters/yards) the units cancel
your equation is some what different.
with size on sensor in mm/ focal length mm = subject size (feet /meters/ yards) / subject distance ( feet /meters/yards) the units cancel
your equation is some what different.
Mar 15, 2018 21:31:05 #
John_F wrote:
My equation came from the image magnification formula and the other is the lens formula. See my earlier post in this thread. Or refer to any Physics of Optics book.
Is that different to the formula I posted on the first page?
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