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View Full Version : Do the apertures run through a smooth gradients?


WonJohnSoup
11-17-2009, 01:47 AM
So on non-constant aperture lenses, do the apertures run through a smooth gradient as you zoom in and the aperture value goes up? Say, on an EF-S 18-200mm, the max aperture will read f4.5 at 50mm, and as you zoom to 80mm it will read f5.0 as the max. Would it be "worth it" to keep the shallower depth of field of f4.5 at 79mm and then crop in during post to a 80mm field of view, or is it more of a matter of the camera readout simply not being programmed to display f4.9?

I assume the apertures run through a smooth gradient, for a bunch of reasons, but just looking for confirmation. Thanx for any help.

And for those looking to nitpick, those were just theoretical values I threw up, so no need to tell me how there's very little difference between 79mm and 80mm or f4.5 to f5.0.
ydgmdlu
11-17-2009, 06:00 AM
The answer is no. Sorry.

http://www.dvxuser.com/V6/showthread.php?t=190667
WonJohnSoup
11-17-2009, 10:44 AM
Interesting, so these lens go by distinct stops. Guess that's not too wild to imagine, but interesting, because I never noticed a significant drop in exposure in my real world use so far, but I'm pretty distracted by all the new things to learn on the camera, haha. Thanx for answering my question. I guess this means it actually is worth it to keep the lens a millimeter away from the next stop and just cropping in post.
KeithAndrews.TV
11-18-2009, 07:46 AM
Zoom lenses that are not constant aperture do have the standard f-stop values known in the photography world, however as you zoom, the change in exposure will be linear. In other words, there won't be any sudden change in brightness as you slowly zoom the lens through the f-stop range. I have a Canon EF-S 15-85mm f/3.5-5.6 and the change in exposure as I zoom from 15mm to 85mm is smooth and linear.
WonJohnSoup
11-19-2009, 12:17 AM
Hmmm, thanx, Keith. That seems to not jive with the link the first responder posted, but I'll see how it ends up working for me in the real world in regards to any sudden exposure changes or if 1/3 stop on an APS-C sensor ends up being significant in my work.