Cameras and Lenses
What else determines Depth of Field?
I just received a Vortex Fury 8x28 (supposedly moved to the Viper line now) and it's a very nice little binoc for $229 but the Depth of View is really shallow. There's a large school sign about 200 yards behind my house and although the view is clear and very, very sharp, there is no "range of adjustment" when focusing whatsoever. It's back and forth, back and forth, and then sharp. Seems like if I set it down, pick it back up, it's out of focus.
I understand that magnification reduces Depth of Field but this is an 8x28 binoc. On my Leica 8x20 I have alot of adjustment range while still in focus as well as my Zeiss Victory 8x42 FL - so there has to be something else that affects Depth of Field besides magnification. Can anyone explain? Thanks.
Your focusing knob on the Vortex is probably much faster than the one on the Leica. The Leica, being slower, (I have one.) is easier to "fine tune" when focusing back and forth and easier to get (and keep) a sharp view.
The Zeiss 8 x 42 has a much longer focal length and so it's DOF will be greater than the short focal lengths your 8 x 20 and 8 x 28 have.
As a personal example, I can see a big difference in DOF between my Leica 7 x 42 Trinovid and my Vortex 7 x 36 Diamondback.
Bob
The change in f/number (even for a long bin like the ZR 8x43) doesn't have a perceiveable impact on DOF. It feels like it has more DOF because it has a slower focus rate.
Focuser "speed" i.e. focuser rate and focuser stiffness contribute to what people "perceive as DOF" though. It's very clear in 10x bins: I have a Zeiss 10x42FL which had very low friction focusing that was a pain to use in the field. Increasing the focuser friction made it a more usable bin (these bins already have a pretty high "rate" a bit more than half a turn from close to distant).
Field curvature (and amount of accommodation in the user) may also have an impact on perceived DOF. Older folks may feel a bin had less DOF than younger folks (as their eyes can't do the work for them).
After some argument the technical basis shows that only magnification impact the true DOF. There are heavily argued thread on this here as I'm sure Bob knows 