Posted 26 May 2007 - 02:51 AM
Posted 26 May 2007 - 03:02 AM
Its such a big open ended question not many people will give you the time if a. they think you are being lazy or b. have no direction in which to go with the enclopedia of possible replies ...
Posted 28 May 2007 - 10:57 AM
Back Focus has become something associated with digital cameras where it has to be checked regularly. Film cameras also need this checked, but less often. The reason is simple: video cameras are often constructed poorly (lots of plastics) when it comes to hardware and the mounts are not solid enough. They're also more sensitive to heat, which means the mounts in relation to the CCD will move a lot more, which screws up BF. If they built them correctly, you wouldn't have to check BF constantly.
Mind you - Flange Focal and Back Focus are all part of a relative chain: ANY lens ever made will focus, or defocus, as you move it forward or backwards (anamorphic lenses being the only exception). I.e. you could have a lens with no focus ring at all, but a mount that moved forwards and backwards instead and achieve the same thing. This is how projectors or many medium and big format stills cameras work. So the main purpose of the FF or BF-setting is to line the lens up so that the focusing ring marks on the lens correspond with reality.
Posted 28 May 2007 - 02:29 PM
And keep in mind that a zoom lens has a front AND back focus adjustment that must be set up right or the lens won't hold focus as you zoom.
Posted 28 May 2007 - 05:00 PM