Hi all,
I wonder if I use an adapter for my Canon lens on a Sony Camera, which is just a ring with no glass (or see-thru plastic) inside, just some electronics for the aperture and AF, does the focal length change (for a higher one)? Or it just changes the depth of field (deeper, less light) and focusing point (closer)?
I know, that extenders use some glass inside with electronics, and they are a lot more expensive - so it suggests, that an adapter only adapts, does not change the focal.
Alex
It does work just like the Canon EF to RF adapters, it changes the back focus (lens distance to sensor) but it does not change the focal length of the lenses used.
The adapter allows the use of SLR lenses to work on MILC camera's
anhy kind of obstruction inside should be avoided even planeparallell filter glass and a plastic element inside sounds suspicious.
The lens itself does not react to what mechanics it is attached to and does not change, so aperture numbers remain the same and as long as the distance between its mount and the sensor plane is correct, focus remains unaffected. BUT if the sensor size is smaller, it is like taking a scissor to a full frrame print. If you wish to have the same final size you must enlarge the picture, and this entails certain drawbacks, see the numerous discussions of "Equivalence" in the former DPR.
p.
Without those optical elements there is nothing that can change the actual focal length.
Adapters without optics are usually designed to keep the same focus as the original camera mount. With some mount combinations this is not possible & you will get closer focus - the adapter ends up working as an extension tube when it's not possible to fit things in, but EF lenses (44mm registration) on e-mount (18mm registration) leaves 26mm that has to be added for normal function.
DOF also will not change if the sensor size, aperture etc remain the same.
Most of the adapters I have do not need electronics or optical elements as my adapted lenses typically are manual only mechanical beasts that are controlled directly from the rings on the lens.