SLR Magic Rangefinder vs. FM vs. Rectilux..?

[Brian Caldwell]

Interesting, Brian. Does the size of the front optical element (of the taking lens) affect the sharpness as well?

Andrew - how was the FM's performance in comparison, from your experience? (I know there was some shitstorms with the seller, it's quite faffy and cumbersome, etc etc - but I mean purely in terms of unbiased optical image quality...) Was it soft wide open as well?

The front element diameter doesn't have any direct affect on sharpness in the sense that you can always conjure up a counter example.  For instance, I could add a foot diameter filter to the front of any taking lens and the sharpness would hardly be effected at all.  Again, what really matters a lot is the entrance pupil diameter, which is the diameter of the image of aperture stop as viewed from the front of the lens.

Of course, there are limits to the sharpening effect of using a shorter focal length taking lens.  If you go too short then you'll encounter aberrations and/or vignetting in the outer parts of the image.

[Jim Chang]

The front element diameter doesn't have any direct affect on sharpness in the sense that you can always conjure up a counter example.  For instance, I could add a foot diameter filter to the front of any taking lens and the sharpness would hardly be effected at all.  Again, what really matters a lot is the entrance pupil diameter, which is the diameter of the image of aperture stop as viewed from the front of the lens.

Of course, there are limits to the sharpening effect of using a shorter focal length taking lens.  If you go too short then you'll encounter aberrations and/or vignetting in the outer parts of the image.

The entrance pupil diameter affects the calculated f number of the lens (not necessary the measured T stop value though), which indicates how much light the lens can pass through theoretically. If you have a smaller entrance pupil, you will have less light passing through, and less abberations (that's why usually stop down your taking lens, will increase sharpness).

Using shorter focal length taking lens means larger depth of field, which can tolerance more abberations, that's why it could be a little bit sharper, but shorter focal length also means wider angle of view, which increases the chance to have more abberations, and vignetting. So, first thing is to make sure your shorter focal length taking lens is very sharp when wide open. That's my taken from Brian's comment. :-). Please correct me if I am wrong.