Tilt Shift question

I've been considering either a 17mm TS-E or 24mm TS-E. I did a search of the forum, but couldn't find someone discussing this. Is there any specific reason that they're only made in manual focus? Since you can manually focus the lens from MFD to infinity, I would assume that it has nothing to do with the lens elements, so I'm just curious as to why.

I'm no TS/E expert but I'm going to say that because you are tilting/shifting the focal plane, the AF sensors would not be getting the correct information to focus with. Maybe it could focus when locked in place and not tilted or shifted at all but I'd guess they made the designs simpler by not including AF at all.

If you've got it all tilted and shifted to get everything from here to there in focus, where does the lens grab AF then?

Pimped by The Hoff...

I get that part, of shifting the focal plane, but the subject will still have contrast and everything that AF is programmed to lock on to. If I set AF to center point only, even if the focal plane has shifted, it should still be able to focus on the object at the center of the frame, shouldn't it?

Perhaps this will answer your question

http://www.luminous-landscape.com/tutorial​s/focusing-ts.shtml

Also read the bit at the end about why the TSE lens is not a flat field lens.
Mike K

TaDa wrote in post #9160364
I've been considering either a 17mm TS-E or 24mm TS-E. I did a search of the forum, but couldn't find someone discussing this. Is there any specific reason that they're only made in manual focus? Since you can manually focus the lens from MFD to infinity, I would assume that it has nothing to do with the lens elements, so I'm just curious as to why.

It is exactly because because of tilt and shift, that these lenses don't have AF.

Let's say you tilt the focus plane horizontal. Where would you let the lens focus now? Anywhere in the focus plane, focus is achieved. How can you let the camera know where to focus, even if redesigning the EOS mount completely, just for tilt shift lenses? BTW, this is also true for contrast focusing. How would you go about it and how would you tell the camera and/or lens?

Furthermore, as you know, the AF points all are within about 1/3 of the image in the centre, certainly on FF. This is because the AF sensors can't handle light falling in from very obtuse angles. When tilting and/or shifting a lens, these angles get much greater, to make AF even more impossible.

Also, with the movements possible, it gets rather hard to put in an AF engine, and keep the movement of the focus ring large and accurate enough to do proper, precise and acurate manual focusing, something you would always want to have with such a lens. A small difference in focusing may mean a world of difference, especially when using any of the movements.

Then there is the question where to put the focusing engine, and the ancillary stuff it needs? With the movements possible, it would likely mean making the lens a lot wider than it already is.

The most important reason, however, are the first two mentioned. There is no rhyme or reason on how and where to focus when using tilt, and it would be hard, no impossible, for shift because of AF system limitations.

Kind regards, Wim

Mike K wrote in post #9160472
Perhaps this will answer your question

http://www.luminous-landscape.com/tutorial​s/focusing-ts.shtml

Also read the bit at the end about why the TSE lens is not a flat field lens.
Mike K

Other than the fact that they kept spelling "center" wrong, that helped explain it, thanks

TaDa wrote in post #9160546
Other than the fact that they kept spelling "center" wrong, that helped explain it, thanks

That's "wrongly".

incorrectly, erroneously, happy?

TaDa wrote in post #9160546
Other than the fact that they kept spelling "center" wrong, that helped explain it, thanks

It's not wrong unless you live in certain places :P