On 9/1/11 22:18, Toralf Lund wrote:
On 9/1/11 0:24, Larry Colen wrote:
I think that part of the reason that the adaptall mount went out of
favor is the difficulty and complexity of doing a screw-drive
autofocus version. It's one thing to make a linkage that'll handle
f-stops, but the tolerance you need for screwdrive would be really
tough to pass through an adaptall style mount. However, SDM is an
electronic connection, not a mechanical one. For that matter, you
wouldn't even need a mechanical linkage for aperture, just the
stop-down actuator.
Hmmm... I haven't actually looked into the details of how the
electronic linkage works, but since the motors are essentially
steppers, and the focus sensors are still in the body, there must be
some kind of signalling that's quite a bit more complex than, say, a
voltage to drive a traditional electric motor, and it's not unlikely
that different camera producers have different solutions for this, or
different signal levels etc. Which could mean requiring rather a lot
of electronics to convert the signals to something universal...
Actually, the electronic requirements may have been part of the issue
even for a mechanical drive, as there is (as I understand it) position,
or rather rotation count, information from the lens to the camera...
- Toralf
- Toralf
I was contemplating that with sensors improving so quickly, that it's
barely cost effective to spend the money making fast glass, to get a
stop or two, when sensors will give that same speed in a couple years
time anyways, for a lot cheaper. Therefore, fast primes are going to
quickly become a niche market, especially in DSLR mounts, and that
there probably aren't enough Pentax mount DSLRs out there to justify
the development costs of new fast prime optics. However, it might be
economically feasible for a boutique optics company to make fast
primes using something akin to an adaptall system.
--
Larry Colen l...@red4est.com sent from i4est
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