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...
- 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 [email protected] sent from i4est
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