Godfrey DiGiorgi wrote:
On Oct 5, 2005, at 7:59 AM, Toralf Lund wrote:
The most important factor is how efficienty the overall system
works.
Lens driven AF is more efficient than body driven AF.
I very much doubt that this holds as a general claim.
This is a general truth in the mechanical engineering of servo
systems. Reducing the number of bits between a motor and the thing
being driven always reduces power losses and increases control.
Motors can be made smaller and lighter, lower power, etc.
Yes, but they probably *have to* be made smaller, lighter and lower
power, too. Right, you do save something on a reduction in
mechanics, but you get some new ones in that you introduce power
transfer, switching etc. to the lens (not needing *any* electric
connections to the lens is definitely attractive in many ways), and
you also put much more serious restrictions on the motor size etc.
Since the technology to do the job is now available, it's the
direction that the manufacturers are going because it's a better
solution. None of your reservations are of much consequence: power
transfer on this scale in the 21st century is not a problem,
I still get a bit shaky when I hear about this high frequency thing. And
all the electric contacts are quite very likely failure points. 21st
century equipment actually has a quite annoying habit of failing or
becoming unreliable because of bad connections...
lenses without electrical connections of some sort literally don't
exist for automated cameras anymore, etc.
Yes, but there's a difference between simple digital info lines and
motor power/high freq AC. And my MZ-5n will still be able to work and
focus AF lenses correctly even if all electronic connections are lost.
Also, it seems to me that the bits between the motor and what's
being driven are in any case so few and close together anyway that
it doesn't really matter that much.
Mechanical inefficiencies are always important. They deal with the
bottom line of moving the components precisely and quickly, address
the physics of inertia and acceleration.
No, I don't think they necessarily are that important *as such*. Once
you can move the parts precisely enough to be within the tolerance of
(in this case) the rest of the AF system, and quickly enough for the
response time of the other components, the actual performance of the
mechanics ceases to matter.
- T
