Re: LUG[Leica] Rangefinder Accuracy

[Eric Welch <ewelch@neteze.com>]

sometime around 12/19/99 6:41 AM, Rod Fleming at rodfleming@sol.co.uk was
heard  to write:


> The first would be the angle that the moving prism or mirror moves through
> between any two focus points. For example, say the moving prism turns
> through an angle of 5 deg. between infinity and 10 feet- surely a
> rangefinder in which the equivalent movement is 10 deg would be twice as
> accurate? (I don't know the specs for the various Leicas-but I can't see how
> that affects the principle.)

I'm not sure about this one, but it seems to me that the only way there
could be a difference in the angle it rotates would be the
rangefinder base. After all, all light relfects at the
same angle regardless of the mirror. I guess if the mirror isn't flat...

> And then, are we not talking here about ease of focus, rather than accuracy
> of focus? The latter is surely an absolute term, within a tolerance (which
> we can specify) - the former raises questions about the user's vision among
> other things, like the brightness of the RF image etc.

But if it's not easy, the accuracy is off. So is this not inseperable
features or deficincies? One quality?
 
> Another thing. Look at the Contax style rangefinder. This tranfers
> rotational movement of the lens barrel directly to the rangefinder via
> gears. The rotational movement of the lens, between infinity and 1 metre, is
> about 3/4 turn on a diameter of just over an inch- say 2.5 inches. The same
> range of lens extension is transferred to the Leica style rangefinder by a
> cam moving approx 0.1 of an inch!

This would seem to me to be a question of precision manufacture. Either one
could be better than the other, though one might be harder to make so than
the other.
 
- --

Eric Welch
Carlsbad, CA
http://www.neteze.com/ewelch

"You can't cajole someone into loving you by simply being nice to be
around." - Garrison Keillor - As heard on "A Prairie Home Companion"