Re: What am I up to now?

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>One question about rack and pinion:
>
>Why have it?  I know it's a niftier way to focus, but I very rarely ever
>focus my viewer.  As Ron Popeil says: "Set it and forget it".
>
>Is this because I use mounting gauges and don't have convergence
>differences?  Or is it that the focus needs to be adjusted for showing
>the viewer around to different people? Or maybe people are after a finer
>adjustment than sliding can offer? (No fair answering "yes" to all of
>these ;-))

  I mentioned rack and pinion in regard
to an ultimate viewer ($500 retail like
the Hugo Comby perhaps).

  I currently have a homemade fixed focus viewer
and it works well. But I am fairly near sighted
and would like to be able to view without
my glasses sometimes. So focusing would be a
big plus for me and rack and pinion seems like
the elegant way to do it.

  My brother in his multiformat viewer made
a sliding tray type and has a knob on the back
you turn to move the tray. This is an awkward
position and the screw pitch is way too fine
so that you can spend quite a bit of time straining
your eyes as the image slowly comes into best
focus. A much coarser pitch would help as would
moving the knob from the back bottom to the
front top (like on center focus binoculars).


>BTW: sliding focus can be just as precise as rack and pinion if one uses
>a "pivoting" finger method rather than a push/pull. If you use your
>index finger knuckle as a pivot against the wood then it really turns
>into a lever focus.
>
>I can say that using rack and pinion for focus in a limited production
>viewer will increase the cost.  Is it worth it?
>
>What if the sliding focus that I use (like in the MF kit) were designed
>to eliminate having to loosen and tighten the screw, just slide it and
>it stays? How about a lever on the bottom of the viewer that forms a
>fulcrum with maybe a 3:1 ratio for finer adjusting?

  I recall the description of the
focus function on your kit as being
described (more or less) as a set it
once and leave it there. So I got the
impression that focusing regularly
(like when passing it around a group
of people) would wear it out and cause
excessive play.

  If that is not the case then some
of my objection (not the right word)
for this focusing method is removed.

Greg E.