[ATM] testing an f/2.6 mirror?
gfbrandenburg at yahoo.com
Wed Dec 19 09:43:25 JST 2007
Thanks. I think I got one of the surplus shed adjustable slits some time ago and havent yet put it to use.
Bob May <rmay at nethere.com> wrote: The wire test isn't hard to setup.
First you need some fine wire. This can be some wire from an
old small transformer of low powr as the wire will probably be in
the high 60s for gauge. This stuff is on the order of about
.005" in dimeter. Stretch it out a bit, makeing sure that you
don't break it, and then do a slit6 and adjust the slit until the
slit shows the ringin the return image. Surplus Shed has had
some decent adjustable slits if you want to go that way although
the slits are sort of buried in the device which will make them
not to bad as a light soureceif you put the light right behind
the slit. I've gotten several and some of them needed to be
"adjusted" with a stone to make the slit even over the height of
the slit but thatt is just a little bit of fiddling.
Another sournce of fine wire is piano wire. I've got some on
spools from somewher some time ago and that would work well.
One thing to be sure of is that you are able to see the full
mirror when you do this as the short FL will fairly fill any
eyeball and a small security camera may be somewhat necessary to
be able to see the mirror. An alternative is to put a short FL
lens behind the wire to relay out the image to your eyeball. Set
is so that there is some eye relief to your eye and things should
be good. Remember that the test is done to the wire and not to
the eye so distortion with the lens won't cause any errors in the
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