[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]

Re: ATM Aligning Secondary stalk

At 7:31 PM 5/19/97, thomrob@iamerica.net wrote:
>Dear ATM's
>
>After lurking for a few months I have come out of hiding.
>With a question. It's probably has a very simple answer.
>
>I have built my own secondary mirror stalk using a sturdy, but narrow
>square rod of brass with a flat plate soldered on the end. I want to bend
>the stalk
>before I attach the secondary mirror. How many degrees should the stalk be
>bent.
>Also, where should the bend be. The scope is a 6" f/8.2.


My 6" uses the same kind of setup, only I used a threaded rod instead of
the square rod. I soldered a washer, which I filed oval, to the end and
then made a 45 degree bend a little more (1/4") than 1/2 the long dimension
of the secondary mirror. Perhaps I should try an ascii drawing to show how
it should work:



<html><pre>
     |     | <- focuser tube
-- o |     |-------------- tube
   |
   |
   |
   |
   |  <-- extra distance because stalk hole is at the side of focuser
    \\
     \\
      \\            - - - - - - - approx center line of tube
      ^\\ <- secondary mirror
      |
  washer
</pre></html>

The thing to remember is that the stalk will be to the side of the focuser
tube, so make the bend long enough to get it there and still cover the
washer well. I placed the washer on the bend afterwards while looking
through the eyepiece holder to get it approximately centered. Then I
soldered it and then I used silicone to attach the secondary to the holder.

Since you've already soldered the plate, you'llhave to measure or
guestimate the extra amount from the bottom, but it's not too critical. If
you really botch it, either make another, or add 2 more bends to the stalk
as below

<html><pre>
___
   |
   |         <- extra bend to move diagonal under the eyepice more
    \
     |       <- 2nd extra bend to keep stalk perpendicular to tube
     |
     |
      \      <- 45 degree bend for secondary
       \
        \
         \
</pre></html>


Hope this is clear enough to help.
If not, maybe you can tell something from looking at my 6" scope photos on
my web page.



Robert Duvall

Software Engineer, Amateur Astronomer (TN),
and General Scientist (according to my son)
---------------------------------------------------------------
http://www.earthlink.net/~forcefive    <- Our Astophotos and ATMing
http://www.system.missouri.edu/atm/    <- ATM list archives