anyone use a RF newt for a large finder?

.. If so how does it perform? How did you mount it? can you post a picture of it?
I have a 114mm f5 newt that missing a focuser, I'm thinking about putting it on my 13.1inch Dobsonian as a super finder.
Matt

Yes, I've done this with a 4.25" F/4.4 Newt. on an 18" Dob.
Works spectacularly well. You can actually find the faint
fuzzies in the 4.25" and then see them in detail in
the 18". Its fun to just go poking around the sky with it,
even without a star chart. You can find a lot of stuff
in the RFT under dark skies.

How it was mounted: I'm embarrassed to tell you.
I mounted it on the mirror box. Took 5 minutes.
Get a cardboard box about 4" tall and a little shorter
than the length of the RFT. Fold the top flaps in and
tape them inside the box place. Cut indents in opposite ends
of the box to match the RFT tube radius, and put the RFT
in the indents. Get 2 short pencils and jam them through
the bottom corners of the box near the front of the RFT.
Set the RFT + box on the top surface of the Dob mirror box
with the pencils hanging on the front edge of the mirror
box (these carry the weight). Put a bungie cord from one
Dob altitude bearing, over the RFT, and across to the other
alt bearing. Shim under the box as needed with
tape + cardboard bits to align the RF. If you decide you
like it, you can build something better. (Sorry no photos.)

You obviously want to keep the mounting as light as possible,
since it will be far off the axis of the Dob. Don't want to
mess-up the Dob balance too much.

Matt affenita said:

.. If so how does it perform? How did you mount it? can you post a picture of it?
I have a 114mm f5 newt that missing a focuser, I'm thinking about putting it on my 13.1inch Dobsonian as a super finder.
Matt

Hi: I know people do it and I have tried it myself. A couple of issues:

- Balance. A 114mm F/5 Newtonian is going to weigh maybe 4 pounds. Few Dobs can handle that much extra weight without causing balance issues. People mount them low to minimize the balance issues but that can be a problem too.

- I am not sure the exact focal ratio of your 13.1inch but typically they are about F/4.5. You 114mm F/5 with a 1.25 inch focuser will provide maximum of a 2.7 degree field of view, your 13.1 with a widefield 2 inch eyepiece could do 1.6 degrees which is quite an effective SuperFinder of it's own.

Jon

I used a 4" f/5 based on an Edmnunds mirror on my 20" for many years. I mounted it on the back of the mirror box. Very effective. People in line to view could "preview" objects.