13" F/3 telescope build

[Mitch Alsup]

No, your build pictures are excellent! I mean do you have provisions for a camera hooked up to the telescope to take pictures of distant galaxies?

Sort of:: I have an adapter and t-ring that attached to my Canon dSLR; that goes in the focuser and enabled astrophoto.
But 99.9994% of my telescope use is visual.

I thought about building a fork mount for the 13 (maybe after I get the other telescopes done) that would be good enough for long exposure astrophoto. But its in a not yet category.

 

[Mitch Alsup]

An update: I finally got a working version of the MIPS plate I talked about 1/2 way up this thread.

As you recall the purpose is to lower the cantilevering forces on the focuser and the base plate mounting it to the upper assembly.

But let us start with the process of discovery:: the following is a Paracorr 2 with the inner (focusing) barrel removed.

 

[Mitch Alsup]

The outer barrel on the Paracorr 2 is threaded onto the optics barrel.

For a long time, I wanted to machine a thread in a part and simply screw the P2 optics housing onto some plate. But making 2.78" M0.75 threads to a blind stop inside a bored hole 1mm deep is "beyond" my abilities to machine. My guess is that the manufacture made a bottom tapping die and uses it to perform the threading.

So rats.......That is, until I realized threads go the same direction backwards and forwards! So, I use a piece of the P2 flipped it over and I have my threaded adapter--and it already had a thread (cam) machined around its periphery. So this next picture shows the outer barrel flipped.

 

[Mitch Alsup]

I machined up a barrel that is a nice fit to the outer housing, threaded a hole, turned a thumbscrew to fit the cam profile and put dimples on th ends where set screws hold the barrel to the base plate (later).

 

[Mitch Alsup]

The first image shows the P2 out as far as the cam allows:


While this next picture shows the P2 in as far as the cam allows.

 

[Mitch Alsup]

This mechanism was designed to allow the Paracorr 2 optics barrel to be installed from the back (inside) of the upper assembly.

The base plate started life as a 9" by 4" by 1" piece of 6061T6 aluminum. The first operation was boring a hole at an offset but centered just smaller than the outer size of the barrel machined to hold the Paracorr 2 optics (2.700"). Then 1/2" from the front was faced off, and 1/4" from the rear was faced off so that there was enough projection on the front side to pass through the upper housing and allow installation of the focuser.



After being faced to size, the plate was mounted on an arbor on the rotary table where it was lightweighted.
A picture of the side profile:

 

[Mitch Alsup]

Next up was a means to focus the Paracorr 2. In effect one has to hang a transparent film 52mm above the top surface of the last lens in theP2 optical barrel.



The inside was cut with a taper such that the outer edge has a snug fit to the threads at the end of the P2 optics barrel. Then after this end was fit to the P2, measurements were performed to determine how deep to bore a recess and ledge. Then a small ring exactly fitting this bore and lege were machined.

 

[Mitch Alsup]

The outer barrel was turned to 1.998,5 to fit easily in a 2" focuser barrel.

A piece of scotch tape is tapped to the ring, the ring inserted face forward to the ledge, and we have a device that will hold the transparent plane at the correct distance to th optics. The telescope is pointed at a bright object, and th P2 is rotated until the object reached sharp focus (zero power observation.)

This picture shows the focuser assembly covering the front lens element and ready to hold the scotch tape at the correct distance.



More later.

 

[Mitch Alsup]

Here is a picture of the plate mounted to the upper assembly, face first:



and from the side:



And from the inside"

 

[StevSmar]

... I invented a new mirror cell architecture which one can puruse at
https://www.cloudynights.com /topic/547689-mitchs-mirror-cell-architecture/

Nice project! I enjoyed seeing how you modelled the mirror support.

I’ve been wondering, when mirrors are ground and lapped they appear to be fully supported. Does the mirror support you’re using introduce some distortion, or are the mirrors lapped using the same support points as your mirror support has?