Autoguider scope mount

[bojan]

After some experimentation and lots of deliberations, I came to this solution.
3D printer is again in the focus...

[OzEclipse (Joe Cali)]

Bojan

Nice neat simple solution.

I have one of these lenses myself, it looks like a 1970's Tamron 400mm f6.3? My first accessory lens purchase as a 15 year old $60.

As a telephoto it was really awful. It had terrible flare. Good life lesson.

That $60 was earned in holiday jobs, cleaning up apartments following completion construction preparing them to be opened for inspection. Windows, sills, walls floors and kitchens and bathrooms.

Many years ago I disassembled the lens. I found one element a negative biconcave lens used as a tele-extender was never polished properly and still had pits in the glass. On reassembly and without that component, the lens flare cleared up fine but of course the focal length changed and won't focus when a camera is attached. That was ok, by that time I had much better 300 & 500mm telephoto lenses. I kept it as I always thought it might make a good finder or guidescope. As I'm sure you know, the barrels are sectioned and can be easily removed and shortened to modify the focus.

A few Q's
How do you focus? It looks like the helical focus on the barrel is locked in place?

It also looks like it might suffer from some flexure mounted on those springs, no problem for a low power finder, but a bigger problem for an autoguider?

How strong is the 3D printer plastic? The front ring doesn't look very thick for a plastic, but I have not seen any 3D printed parts and am unfamiliar with its properties.

How much do the 3D parts cost to print?

Cheers

Joe

[bojan]

Hi Joe,
Yes, this is Tamron Popular 400mm f6.3, and it is pretty awful optically.. but very good mechanically.
I tested it some time ago.. see thread here: http://www.iceinspace.com.au/forum/s...hlight=Popular
But, it should be OK as a guider.

I also removed the tele-extender group from the lens (it was slighly damaged by moisture, a bit foggy).. and because my guiding camera is Philips Vesta housed in home-made enclosure and because the chip is close to mounting flange, the focussing is not an issue.

Focusing is as per normal - the screws holding the lens in place have nylon pads and are not tighten too much, so the lens can rotate in ring.

I used ABS for printing (and my home made printer so there is no cost here.. at least I do not take it into account), this plastic is quite strong (Lego is made of the same stuff). I already made couple of adapters for finders and never saw any issues. It is important to use 3D printout only where appropriate, and i feel it is OK for this application. Time will tell :-)

As for flexures, the screws are placed in ferules acting as bearings.. so I hope for the best
And springs are pretty strong, they easily carry the weight of that lens.

[bojan]

The result of 4 hours of printing and 15m filament.. the modified version (a bit stronger, to fit around the narrower part of the front part of lens), 66mm internal diameter.