Hi all
I thought that I'd do something similar to Glenhuon's project (thanks for the heads-up on the eBay item Bill
)and use the 80mm achromatic objective cell that I bought off eBay for US$29.00 (AU$46 landed in Sydney) It claims 400mm FL which makes it around f/5. These guys - "Surplus Shed" have tons of cheap ATM stuff, and they also have a direct website at
http://www.surplusshed.com/
It took about 15 minutes to build, excluding time taken to buy the 1m section of 90mm OD pipe at Bunnings for $9.00.
I had a spare William Optics SCT focuser and a Meade SCT visual back to use. They were otherwise sitting on a shelf doing nothing. Added benefit is that the focuser rotates.
I used a 175mm section of the 90mm poly pipe which slides into the objective cell beautifully - no gaps, of which 30mm disappears into the objective cell flange, leaving an exposed length of 145mm. I determined this by lying on the floor with the SCT focuser, with a 27mm EP mounted via a 2" star diag, and the cell just held in my other hand. I moved them back and forth until an image focused on an object several km's away. I did this with the focuser travel at the 1/2 way point.
Once the pipe was cut to length, the visual back slid into the end of the tube, which needed a light internal routing so that it was a tight interference fit. This gives me a wonderful SCT threaded adapter from which lots will hang off - including the WO SCT focuser.
Works a treat! Focuses with the 25mm and 11mm EP's with minimal focuser travel difference. A 2" straight extension tube lets me mount my DSLR and get great focus at infinity.
I'm just about to flock it and mount a male dovetail. (Done)
Paint colour????? Mmmmmm.....
Still have to figure out a proper dew shield and cap system. Tomorrow...
Weight (with focuser and dovetail but without 2" star diagonal, has ended up at 1.6kg (3.5 lbs) so it's reasonably light too.