My version of a homebuilt refractor based on a cheap eBay objective cell

Omaroo (Chris Malikoff) · #1 10-10-2007, 05:13 PM

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.

joshman (Josh) · #2 10-10-2007, 05:54 PM

i would love to see some test photos taken through that!

Omaroo (Chris Malikoff) · #3 10-10-2007, 06:12 PM

Quote:

Originally Posted by joshman

i would love to see some test photos taken through that!

hehe.. thanks Josh

I'll be taking it to Magellan Observatory this weekend, so i'll give it a go with my DSLR and with Zane Hammonds' SBIG. if I can.

Looking through it for the past few minutes has proven that it's pretty sharp!

Cloudy out........

jjjnettie (Jeanette) · #4 11-10-2007, 09:00 AM

So how many telescopes are too many? LOLOLOL
What a great job you've done on that. I'm impressed.

Omaroo (Chris Malikoff) · #5 11-10-2007, 09:31 AM

Thanks Jeanette

It's nice to see something that you've put together yourself work like a bought one. Too many now... you may be right.

Omaroo (Chris Malikoff) · #6 11-10-2007, 01:55 PM

Here are a few terrestrial examples taken just now. It's pretty hot here today, so there is a lot of heat haze upsetting the scenery, but there you go. Focussing is a moot point if the air moves so much - but we get an idea of what it's like. I'll try to take some star fields tonight if the cloud stays away...

Pic 1) A neighbours house some 250m away.

Pic 2) Flower pot about 50m away.

Pic 3) Light tower about 500m away.

Pic 4) Workers on the oval down the road - about 750m away. Notice that the trees in the background are already outside the DOF as there is a fair distance between them and the workers.

johnno · #7 13-10-2007, 03:44 AM

Quote:

Originally Posted by jjjnettie

So how many telescopes are too many? LOLOLOL
What a great job you've done on that. I'm impressed.

So,Am I.

Very,Very,Well Done.

Regards.
John

Glenhuon (Bill) · #8 13-10-2007, 06:44 PM

Just had a look on the SurplusShed site for some other bits and pieces. They have a 102mm x 600 FL objective very similar to the ones we have used. Was tempted, but enough scopes for now

Bill

xelasnave · #9 13-10-2007, 06:58 PM

Terrific simply terrific.
alex

xelasnave · #10 13-10-2007, 07:03 PM

May I suggest you consider a dew shield which has baffles.
I have a baffled "dew tube" asnd the baffles eliminate much stray light..It is my opion that the reduction of this stray light helps improve a lens because it is not bouncing around at all sorts of angles.

If you look at the Hubble Space Telescope you will notice they have baffles extending well past the secondary..maybe these guys know something about the merits of such an approach... but on my tests I am convinced they are on to something.
alex

Aprid · #11 13-10-2007, 08:34 PM

I put together one of these surplus shed scopes and I used the flanged end of the 90mm pvc pipe which is about 95mm outer diameter as the dew shield but had to file down the ribs on the lens cell to allow it to slide on, it's very nice tight fit. Just a thought , you may come up with a better solution, it works quiet well as a cheap guide scope.

Glenhuon (Bill) · #12 13-10-2007, 09:09 PM

I used a 100mm Pad Repair fitting. It has two diameters, one that fits inside a 100mm Stormwater PVC pipe and the other over the same size. It is a perfect tight fit on the smaller inside diameter for the dew shield spigot on the lens housing. The major diameter is covered very neatly by a 100mm pipe cap as a dust shield. http://www.iceinspace.com.au/forum/s...ad.php?t=24368

Omaroo (Chris Malikoff) · #13 21-10-2007, 10:33 PM

OK all - here's a quick moon shot through this cheapie home-built.

Nikon D40 at 160th sec ISO400

Actually surprised me!

Cheers
Chris

http://www.omaroo.net/albums/album36...urplusshed.jpg

joshman (Josh) · #14 22-10-2007, 05:52 AM

wowee

that's damn good, tad soft, but who's complaining?