Home made 80mm scope from US$29 eBay objective lens

[omaroo]

Hi all - haven't been around for a while so I thought I'd post something useful ;)

I thought that I'd do something crafty again and use the 80mm achromatic objective cell that I bought off SurplusShed's eBay store for US$29.00. 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/ I notice that they also now have a 102mm version for US$79.00 - might have to try it our next...

All up, it took about 30 minutes to build, excluding time taken to buy the 1m section of 90mm OD pipe at our local Bunnings store 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've flocked it and mounted a male dovetail. I'll mount a finder dovetail tomorrow.

Paint colour????? Mmmmmm.....

Still have to figure out a proper dew shield and cap system. ..

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.

ONE THING: IF YOU GET ONE OF THESE CELLS - make sure it's the right way around! Looking at some peoples' version, they usually have the rear of the cell facing forward. The part of the cell that connects to the scope tube is on the OUTSIDE of the scope tube. There was a sheet of paper in with mine explaining that you use it the wrong way around from what you might think. It explains that if you have it the wrong way around you'll get flaring. It goes on to say that as long as you keep the two elements relative to each other - turn them around inside the objective cell and you should be OK!!

Cheers
Chris

http://www.omaroo.net/albums/album34/parts.sized.jpg

http://www.omaroo.net/albums/album34/tube_sct.sized.jpg

http://www.omaroo.net/albums/album34/assembled.sized.jpg

http://www.omaroo.net/albums/album34/withcamera.sized.jpg

http://www.omaroo.net/albums/album34/mounted.sized.jpg

[rmcpb]

Chris,

Great project, how does it go?

Had a look at Surplus Shed for long focal length mirrors but could not find one :crying23:

Cheers
Rob.

[Radar]

G'day Chris,

That is an awesome project you've done there.

What exactly is the front of this scope from?

Have you taken any shots through it yet? Make sure you post em when you do.

Cheers

Ray

[Tenacious Del]

wow mate, that is very well done. looking forward to seeing some images through it. :thumbsupmate:

[wakaleo]

Great project Chris, and good value too! You don't seem like the type to spend money on inferior products hence the question: "Is the $29 objective any good?"

I like the sort of goodies you have "sitting on a shelf doing nothing". I can only hope one day I have such "spares".

Jim

[omaroo]

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

Nikon D40 at 160th sec ISO400

Actually surprised me!

I'll be going back to magellan observatory with it too - we missed out last time because all of their dovetails are Losmandy..... so i couldn't mount it. nexttime though.... :)

Cheers
Chris

http://www.omaroo.net/albums/album68/moon_surplusshed.jpg

[Radar]

Not bad for $29 Chris :thumbsupmate:

Be interesting to see how you go with nebulosity.

Ray

[Tenacious Del]

very smooth looking lunar shot mate. amazing what can be built from stuff that is just lying around.

:pipethinker:

[omaroo]

Thanks all :)

I've now drilled and tapped a 1/4" x 20 hole into the dovetail so that i can mount it on the camera mount at Magellan - and piggyback the whole unit rather than modify a Losmandy dovetail to suit Zane's setup. Now that's done Ray, I'll see what it's like with nebulosity! :)

Cheers
Chris

[mlynch53]

Chris,

After reading about your SS 80mm scope and others at a number of websites (including CloudyNights.com), I've ordered one of these lenses and a focuser. I hope to be able to assemble the scope for travel purposes within a couple of weeks.

I have a few questions. Like you, I plan to flock the inside of the tube. From your experience, does this take care of stray light for all intents and purposes, or do your think baffling would possibly help a bit, too?

You refer to 90mm "poly pipe" as your tube. Is this the same material we call PVC pipe in the U.S.? (It looks like the same material in your pictures.) For the length, this seems to be a good choice.

Finally, what are the shortest and longest focal-length eyepieces you've been able to use for decent images in the scope?

Thanks,

Mike
Frankfort KY USA

[omaroo]

G'Day Mike

Good luck with your build! :smile:

We call it "poly pipe" over here because it's made from polyvinyl chloride, or PVC. Same stuff the world over.

Flocking the tube has made a huge difference to the amount of internal reflection and stray light. I haven't personally worried about baffles, but they're easy to make from plastic foam card donuts covered with the same flocking material and wedged into position every couple of inches. Just remember to taper the size of the holes towards the back of the tube.

I normally run a guide (web) camera in mine, which is equivalent to about a 6mm EP without issue. I have a 5mm Nagler T6 which I must admit I haven't tried in it. I have tried 9mm, 11mm & 26mm Plossls and they all work fine. It really depends on your focuser travel in the end.

Have fun Mike!

[mlynch53]

Chris,

Thanks for your replies. I had read in other places that good flocking of the interior could suffice to absorb the stray light. I wondered what your experience has been.

I have some wide field eyepieces (67- and 82-degrees). Guess I'll find out how they do with this lens! :hmm:

Incidentally, for anyone else interested in building one of these and wondering how to attach it to a standard camera-type tripod, Telescope Warehouse, which is an eBay store, has a bunch of "1/4-20 telescope tube to tripod adapters" for a ridiculously low price-- $4.95 (US) for "Buy it Now." I'm going to attach one to my scope when I get all parts in and build it.

Mike
Frankfort KY USA

[mlynch53]

Chris, et. al.

Both an el cheapo focuser and the Surplus Shed 80 / 400 lens arrived in the mail the past couple of days. I went to a Home Depot to buy a piece of PVC pipe and a reducer for a ridiculously low price because this Home Depot is closing!

With the help of my next-door neighbor, who has a workroom FULL of power tools, we cut, drilled and assembled the thing in an hour. I need to flock the inside of the tube and make a few tweaks.

But I took it outside to show the neighbor "first light" through the thing, and I can honestly say I was shocked! The CA was simply not a problem at low powers, and we were able to easily see the rings of Saturn using a Celestron 6.7mm Expanse wide-field eyepiece. :woot:

The collimation of the lens seems quite good... and I mounted it the right way on the tube, since Chris made a point of telling us about this!!

Total cost: $61.98 U.S. for all pieces and shipping.

This thing is going to serve me very well as a quick grab-and-go and a travel scope. 'Course, I can expect clouds for a month now! :frown:

Thanks for your help! I'll post a pic or two of the scope soon.

Mike Lynch
Frankfort KY USA

[omaroo]

Excellent effort Mike - looking forward to the results! :)

I've just repaired the image link on the previous page, so an image I took of the moon through mine is back up.

[seeker372011]

great project
and I too have found surplus shed a great mob to deal with over the years

[mlynch53]

All,

It was pretty late when I sent my last posting. The eyepiece I was talking about is an ORION 6 mm EXPANSE!! I mixed in about three different eyepieces when I said "Celestron 6.7mm Expanse!"

Mike Lynch
Frankfort KY USA

[mlynch53]

All,

Well, here it is!! Not quite the fine construction of Chris' scope built with the same lens, but it has already given some fine terrestrial and sky views. I'm going to use it for birding in my back yard as well as astronomy.

I've flocked the inside with paper from Scope Stuff, and since the PVC pipe didn't fit tightly into the flange of the lens, I wound several layers of electrical tape around the end of the pipe until it was wide enough for a tight fit into the flange.

The one item I may need to work on is re-locating the tripod block. The scope is currently back-heavy, but the tripod block is longer than the width of the reducer flange that holds the focuser assembly.

The color doesn't show well, but I spray-painted the scope a color called "satin river rock," a kind of beige or very light brown.

I think a finder would be overkill, especially because it would throw the balance off even more.

Clear skies to all!

Mike Lynch
Frankfort KY USA


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[Tenacious Del]

very cool project mate. maybe a laser pointer with bracket at the front end could help with the balance.

very portable unit though.

[omaroo]

Very nice Mike :) Well done!

Where is the actual balance point with the EP in place? Maybe get yourself a 6" strip of Vixen-style dovetail extrusion and fix it in place underneath - and maybe either notch it out to fit the focuser assembly flange or cut the flange itself to fit the dovetail. I've fit one to mine and drilled/tapped several 1/4x20 holes into it 1" apart along the length. This way I can adjust the balance point by chosing the appropriate tapped hole to screw my tripod into or slide it up and down when fixed to an EQ5 or similar.

Very good project though!

[mlynch53]

Chris,

Good thoughts! Thank you! In fact, as I've used this little scope for birding AND skywatching, I've not had much real problem with the balance, though I did realize it is NOT actually balanced with the eyepiece in place.

And, like you, I just HAD to find out how well I can take pictures through it. I was pleasantly surprised, getting a good shot of the Moon, though exact focus, of course is a bit of a chore. :wink: With a camera attached, of course the balance is WAY off!!

I had been thinking about moving the tripod block to a "best-balance" location, but your thoughts on an adjustable arrangement has me thinking... I already have a bar with a sliding attachment for .25-inch / 20-thread screws.

Hmmmmmmmmm.... I'm going to think this through.

Mike Lynch
Frankfort KY USA