Instructables

Turn a telephoto lens into a spotting scope or telescope

In an old Galen Rowell book of photographs, he mentioned an adapter that he could put on his long telephoto camera lens to turn it into a spotting scope.
After some searching, I realized that they were very hard to come by. So I purchased a 45 degree erect-image diagonal and used some old telescope eyepieces and never got it to work: it wouldn't focus.
Then, just before an upcoming trip to Yellowstone, I realized the problem. I needed a Barlow lens in front to shift the focal point back far enough to accommodate the extra length.
Thus, my original project was reborn.
Here is a picture of the completed spotting scope.
 
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Step 1: Gather the stuff (spend the cash)

You'll need the following stuff for the project. You can get the stuff cheap at a local astronomy club swap. Prices are estimates for 2009, purchased new.
1) Silicone glue (or any sturdy glue or epoxy). I used silicone because it can be undone to some degree.
2) A telescope eyepiece with a 1.25" barrel (the most common standard). I use a 25mm Celestron Plossl for wide views, and a 10mm Celestron Plossl for high power. (~$50 each)
3) A 45 deg erect image diagonal with a 1.25" barrel (for a spotting scope) OR a 90 degree diagonal with a 1.25" barrel (for a telescope). The barrel needs to be threaded on the inside. Diagonal barrels are often threaded inside to accept filters. I bought my 45deg one from Orion (~$45).
4) A 1.25" 2x Barlow. The lens element holder needs to be unscrewable from the barrel, and the threads need to match the diagonal. Mine did. It is a bottom-of-the-line Celestron ($40)
5) A telephoto lens. There needs to be room to shove the 1.25" barrel of the diagonal about 1" into the backside of the lens. (Some zoom lenses have lens elements right near the opening, which is true of my Canon 85mm to 200mm lens and you'll have to figure out how to get that to work). I'm using a Canon 100-400mm IS zoom lens. (Lots of $$)
6) A lens cap for the back end of the zoom lens (the side that connects to the camera).
7) A 1.25" hole saw. (~$8)



you should make a couple of these and put them on ebay, because I want on and do not have tha parts to make one.
bmaney (author)  aidanjarosgrilli2 years ago
So many projects. So little time....
dseeram3 years ago
did you try having the barlow on the eyepiece instead of on the diagonal? That could help with lenses that have back element further back and also adjusting for various lenses gets a little easier.
bmaney (author)  dseeram2 years ago
I didn't try it but I'd be surprised if it works. The camera lens focus is inside the lens. I believe the barlow has to be inside the focal point. After the diagonal would be way outside the focal point.
Let me know if you get it working. I'd be interested to see your solution.
A much better (and easier & a lot cheaper) way to convert a camera lens into a scope is by using an eyepiece with an erecting element already built in. Then you can skip the diagnol and the barlow. A few years ago, before we had instructables, I wrote an article on how to make one like this. It was geared towards a Nikon audience, but obviously, the concept works with any brand of lens. It's still online here:
http://photo.net/nikon-camera-forum/00HfRR

Enjoy.
   - DC
bmaney (author)  wackyneighbor2 years ago
Wackyneighbor,
Wow, that's pretty cool. Nice work.
Your link is broken and I couldn't find any erecting eyepieces available in the US anymore, but some of your UK links are still good.
There are two advantages to the way I did it. First, on a spotting scope, it's nice to have a 45 degree prism, so it's a little more comfortable, or you don't have to raise your tripod so high. I'm 6' tall but my tripod isn't.
Second, it is nice to be able to use a few different eyepieces depending on how far I want to look or how wide I need my field of view to be. I can even use my zoom eyepiece (when I buy one, its on my list!).
I had all the other components already, so I only needed the diagonal, so the total cost was not so important for me.
Thanks for the comments.

RAM4 years ago

Nice!
But why would I want to turn an expensive telelens into a scope?

bmaney (author)  RAM3 years ago
If you only want to carry one heavy hunk of glass on an airplane, you don't have to pick between spotting scope and telephoto. It has way more magnification than a pair of binoculars (see the last page on performance).
If you're headed to Australia, you can take pictures of the wallabies and then check out the tarantula nebula that night!