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.

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)

<p>Kenko makes them, they are $140. They support Canon, Nikon, Pentax, and Sony, and have a number of different eye pieces.</p>
<p>Hi there great instructable!<br>Would a cheapskate option be to track down a damaged film slr camera of the same mount and just chop off and then reseal everything but the mirror and viewfinder? The pentax K mount monocular converter costs a small fortune on the rare occasion that they come up on ebay but a K1000 where the battery corroded is dirt cheap.</p>
Cool idea. It will be a little weak on magnification though. <br>I just looked through my canon 20D through the lens. The image is about 1x magnification at about 55mm. This means the focal length of the view finder lens is about 55mm, since magnification is just the ratio of the two lenses. <br>That means for a 400mm lens, the magnification is ~7x through the lens. That's a little less than you'd get with most low end binoculars. <br>But if you use a 2x barlow and a 10mm as I've described, then the magnification is 400mm*2/10=80x. <br>
<p>Don't you need filters for that? I mean, for sure you can't watch an eclipse with that right? Or maybe... ?</p>
For a total solar eclipse, where the moon fully blocks the sun, you don't need any filters. If there's any bit of the sun showing, you'd need a filter to not go blind!
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.
So many projects. So little time....
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.
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. <br>Let me know if you get it working. I'd be interested to see your solution. <br>
A much better (and easier &amp; a lot cheaper) way to convert a camera lens into a scope is by using an eyepiece with an erecting element <em>already built in</em>. 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:<br> <a href="http://photo.net/nikon-camera-forum/00HfRR" rel="nofollow">http://photo.net/nikon-camera-forum/00HfRR</a><br> <br> Enjoy.<br> &nbsp; &nbsp;- DC
Wackyneighbor, <br>Wow, that's pretty cool. Nice work. <br>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. <br>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. <br>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!). <br>I had all the other components already, so I only needed the diagonal, so the total cost was not so important for me. <br>Thanks for the comments. <br> <br>
<p>Nice!<br /> But why would I want to turn an expensive telelens into a scope?</p>
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).<br>If you're headed to Australia, you can take pictures of the wallabies and then check out the tarantula nebula that night!<br><br>

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