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Lens to Telescope follow up

L J Cappleman , Jul 29, 2010; 05:36 p.m.

I had followed several posts about using lenses as telescopes and decided to do some experimenting.
First- if you have a good spotting scope hang on to it. Using tele lenses as telescopes incorporating inexpensive parts will not produce superior images. I obtained an image quality that was acceptable to me since I only wanted something to scout a bird or animal before hiking close enough for a decent shot.
That being said- I do some short distance hiking and carry a tripod, camera, 17/40, 24/105, 300 f4, and 500 f4. Even after a short walk this all gets heavy and the thought of adding a spoting scope was close to the proverbial straw that broke the camel's back. I looked for prior postings, found some, and followed the instructions using a lens cap and a 1 1/4 lens adapter.
Then the fun began. I had an assortment of old eypieces from spotting scopes and experimented with them. I could get a decent image but the image was upside down and left/right reversed. My brain doesn't adapt well to that kind of viewing so I decided to try some other approaches. I tried adding a 90 degree mirror but lost focus beyond 20 ft. Added a 2X barlow-this got me right side up but still left/right reversed. The image quality was only so-so. I looked on Ebay and found a Celestron 20mm erecting image lens. It didn't work by itself but did all right when used with the barlow.
This combination works only with fixed length lens because , at least with my barlow, the barlow had to go about 3/4 inch inside the lens. This means no zoom or non tele lenses. It also means no 1.4 or 2.0 extenders. I used the combo of the barlow and the erecting lens on my 300mm and 500mm with no problems BUT- proceed at your own risk and measure carefully.
The total cost for the adapter, barlow and erecting lens was about $70. Perhaps if I had used better quality components the image quality would have been better but, for my purpose, image quality was adequate.
Again, be very careful as you could run the risk of scratching an interior lens if you insert too far.


JDM von Weinberg , Jul 29, 2010; 05:55 p.m.

That's interesting, and a worthy project.

However, those who are construction-challenged might want to look at some of the commercially-made inverting eye-pieces that have been sold to convert various telephotos into spotting scopes. There are names of such units and pictures at (link).

The cost of either of the units I have was far less than $70, although they can be hard to find at eFence because the vendors don't know what to call them.

L J Cappleman , Jul 29, 2010; 06:03 p.m.

I looked for the converter you talked about but did not find one for the Canon EOS. Also the write-ups that I saw were not very complimentary.

JDM von Weinberg , Jul 29, 2010; 06:18 p.m.

The two I have both work fine, I'm not sure which ones the "not very complimentary" comments were about.
But mine are for M42x1 and T-mount lenses (M42x0.75), to be sure.
You do have to have a tripod mount for them because a 500mm mirror lens, a 2X converter, and the tele/spotter-adapter are impossible to hand hold steadily.
You would think there'd still be a market for newer adapters for the reasons you state, but maybe not.

Tommy Lee , Jul 30, 2010; 01:46 a.m.

There are easier way to do this. One is to use an erecting eyepieces with a built in roof prism. Like a monocular, the image with an erecting prism are right side up and left right correct. I think if you get rid of that barlow lens (aka: may be cheaper then a cheap 2X teleconverter), the image can get better.

Robin Sibson , Jul 30, 2010; 07:12 a.m.

LJ, I'm amazed that you can even carry all that kit – if it were me, the camel's back would have broken long ago!

Many years ago in my Canon FD days I had a telescope adapter, which I used on an FD 200/4. The principle was fine, but the optical quality of the adapter was disappointingly poor and the optics had nothing like the generous dimensions of the eyepiece on my Swarovski, so it was a real pain to use. I don't remember what make it was, but it looked very similar to the "Spectralstar" adapter in the thread to which JDM gives a link, and the magnification was also focal length / 10. 20× is quite a modest power for a scope – a typical zoom eyepiece will give 20×~60× on an 80mm-class scope – but I certainly agree that even at 20×, a tripod is almost essential.

Given that this idea is workable in principle, as demonstrated by adapters like the Spectralstar, it's a pity that no manufacturer seems to have done a proper job on it, and I'm not even sure that any adapters of this kind, of any quality, have ever been available for Canon EF. I suppose the ideal would be an adapter that converted the camera lens to the equivalent of a telescope without an eyepiece (so the adapter would have all the stuff in it to orient the image appropriately), and then you could put your own choice of eyepiece on it. But a decent integrated adapter would be more compact, and might well slip easily into a corner of a camera bag.

L J Cappleman , Jul 30, 2010; 12:03 p.m.

Tommy, I agree you can use the eyepiece alone. But, as I said in my original post, focus beyond 20 ft is lost. I know just enough about optics to be dangerous but I understand the addition of the barlow is necessay to extend the focal length and enable infinity focus.
Robin, I agree that it is a pity that no one has manufactured a quality telescope adapter for the EOS. If I could have found one I would have snapped it up.

Jorge Garcia , Jul 30, 2010; 03:13 p.m.

I looked for the converter you talked about but did not find one for the Canon EOS

I made one, look here:

Matthias Meixner , Jul 30, 2010; 06:02 p.m.

You should look for an amici prism instead of an erecting lens. This should give you better quality.

Tommy Lee , Jul 31, 2010; 02:52 a.m.

EF70-200/4 (6X-17X Scope) No Barlow lens and focus a little pass infinity (I over did it for san eye glass). FYI: Minolta made a real good one for their manual focus MD mount. That one has even less flange/film distant then the EOS mount. They did it without a barlow lens as well.

EF70-200/4 or 6-17X Scope

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