camera lens as spotting scope? (1 Viewer)

Hi,
I have a 300mm f2.8 camera lens that I would like to adapt for occasional use as a spotting scope off my deck. It has a tripod collar and a m42 thread mount. I know nothing about spotting scopes and I am not near a store to look at one, so I've been looking on the web for info (and am confused.) I am looking at getting a Plossl-type eyepiece, probably in the 25 to 40mm range. Looking at these things, I'm afraid I have some dumb questions:
1) A camera lens projects an inverted image upon the filmplane. Will an eyepiece flip the image rightside up or will I have to use a prism to right the image?
2) As far as I can tell, the eyepiece's OD is a simple tube without threads. I assume I need to acquire a tube with an m42 female thread that the eyepiece slides into and locks with a setscrew (or something similar)? Is there such an animal and what is it called?
Thanks,
tua

Hi tua

Years ago I bought an adaptor to allow me to do the same. The image quality is not up to much. Appears very grainy and quite a lot of light is lost when using long lenses. I have just re-tested using a Nikkor 50mm f1.4 to confirm. Against my scope that shows a loss of at least 2 stops. So even a 2.8 lens will be way down in terms of light loss.

Yes these devices do give an erect image.

Even a budget scope when used at minimal magnification will give a superior image. I say that as a lot of budget scopes come with a fixed zoom lens. On the ones I looked at as the zoom was increased so did the effect of looking down a tunnel.

Worth checking the price difference between what you have been looking at and the price of a budget scope.

Don

Thanks Don for going to the trouble to check out your old adapter! But I'm not sure why a setup with a conventional camera lens would lose anymore light than a typical spotting scope. If I look at a basic scope, like a Tele Vue 60, it seems to me to be nothing more than a 360mm f6 lens that you hang an eyepiece on. The eyepiece increases the magnification, presumably at some light loss. If I take that very same eyepiece off the Tele Vue and hang it on my 300mm f2.8 (which I haven't figured how to do!) seems like it would have slightly less magnification, yet a brighter image (assuming everything else is equal, as both optics have APO glass, etc.)

Years ago, a cheapo camera store called Spiratone in New York used to have an "adapter" that simply fastened to the mount of a lens (turning your lens into a high-powered telescope!) It was only about an inch long, had a prism in it to produce an erect image, and magnified the image about 5X. I had a buddy who bought one and he said, don't bother. But I always thought it was because the optical elements in that $29 thing were so awful, not because the concept was bad.

tua,

Using an eyepiece only will result in an inverted image. Inserting an erecting prism between the eyepiece and the lens will make it impossible to reach focus beyond a few feet. A device like Don's contains a transfer lens in front of the prism which allows longer focus. I recall seeing one of these things offered by Adorama (I think) about a year or two ago. I don't recall the price. The light loss Don describes probably results from vignetting in the device itself. I agree with him that your money would be better spent on a budget scope. Believe it or not, even good telephoto lenses make rather poor telescopes, particularly at low focal ratios.

Tua,

Have a look at this http://www.kenrockwell.com/nikon/lsc.htm for a lens scope conveter.

Sassi

henry link said:

tua,

Believe it or not, even good telephoto lenses make rather poor telescopes, particularly at low focal ratios.

Click to expand...

Henry,

Am I missing something?
the scope is technically a 500mm f/6 lens.
Does an slr lens like the sigma 50-500 apo or any equivalent lens from Nikon Canon or others, inferior opticaly? until now I thought it was vice versa.
There are some great EP's for scopes and telescopes out there...
Isn't it possible that some of this makes will construct a first rate device
that will conect to the slr lens and will give an excellent scope?
Now consider this, birders will by two piece or better three piece scope!
want to take a photograph ,no problem take your slr out of your bag and shoot, you prefer video ? no problem either, take your xl1 ($$$) out of the other bag...

A few miniutes ago I have sent that link to Tua http://www.kenrockwell.com/nikon/lsc.htm

Sassi

Thanks Sasi! The device on that link looks a lot like the old Spiratone unit of 20 years ago. But it was only $29! (And I'm sure it was optically inferior; for instance, it did not have diopter adjustment.) For the $300 that Rockwell mentions, I could buy a decent real spotting scope. Still, your point about the flexibility of such a device is kind of cool. Unlike most of the folk here, who are birders first who want to take some pictures, I'm more of a photographer first who only occasionally wants to have a spotting scope. The idea of being out in the field and having something small in my pocket to clip on my lens (that I already have with me) is a good one.

If I went that route, it sounds like I would need four things: an eyepiece, an erecting prism, a tube of the correct length to mount the prism and an adapter at the other end of the tube to mate the tube to the screw thread of the lens. There are some cheap telescope EPs ($25 on ebay) but I assume they are low quality and I'm not sure even if they would give me a correctly oriented image. (Telescopes present an image erect, but reversed left to right? Is that right? So, do these EPs only flip the image right to left?) In truth, I'll probably just use a scope off the deck from time to time, so Don and Henry's advise to get a budget scope makes the most sense.
tua

This site that I just ran across explains why my thought of using a telescope diagonal would not work - the optical path would be too long, it would require a transfer lens, which I guess was Henry's point. Anyways, it shows one guy's home brewed solution for a field scope from a lens (though it resolves as an inverted image, not too useful.) http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00DvVD

tua

I can not get Ken Rockwell link to work - problem with his site - tried it through Google.

Found this page of images of the Nikon lens scope converter that looks similar to the device I have but would have cost big bucks new. http://khoking.photomalaysia.com/myphotography/mynikon/lens_scope/

Cannot find any reviews. Will go and see if I have any info in my Nikon books that Henry can comment on.

tua said:

For the $300 that Rockwell mentions, I could buy a decent real spotting scope. Still, your point about the flexibility of such a device is kind of cool. Unlike most of the folk here, who are birders first who want to take some pictures, I'm more of a photographer first who only occasionally wants to have a spotting scope. The idea of being out in the field and having something small in my pocket to clip on my lens (that I already have with me) is a good one.

If I went that route, it sounds like I would need four things: an eyepiece, an erecting prism, a tube of the correct length to mount the prism and an adapter at the other end of the tube to mate the tube to the screw thread of the lens.

Click to expand...

If your main point is not to have much additional weight, I suggest getting one of the really small scopes like Nikon's ED50 or Opticron's Mighty Midget. In that way, you don't have the bother of changing things, and your camera AND scope are both ready all the time. And I think those additional items you need will cost a fair bit as well, without really providing the image you want.

Just been through my Nikon library.

The only reference I have been able to find is in The Nikon Compendium by Rudolf Hillebrand and Hans-Joachim Hauschild. They describe it as giving a magnification 1/10 of the focal length of the lens and say with an exit pupil of just 2.5mm diameter that it only makes sense to use it as long as the subject is brightly lit.

Have finally managed to get Ken Rockwells pages to load and I am far from convinced by him. I have read his review of the Nikon 400mm f/2.8 lens in full as he mentions this scope converter there. http://www.kenrockwell.com/nikon/40028afi.htm
I am not at all impressed by Ken Rockwell at the best of times. His description of the converter - " Put the no-longer-available Nikon Lens Scope Converter on it for the sharpest 40 power telescope you've ever seen. If you're an astronomer you'll want to make a special adapter to allow you to mount a 20mm wide-field eyepiece to give you a 7mm exit pupil on a 20 power scope, heh heh. " - says it all.

I'll go with Rudolf and Hans-Joachims recommendation as being a more accurate reflection of the scope converters abilities.