EP adaptor for SLR lenses?

[Kaptain Klevtsov]

It seems possible that I could use my SLR lenses with astronomical eyepieces to make a refractor telescope, is that possible and does anybody know of such an adaptor for Nikon lenses?

Captain Chaos (who is getting bored because of all the effing

[The Warthog]

Funny, I was thinking avout that very same topic tonight. Even if you can't buy one, it should be possible to make something that works. My ancient 135mm lens with a 12mm ep would make a nice 11x monocular, eh?

Edit: I tried this, and it works very well, but I need something to hold the ep about an inch away from the back of the lens. Hmmm. I want to get a new camera body for my lenses, too, as there are some mechanical problems with my excellent, but old, Fujica SLR. An ep holder would give me a nice tool for scouting out the sky, and with a new camera body and a good mount, I might try some widefield shots.

[Kaptain Klevtsov]

I tried the "thin air" spacer technique, that sort of thing happens around here when the office has stuff lying around. I'm guessing that a good lens rear cover could be adapted by making a hole in the centre and glueing a short piece of, say uPVC pipe on. When I get hold of a real eyepiece in the flesh I'll definitely chech this out.

Captain Chaos

[Naz]

A few years ago, Jessops used to sell an attachment that contained an ep for turning your telephoto lenses into a scope. They have stopped selling them, occassionally you see one pop up on e-bay.

Yes a rear lens cover / short piece of pipe would work, using the lenses own focusing. just need to figure out how far behind the lens is the focal plane.

I have a 500mm f8 cat lens that I have often thought about trying as a spotting scope.

nabban

[Kaptain Klevtsov]

Focal plane position and how this relates to the eyepiece position for several eyepieces. I would make mine adjustable in some way even though, as you point out the lens focussing could be used. Never thought of that , Doh.

Anybody know how the eyepiece is positioned WRT the focus of the main objective lens? Gonna look this up later but work is imminent.

Captain Chaos

[Naz]

Yes CC, Quite simple, I have measured it on my Nikon F80, and the lenses are compatible with the D70, at 48mm for the focal plane. If you look on the top of a film slr camera, at the or near the back edge near the prism will be a mark of a circle with a line running through it, parallel with back edge. that is the film plane, hence focal point. There isn't a mark on the D70.

nabban

[Kaptain Klevtsov]

Are you sure there's no mark? There is on the lesser D50 model that I have.

My point was not where the focal plane is, you see I don't know where the EP goes WRT the focal plane. Is the lens (which one?) of the EP at the focal plane or somewhere else? Some playing would sort that out fairly easily.

Captain Chaos

[The Warthog]

Here's one: http://www.rugift.com/photocameras/tourist-fl-eyepiece-attachment.htm which appears to be a 9mm erect-image eyepiece.

I also found a site that had a description, but no photos, of scopes made from telephoto lenses with ep holders made from PVC tubing, or cardboard.

I think I could do this. I would need a PVC tube with a 1.25" inside diameter, if such a thing exists, and a plate that the tube would fasten into. If I then cut the plate to the diameter of the adapter on my 135mm telephoto lens, I could use the adapter to hold the ep holder in place, and stick an ep in it, and use the lens focuser to focus the thing. It would give an upside down image, but who cares, if you're using it to scout out the sky? I'll have a look round the hardware store.

[Ambermile]

If you have two lenses, try them back to back...

Arthur

[The Warthog]

This whole thing has me wondering about using a camera lens as a long ep...

[Kaptain Klevtsov]

Cool link WH. Check out the Kiev88 cameras, look like Hassy clones.

I think one of those hung off the telescope would look cool.

I've got a Zeiss 135mm lens with integral hood that slides out of the front, looks about 2" diameter so that might fit in the hole for a 2" EP. I don't know if these lenses have a front and a back though. Lenses are commonly used reversed on SLR cameras for close-up because they work better that way so there must be some asymmetry in there.

All good fun

Captain Chaos

[Naz]

Yes CC, it was to early yesterday morning when I looked, it is over to righthand side near the top lcd.

yes you would have to make the tube longer than 48mm, but if you check how far in front of the ep you obtain focus and add that plus a bit, then it's trial and error, trimming the tube until focus is obtained at infinity, with the lens at infinity.

nabban

[Kaptain Klevtsov]

I'd do it the easy way which is not as good, I'd chop off a bit more and then use the lens focussing and disregard the distance scale. It''s not like you want to use it measure distances or anything, or do bits in the lens move relative to each other making the infinity focus point the best place to have it?

Captain Chaos

[Naz]

if you are only useing it for the sky then it wont matter, just that if the lens is wound back, then moving around it might be easier to keep focus. No matter how you do it, if it works, great, just depends how versitile you want it.

nabban

[Naz]

Hi CC, inspired by your thoughts, I have dug around in my bits and pieces and come up with this prototype.

The bits are, A 500mm f8 mirror lens / an ep from an old pair of binoculars / T mount / rear lens cap / black film canister.

Drilled out a 30 mm hole in the end cap.

Cut the end off the film canister and pushed it through the hole, had to do a bit of fine adjusting with a file. then slid the ep into the end, and adjusted the position until I could focus at infinity.

Still got to fine tune and glue the contraption, tried a quick look at the moon, but a lot of cloud. Think the magnification is about 50X. Got to check it all out yet , but hell it WORKS!!!!

nabban

[Kaptain Klevtsov]

Looks great! Now I've got to build one of those!

This sounds like a job for the school holidays (this week).

Thanks for the pics, worth a thousand words as they say.

Captain Chaos

[Naz]

Well CC, I managed a quick look with the modified mirror lens this morning, it was clear around dawn with the sky just showing the first hints of colour.

The view of Venus was clear, no sign of CA, needed to square up the ep tube, it just proves what rubbish my short tube reflector is, No sign of flareing or any diffraction probs.

Jupiter didn't show any detail, could just make out two of the moons before the sky got too light.

I will keep the end plate in my camera bag for a really handy grab and go.

nabban

[Kaptain Klevtsov]

So if you buy a couple of teleconverters you won't need to buy a fancy telescope.

Captain Chaos

[Naz]

Probably, I have a vivitar one knocking around somewhere, but as the lens is an 500mm f8, the mirror is only 62.5mm dia. A 2X convertor would effectively give me 1000mm at f16, I will try it but not expecting too much. Be ok on a few of the brighter objects.

nabban

[Ambermile]

You know, surely if you have to put an M42 extension tube bit in the end, is there any reason why you can't just turn a lump of delrin or other nylon to fit inside the tube and then drill your 1.25" hole in that?

Arthur

[Naz]

None really Arthur, I have just used the T mount, I had from an old Konica slr, and the ep from a pair of 8 X 21 bins that got soaked in orange juice in the glove box, (THEY put some things in stupid places.) and the ep was the only bit not to get soaked. (must buy water proof ones next time)

If you wanted it to be able to change the ep's your idea is way. You could be on a winner there?

I just tried the 2X convertor and the image dims considerably, (effectively giving a f16 at 31.25mm dia mirror)

The end plate can stay in the camera bag and provide a simple scope for whenever.

nabban