Eyepiece adapter for lens, exists?

[luigi]

Hi,

I found a tutorial about building an eyepiece adapter for a telephoto lens.
http://www.samirkharusi.net/lensdiagonal.html
I'm curious about how my 400mm F5.6 will work as a telescope but I can't drill, I can't glue, I can't solder, etc.

Do you guys know if the adapter exists somewhere to buy it?

Anyone tried this before?


Thanks!
Luis

[Waxing_Gibbous]

Hi Luis.
Yes, I tried it with a 500mm f4L Canon USM.
The results were very good, though there was a noticable lack of contrast compared to a very fine 5" doublet I had at the time.
It gave very fine wide-field views but ultimately not as good as a MUCH cheaper telescope that weighed 1/4 as much.

The 400 5.6 is a good, sharp lens but very aperture limited and with multi-lensed construction, I would count on fairly average contrast and you won't be seeing any mag 6 stars! IMO for this to be worthwile, you'd want at least a 200 2.8 or older FD 300 2.8, 400 2.8 or 5-600 f4.5.


Having said that, I would think the 400 f5.6 would be perfectly useable as a daytime scope.

I also found the contraption a little fiddly to make, but I'm not a good DIY'er either.

I may be wrong, but I think someone does make a similar device which I saw on an e-bay euro site. Sorry. I can't remember exactly where.
Unless you really wan't to double-up and/or can get one made or buy one cheapish, I think I'd leave it alone unless you can get a large aperture lens for little money.

[Barrykgerdes]

I have made a few adaptors to make telescopes(?) out of camera lenses but I don't know of comercially available adaptors. I have turned them up on the lathe to mainly fit the zenit screw thread.

A few years ago there were a few Russian made 1000mm Mak telephoto lenses around that could be made into reasonable telescopes but they could not be brought into focus with a diagonal fitted. I made a special diagonal that just worked

Barry

[bojan]

They could ;)
The trick was in removing the focus lock screw (see picture below - it originated from here (http://www.strickling.net/russentonne.htm)).
Then, the focus can be pulled out as much as needed (this of course increases the focal length considerably).
I still have one of those, and it is quite a reasonable telescope.
As far as it's intended purpose as a photolens it is OK, however it still has a bit of astigmatism (even after treatment described in the website above), but it can be tolerated (maybe not by perfectionists, though..)

[luigi]

Ty Peter. I was curious about a comparison between the 400 F5.6 vs a 400mm refractor and the adapter was a good way to compare.

[bojan]

Yes, 400mm FL refractor will always be better as telescope (visual).
All those lense elements that are present in telephotos are mainly to achieve the focal plane flatness (because the sensor/film is flat) and to deal with other aberrations that are much more pronounced in the corners of the frame.

[Barrykgerdes]

I can't read German

Yes I knew of that trick but it was still messy and I still could not get sufficient focal range and keep the focal ring calibrations. I did not want to go into that.

I made a new lens holder that that held a standard series 4000 eyepiece OK and kept the focus calibrations but to use a diagonal there was still not enough unless you cut the diagonal down and attached it right at the back. I got that to work but it was messy.

However I could make a diagonal work if I took the lens out of a Barlow and screwed it into the nose of the diagonal. That made focus possible but increased the focal length.

As a telephoto lense I had the lense on a camera mounted on the telescope and took some shots of a moon eclipse.

I still have the lens and fiddle with it every now and then.

Barry

[dannat]

I see peter tan in HK has some for canon /Nikon link canon-Nikon ep (http://www.tan14.com/Others.htm)