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 (Peter)]

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]

Originally Posted by Barrykgerdes

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

They could
The trick was in removing the focus lock screw (see picture below - it originated from here).
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]

Originally Posted by 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.

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]

Originally Posted by 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.

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]

Originally Posted by bojan

They could
The trick was in removing the focus lock screw (see picture below - it originated from here).
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..)

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 (Daniel)]

I see peter tan in HK has some for canon /Nikon link canon-Nikon ep