Daft Question

[Rob_Wilson]

This may be a daft question but.....  I have a reasonable quality 400mm f6 slr camera lens - would it be utter lunacy to try and find a focusser/eyepiece adapter to use it as a telescope?  Any advice welcome.  I think I can hear the laughter already

[Ian]

in theory what you're proposing is entirely reasonable. After all, it's not that different to putting a camera on a telescope. However, in practice I think you'll struggle to get adaptors. //www.trutek-uk.com may have something, but as per the first comment, we're usually trying to do the opposite.
Maybe take the lens outside with an eyepiece and see what you can see, decide how much hassle it's worth putting up with sorting out a proper adaptor.[/url]

[JohnP]

Hi,

Not a daft question... It's certainly do-able as a lot of imagers regularly connect their webcams/ camera's with a 1 1/4 inch adapter to a camera lens - My concerns would be quality of optics & how bright the image would be in the eyepiece.

Cheers,  John

[Mike]

It has already been done by Paul. He made some sort of adaptor to use an eyepiece on his camera lens.

I know a guy that does astro engineering that would be able to make a custom adaptor for you.

[Rob_Wilson]

Thanks for those tips - the True Technology website looks helpful and I'll try contacting them.  I'm just looking for a cheap way of getting my first proper telescope.  I have a feeling though that as suggested by JohnP the optics may not be up to it in the end (it's not a top of the range model) and I may be better looking for a second hand scope.

If only I had the time to do my own metal working.... Not to mention the skill etc.

Thanks again
Rob

[Whitters]

The cheapest way to do it is the way I have converted an 800mm f5.6 Canon lens. Get a spare rear dust cap, a pice of tubing with a 1.25 inch inner diameter and a jubalee clip.

These guy's used to have 1.25inch Internal Diameter(ID) reflex ports. Worth a try.
https://secure.wilmslow-audio.co.uk/acatalog/Wilmslow_Audio_Reflex_ports_53.html


Drill a hole in the centre of the dust cap, and glue the tubing in place with an epoxy resin based glue.


Take an eyepice and hold it to the back of the lens, as if it was a telescope, set the focus to 3/4 the way to infinity, then with a rule measure the distance between the lens, where the dustcap is mounted, and the back of the eyepice draw tube.


The length you measure will give the length of the dust-cap tubing combination you need.
Take a hack saw, or better still a mitre saw and cut the tubing.

Add the jublee clip and you have the eyepice holder. You now have a telescope and camera lens.


Not bad for a few quid. Have fun.

[Whitters]

To answer the question on the optics, a camera telephoto lens is fine for visual observing, there are plenty on e-bay. I made myself a finder scope from an old 200mm F3.5 lens, effectively a 62mm wide field telescope. Images are crisp and bright. that lens cost me £20, and I made the eyepice mount from MDF scrap and plumbing tubing, with some electricl insulating tape to reduce the inner diameter.

As for astrophotography with camera lenses, they are better with narrow band filters as they tend to flare in the very blue end, where film is usualy less sensitive. The filters will avoid this problem


It's a great little finder.