Looking for a telescope to connect to my MILC

Started 4 months ago | Discussions thread
Lyle Aldridge Senior Member • Posts: 1,101
Re: Looking for a telescope to connect to my MILC
1

Yannis1976 wrote:

What about those telescopes from Celestron and Orion?

https://www.amazon.co.uk/s?k=celestron+telescopes&crid=27VX6KYTIW9I9&sprefix=celestr%2Caps%2C213&ref=nb_sb_ss_i_1_7

https://www.amazon.co.uk/s?k=orion+telescopes&ref=nb_sb_noss_2

Their price is quite affordable and maybe with a T-Ring I can get some nice moon or other close planet shots.

Thx again!

The Newtonian telescopes in that Amazon listing might be usable for some basic lunar imaging, because you don't really need tracking for that. But it's not likely to be done so simply as you suggest.

Those scopes are made for visual use with lightweight eyepieces, and with only rare exception, they don't bring the image to focus at a place that can be reached by the sensor plane of most interchangeable lens cameras. A Newtonian made for photographic use has its focuser closer to the primary mirror, and uses a larger secondary mirror, so that the image plane of the primary is projected a few inches farther from the optical axis, and can reach the sensor of an attached camera. They also are usually made with stout focusers that can steadily support, and more accurately position, the greater weight of a camera. You won't find one of those scopes within your budget unless it's a used model and you shop with care and knowledge of what to look for.

You did mention in your OP, however, that you'd be using a 4/3 or MILC, and that gives one glimmer of hope. With a flange distance of only 17.5mm, a Fuji MILC attached to the focuser would have its sensor significantly closer to the optical axis than a DSLR, and might be able to achieve focus with one of those Newtonians. This would require, however, that you use a shorter than normal T-ring likethis "T-Minus" ring Those short adapters are also made for 4/3 cameras. Since the MILCs tend to be lighter than a DSLR, the lower-spec focusers on the cheaper scopes would also be less of an issue. Unfortunately, I can't say for certain whether the T-minus option would work.

You should also be aware that Newtonians in that listing use spherical mirrors, which introduce spherical aberration. The true Newtonian design calls for a parabolic primary, which is more costly to make. Many visual users don't notice a lot of difference, but cameras aren't so forgiving. Even parabolic mirrors have some "coma," and require a supplemental corrector for those who want objects off-axis to look as they really should.

As for the refractors in that listing, they're practically toys, and tend to have even worse issues. The focuser problem is the reverse, though - they're made to be used with a star diagonal, and when you remove the diagonal to replace it with a camera, the focuser can't extend enough to focus an image on the sensor plane. So one must add an extension tube. The plastic focusers also aren't made to support the weight of a camera, and this becomes more critical than with the reflector focusers, because the focuser has to be extended, rather than retracted, and is usually extending at an angle where gravity will distort the whole image train. The objective lenses of those scopes are also of relatively short focal length for a telescope, and since they're achromats, rather than apochromatic, they tend to produce a lot of chromatic aberration.

At the focal length of those refractors, you would be far better off finding an older, used telephoto lens and using an adapter to fit it to your camera.

Finally, planetary imaging requires much more focal length than any of those scopes can provide. Barlow lenses might come to mind as a means of increasing the focal lengths of the Newtonians, but that would involve some other issues that would make this post twice as long.

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