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This might earn me stupid question of the week honors, but reading this question made me wonder whether it would ever make sense to use a astronomy telescope + camera mount as an earthbound zoom lens?

I assume they are "slow" but can they focus? It seems they might be useful in certain circumstances, such as shooting shorebirds such as terns and gulls which typically stand around without much movement.

EDIT - ok I got my terms confused here - I meant telephoto not zoom. I was thinking of the utility of a telescope used as a telephoto prime lens versus a made-for-cameras telephoto prime lens. They surely provide differing characteristics with respect to price, aperture, and distance?

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Drew
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  • Never heard of someone do that but they do use spotting scopes for cameras though. – Itai Jan 08 '13 at 02:24
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    +1 I've been wondering this myself for a while. I suspect that the answer is that because telescopes are optimised for a different use, telescope won't be able to compete with a similarly priced telephoto lens. – Chinmay Kanchi Jan 08 '13 at 02:53

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would ever make sense to use a astronomy telescope + camera mount as an earthbound zoom lens

As far as I know, telescopes generally (always?) have a fixed focal length. Instead of changing magnification by moving internal lens elements as a zoom lens does, the magnification of a telescope is changed by switching eyepieces. So technically, no, you can't use a telescope as a zoom lens.

That said, yes, you can use a telescope as a long focal length lens. Telescopes I've tried in the past had no problem focusing on objects much closer than celestial objects, perhaps a few hundred meters away, so focusing shouldn't be an issue.

Caleb
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I used an 805mm refractor with a Nikon DSLR, mounted on a german equatorial mount to shoot a sailboat race from the shore. It worked great, but then I am accustomed to manual focus. The mount was surprisingly great. With the rig carefully balanced, and the tripod head high with me sitting on a picnic bench, panning was smooth as silk, and it all stayed put when I let go of the camera. Depth of focus was thin with the long focal length, so I had to pay close attention to focus.

Whitebark
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Yes you can. That's how many (most?) astrophotos are taken. For terrestrial use, using a newtownian reflector would be awkward, but refractors, SCTs, and Maks would work fine.

Most telescopes have curved focal planes, so you might need to add a field flattener (or reducer/flattener) for best quality results, but there are some telescopes designed as astrographs (scopes for taking images) that use designs that give you a flat focal plane.

One example of this are Takahashi's FSQ106ED scopes - a flat field 530mm f5 astrograph refractor, corrected out to near IR and UV wavelengths, with a huge 88mm native image circle, with optional extender to take it up to around 840mm focal length at f8 (with a 44mm image circle big enough for full frame)

I've read of at least one professional wildlife photographer who uses one - it's a fairly hefty setup to cart around, but (as usual for tak) the image quality is excellent.

Here's a central crop of an image (of a Bluetit in the UK - they're small birds, about half the size of a sparrow) I took with a FSQ106ED and extender at 840mm / f8 with an APS sensor Nikon D300.

central third of an APS sensor image with a FSQ106ED at 840mm

and here's the full image:

enter image description here

So you can see that if you can live with manual focus, it's certainly a possibility. You can also use less expensive telescopes - but there are some potential quality issues with some of the cheaper achromatic refractors, since they don't have as good colour correction. But if you already have a scope with a 1.25" or 2" focuser, it might be worth getting a T ring and suitable nosepiece and give it a try (You can also barlow lenses (the astronomical equivalent of a teleconverter) threaded to take a T ring, and more or less double your focal length that way.

With my Nikon, I still get the focus confirmation light when focusing manually with a non-electronic lens- I think Canon's may need an adapter to enable this.

JerryTheC
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Actually you can 'zoom' a telescope (in fact change focal length) just not on the fly as with a zoom lens. You can increase the focal length with a barlow lens - simila to a teleconverter, or reduce it with a focal reducer (and increase the relative aperture). They both come before the ocular or camera in this case. What you cannot modify on a telescope is aperture which is always wide open.

radub
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I have a celestron to micro-4/3'rds adapter that I have used for exactly this purpose.

I had difficulty focusing, more due to the nature of the camera, than the lens.

Here's a sample.

Don Simon
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Telescopes lenses are more suited for long exposures where everything is focused at infinity.

I used a telescope (Schmidt-Cassegrain lens aka mirror lens) to make a gigantic telephoto lens. It was gave utterly phenomenal magnification, but wasn't that great quality wise. Nor could I carry it.

I took this picture with it: https://www.facebook.com/photo.php?fbid=582370470593&set=a.503548440573.322.284200469&type=3&theater

It was a real pain to focus.

Robin
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I have a Celestron C5 spotting scope (5" diameter and a focal length of 1.250 meters) photographing anything from 26 feet to infinity with excellent results. Also with the right filters, I photograph sunspots and granulations. Then at night I can shoot Saturn and Jupiter. I would recommend the Celestron C5 to any photogapher.

scottbb
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david maddern
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In a previous career, I worked a lot with wildlife, including shorebirds. I've never worked as a wildlife photographer, but I did work with some people who photographed shorebirds professionally. There were spotting scopes that users had purchased adapters for to use the scopes with a DSLR. I'm not sure what brand the adapters were or for which spotting scopes, but the images were very useable. I would imagine a similar system could be set up for use with an astronomy scope.

If you Google "Digiscoping" you have a good chance of finding a system that will work for you.

Hurst Gannon
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It makes no sense to "zoom out" on an astronomy telescope, you want to zoom in as far as possible, so a fixed focal length makes sense and is cheaper. Plus, zoom lenses are always lower image quality than primes (aka fixed focal length).

Are you confusing the term "zoom" with "telephoto"?

Lots of folks have used small telescopes on earth. Probably used to be a prime usage back when college dorms were single sex, the guys would aim at the girls' dorm.....

Pat Farrell
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  • I have updated my question, please reread it Pat. – Drew Jan 08 '13 at 23:00
  • Actually, you often do find yourself wanting to zoom out when using a telescope on astronomical objects. For example, one of my telescopes has a 2000mm focal length. I cannot get both clusters of the Double Cluster in a shot (or in the eyepiece), same for M31, the Andromeda Galaxy. There is a whole market of "wide field" telescopes which have a larger field of view just for these objects. – Paul Cezanne Jan 09 '13 at 11:43
  • @paul, are they really zooms? or just a different type of 'scope for different objects to view. I bet that they use two "prime" scopes for the two use cases. – Pat Farrell Jan 09 '13 at 17:48
  • oh, primes, absolutely. Sorry for the confusion. It just that with certain scopes you WANT to zoom, you just can't... – Paul Cezanne Jan 09 '13 at 18:04
  • spotting scopes with a zoom (ie, variable magnification without replacing the eyepiece) are absolutely a thing, more common in small spotting scopes intended for shooting sports though, I don't think I've seen an astronomical one – Joseph Rogers Sep 13 '17 at 15:05