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Photography through the telescope

There are 3 distinct ways of attaching a camera to look through an astronomical telescope:

In all cases the telescope needs to be on a motorised mount for photographing stars and nebulae. The considerations on the previous page about the need for multiple exposures still apply, only more so: alignment and drive errors are magnified and the amount of light collected is greater.

A misconception about astronomical telescopes is that their main purpose is to provide a high degree of magnification, as a super-telephoto lens in photographic terms. While that is useful for studying the moon and planets and perhaps the sun, for other subjects it is more important to collect as much light as possible. So aperture is significant.

 Maksutov-Cassegrain reflector

The Meade telescope shown below has excellent optics for lunar and planetary photography but, in common with all catadioptric telescopes, its photographic aperture ratio is poor: f/15. So it is excellent for photographing bright objects such as the moon and planets but it is not so good for stars and nebulae.

Here is a Canon SLR mounted at the prime focus of a Meade ETX-125 telescope through a port on the back of the scope:

SLR camera mounted at prime focus of a small telescope

That uses a T-mount adaptor, having a Canon fitting at one end to fix to the camera body and a T-mount screw thread for attaching to the telescope. Telescopes and microscopes commonly use the T-mount standard for fitting accessories. The little white spot at the back of the telescope is a lever which flips a 45-degree mirror out of the way to give a clear path to the camera instead of reflecting up to the eyepiece on the top of the instrument.


 Newtonian reflector

Newtonian reflectors have larger photographic apertures and so are more suitable for photographing nebulae. I use a 254mm (10 inch) aperture SkyWatcher Newtonian:

Annotation for the next imagePhoto of the telescope on its mount

Its focal length is 1200mm, so the aperture is f/4.8. That is probably as large a focal ratio as possible because it does cause some distortion at the edge of the field of view, of a kind called coma. It is possible to use a coma corrector and I have evaluated one (as described here).

Details of how I attach the camera at prime focus are given here.

As a rough indication of cost for this set-up: the telescope plus equatorial mount together cost only half as much as the Canon camera body (all purchased retail, brand new).

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