astrophotography

[tombo]

Hi guys,

I've got a canon 450d with a cgem 1100 and thinking of taking some photos of planets. I have orion eye pieces. Do you think a telescope extension tube like this

http://www.aliexpress.com/item/1-25in-Telescope-Adapter-Extension-Tube-T-Ring-for-Canon-DSLR-SLR-Camera-DC618/32528710613.html?spm=2114.01020208. 3.1.BMc1rS&ws_ab_test=searchweb201556_3,search web201644_5_9994_10001_10002_10005_ 10006_10003_10004_62,searchweb20156 0_1,searchweb1451318400_6150

would fit the body of an orion eye piece. The orions look fatter that the Plossl. So I'm not sure and I can't see a need to spend much on the extension tube since it just holds everything together.

Thanks,

[Somnium]

what you are looking at there is a T ring with a 1.25" nose piece. it is designed to go directing into the eyepiece holder without the need for an eyepiece. this is for taking images at the prime focus point, not imaging a projection in an eyepiece. you may need a 2" nose piece for your scope, not sure.

you have a pretty long focal length telescope there which will be pretty good for planetary work.

[barx1963]

Actually that is an eyepiece projection adapter. An eyepiece fitts inside the larger barrel. That is why there is a thumbscrew on the side to hold the eyepiece. Usually use a plossl or similar.

Malcolm

[pdalek]

Using a barlow to get higher mangnification is generally better than eyepiece projection.
You need:
1- a 2" visual back to suit your scope,
2- a 1.25" barlow lens,
3- a 2" to 1.25" eyepiece adapter with a male T-thread on top, and
4- a T-ring to suit your camera.
Fit the visual back onto the scope.
Unscrew the front part of the barlow (lens cell and 1.25" barrel) and secure it in the eyepiece adapter. You may wish to use grub screws instead of the standard knurled ones so that you cannot loosen the barlow by accident and drop it into the scope or camera.
Screw the T-ring onto the eyepiece adapter and attach the camera.
Mount the assembly in the visual back.
Magnification can be fine tuned by adding spacers between the eyepiece adapter and T-ring.

If instead you wish to use eyepiece projection, you can get special eyepieces which have a sliding outer barrel with a T-thread on top.
Alternatively some eyepieces have an optional T-thread adapter which replaces the rubber eyeguard.
There are various telescoping tube systems inside which an eyepiece is mounted. Choice of eyepiece is constrained by the tube internal diameter.

The barlow method is optically superior, the most compact and uses parts which are useful for other applications.
Which power barlow to choose? This is a more complicated subject if you are after optimum images. A 2.5x is slightly less than optimum for your scope and camera, but easier to use - more light and less vibration sensitivity. You can boost by adding some spacers.