Beginners Astrophotography Question

[DonXabi]

Hello, I'm new here and been reading (and learning) some really interesting stuff!

I have a question on astrophotography.......

I have an 80x800 refractor telescope - its not an expensive one but is good enough to keep me and my kids happy (we did see Jupiter and her moons last weekend!).

As I am into photography and have taken some reasonable shots of the moon and constallations with a tri-pod set-up etc. I thought I'd move on to trying the telescope method.........I have a Canon 400D with a T-Piece and adaptor ring..........but cant get it to focus through the telescope.

Am I missing something, doing something wrong or maybe just the scope is not good enough?

[jgs001]

Hi and welcome to SGL. In most cases, refractors are designed to focus for viewing with a diagonal in place to allow the focus for the eyepieces. This means that to achieve focus with a camera attached directly to the rear of the scope you need an extention tube between the camera body and the focuser of the scope. I have this with both of my refractors.

The scope is probably an Acrhomat, which means that it's only corrected for 2 colours, but, you ought to be able to get some nice shots of the moon at 800mm with it. You need to spot meter the moon and probably want to underexpose by about 2/3 to 1 stop (the moon is very bright).

[DonXabi]

Many thanks John - do the extension tubes come in certain lengths? if so what size would you recommend?

I have some decent images of the moon with my 400 lens on a tri-pod, just be great to get some close ups!

[jgs001]

You'll need some tubes in the appropriate size fitting... I'm guessing 1.25". That will cause vignetting, but it's not a problem on the moon. It's hard to give a precise length of tube needed as it'll depend on the scope in question... you can probably get a rough idea, by holding the body up to the rear of the scope until it's about focused and see what the gap is (downside you need to leave the body open).