Designing a barn door mount for use with a telescope - help!

[Owen]

So....

With the purchase of an EQ tracking mount out of the question until my lottery winning plans come to fruition I've decided to build a 'barn door' mount for astrophotography which I should be able to do all in for less than £100 including the tripod head. Having looked around the interweb for some instruction I've found some good step by step guides to building one BUT....

They're all designed for use with a shortish camera lens - the tripod head connecting at the base of the camera. Having scribbled on a bit of paper it is immediately apparent that this design would face some serious restrictions if you try and put something on it that connects mid way on a long structure; my SW ED80 for example.

On the current design it would effectively restrict the field of view to anything at low elevations, or high elevations between West and North West or East and South East, depending on orientation. Does that make sense?

The simple solution is to photograph things only when they are in these areas of the sky, but since I'm going to all this trouble that seems like a bit of a lame end point.

If you've managed to figure out my ramblings and know of any (cheap) engineering solutions I'd love to hear from you.

Cheers

Owen

[Stephen]

A decent ballhead camera mount (easily holds several kilo of DSLR) should hold the ST80 no problem - this should be tall enough to then pivot around enough?

It's not the best engineering solution in the world, but the short dovetail that holds the ST80 tube rings, has a whitworth hole in the middle I think, that screws directly onto the ball head - job done?

Or did I misunderstand?

[Merlin66]

The OP mentions an ED80 ....about 3Kg loaded....THAT would need a little bit more engineering....

[Stephen]

The OP mentions an ED80 ....about 3Kg loaded....THAT would need a little bit more engineering....

Damn my rubbish eyes again, sorry OP!

[Owen]

No problem! Having done some more detailed designs at home the only solutions I can come up with all involve placing the tripod head further out from the hinge on a thin structure, which would need to be metal probably, which means welding, which I can't do. In any case the price then starts to edge into the EQ mount territory.

Is there any point buying something like a EQ3-2 for about £150 or should I just wait until I can afford an EQ5 type thing?

[MjrTom]

I would have thought that a ~600mm focal length of an ED80 would be quite a challenge to track accurately with a barn door tracker.

My astrotrac struggles with my ED80 and that is pretty accurate at tracking to be honest.

The tricky part will be nailing polar alignment accurately enough to prevent star trailing.

[Owen]

You're probably right Tom. If it doesn't work I'll just use it with camera lenses anyway, so I think I'll build a simple one and see how that pans out until I buy a proper EQ

[MjrTom]

You're probably right Tom. If it doesn't work I'll just use it with camera lenses anyway, so I think I'll build a simple one and see how that pans out until I buy a proper EQ

Good idea

If you stick to 17mm-50mm focal lengths say you should be able to manage 30 seconds or more quite easily.