Zoom lens for Auto guiding

[RKenning (Robert)]

I have a Sigma 150 -500 zoom lens. I have it piggy backed on my SW ED 80.
I was wondering about the feasibility of using the Sigma zoom as an auto guider lens. To do this, I would need a female Nikon T bayonet - 1.25" female adapter, so that I can mount a guide camera into the end.
Does anyone know whether such an adapter is available?

Many thanks for any advice and Clear skies.

Rob

[Somnium (Aidan)]

how is it mounted? the only issue i can think of is that if it is not extremely secure then you are going to get flexure issues where the main scope moves ever so slightly in a different direction to the guide scope. this can be extremely frustrating. but if it is secure then i dont see any issue ...

[RKenning (Robert)]

The lens has a solid foot with a rubber base that I have mounted on a custom made aluminium plate. I use the standard bolt into the foot including a lock nut, so it is extremely well fastened. The plate is fixed to the two mount points of the SW ED 80 scope. I have been using the lens for wide field tracked shots without too much hassle. Getting hold of an adapter is going to be the trick.

[ZeroID (Brent)]

There must be various adapters to mount it to other cameras cheapish on the web. Get any one of them and start modifying it.

[RKenning (Robert)]

Hi Brent,
I have been searching the web and Kenko have a straight through EP adapter. The trouble is the EP is fixed, so fitting a guide camera is not possible. I just need the female t-ring with a 1.25" hole to slide in the camera. I'll keep searching.
Cheers Rob

[jamiep (Jamie)]

Originally Posted by RKenning

I have a Sigma 150 -500 zoom lens.

I have a canon mount version of this lens. I find it creeps both in zoom an focus under it's own weight if you tip it up. (ie if you point it at zenith the zoom slowly creeps back).

If you can find a way of securing this (might be as simple as taping it up) you may have a chance, but i would think it would be hard to achieve... Maybe a simpler finder guider might be a better choice.

[RKenning (Robert)]

Hi Jamie,
Yes, I have experienced the zoom creep and have fitted a thick red post office rubber band across the main lens body and zoom ring and it holds it well. I also have a spare 7 x 50 standard Celestron finderscope that I can use if all else fails. I think I should be able to get a male (threaded) to 1.25 female adapter for it quite easily. I would really like to use the Sigma lens though, so, I will keep hunting for a solution.

[rmuhlack (Richard)]

this adapter provides a T thread (both male and female) with a 1.25" hole.
http://myastroshop.com.au/products/d...p?id=MAS-029G3

[Merlin66 (Ken)]

Richard - good find! that could be very useful in different applications....
Robert - I though you needed a Nikon body adaptor for the rear of the lens going to a 1.25" female.
Are you going to use a Nikon lens to T thread followed by a T thread to 1.25" adaptor????