Just been out in the observatory,and looking at the piggy back set up on scope (see pic),I am wondering what others have on their scopes.and how to
go about keeping a heavy camera lens closer to main tube.
I bought a manfrotto 484RC2 head,and had a engineer ream out the hole on
the vixen carry bar and re-thread it 3/8,I put a 3/8 bolt thread in head,and all
fits well.When I use camera with kit lenses,it works well.
I have some heavier higher grade lens,I can use the above set up,but because of the weight,I have concerns-flexing,and the way it is ,the camera lens-along way from main tube,causing balance issues.Using carefully still getting reasonable results,But would like to get camera and lens closer to main tube.
You can get 2 Losmandy dovetail adapters that fit on Losmandy dovetail bars which are a lot heavier duty than the Vixen style. Then you get 2 100mm guide scope rings from Losmandy and you can mount your lens through them.
This is what I use for mounting my guidescope and it works well although the tightening knobs on the dovetail adapter can break off part of the knob easily.
Mount a ring or clamp around the back of the big OTA directly under the DSLR, then screw a long bolt or threaded rod (same diameter and thread as the DSLR mounting threaded hole) into the top of the ring/clamp and the other end of the rod into the DSLR mounting threaded hole, lock with a nut on the rod up against the bottom of the DSLR and another nut at the bottom.
It looks like you can swivel the small OTA mount adaptor, if so you will lose that ability (cant see why you need that anyway).
The ballhead is your weak point there. Why not fix the camera/lens directly to the dovetail without the ballhead? Just fix one of these RC2 quick release plate connectors directly to the dovetail.
It works well up to 10 minutes exposures. I was getting some eggy stars starting at 15 minute exposures so there is some flexure occuring.
I have recently acquired a Vixen VMC95L with a focal length of 1045mm
but it is very small and light and does not require a diagonal to replace the Astrotech 66ED and hopefully even better guiding. I can always find a guide star with this setup.
I had a bit of a think too,and like what I see in Gregs' picture,with the bar between
each ring,is something I can do,the vixen rings have a threaded hole,and I
like the look of troys' link of attachment point,if that was put in middle of plate or slightly towards front end.I would have a much better piggy back point,than the current set up.I can use the RC2 on a tripod or for daytime stuff.
Thanks again for the pointers,
cheers Chris
Last edited by hotspur; 24-04-2010 at 07:20 PM.
Reason: word
I'll play the odd one out, I don't use my camera lenses in conjunction with a scope, why add more weight. If I am shooting wide-field stuff I use Pentax 6x7 lenses, and either a 200mm f4 or a 55mm/f4. Both mount directly on the CCD, with or without a filter (normally Ha shots).
So, the CCD/lens combo sits on the rail, along with my finder/guider, and nothing else. The composite picture shows it, but since shooting this I have refined the finder/guider mounting, and it is neater/cleaner/better.
Gary
That is a fine suggestion gbeal.I have seen something like that before.
And think a plate with Troy's bracket straight on to the mount would be really very stable,and no mess,easier to line up targets etc,These L series lenses are very large and heavy,I would like to may be use the 400mm on M31,or Leo triplet,
