Piggyback flexture: How can I fix this?

[Star Hunter]

I'm thinking of piggybacking a SW 180Mak (5.5kgs) on top of a C14 OTA.

Both top and bottom of the C14 will have the thick Losmandy D plates. To hold the Mak to the C14, I've fitted a pair of back to back two-handle locking saddle plates, take the C14's D plate to the Vixen type bracket.

However, if I discard the Vixen saddle plate and replace it with a Losmandy plate, do you think this would stop any flexture or do you think it would be wiser to get a set of Parallax C14 OTA rings and then, use those the D plates?

The two scopes will ride on a Titan 50 mount.

Decisions, decisions..

Jim

[Paul Haese]

Flexure is inevitable Jim. You cannot eliminate it altogether. You can lessen it more and more but if you intend on doing deep subs such as 20-30 minutes or more then you will find at some point up to that 30 minute mark you will see it creeping in. The best way to test for flexure is take a shot at 1 minute, then 5 minutes, then 10, then 15, then 20 and then 25 minutes. You will see elongation in star shapes over the entire frame at some point and it will get worse with longer and longer subs. Making the system really rigid will help but things like focusors also have to be looked at too. Connections to cameras and the like also play a huge part. It will take quite a while to eliminate the flexure to an acceptable level. Your primary aim will be to get 10 minute subs without flexure and in your next of the woods I would be aiming for 20 minutes with the dark skies you possess.

The better solution is to use an AOG. Using this will help but you will also need to address mirror flop. As I understand it you are using an older C14 which does not have the mirror locks in place. You can make your own and install them to help with this problem too.

[Star Hunter]

Originally Posted by Paul Haese

Flexure is inevitable Jim. You cannot eliminate it altogether. You can lessen it more and more but if you intend on doing deep subs such as 20-30 minutes or more then you will find at some point up to that 30 minute mark you will see it creeping in. The best way to test for flexure is take a shot at 1 minute, then 5 minutes, then 10, then 15, then 20 and then 25 minutes. You will see elongation in star shapes over the entire frame at some point and it will get worse with longer and longer subs. Making the system really rigid will help but things like focusors also have to be looked at too. Connections to cameras and the like also play a huge part. It will take quite a while to eliminate the flexure to an acceptable level. Your primary aim will be to get 10 minute subs without flexure and in your next of the woods I would be aiming for 20 minutes with the dark skies you possess.

The better solution is to use an AOG. Using this will help but you will also need to address mirror flop. As I understand it you are using an older C14 which does not have the mirror locks in place. You can make your own and install them to help with this problem too.

Paul,

I've made a set of mirror lock for both C14's. Simple and it works. What I've decided to do now, is keep the Tak 180, the SW 5" guider and mount the Mak 180 alongside the Tak, all on the Titan 50 mount.

The modified G11 mount will take the white tube C14 with its JMI focuser and an F6.3 reducer. I'll use a lighter guide scope on the C14 that doubles the F/L of the C14 @F6.3 or I can use my trusty Lumicon off-axis guider and a Lodetstar. I think this set up will work better than first thought.

Your thoughts, mate?

Jim

[Paul Haese]

Use your OAG you have and the Loadstar. I never fail to find a guide star on my RC12 and the same sensor in the STXL integrated guider. Don't bother with a guide scope. You are going to give yourself such grief by doing that. I use OAG's on all my scopes and would never go back to the a guide scope.