No more flexure induced guide error.

[tornado33]

Howdy.
Ive always had problems with flexure induced guide error on exposures longer than a few minutes with my 10 inch F5.6 newtonian with refractor guidescope. I bought this from Alaska http://www.aeroquest-machining.com/page9.html (its why ive not been taking images with my 10 inch for a while of late, getting it all set up and installed)
All I am waiting on now is a 1.25 inch illuminated recticle eyepiece to arrive. Tonight, I set it all up and, unable to wait, tried using my old 1 inch guider by putting bits of styrofoam round it to hold it steady in the 1.25 inch off axis guider holder. Didnt work well, it moved about, but I did get one reasonable 5 minute ISO 200 shot of Omega Centauri
Heres images of the setup I now have
http://www.users.on.net/~josiah/focuser/
see the pick off prisims here http://www.users.on.net/~josiah/focuser/IMG_9935.jpg
Its a clever design, the whole thing can rotate 360 degrees to find guide stars. My secondary isnt big enough for the prism to get 100%, I estimate I get about 4 inches of the mirror, but I get all the focal length and no flexure induced errors.
I also got a 2 inch to T thread adaptor from Lumicon, so should get less vignetting as well. Focus point is good, I didnt need to move the primary mirror

[[1ponders] (Paul)]

Neat looking setup. Ingenious design. Great image too.

[Robby]

I love your scope!!!
That's gotta be one of the best used scopes on the forum... Good to see there's no love lost there!!...
As I always say the best scope is the one that gets used the most. Top stuff.

Awesome image too!..

Cheers

[seeker372011 (Narayan)]

scott
newbie question
how does the problem of differential flexure manifest itself? what do you actually see happening? the reason I ask is because i have just started using a guide scope for auto guiding and dont even know if I 'm having a problem

or is simply that the guide log shows the guding is perfect and the image shows trails?

[Robby]

Not being perfectly polar aligned will also cause guide errors due to field rotation.
When I first started auto-guiding, I was dissapointed to see I was still getting guide trails. At first I thought it was flexure, but later realised it was because I was poorly polar aligned.
Cheers

[mch62 (Mark)]

Seeker it will depend on the scope design , but Newtonians are prone to it due to the mirror cell movement and the overall tube length flex.
If an OTA and guide scope mounting is well designed it can be eliminated .
I don't have problem with my Newtonian but it's not an ordinary mirror set up.
Refractors are less prone to the problem.
I have has several scopes in varying configurations and have used a guide scope in all except one .
Didn't have any problems.
A certain SCT I once had did have problems due to mirror flop and I used an off axis guider for that but others get away with a guide scope now with better mirror lock up.
Time will tell with your imaging results.

Mark

[tornado33]

Thanks.
Seeker, it almost always appear as trailed stars in one direction only, and the longer the exposures the longer the trails. No matter what I did I couldnt get rid of it till I went to the off axis guiding system.
Yes it is a well used scope lol, painted once only lol.
Polar alingment is fairly close, adjustments needed only every minute or so, and very small ones at that. The mount is left permenently in the yard (covered against the weather though). Its very heavy with counterweights attached.