After much trial and error I have finally got the TAL 200K working very nicely as an imaging system. The first step was to replace the drive motors on the HEQ5 mount with Astromeccanica motors. The system is guided by a 90mm dia 1250mm FL MAK with a focal reducer in the diagonal to reduce the FL to about 700mm. This is fixed to the TAL by SS hose clips and a wooden (no flexure) mount. A GSTAR-EX camera is used as the guider and finding a guide star is never a problem as its sensitivity is adjustable.
The focusing system on the TAL is made from BORG parts and is not standard. Filters can be easily changed and there is very little vignetting on a full 35mm frame camera.
The Hutech (adjustable) focal reducer gives a flat field over a full frame.
Here are some pictures of the setup.
Note this system has a focal length of 1790mm and an aperture (8") ratio of F9.
Here are a couple of pics taken with this system http://members.optusnet.com.au/~trlee8/47T2.jpg
Tony some say it is almost as good as an RC! I think it is a bit better than an SCT and not as good as a 'good' RCT. Have a look at Hutech's site they have some really good 'new' focal reducers on the way. The adjustable Hutech (7887) is really good as you can vary the distance between the optical elements with spacers to suit your optic.
As to what system of yours it will or will not fit, I cant fortell the future!
Bert
I like the curved spider design on this scope. I never really thought about it before but looking at this thing makes me realise it's the most efficient design that is free from anisotropic diffraction artefacts, i.e., from directional preference: diffraction spikes, or even much more gentle brightening of the diffraction amplitude in certain directions.
The vanes look to be 60 degrees of a circular arc, and the three of them cover 180 degrees, i.e., all possible orientations of a spider vane, in equal proportion. Normally in curved spider designs, you see one spider vane covering 360 degrees or 2 with 180 degrees each, even though 90 deg each would be more efficient.
I cannot be bothered to do the numbers now, but for 2,3,4,or more curved spider vanes to cover a semicircle (180 degrees) which is required to eliminate any hint of diffraction spikes, 3-vane setup seems (by inspection) to give the shortest total length thus being the most efficient (i.e., yields max. contrast).
It is even better that that Steve, ALL surfaces are spherical ( easy and accurate manufacture) and the corrector elements (lenses) in the secondary are traversed twice so negating any CA. It is a very cunning design worthy of Broderick. The images tell the story. My mount was not good enough to get images without 'JUMPS'.
The main mirror is tapered and also mounted by being held centrally and there is no mirror 'flop' as it is held and adjusted by six bolts for collimation and focus is done by a helicoid focuser outside the tube assembly.
I think it is more than that. Original ideas don't come easily. I saw the potential straight away and bought it from RD without looking through it purely on his recommendation, I was not dissapointed.
