In the real world there is no such thing as a perfect optic only an affordable one. The advantage the Kletsov design has, ALL surfaces are spherical so making it easier to manufacture near theoretically perfect. The sub aperture corrector behind the secondary is designed in such a way that all light passes twice through the corrector so eliminating or minimising chromatic aberration.
The main mirror is conical and and centre mounted which is held by six bolts to the main tube.These bolts swivel the assembly in a cup arrangment and can be adjusted for collimation. The secondary should not be touched as it is factory aligned with the optic axis or tube axis.
Collimation is done by getting an out of focus star image ie torus centered at very high magnification. I actually adjust with the 5DH attached and look through the viewfinder with a Canon right angle viewer at a mag of 2.5. I then take an image of this and view at high mag to check for the slightest misalignment. Repeat until as good as your patience will let you.
Once set collimation holds well unless you drop the tube that is any sudden shock or high g forces.
The focus position is rather vague if done by eye I am in the process of making a stepper focuser for it. I have replaced the original focuser with a borg helical as the original is crap and only 1 1/4" and barely usable for visual. A borg FR/FF (7887) has also been fitted and gives a final FL of 1790mm at f/9. The native is 2000mm at f/10 for the TAL 200K.
The tube is open so cool down is quick. The mirror being conical and held only by its center also helps. I have never had condensation on any of the optical surfaces.
Cleaning the mirror is relatively easy as the back of the optical tube is easily removed with the mirror in situ. This does not upset collimation if you replace in the same orientation.
Below is an image(s) taken some time ago. The FR was not yet optimised to get a flat field but it is way better than without it on a full frame.
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http://members.optusnet.com.au/~avandonk2/CAR_tal.jpg
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http://members.optusnet.com.au/~avandonk2/OC_hdr2.jpg
I think Scotts Tornado33 10" newt could be a bit better than this judging by his images.
I dont know how good the TAL 250K is.
I am only putting up this as information. I am happy with the TAL's optical performance. I would not use it for intensity measurements as the secondary does attenuate the UV end.
Bert
