|
Focusers
I'm probably a victim of both GAS and reading too many forum posts but often with the scopes I have the comment is "the focuser is the weakest link".
I have the synta focusers on all my scopes. The Saxon 8" Newt has an old rack and pinion with plastic knobs, the 12" Dob, ED80 and ST120 scopes have single speed Crayford focusers and the ED100 has a dual speed Crayford. My adventures with photography (DSLR with a finderguider) seem not to be hindered by any focuser slip or lack of orthogonality in either the ED80 or the 8" Newt and they both are easily focused with a Bhatinov mask, although a little fiddly at times, and can be reliably locked down. With the 12" Dob there is no wobble when adjusting the focuser for planets say, although I don't attempt to 'chase' the focus but rather let the planet emerge in and out of the atmospheric disturbance as it drifts across the FoV. The ED100 is relatively new to me but see how the dual speed is an advantage on the AZ4, which does tend to wobble a bit as coarse adjustments are made. The fine adjustments are barely noticeable in terms of image stability.
Mechanically the 8" Newt is the oldest and stiffest to use and they all required some adjustment to help tighten them up a fraction.
So why upgrade anything? Where focus seems most crucial (AP with the ED80 and 8" Newt) I don't have any major issues (unless I'm missing something) and the dual speed on the ED100 makes sense on the mount I'm using with it. Maybe the 12" Dob would benefit from a dual speed focuser to help visually chase focus at times? Do people upgrade the focuser when the image train gets heavier perhaps (CCD, filter wheel and OAG)? Or is it the quality mechanics that inspire the change (smoother, less fiddly)? Or are there other reasons?
|
