Quote:
Originally Posted by Paul Haese
That's nice resolution and colour MnT. It still looks quite faint at 30 minutes subs. It must be very faint.
I have often wondered what you thought of using a big scope like that with a fork mount. How much flex do you get with the forks? I am thinking that one day I might travel down the same path with at least a 16" scope.
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Thanks, Paul.
Having a fork mount at all is great - no meridian flip, and it means you can photograph through the very best part of the sky without anything funny happening. The forks are huge heavy aluminium castings. My pointing model says the droop is only 0.01 degrees. (Note to self: redo pointing model for summer). On the other hand, we feel that to be honest, the motor drive for our particular MI-750 fork as delivered left a lot to be desired. We suspect that despite asking for a southern hemisphere version (Australia), we actually got a Northern hemisphere version (Austria?), because the main RA worm gear would creep up the face of the gear and then drop down repeatedly, causing utterly shocking tracking. We added some extra ball bearings and a pressure plate to hold the gear down, not against the worm (it's spring loaded - that's fine) but in the other direction, parallel to the axis of the earth). We made the same mods for the dec drive, and that hugely improved the Dec backlash. We also changed the servo gearmotors to ones with three times higher gearing, and that also greatly improved tracking at the expense of slow maximum slew. The RA clutch also had some missing bolts. Mathis talked us through replacing them and that was fine. Having made those mods, we're delighted. The mount was only $18K, and having made the mods, we think it was good value for money.
But if we were ever to buy another instrument (unlikely), we might think about an alt-az fork mount and a field rotator. We'd never try putting a really big scope on a German mount.