Quote:
Originally Posted by Poita
The secondary mirror holder on my C9.25 EdgeHD scope has come loose and rotates fairly freely.
I tried removing the corrector plate and tightening it, but it loosened up again, which makes Hyperstar usage rather annoying.
Anyone know of a safe way to tighten it and have it stay put?
Also there is a little side by side movement once it loosens, how can I be sure I have centred it?
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I've had both a C14 and a EdgeHD14". With the secondary cage, there are two washers one on the inside and the other the utside of the glass surface of the corrector plate. The ones on my C14 were made of some fibre-based substance - possibly even leather for one of them and I found that if one of them became damp for whatever reason, t's grib loosened and the secondary frame was able to move around in a circle. That is a disaster of course because the secondary has to be aligned with the primary for optimal performance.
This problem always occurs when you remove the correector for cleaning or whatever.
The primary is normally positioned so that the indexing position is at the 3.00 o'clock position as you look down the OTA from in front - i.e. opposite the focuser knob. That means that the little indexing knob on the secondary mirror (where it notches into the frame holder) should also be pointing at the same location - 3.00 o'clock.
Assuming that the secondary mirror itself has not moved on it's own holder, then all you need do is make sure that indexing slot is lined up to 3.00 o'clock and that the frame is tight in that position. If you've already removed the corrector there is no harm in doing so again to make sure it is tight. Then return it to that position.
That means grabbing hold of the shroud on the inside and tightening the frame on the outside by screwing them together. These can sometime be quite tough to budge and I have resorted sometimes ot drastic measures including a rubber strap/lever device that is sold for removing oil filters - it doesn't mark the surface which is the key.
With the C14s, there were small cork shims around the rim tnat positioned the corrector dead centre. I understand the newer Celestrons have abandoned the use of these and instead use grub screws. Have a look for them around the perimiter and see whether that is so. Assuming it is, then the trick is to use them to ensire the corrector is dead centre.
To do that, I have cut a very precise translucent ring of plastic with a target on it that is dead sentre and place that over the opening where the secondary will go later on. I then used a laser from the back to position it. That may not work as well with the rear ooptical elements of the Edge - I don't know.
Peter
