My flocking material arrived so time to try and eliminate my diagonal star problem, which has sprung up recently. Last November I sent my mount off to be overhauled ( a lot of play in the worms ). So hopefully that's eliminated.
Thanks to Polemaster I've great PA and PHD backs that up when seeing conditions allow my total error is under 0.50 arc minutes. Apart from the small dither as my images come in I see no movement between frames. Yet my stars have this distortion along the diagonal. My thinking is the weight of camera and filter wheel in my drawtube, is knocking my calibration out of kilter. So while the scope was stripped to apply the flocking time to calibrate the drawtube. I've never done this before so followed Dion of Astronomyshed;s excellent video tutorial found here.
https://www.youtube.com/watch?v=3LbR1nIx-jw&t=3901sPic A: Flocking started.
Pic B: opposite the drawtube with the holes centre marked. Laser shows where my drawtube was centred.
Pic C: Drawtube collimated although not far out originally, this could be the reason for my star distortion?
Pic D: Scope back on the mount ready for any clear gaps in the forecast clouds.
Pic E: Test image on Vega. Shows a Collimation error on one side. RGB 10x30s each filter.
Pic F: Following night was clear so some in situ calibration to eliminate the error in Pic E: There's still a small error in the upper right quadrant which I'll try to iron out in the next clear spell. At least I feel like my star problem is getting close to being resolved. Although I collimate the mirrors you then have to hang an extra few kilo's onto the drawtube which knocks the collimation out again.
Rev G: I replaced the standard steel grub screw, one of three that holds the puck, the effect of this one grub screw was amazing. It seems my diagonal stars was coming from the whole scope rocking slightly during the guiding corrections, as it was only being held by two of these original grubs. My stars looked better straight away with one stainless steel grub!
Rev H: a 300s sub the last one with the original soft grub screw. Stars have some distortion still, but are still better after all the other tweaks. After this run I parked the mount and swapped the dodgy grub, head was damaged so tightening it was difficult.
Rev I: Half an hour later after changing one grub screw. A 600s sub and stars are just better all round. I was gobsmacked. I have brought several packets of stainless m3, m4, m5, and m6's and am replacing every grub screw I can find with Stainless ones as I find them.
Rev J: My subs since the screw swap were showing some extended coma across the bottom of the sub. Which can only be my chip not being square with the secondary. I'm making tiny adjustments in the drawtube each session to iron out this last problem. Here's my 1st 20 minute sub in a long time. Taken with confidence as well. A 1200s Ha of Abell 21 taken with a full moon and a hazy sky.
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