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I am thinking on grinding my own lightweight mirror (first f4 16", later f4 24"). The lightest and cheapest option is to get a thin blank and slump it in a decent kiln.
Anyone has longer term experiene with slumped mirrors? Overall doesn't seem to be more work than a normal (not pregenerated) blank.
Do I have to grind the backside as in case of normal flat back mirrors to avoid astigmatism? How do people support a convex back while grinding? Does it make sense to grind a hole in the middle for additional support? I am remotely considering a convertible Newtonian/Cassegrain system anyway...
It's been a long time since I've posted in this forum, anyway I've picked up a Skywatcher 200p F/6 dobsonian as a DIY project whilst I continue to work on a new telescope from scratch, (I've started to grind the mirror).
I'll be making improvements to this dobsonian as a project and learning experience, I've already got a temperature controlled fan which has a probe that can measure both mirror and ambient temperature. I'll be measuring the primary mirror with my in progress Foucault/Ronchi/Bath Tester when that's finished in the next couple of weeks, may even refigure it depending on results.
But I'm most excited about this right now. The blackest Black Paint as an alternative (hopefully better alternative) to flocking!
This stuff is seriously black and flat, I backed it on kickstarter and received 3 bottles along with goodies.
I plan on painting the area opposite the focuser, area around the primary mirror, inside the focuser drawtube, potentially the secondary mirror holder and edge of the secondary also.
It's a shame I don't have any flocking to compare it with but it looks incredible.
This video shows just how impressive it is (moreso than my little tester I've done).
I'll try and get some decent before and after pics.
It's about time that I got together a thread describing my rebuild of my old Orion Optics SPX350. I'd bought this a *long* time ago with a mind to doing it up to use for AP, but then house move, life, etc meant it sat around doing not a lot for a long time. When I came to use it, I got some good results, esp on planetary work, but also found that under the weight of the heavier SBIG CCD, the thin tube didn't hold collimation particularly well. Here it was:
So, eventually, I decided to have a rebuild. I plumped for a truss tube over a remount inside a carbon tube. Not sure whether carbon tube would have been cheaper now though to be honest!
As the scope is mounted on an EQ mount (my Losmandy Titan), it needed to have a central brace, and so I shamelessly borrowed many ideas from Rolf Olsen's excellent scopes (see: https://www.rolfolsenastrophotography.com).
It started with the three rings - these were routed out of 21mm Baltic Birch Ply (sourced free from a mate who works in wood sales...). Internal diameter is 390mm.
Onto these were mounted a new Orion 9 point primary cell (to replace the naff original 3-point cell) - shown here without any connecting hardware!):
and with a bit of 1.5" aluminium tube, some drilling and making of small recesses using a spade bit, a secondary cage was constructed -- again without the final countersunk parts and connecting hardware:
To be continued!!
I've been continuing to work on my 14" double truss newt - recent activities include mounting a PC (a Gigabyte Brix - pictured) on the scope along with power distribution - I now have it down to 2 wires between scope and the floor (SBIG ST power cable and 12V) which much reduces drag/snag type situations. I also found and corrected an issue with the Moonlite CR2 (I was a bit shy in the Crayford tension, which gave rise to play in the drawtube).
Fixing that, and sorting out balance issues and tweaking up the polar alignment has helped enormously in getting much tighter stars - here's an example of my guiding last night once I'd sorted out the right calibration steps for PHD2 (this at native 1582mm FL with an OAG using an ASI120MM).
Also, I've been using a trial of SGP to try and rationalise the number of bits of software in use - it's quite a learning curve (!), but I managed to get 75min of data to fall out last night until the clouds stopped play. So here's M106 in CVn (along with NGC4248 and some other much fainter and distant galaxies - at full res for pixel peepers...) - 25x3min Lum using an ST2000XM. t's a bit noisy in places as it needs more signal, but that's not the scope's fault! Processed in PI, but haven't got anything to shoot flats sorted out (yet...: I just got a 600mm LED panel light to mount in the dome for doing flats). I would quite like a good clear run to get a full set of data here (and flats to follow!)...
All in all, this looks like justification for embarking on this project from the early days of starting rebuilding the original Orion SPX350 - it's taken ages really, but I think it should be worth it from these early results.
One happy astronomer
do any members remember the site ATM "Amateur telescope making" before the days of the wonderful websites of today, Mel bartels etc, I was going through an old hdd and found a load of emails of the daily updates from the site, probably in those days is was a bulletin board rather than a website... blast from the past... god hasn't life changed since mid 90's. I started back in IT as an engineer with an ibm pc xt50 10mb hdd 640kb ram mono display cost new thousands, mono display green...... and pc dos. before ms dos.... my next was a compact 286 laptop more like a brick on steroids still slow and a black and white screen, how the tech has changed over the years, I was in IT for 20 years but gave it up for a better life too much change and more exams to pass as the software changes to stay up to date, at 50 brain to slow to update. (to err is human to really mess things up takes a computer)..
any more ex IT people care to add