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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...
I am thinking on astrophotography with a reinforced/DIY upgraded 16" travel Dob, 3-5minutes subs. Seen that the Tom O' dual axis platform does exactly that but got two problems with that:
#1, price: costs more than a GEM capable to carry a 16" Newtonian (CEM60). I know there are stronger, more expensive mounts out there - anyway, 2000$+ is beyond my budget.
#2, fixed latitude. The scope is a travel Dob which I intend to fly e.g. to Namibia - unfortunately I don't live South enough to be on its Northerly counterpart. Neither I want to pay TWICE the $2k+ price tag.
#3, polar alignment: no polar finder, better PoleMaster no deal. In 2020 the maximum time I want to waste with PA is 5 minutes. I have two trackers meant to be used with small telepoto/standard lemses: both came with polar finders.
Any recommendations? I am also open for DIY, however need a decent low-latitude design first.
Having some trouble focusing my Dobsonian. I’m seeing objects but there very blurry, I’ve collimated my telescope already, adjusted the focusing knobs (made sure the screw was loose to be able to adjust), have tired with both 25mm and 10mm 1.25 eyepieces during the day and pointing at bright objects that are far way. I’m not sure if it’s just beginners struggle and eventually I’ll get shard images, but any tips would help! Thank you.
Looking for a 12" DOB (or larger) which can be transported to Prestwick, Ayrshire. Any brand, as long as the telescope is optically sound and in good working order. I'm a reliable buyer who has bought and sold on this site before.
Hope someone with more experience than I, which basically means anyone that has successfully collimated a Newtonian, can answer a couple of compound questions I have based on my first and only attempt at secondary collimation of my SkyWatcher Flextube 250.
1) All three of my secondary collimation screws were extremely snug before I did anything and I was only able to comfortably turn them counter-clockwise. Is this normal? Do I need to loosen all three screws first before I can properly start collimation? Should I be turning any screw beyond "snug"?
2) Before collimating, I placed a yellow sheet inside my OTA opposite my focuser tube and I placed a red sheet between my secondary and primary. The view this gave through my focuser tube was of a red circle surrounded by a partial yellow ring (the secondary mirror stalk blocking a portion of this yellow annulus). While independently turning each of the secondary collimation screws counter-clockwise I looked down the focuser tube (both with and without a sight tube installed) expecting to see some change in the shape of the red area (more or less circular) and/or the yellow area (less or more even thickness). I turned the screws no more that 2 complete revolutions. I did not perceive any appreciable difference in what I saw and I turned each screw back (clockwise) to their original tightness before working with another of the screws. Does it make sense that I didn't perceive any change? Should I have turned the screws more revolutions? Should I have loosened more than one at a time?
Very confused and looking for your help. Thanks