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By Geordie mc
LaserColli mkiii in good condition. Makes keeping your Newtonian scope aligned very easy. Comes still boxed. Only selling as I’m selling my scope and won’t need it. It takes 3 small button cell hearing aid type batteries. The existing ones are flat so you’ll need new ones. Some very small marks on the barrel as seen in picture which make no difference to its operation. I don’t have the instructions but I’m sure they will be online somewhere. If I find them I’ll include. I think these units go for around £85-£90 new. Happy to take £55 inc. postage from France. PayPal only please.
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...
As new condition ultra narrowband 1.25" Baader filter. 3.5nm bandpass for nice small stars.
Bought and loved it, but using a DSLR again and have no use for this filter.
£140, can post.
Time for yet another cry for help when it comes to choosing diagonal. I have read the many similar threads and gathered some knowledge (too many to start linking). I have come some way in my process and now that it is coming to final decisions I would like to hear from the experts. Not many of threads I have read end with the OP returning to deliver some review/verdict of his/her final decision. While I wait for response on some thread where I asked about the result, the eagerness in me forces me to write my own thread. Perhaps some of the people asking these questions before can now answer in my thread as experts!
I have the Nexstar Evolution 9.25 and am currently using the stock diagonal. My eyepieces are the Baader 8-24 mm zoom and the stock 40 mm Plössl. I would also like to upgrade EPs and there I'm looking at something better in 24 mm range, as well some nice low power for more FOV. I'm following threads about EPs and SCTs with great interest for this (on CN). Can say that I'm currently leaning towards the 1.25" 24 mm ES 68° and 2" 36 mm Hyperion aspheric (if going 2" route).
I'm thinking 2 alternatives (including a budget alternative for one of them). I'm looking at Baader mainly for ClickLock (and expect good optics):
Baader T2 Zeiss prism with a 1.25" ClickLock EP (T2 part #08) -OR- the 2" prism with 2" ClickLock (splurging that is). The budget alternative would be to get the non-Zeiss T2 prism instead for the 1.25". Worth noting that I would like to get the Celestron f/6.3 Reducer/Corrector. This would be for future purposes of delving into EAA but of course I would use it visually as well (especially if choosing the T2 route). The reasoning for my alternatives:
Go for the 2" Zeiss prism to theoretically get the best of the best in visual terms. I would make better use of the 46 mm baffle tube opening. Theoretically possible to combine with the R/C thanks to relative short light path (although not necessarily needed with 2" EPs). Downside of going to 2" accessories would be the cost, EPs, filters etc., on top of diagonal. Would not be able to spend all these costs at once. Cheaper route with T2 prism (especially the non-Zeiss), not only diagonal but also the other accessories. Cost of the R/C would be comparable to e.g. the 36 mm aspheric and give similar power and FOV with the 24 mm ES, i.e. the 24 mm would act as both. Extra plus is the ClickLock clamp for 1.25" with built in fine focusing not involving the mirror. Downside of knowing that not all light coming out of baffle tube is used. To get the wide FOV (24 mm + R/C) I'm adding glass to the optical train (theoretically not a good thing). I'm leaning towards the T2 as it would be a cheaper diagonal and for EPs I would only need the 24 mm and then the reducer instead of a 30-40 mm, so saving the expense of one EP. Then I would already have the reducer for continuing into EAA. The questions I hope the experts here can help with:
The old reducer vs 2" diagonal question. With R/C and the 24 mm I can get roughly the same mag and FOV as e.g. the 36 mm Hyperion (technically 38 mm vs 36 mm and 68° vs 72°). Also reading good things about the ES 68° and with R/C the EP should behave the same. Am I missing something here? The logics say that the I would lose some contrast with the R/C (not using full opening + adding elements), correct? Possibly flatter fields though (not important now, hopefully the EP threads might tell soon enough). The Zeiss vs non-Zeiss T2? Big differences? I have read a few posts on this so most to get some updated views here (have read that Baader has changed some things over the years). Using the R/C (f/6.3) with these prisms. I know f/7 is mentioned as "the limit" but also remember BillP's test where he was happy down to f/6 with the prisms (in 2014 at least). Perhaps most important: have I missed some other obvious alternative here? Maybe I have forgotten some question here but perhaps for the best as I assume those who have gotten this far are tired of reading now. Thanks for getting here though!