davidc135

Aldrin and Collins are a different kettle of fish to the large and contrasty Armstrong which I should think could be spotted in 75mm, maybe less. I was surprised how good the seeing was with the blustery breeze pushing my long Dob about. I couldn't manage the two smaller until a break in the clouds, good seeing, stillness and complete nightfall came together to yield enough contrast. Which it did eventually for long enough to catch them. I'm not sure what Aldrin and Collins compare to in difficulty. Maybe the larger Plato craterlets are a touch harder. Anyway, I'm chuffed as I've waited months for a clear view. David

The terminator was well placed tonight to attempt to see the three astronauts. Armstrong was easy and a moment of still conditions with a gap in the clouds combined with good seeing gave me a glimpse of Aldrin and Collins before it all closed over. X400, if the seeing is fine, works better for me than the alternative x215. The smaller pair were tough enough in the 8.5'' f7.5 Dob. David

That's good going spotting E with with the Tak 76. I've seen E easily with my 8.5'' f7.5 Dob under B 3/4 skies and fine seeing. F not easy, came and went. The few attempts at the pup have been unsuccessful. David

The moon will be nicely placed in a few days and you'll be able to see how the Mak does on craterlets and fine detail. David

I'm blessed with fairly dark, Bortle 3/4 skies with good seeing from time to time. If conditions are helpful, my 8.5'' f7.5 Dob with 21% co gives sharp lunar views at x400 which I prefer to the next step down, x220, partly because the 4mm ep is better quality. If quality was the same maybe x300 would be best of all but I expect that there is a range, especially on the moon. My 71 yr old eyes probably appreciate a bit of extra magnification if there's plenty of light. David

It's all personal choices but I'd give an 8'' the best chance of excelling on the moon and planets by getting a 1/10 wave wf f6 with a 25% secondary from OOUK. I'd want it to snap and sing at x400 on the best nights rather than feel it fell just a touch short. David

I'd have a look at the threads and check to see if there is any damage preventing the reassembly. If so, a local machine shop would be able to repair it. Either way there must be some such businesses in Inverness who could help. If the threads are good and clean but difficult to engage I've found that slowly rotating one element counter clockwise against the cell until a slight click is felt sometimes does the trick, but you may have tried that. David

There is a thread over on CN where one Askar 185 was so so in the indoor Ronchi test being a bit over-corrected with a wide central hill. Whilst the owner felt his 150 apo showed a bit more planetary contrast, he still thought the Askar was no slouch and was pleased with his purchase, especially given the price. But he bought it more for DSOs. I expect the 8.5'' achromat, in spite of CA, got the best out of its aperture by having an excellent figure and it may be that it's that consistency which suffers with lower priced large apo objectives. No doubt there will be more indoor tests/field reports on the 7'' Askar in the near future. David

It isn't too difficult to disassemble and clean the objective if it's taken step by step. Remove dewshield. How is the cell fixed to the tube? I'm assuming that it isn't collimatable but screwed in place. Collimatable cells would be attached by three pairs of push/pull scews. Remove cell. As Louis says check for a retaining ring which should have two indents to aid removal. Usually it would be on the outside of the glass but it's possible that it screws in from the rear. Remove ring. To remove the objective first find a cylindrical object say 3'' diameter and of ample depth such as a small glass on which is placed a protective tissue or cloth. This supports the objective whilst the cell is lowered down carefully avoiding any jamming on the sides and possible resulting 'clamchips'. With the objective high and dry, inspect for any side pencil marks or scratches indicating best orientation. If there are none it's still an idea to mark a V or similar with a waterproof sharpie just in case it matters. A V can also be a quick check on the order of surfaces during reassembly. Check what they use to separate the two lenses. It could be a ring, or three foil or similar spacers. Retain as the spacer thickness is especially important in a fast doublet. I'd give them a soak in tepid soapy water and carefully rub the surfaces with fingers. The lenses can be rinsed and drained with the last drops removed with a tissue before being allowed to thoroughly dry. Ensure objective is reassembled in the correct order. Hope this helps David

An update. I'd assumed that the surfaces of the B270 float glass were sufficiently parallel and hadn't checked. A disappointment to see Airy discs as little spectra! What can I say? Both corrector discs had around 125 microns of wedge where 25 should be the limit and so there was nothing for it except to regrind one side of each plate. It's likely that the nearly finished corrector will suffer some astigmatism due to irregular polishing. Avoiding pressing down too hard will help whilst interference fringes will show likely problems. The pattern around the neutral zone should be circular with any variation being improved by selective pressure. On this earlier 4'' c.p extra time spent pressing down at 10 and 4 O'clock evened the fringes out. The gram weights were to centre the fringes. There's still a little astigmatism in my DX-6 but it gave sharp images at x370 during spells of good seeing in the garden, on high contrast objects. David

If the Orion Optics VX8L upgrade is truly 1/10 pv and smooth I don't see it being easily bettered visually on the moon and planets. David

I'd contact Stathis Firstlight in Germany who many people have dealt with, unless you have done so already. If he doesn't have your thickness in stock he can order it. David

My orange tube C-8 has an SN of 870505 and was made in the early 90s, I was told. I wouldn't offer more than you would want to resell it for, in good conscience, if it turns out to be disappointing. It may well be fine but I expect it's a bit of a lottery. David

Very nice find. Highly respected manufacturers. Look forward to hearing how it performs. David

Definitely spend a few pounds on a double layer of reflectix. I'm not sure how much seeing varies from place to place throughout the UK. I suppose it must be influenced by local microclimate but I'd be surprised if the 9.25 sct didn't live up to its potential where you live, at least reasonably often. David