Peter Drew

It would never be any use if it had to be at 21c here. 🙂

If home made, make sure you've peeled off the protective film on the filter material. 🙂

Wot! no sunspot image? I had a wonderful albeit brief view of it in a rare clear patch, teeming with detail and hiatus flaring. 🙂

Hello Steve, welcome to SGL. Sorry you have to start with an unfortunate problem. As Ken has said, a likely outcome is that the impact has decontacted the etalon plates. These very high precision plates are kept together by molecular bonding of the material, no glue or clips, a sudden shock can break this bonding and it is extremely difficult to reset them without laboratory standard conditions, hence the high repair price. Where in the UK are you based?

A definition of "expert" that I heard from a Sage was someone who came from more than 25 miles. 🙂

I have more refractors than SCT's, I just use the SCT's more often. 🙂

@Joanna. Apologies for not bidding you welcome to SGL, hope you enjoy our company. 🙂

The telescope is a Skywatcher refractor on a AZ3 mount. It is 90mm (3.5") aperture. They retail at £156 new. 🙂

Then why doesn't Damian use a refractor for his superb images? 🙂

I was surprised at how little focus adjustment was needed to nail the focus with the fine knob on the focuser, definitely an essential feature. Having it piggy backed on our 16" SCT that is mounted on a massive Ealing-Beck assymetric mount is a great help as well. 🙂

I'm happy to use whichever telescope is giving the best image on the night or object, many a time it's the SCT. 🙂

First proper planetary session with this telescope last night, first sessions were squandered on viewing Neowise 🙂, subsequent session ruined by wind turbine turbulence. Off to a poor start last night, despite Jupiter glaring down by 10.30, by the time I got to the observatory a thick haze had formed and Jupiter could barely be seen naked eye. Having made the effort I decided to give it another half hour but it deteriorated to the point where it took the 16" SCT to glimpse the moons. Just at the point where I was about to give up for the night Jupiter started to appear again dimly, no sign of Saturn at this time. As luck would have it conditions continued to improve and by midnight Jupiter was putting on a fine show. 150x-200x gave the best views, atmospheric dispersion was evident but not obtrusive, it will be interesting to see what difference my incoming ADC filter might make. There was too much detail for my ageing eyes to take in accurately but the views of belt detail, shadow transit, moon egress and the GRS were well seen. Saturn was now also visible and at last the Cassini Division could be seen from here!, I don't do well on Saturn and fail to see the subtle details that others do but the overall appearance was excellent and even stood 400x. Mars was still covered by cloud which was disappointing, after shutting everything down and driving home Mars suddenly appeared, I almost turned back but it was 1.30am by then and Mars will be around for some time. The session not only confirmed that the telescope is superb but that good planetary images can be achieved despite their low altitude. During the session I also compared a good C8 and the 16" SCT, they also gave good images but the refractor was the crisper. (Cue lots of "told you so") from the Fraccers! 🙂

Surely there must be a large potential business for retrieving space junk, a space age Steptoe? 🙂

I watched the whole total lunar eclipse sequence on a night flight back from Tenerife. Everyone else was asleep! 🙂

Pass! 🤣 Tick Tak, tick Tak.

Good result! 🙂

Is there not another screw between the four plate screws?, if so, that one needs tightening slightly.

Back to the topic and putting my pedant's hat on over my Beanie. The shift in focal plane in a SCT due to variation in the inter-mirror separation is around the change of distance times the amplification squared, hence 25x times in the case of a typical SCT. The effect of this is that due to thermal expansions and contractions the image plane moves much more than that of a Newtonian and a refractor. The reason one is always fiddling with the focuser on a SCT a lot of the time. 🙂

If the central stars present oval stars when defocused and the major axis of the ovals reverses inside and outside of focus that is astigmatism of the objective/s and also caused by cementing strain. If the effect is round only the edge of the view that is astigmatism caused by the inability of the eyepiece to cope with the fast focal ratio of the objectives, typically F4 or less. 🙂

Many focused star misshapes as opposed to collimation issues are caused by strains in the objectives due to the cementing of the lens components. Notably in the cheaper models. 🙂

A 8" SCT would be your best bet but it would have the seeing restrictions terrestrially as explained by Cosmic Geoff. I have, in the past provided 8" SCT's specifically for long range terrestrial use, it's quite doable provided that the atmosphere is suitably steady. We often, for fun, use our 16" terrestrially and can recognise people at a range of 10k. The air is usually fairly steady early morning and evening. You would ideally need an alt-azimuth mount or an equatorial that could be configured to alt-azimuth. Slow motions, either manual or powered would be essential. 🙂

I can compare, virtually side by side a 8" F10 SCT and a 8.5" F12.5 refractor. The refractor generally gives the better image. Both telescopes are subject to the seeing cell issue, the difference in the main is the light path through the system. The light in the SCT passes three times through the tube, the first pass hugging the tube wall, the second hugging the external surface of a radiating baffle and the third hugging its internal surface. By contrast, the light through the refractor is converging, getting ever further away from the tube wall as it approaches the eyepiece during its one and only pass. Which do you expect to have the steadier image on the average?. Place your bets! 🙂

I missed the one on the 21st. ☹️

Specially if an attempt has been made to use it for solar. 🙂

Hence the (?), could be either. Proms rarely elongate like that unless they lift off just one end. Interesting object, the Sun!. DSO imagers see stars only as points of light, we solar enthusiasts see a star in action with close up detail! 🙂