Peter Drew

I also have one of the rare six Beloptic triband ERF's that I use on my 150mm solar telescope. Works well. 🙂

Good as it may be, I wouldn't buy an alt-az mount that didn't have at least manual slow motions. 🙂

"Clocking" seems to be an ultra fine tuning effect, just a few degrees of rotation can produce a considerable improvement in performance. A rotation adaptor makes this easier but not necessary to "have a go". 🙂

Possibly a geostationary satellite. 🙂

I suspect something is amiss with the secondary alignment as the image seems to show gross collimation error. A screw protruding into the light path would only show up as an indentation to the defocused star image. Check that the secondary collimation screws are all positively attached to the mirror holder. If adjusting them provides no difference it could be that the secondary has detached partially from its holder. Do these checks with the tube horizontal, just in case! 😱

I would opt for the SW 150L, it will have better resolution and wider spread of magnification potential. Seeing conditions play quite a significant impact on the magnification that can be used but when they are good, the 150L will also shine. 🙂

Tilt of the complete objective. 🙂

The images in the bottom row are indication of tilt, usually. Not sure of the Cheshire image to the right, looks like gross decentring of the individual lens components which is unlikely. If the cell does not have a facility for collimating it I would suggest first rotating the lens pair to see if the deformation turns with it. If it does, remove the lens, mark the original orientation of the two components relative to each other then slightly separate them and turn the front one relative to the rear. Replace the lens complete in its cell and retest. 🙂

Hello Eric, yes I remember it well. Good to know that you are still "up and doing". Cheers. Peter. 🙂

I can't specifically directly answer the optical characteristics as these will vary being that the optical sets will be unique to each telescope. I can confirm that amplifying additional optics will give increasing back focus dimensions and focal reducing elements, the reverse. As a rule of thumb, the increase of back focus due to an inter mirror change is the amount of change x the amplification factor squared and the amplification factor in your case will be x4. All Cassegrain types are susceptible to inter mirror variation due to varying temperature, one of the reasons one seems to always be fiddling with the focuser on this design so any mechanical modifications that can be included to mitigate this are worthwhile. When making Schmidt cameras, the most sensitive of Cassegrains, I used to separate the optics on Invar rods! 🙂

For housing Dobsonians over 14" aperture I use fixed buildings and the telescope rolls out on rails. 🙂

I've had pleasing solar views at 80x using a C8 with a full aperture white light filter. Just pick a good day/time of day. 🙂

Probably someone has but not worth doing seriously, you would lose the benefits normally obtained by binoviewing.

I think most amateur available mirrors are overcoated with silicon dioxide as a protection for the softer aluminium. Mirrors, like star diagonals, can be dielectrically overcoated for greater protection but the process is very expensive. 🙂

We get several requests each year for recipients of stars etc to help them with the location and the possibility of visiting to have a look at them through one of our telescopes. Almost invariably, the star is far too dim or badly placed for little to no chance of a view. I have often asked whether they had any input with the choice as the high magnitude numbers suggest inexperienced selection, apparently not. We were able, on one occasion to show someone their patch of land on the Moon thanks to the services of Quickmap which zoomed to show that it even had its own small crater. I know that many astronomical groups, including our own, to a degree frown on these star naming sites but it does give pleasure or condolence depending on the circumstances, I just wish that, as mentioned by the OP that the vendors would pay a little more attention to the reality.

Another vote for a zoom eyepiece for single unit use. I use binoviewers these days though. 🙂

Pity about the distance to Oz. I could fix it in less than 15 minutes if down your street. I would just pop it in the lathe, drill out the remaining bit of thread, re-tap it with the correct thread and screw in a new length with some threadlock. Surely someone close by in Oz could do this for you? 🙂

Open a bag of salt, take a large pinch ...........etc,etc. 😀

I'd rather have an achromatic doublet lens made by Skywatcher than a Flourite doublet lens made by me! It's not always just about the glass. 🙂

By contrast, I have a 4" Flourite and a 5" triplet that I've used probably no more than twice in the last 5 years. I also have a 150ED that gets used frequently as it's mounted on a larger telescope as a finder/general purpose telescope. I don't need to G & G and I rarely take a telescope anywhere else, usually once a year to Kelling. 🙂

@Goldenmole. Your telescope has an erecting prism diagonal, the prism will show a bar across the middle when used at night, if you plan to replace it make sure you get a standard 90 degree star diagonal. 🙂

Some years ago now Nigella, life still goes on though. 🙂

Of the many PST etalons that I have used, all were good enough, quite good and a couple were exceptional. One of the latter couple was stolen along with the modded 6" refractor and its full aperture ERF, the other is in my 6" replacement. 🙂

Just been reading a thought provoking thread on another forum about the distance of the Andromeda Galaxy. The OP asked, being as the galaxy is accepted as appearing as it was 2.5 million years ago, how much nearer to us is it now. It appears that at its speed is 110 kilometres/sec it will be 917 light years nearer, in other words not a noticeable amount. It was then said that if scaled down to the galaxy being equivalent to a human being the distance would be 1/2" in 2.5 million years and the distance to the galaxy about 7.5ft. A further thought was that due to its supposed diameter of 200,000 light years, light observed from its nearest edge reaches us 200,000 years sooner than light from its furthest edge. Something to think about when you next observe it. 🤔

I think it's a real but frustrating issue that some people just don't get on with binocular vision, be it binoculars or binoviewers. You have already tried the obvious experiment, adjusting the IPD as this is often the problem. I can't think of any further advice unfortunately. ☹️