Peter Drew

I worry more about the MOT for my car. 🙂

I also have a magnetic tray. 🙂

My problem too! 🙂

I managed a couple of sessions with 35mm and 150mm apertures. Earlier rain showers had cooled and cleared the air so the seeing was quite good, the large aperture providing detailed closeups of the full disc features shown by the 35mm. 🙂

Precisely. The ellipse is still the most effective solution for manufacturing purposes. 🙂

Geometry suggests so. If you draw an axial centre line and converging beams from the primary, cutting through the light cone at 45* shows that the cone radius is greater below the centre line of the diagonal than that above the centre line. The "faster" the primary mirror is, the more this is exaggerated. 🙂

Superb animation, shows how much we miss observing visually in real time. 🙂

The light cone from the primary mirror gets larger as the cut off position of the secondary gets nearer to it. A secondary just large enough to accept the full aperture of the primary at the centre line of the secondary would be slightly oversize above the top half of the secondary and slightly undersize on the bottom half. Theoretically, a pear shaped secondary with wider portion towards the primary would correct this. Due to the mentioned difficulty of manufacturing such an awkward shape, secondaries are usually elliptical and slightly oversized, offsetting them also helps to address the issue. 🙂

The image shown by AstroKeith perfectly shows the issue. Although the radial offset of the focuser is relatively unimportant provided that the focuser is square to the tube, it's rather sloppy construction by the manufacturer as it means the buyer has to rotate the secondary to remedy it. ES is correct in their description of the secondary offset, the cone of light from the main mirror is wider at the lower half of the secondary than it is in the fop half. Ideally, a Newtonian secondary should be pear shaped but this would be more difficult to manufacture. 🙂

It's been hovering there most of today and is still there now at 18.40pm. 🙂

A polarising filter or a neutral density one to cut the brightness down can improve the contrast of surface details, specially filaments. The solar surface is generally bright enough to swamp the available contrast. 🙂

Difficult to tell colours from photos but in a good specimen of iron pyrite the internal structure usually looks a lot more golden. Hence the adage "fool's gold". 🙂

I made a small number of 8" F20 Schmidt-Cassegrains wih optics made by Jim Muirden. Jim hand figured the correctors by the ATM book 2 method that you mentioned. The secondary obstruction was no more than 25%. A user who contributed observations of Jupiter to the BAA planetary section was challenged as to how he could make such detailed observations with a 8" SCT assuming that it was a Celestron of that era. 🙂

Is this a current technique?, my understanding was that the SCT corrector plates were vacuum deformed against a master former and the exposed surface ground and polished flat. When released from the vacuum the plate assumed the correct profile for the corrector. 🙂

We have one that we use visually on a 16" SCT. It is very effective whilst the planets are low in declination, the AD can be completely dialled out. Not so sure as to its value on small apertures. 🙂

Although expensive, at least with the complete tube you get a new 5mm blocking filter as well. When the ITF in a PST fails, prime time for a mod to a larger aperture! 🙂

We were recently donated a telescope I made some 40 years ago. I made it for a textile millionaire from North Yorkshire. It is a 10" F5/F10 Newtonian with A quality optics by David Hinds. The dual focal ratio is derived by having two focusers in tandem carrying a quick change of secondary mirrors. The upper focus position has a fixed 2x Barlow providing the F10 fed via a small secondary to suit high resolution lunar and planetary observation. The lower focus position reveals a large secondary for wide field benefits. Both diagonal mirrors are mounted on pre collimated shafts and a detail when the units are interchanged ensures that each is collimated following the swap. Fine focusing is via the central knob, the platform carrying the two focus position is on spring loaded plungers. The mount is a Vixen Super Polaris which has a stiffening cage built round it ensuring adequate stability for visual use. The pier is an all aluminium fabrication. 🙂

10mm advantage over a Tal1 isn't going to be a significant upgrade as far as performance goes but, as they say, "every little helps". 🙂

Monk are not a household name in binoculars but I'm sure I've heard that they are of decent quality. The 2x zoom factor is on the sensible side of zoom ratios so the performance should be acceptable, particularly for daytime use. Most likely still have the restricted FOV characteristics of zooms. 🙂

I agree. 🙂

Wonderful capture of the event I posted earlier. I visually just caught the final stages, great to see the whole action! 🙂

Unfortunately no, I was at home using my "Luntonado". 🙂

As per title.

First thing we need to know is what type of telescope your Celestron is as this determines the best type of filter. 🙂

Bear in mind this is a Takahashi. "Something wrong" with the telescope is the least likely cause of any optical problems. 😀