andrew s

I think that's Weetwood but tasty just the same. I like a pint of "cat". Good talk and discussion to night. Regards Andrew

Monday and Friday for the days of pain. However, it's worth it. Getting fitter and lighter. Regards Andrew

Sorry, dinner with white wine, chicken, Jersey Royals, young carrots etc. Regards Andrew

All set, ordered tea from SWMBO for 6:30 so as to ready for 7:00 ?! Regards Andrew

Have you tried it yet? With my ONAG the transmitted beam definitely suffers from astigmatism does your? Regards Andrew

I think we are in to aesthetics and personal preference. A lot depends on screen / image size and viewing distance. Where should you view an impressionist painting from. Close up to see the dots or afar to see the whole merge in to ... Regards Andrew

A Tak for every celestial body. Regards Andrew

@vlaiv that looks conclusive. Thanks Andrew

Visual acuity varies considerably and spotting subtle differences is strongly impacted by training. I don't know if these differences can be spotted or not, but if to identical scale, maybe subtracting them and looking at the residual might be informative. Regards Andrew

You will vignette the field if you place the baffles like that. You needed to draw two cones to the extreem edges of the field of view not the centre. Regards Andrew PS the book shows the same idea. If you measure an eyepiece field stop to get the field of view use the lowest power, longest focal length you have.

@ollypenrice the only addition I would make to what you say above is the with modern, low read noise, CMOS cameras over sampling is not an issue. Regards Andrew

Google "Setting an equatorial head Baryebrook Observatory " that seems to be what you need. Regards Andrew

Cone error is when the telescope is not exactly parallel to the dec axis. So if your aligned on a star close to the meridian on one side a meridian flip will not centre the star again. By system I intended scope and mount but the picture answers the question. Regards Andrew

You don't say what system you have but cone error will put you out. Regards Andrew

Basically, you need to balance about 3 perpendicular axes. Once it is balanced in 3 d it will stay balanced in any orientation ( assuming no cable drag). With the dec axis horizontal you need to balance 1) about the ra axis 2) balance about the dec axis with the scope horizontal and 3) balance about the dec axis with the scope vertical. Regards Andrew

It will still be in balance. Regards Andrew

Seeing and guiding accuracy are not the same thing. Your guiding needs to be better than the seeing otherwise you will be guiding limited not seeing limited. You guiding could be very good but still have poor seeing. Yes poor seeing can if you are not careful, reduce your guiding accuracy but only if badly set up. Regards Andrew

Yes, seeing dominates if it is larger than the diffraction of the lens. The diffraction limit is not based on focal length but a reducer will have an effect. It may flatten the field making things better or add aberration making it worse.! Regards Andrew

This is well worth repeating. Regards Andrew

The diffraction limit it is just under 1 arc sec for a 120mm objective and about 1.45 for 80mm. Regards Andrew PS aperture determines theoretical diffraction limit. Focal length the image scale.

The same is of course true for the optics. Very few locations and or nights can deliver diffraction limited seeing for a 4 or 5" scope. Regards Andrew

It is easy to forget the transformation brought about by the introduction of mass produced SCTs. They opened up astronomy to many with a compact instrument that could easily be set up and transported. Regards Andrew

Surely your analysis is better than a range of opinions. Provided you sample was fair and reasonably comprehensive why not go with the result? Yes to more data but beware biasing the result. Regards Andrew

Rendering is a much neglected or misunderstood issue @vlaiv. Your point about sample data is well made. Regards Andrew

If you want to get a real understanding of mounts and their control then read "Telescope Control" by Trueblood and Genet. Some aspects are obviously dated but the core issues remain the same and you will see that direct drive, shaft encoders and the like are not new just cheaper now. It covers everything you could imagine from shaft flexing, via control strategies and drive types to pointing models etc. Regards Andrew I lent my copy out and never got it back but got a second it's so good, £20 on Amazon second hand.