Peter Drew

My take has been that for refractive optics, the more the surfaces, the more options the optician has for minimising aberrations, one of the more noticeable ones being chromatic aberration. Given optics of the same aperture, focal length, quality of figure and best glass for the purpose, a triplet should have the edge for imaging. The downside of the triplet, apart from the higher cost, is cool down time and sensitivity to alignments of the optical components. Visually, the difference is unlikely to mirror the cost difference. Speaking of mirrors, it's remarkable that a one surface optic can achieve most of what a sophisticated multi element refracting objective can do. 🙂

Three of our members, to my knowledge, hold PPL's. 🙂

My two 12" Dall-Kirkhams and 10" Dall-Kirkham-Dall are self built, the DK's contain no correctors, the DKD has an erector transfer system. Looks like visual use is, thankfully, much more tolerant of aberrations than imaging. 😀

Whilst acknowledging the superiority of the Stevik-Paul system, I'm surprised that the plots look so bad for the Newtonian and the Dall-Kirkham. I have a 12" F8.5 Newt and 12" F20 D-K and don't notice coma over a 0.5 degree field visually. 🤔

Two wishes left! 😀

Justin Quinnell <www.pinholephotography.org> is another enthusiast. 😀

With spacings being critical I would expect that focal lengths of imaging surfaces to be equally precise. 🤔

It would have been pre laser collimation. 😀

Bit early to say yet as it's still 2019! But looking ahead:- Buying - nothing. Selling - maybe my place in Tenerife as I don't seem to have the opportunity to use it enough to be cost effective. Ambition - get the remote scope operational. 😀

Fog cleared at last so had a look at the "pylon". A little faint and awful seeing but at least the Sun is in view! 😎

GONG shows a "pylon" on the Sun's limb today. 🙂

I can get the Sun all day. If it's clear. ☁️

So many "cans of worms" in AP it's surprising that it doesn't come under Biology. 😄

Are you sure that they are optically misaligned? They may be physically out but the optical centres may be coincident. 🙂

Be careful not to confuse etalons and blocking filters. 🙂

The problem with theory is that it's relatively fixed whereas practice is generally not. Some of us are getting on a bit now and despite experience the visual acuity starts to drop. I now find I need more aperture and magnification than I used to use to be able to see the same as I did in the long past. It also depends a lot on the nature of the object, a line can easily be seen although a section length of the line equal to its width would be invisible. This is how the Cassini Division can be resolved with telescopes whose apertures are theoretically not large enough. 🙂

Just seeing the Sun at all would be a good start! 😎

I think this might be the lunar version of nacreous clouds, normally associated with solar apparition. 😀

Certainly more likely that it will yet again be clear than it would be from here! Snow on the ground at present. 😀

The PST etalon that I use on my 150mm mod gave better views than those shown in the video when in its original form. It was selected from several PST's that passed through my hands. 🙂

I seem to have quite a collection of Vixen SP and GP mounts as well as a Sphinx. Telescopes are a 102mm F10 achro and a 102mm F9 Flourite. Sorry no pics but they are the same as others on this thread. 😀

We seem to host an "Astronomer Badge" group at least once a week, amazing how many groups there are! One item on the required list is constellation recognition, as the sky is seldom clear when you need it we have set of cardboard tubes, closed off at one end with a thin metal cap that has the obvious pattern of a constellation pierced through it. When pointed at an illuminated screen the candidate sees the pattern and tries to identify it. The tubes are numbered against a correct list and a mark indicates the correct orientation. Practical and popular. 🙂

It could herald a resurgence of ATM. 😀

It appears to be a "Dark Star" brand Dobsonian. Keith, the original proprietor used whatever mirrors were available or specified by the customer. Some were very good so you could be lucky. Worth the purchase price plus the recoating if necessary. 🙂

Moon filter still attached to eyepiece? Has been known! Welcome to SGL. 😀