Peter Drew

I did the opposite out of sentimentality. Despite already having 5 "modern" SCT's I bought a 1980's orange C8 simply because I had always wanted one! 🙂

The azimuth bearing system should work fine, I use a similar approach on my 30" Dobsonian. 🙂

I think that the corrector, being a correcting rather than image forming component works in its favour as it doesn't have a focus. 🙂

I actually met and shook hands with the gentleman who made the UK Schmidt camera corrector. Sadly nothing rubbed off! 😆

The main potential cause of chromatic effects in Maksutovs and Schmidt-Cassegrain telescopes is mechanical "wedge" across the optical diameter of the corrector elements. If the wedge is severe, the component operates as an objective prism and introduces false colour.

I have been a Ha solar observer for over 20 years. I began with a Coronado Helios1 70mm telescope, bought used for £2000, it was the one originally used for Coronado's publicity photos. When the PST arrived on the scene I was amazed to find that a good one gave very similar performance at the then price of £499. I purchased a used one and subsequently another to make a PST binoscope which gave wonderful results. The cost of larger apertures then, as now, gave me no option but to make my own so I joined the early pioneers of PST modding and have made more than 20 in the 100 mm- 150 mm range. My current PST (Peter's Solar Telescope) is a 150mm F10 optimised for high resolution, high magnification binoviewing. I have no interest in imaging or full disc viewing, I have a 60mm for the latter if needed. I have no extra input to the X versus Y "debate", I have seen excellent and disappointing versions of all makes. 🙂

I think the largest currently available external etalons are Solarscope 100mm, lunt 100mm and Coronado 90mm. 🙂

They appear to be early craters that have been inundated by lava at some stage leaving just the tops of the crater rims showing, Nearby classic craters occurred later than that event. 🙂

Bespoke Ha solar telescopes such as those of Lunt, Coronado and Daystar are inherently safe. Each contains several specialised components, if either one or all fails then the telescope just doesn't work. White light solar observing does have a degree of potential danger. Usual safeguard is to use a front mounted filter or a rear mounted Herschell wedge, both of these are safe in good condition and used properly but both rely on effectively one layer of protection. Public involvement solar observing requires close supervision at all times by competent experienced observers. 🙂

Perfectly understandable, particularly in this day and age. Best solution would be to try and get a friend to accompany you. Good luck! 🙂

A Lunt solar telescope is a pretty safe buy, good customer support. Double stacking will enhance the photographic aspect, a double stack 60mm would probably give you more satisfaction than a single stack 80, still pricey though. As far as life span is concerned, etalons last well as long as you don't drop them, blocking filters are also good long term. The Lunt ITF, (and other makes), are known to fail prematurely, the Lunt units are usually replaced FOC either by Lunt or the original vendor. I've always bought solar gear used but with a good track record. 😆

I was referring to a 8" and 12" that I made. 🙂

An interesting design, the Schmidt-Newtonian, a bit of a "Cinderella" instrument. I made, possibly the earliest SN in the early 1970's, I had been making some 8" F20 Schmidt-Cassegrains with optics by James Muirden and Jim thought it worth trying a Schmidt-Newtonian. We made a 4.25" F4 and gave/sold (?) it to noted UK amateur Colin Henshaw who used it mainly overseas. I seem to remember an 8" and 12" version. 🙂

Same here. Brilliant cloudless sunny day. Having already seen the promising solar image on GONG I fired up my main solar telescope for the first time in ages and had a look. Seeing somewhat unsteady but a good assortment of proms, plages and filaments. 😀

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. 🙂