Peter Drew

And mine! Diameter. 🙂

To answer the second part of the question, the intensity of the Airy disc governs the contrast, refractors, with no central obstruction have the most intense discs. Central obstructions rob the intensity of the Airy disc and deposits it into the diffraction rings lowering the intensity and of course the contrast. The larger the obstruction as a percentage of the aperture the lower the contrast. It's generally accepted that 20% or less obstruction causes no noticeable affect. 🙂

"Play" never started here. Typical, whenever it's clear the Sun is almost featureless, yet active when raining. I'm beginning to think there is a correlation!

You must have a good one, I've had some where the parts kept coming loose and had to be re-glued. 🙂

A long time since I took one apart but I seem to remember (?) that they dont pull apart, rather the lower leg passes upwards through the upper leg once you've removed the "feet". As has been stated, the feet are glued on. 🙂

I also used to have a bench collimator when I was in business, that's why I raised the query. Mine was a small ball bearing illuminated by a collimated light source and the resultant artificial star viewed at its image in a 12" F6 paraboloid. 🙂

You can use extension adaptors as long as you avoid "sag". I wonder whether having the artificial star next to the telescope and a mirror at the furthest distance you can place it would give you double the distance, the optical quality of the mirror shouldn't be an issue as you are only checking collimation. (Haven't thought this through yet!) 🙂

No real need for anything sophisticated as long as you can reach focus. There is a big difference between checking collimation and optical quality. Using a shorter than ideal distance just affects the apparent spherical aberration. Not suitable for binoculars though due to parallax. 🙂

Thanks for the view, raining all day here so far. ☹️

@Solar B. I'm sure you are right Brian, I've never tried fitting a binoviewer to a PST, my comment was based on larger aperture PST mods. 🙂

My binoviewers are attached to the PST eyepiece receptacle with just the single nylon locking screw but I'm fitting it to a Coronado diagonal not the unit provided on the standard PST. The binoviewer is always between vertical and horizontal so cant fall out and benefits from being able to smoothly twist it to suit the eye angle. The important bit is to make sure that the nosepiece of the diagonal is firm enough to hold the weight of the binoviewer plus eyepieces, I have 4 locking screws like a 4 jaw chuck to achieve this. 🙂

In archery and rifle target shooting, near misses don't count. Neither do the near misses of NEO's. So we now have the means to detect small but effective objects within a few hours of their impact, doesn't give much time for determining the impact site or organising any form of evacuation. 🙂

If a complete extinction body is to hit us in my lifetime I want to know the when and where so that I can go and watch its incoming. 🙂

The 1.25". 🙂

I've found that a SW 2x Barlow, just the lens in its black cell, screwed on to the nosepiece of the binoviewer allows focus. There is an increase of image scale of course but the image is bright enough and seems to increase the apparent field of the original 5mm blocking filter to that of a 15mm blocking filter without the Barlow. This has the benefit of a high magnification image without the appearance of looking through a straw. I use a Barlow and 5mm blocking filter on my 150mm F10 PST mod with excellent results. 🙂

Thanks for the photos. I would have expected to have seen the scuff marks more distributed across the mating faces, it looks as though the head is bearing on a small land surrounding the shaft aperture. 🤔

I would still prefer to buy a PST due to the potential of upgrading to a much larger PST mod. 🙂

The mount should be a tight fit to the tripod top with just the central shaft done up hand tight, no azimuth screws fitted or spreader plate attached. If its still loose or even rocking then something is stopping the faces from sitting down properly. 🙂

I agree that a single unit with a binoviewer is a better option than a Ha binocular in larger sizes, specially on the grounds of cost!. The slight light loss incurred by binoviewers is of little consequence for solar viewing. 🙂

I think it's only possible to make a binocular from the PST using dedicated units, it should be possible using front etalon and blocking filter sets as the spacings are not confined. I built a PST binocular years ago, the performance was excellent, I eventually went to buy a used SM60 and took the binocular for a comparison, even the seller had to admit that the binocular gave the better view. 😀

One for sale on A,B & S today. 🙂

Have you asked your neighbours if they can hear it and if so does it bother them? 🙂

I managed to effect a repair on the broken Monarchs. I used the washer that sits under the bevelled cap with the degree engravings as a splint and bonded the lot together. So far it has held well enough to make the binocular usable again. They won't get much use as I have better options but I look forward to a few nostalgic observations. 🙂

If I didn't have a lathe I would use a sufficient length of tube to go between the base of the mount and the top of the pier and then bolt through as in plan a) I wouldn't recommend plan b) in this instance. I think the flap wheel would take some time! 🙂

A 12" Dob would be better for nebulae and galaxies than any refractor any of us are likely to own. Aperture is important for this class of objects. 🙂