Peter Drew

Unless someone has measured one of these "undersized" Mak mirrors I suspect that they are the size as specified from the manufacturer. The undersize issue is due to the fact that light passing through the corrector diverges on its way to the primary mirror, so to achieve the full entrance aperture the primary mirror needs to be oversize.

Despite the kind accolade I think I would draw a blank on this one (pun intended). Since I "retired" in 2006 all the suppliers I was familiar with seem to be no longer in business. ☹️

We do this every Saturday night. Good advice about the chair position, we used to do this but now use a short step mount that has a large hoop at the top for the kids to hold on to. Fortunately we have such a large mount for our main outreach telescope that a kid or adult grabs the eyepiece nothing moves. Another issue that can be addressed is eyepiece focusing, adults with all manner of eyesight anomalies use the telescope and we try to encourage them to operate the focuser for the best result, kids seem to have enough accommodation to cope. 🙂

Could be a SuperC8, these were in black livery. Apart from coatings type, all tube assemblies are essentially the same for non Edge models. Earlier ones had Starbright coatings and later ones XLT coatings. Cloudy Nights has a serial number registration so you might be able to check it against this. 🙂

It would always be helpful if the position of the focuser is indicated relative to the secondary mirror in the posted images, this would show whether the offset shadow is correctly orientated. 🙂

You could try a more aggressive Barlow like a 3x or 4x, this would give you more power but as already mentioned it will be more than conditions will allow. 🙂

A pair of rings fitted to a dovetail might allow you to push the refractor tube through enough to give you clearance. The SE mount can carry the 8" SCT so a little imbalance may not matter too much whilst zenith observing. If all else fails, unless you are at the N Pole, everything gets lower in due course. 🙂

A top class 6" F8 Newtonian should give a 4" APO a good run for its money let alone a 4" F10 achromat. The 6" F8 Newtonian will have an advantage in light grasp and resolution, the secondary obstruction would be too small to be a contrast issue. Despite this, preference might be between the look and handling of the types, whether one can see past CA at high powers or whether one has nightmares about collimation. Apples and apples would be a no brainer. I would prefer the Newtonian. 🙂

Many years ago I spotted an antique telescope in the window of a "junk" shop. It was a 3" all brass refractor about f14 mounted on a pillar and claw stand. The price tag was £250, I had always wanted one of these so thought if I could get it for £200 I would buy it. I went in and examined it, the engraving confirmed that it was by Davis of Cheltenham which dated it to the mid 1800's. The focuser was jammed and the objective had a small scuff mark at its centre and the whole thing needed a good clean. I told them that I was interested and being a telescope maker I could probably sort the problems out, to which they said that being in the trade I could have it for £150. SOLD! It didn't take much effort to free the focuser and the small scuff mark was due to the objective lenses being assembled incorrectly at some point and the centres had rubbed together. Once sorted the telescope gives very good views with hardly any CA terrestrially, I have to confess that I've never got round to trying it astronomically, the mount isn't very encouraging. Looks nice as a display piece which is what I wanted. 🙂

What projects do you have in mind? 🙂

Turning the knob clockwise should bring the mirror nearer to the back plate. 🙂

It can take as much as 20 turns to get the telescope to focus. 🙂

Have you tried turning the knob on the rear of the telescope, this is the focuser. 🙂

Newton rings are a very sensitive indication of how well the lens is held and centred. It's one of the first things I look for when assessing one, I would be very pleased with one like yours. 🙂

That looks like it's lifting off, it was lying along the limb earlier today. 🙂

These Taks are such a worry to their owners! My strong advice is to leave well alone. If the telescope gives perfect star images and performance, that's what you pay for. 🙂

I also think it is Newton rings, the mating surfaces have to be quite close to show them and it's possible that thermal equilibrium can make them more or less easy to see. Try looking at the objective under a monochromatic source like a strip light, this makes the rings easier to see. I would be more concerned if the rings were significantly off centre or distorted in shape. 🙂

Not looking for anything at the moment so don't know yet. 🙂

During a TV interview I was asked what did I do in astronomy. I replied that I made keys. The keys that help unlock the secrets of the Universe. 🙂

I like the AZ3, I have two. I wouldn't buy an alt-az mount that didn't have manual slow motions and at their price the AZ3 is a bargain. The out of balance issue is relatively easy to DIY address. I use an AZ3 exclusively for solar observations with small Ha telescopes, an easy method I have found to cure the out of balance problem is to wrap one end of a bungee strap round the front of the OTA and the other end to somewhere on the tripod. If you use enough tension on the strap to hold the telescope horizontal then as the telescope raises so does the tension on the bungee. This leaves the system in equilibrium and nicely controlled by the slow motions. 🙂

Stargrazer? 🙂

The optics are roughly F8 and are usually quite good if well collimated and using decent eyepieces rather than those supplied. The mounts are what you get at the price point. Worth a punt at £40 - £60. 🙂

It's difficult to see any option other than to use it for a telescope. One main difficulty would be acquiring a tube for it, seamless aluminium tubing is rare in less than 3mm wall thickness in suitable diameters so pretty heavy, thinner used to be available from farming suppliers as irrigation tubing which was seam welded. I built my 8.5" refractor by joining together two 8" reflector tubes, two 6" f8 tubes could do the same. The lens could be tested by mounting it on one end of a wood plank and an eyepiece on the other end and focusing on an artificial star, if your colleague made good mirrors he should have had little difficulty in making a decent achromat. Lack of coatings is no big deal, preferable but not essential. 🙂

What did the duck taste like? 🙂

We could well do the same, apart from a couple of good star and lunar atlases the rest are taking up valuable space. We also have a lot of telescopes in the same situation. 🙂