Peter Drew

"Remember me" ? 🙂

If there is no glass in the component that I suggested removing then the small hole is what defines the field stop of a system of lenses nearer the prime objective. There would then be another tube screwed to the threaded portion that also contains a set of lenses, this is what creates the image erection, the furthest end of this last tube will include a female thread to accept a RAS fit eyepiece. It appears that this tube and an eyepiece may be missing. 🙂

Unscrew the final piece that has the external thread on it and see if there is any glass in it. 🙂

Be prepared to pull the drawtube out a long way! Why wait until tonight, much easier to try it out in daylight. 🙂

I think this may well be a terrestrial version There is no provision for a finder and the male threading on the rearmost end will not accept an eyepiece but possibly a camera. its also possible that the last component is actually an eyepiece. I have a few of around that vintage and they have a very small exit aperture that defines the exit pupil to improve terrestrial contrast. Finally there could be yet another tube to screw on to the end thread, terrestrial erecting systems of the period had a number of translation lenses that gave a lot of back focus. Have you tried a look through it? 🙂

As mentioned by others, the pressure pads under the locking screws would be my first port of call as they are likely to be stuck. The bearings on the old EQ5 are plain metal and the grease may have hardened over time. If stripped and cleaned, re-grease with something like Superlube, not lithium grease which is too thin. 🙂

Yes, you can use a 50mm aperture refractor or larger. The larger refractor will probably be a better telescope but it will still operate only as a 50mm. 🙂

Are you sure that it is the blocking filter that needs replacing? It's usually the ITF filter, the one that is fitted before the blocking filter that fails and needs replacing. 🙂

Could cable management have anything to do with the problem? 🙂

Referring back to the original photo there is probably another clutch between the motor and the worm shaft, this is to protect the motor should something restrict the rotation of the wormwheel. It is the bushing next to the motor output. There are two rows of grub screws forming the connection, one set possibly fixed to the motor shaft and the other connecting the worm shaft with some facility for slippage in the event of a problem. If this is the case it is another area for unwanted drive variation. 🙂

It probably needs at least some grease as the clutch has to be able to slip in the event of something impeding the rotation. The "trick" is to adjust the slippage torque to avoid slippage in normal use but also to avoid locking up. Try tightening the nut a small amount. 🙂

If the brass worm is turning then the wormwheel must also be turning which points to clutch slip as already diagnosed. 🙂

Give it a good sanding down and then a coat of silver-grey Hammerite. Available as a spray can 🙂

I'm afraid this is indicative of a de-contacted etalon, the etalon plates are held together by molecular fusion and cannot easily be re-contacted other than by the manufacturer. ☹️

I was given one of these to "play" with some years ago, it is a "Bird-Jones" type. It actually looked quite well made and finished but the performance was pretty sub par. After faffing about with the collimation for ages I managed to get a fairly decent image out of it, good enough to please a complete beginner but not worth spending any extra money on it. Quite a bargain for free. 🙂

I fitted an AM5 to the top of a "Todmorden" pier by spacing with a ring cut from a 5" diameter 1/4" wall thickness tube between the bottom of the mount and a plate on top of the pier. The 3/8 screwed rod pulling it all together would take some shifting to accidentally rotate the 5" ring. 😀

Learning to collimate at F4 will be the least of your AP problems. 🙂

Yes, that will teach us to not scoff at Astrology. 🙃

Google Mel Bartels for further insight. 🙂

To make any headway with this proposition you would have to consider an ultra-lightweight primary mirror. 🙂

Very difficult to assess a repair potential without having the tripod to hand. High grade aluminium doesn't usually snap like that so it's probably the usual "pot" metal casting.

"Super Zenith's" are not a premium binocular and are unlikely to have a sophisticated collimation facility and probably not an economic professional repair. To continue a DIY attempt, first undo the cross head screw from the centre of the eyepiece bridge then withdraw the complete assembly including the eyepieces. Next, remove the rear covers of the prism covers. Then replace the eyepiece assembly without the prism covers, this will give you access to any prism adjustment whilst being able to see the effect of any adjustment. Prisms are usually held in place by metal straps, loosening these a little allows the prism to be nudged into better alignment. Beware these straps are spring loaded and if relieved too far can spring off never to be seen again! 🙂

There are a couple of simple things you can try first. The barrels that contain the objectives can usually be unscrewed, if so swap them over as this usually makes things better or worse. If better, leave them swapped, next, slightly unscrew one of the barrels and note whether the improvement continues, if not, screw it up again and try the same on the other one. If all this fails you will have to open them up and examine the setting of the prisms. 🙂

Be aware of he difference between a 1/6 wave mirror surface and a 1/6 wavefront at the eyepiece. A 1/6 wave mirror will present at best a 1'3 wavefront image at the eyepiece. On this basis, a 1/8 wave mirror would be preferable to achieve the 1'4 wavefront at the eyepiece to satisfy the Rayleigh criterion for a diffraction limited Newtonian telescope. 🙂

Can't see the chips! 🙂