Another James Chapman Telescope

Many years ago I found a James Chapman telescope – made in St Catherine’s, London, in the 1790s. That was a real beauty, with an octagonal wooden barrel, but small, about 23” long: there is a description here on the telescopecollector.co.uk website.

So after several years of watching ebay auction offers, to see another by James Chapman was really exciting. But this one appeared to be something totally different, a design more akin to mid Victorian naval scopes, big diameter, long wooden barrel, single draw. The engraving was just the same, and still quoting ‘James’ as ‘Jas’, and still the address is St Catherine’s. But the total length was 40 inches, and the diameter 2.5”!

(The images above are from the Seller’s Ebay page)

Whilst there was a drawback – the objective lens was cracked, apparently in several places – it was still worth buying out of interest, just to look at it.

Inspection

The brass was black in places, with a thick cake of corrosion externally on the objective and eyepiece areas. The main, single draw was OK, and later polished up well, with little damage. Where this joined the brass fitting to the main barrel, the screw threads seemed to have sticky tape round them, which cracked off – with no nad effects. Inside the big lens cartridges were both present – inevitably the first eyepiece end cartridge had become unscrewed inside the barrel, so the scope was not working. The second cartridge is suspended on the end of a long tube from the far end of the draw, (as an alternative to using a split draw, which was more common then). The threads here had what seemed to have been Ptfe tape wrapped round, long ago, and the tape had decomposed into dust in places: the lenses needed a clean, and it screwed back together fairly well . Both cartridges are large diameter: the draw itself is 50mm external diameter.

Whilst no external damage was evident to the objective holder, the lens assembly there would not unscrew. There was no way to inspect or clean the inner surface of the objective lens, and while there were no screws evident holding the brass assembly onto the wooden barrel, it was fixed in place firmly with some form of glue.

Re-assembling everything and trying it out on an adjacent hill, the view was surprisingly good: not clear, because of dirt on the inside of the objective lens. Plus maybe some sunshine reflections from the cracks in the glass, but at least there was only one image, rather than multiples!

What to do next?

This looks like it is going to be a slowly developing story!

The first task as always is to clean all the lenses – at least the ones you can. Then clean the brass bits. All except the objective assembly were achieved, but not without a lot of scrubbing. 

Then the major decision was how to get the objective off, and whether to sand the barrel down and re-polish that! In that the barrel was at least six inches longer than needed, and the draw had plenty of spare extension room, after a few days thought, the saw came out and the objective was cut off the end of the barrel. This is going to mean the barrel is about 1cm shorter than before, once a shoulder is filed on the end and the brass of the objective is cleaned out, and re-attached with screws.

Removal of the objective assembly!

Inside the far end of the barrel, recessed by about 2.5 inches, there is a metal aperture of ID about 32mm, removing the outer rays from the light coming through the objective. Maybe this is what helps the telescope ignore the broken mess at one side of this lens. It will probably be a good idea to paint out or shield the edges of the lens with another aperture at the lens itself.

The lens assembly was cleaned out from the remaining wood, which was glued down solidly, but eventually peeled out. Four screw holes are evident in the assembly rim, to take such screws. At the other end of the barrel, the grub screws in the brass fitting for the drawtube do not want to move, and the slotted heads are worn away as well, so it looks like that assembly will not come off the barrel.

With the objective lens removed, the barrel was sanded down by hand to be able to re-polish the outer surface.

The picture shows the barrel during sanding. Eventually it was clean, and repolished with several layers of French polish. The external brass surface of the objective lens holder was sanded with wet fine sandpaper, then polished by hand and on a polishing wheel, which eventually made it look like brass again. While doing this the cracks in the objective lenses were covered with Blu-Tak, to prevent anything penetrating between the lenses. Then the assembly was refitted, with hopefully removable screws, so that the internal face of the lens could later be cleaned. Internally a black card aperture was push mounted behind the glass, to shield the broken edges even more effectively.

The following pictures show the final assembled telescope, looking a lot better!

Replaced objective assembly, with polished brass and new screws
Objective lens, with cracks, but working!

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