I'm a retired mechanical engineer. The last time I surveyed was in about 1972-1973 when, as a school project, another kid and I tried to survey the ~200 acre property of our high school in Vermont, after a bit of training by a state surveyor. The survey didn't close, but we learned a lot.
I thought it would be fun to buy a transit and relive that bit of my high school time. I just bought a vintage David White transit (see nameplate) off of eBay. It's mostly operable, but the eyepiece seems to be fogged up from behind. I started to carefully disassemble it, but got cold feet.
Does anyone have any tips on disassembly of a vintage transit, or even a source for a parts diagram? Any general advice, such as whether I'm being an idiot to try to restore an old instrument like this?
If you could post a zoomed out picture of the entire instrument that might help us with this.
I have never taken an older telescope on an instrument apart but I wouldn't be surprised to find some fine brass threads holding the lenses in place.
Licensed Land Surveyor
Finger Lakes Region, Upstate New York
Here are four photos - one of the whole transit, a closeup of the eyepiece end, one with a small screwdriver pointing to a single small brass screw, and one with the screwdriver pointing to one of four black screws around the circumference of the cylinder. I took off the single brass screw and gently tried without success to see if I could get the eyepiece loose. After removing three of the four black screws and starting on the fourth, I could tell there was something inside they are attached to that was moveable, NOT rigidly attached to the brass eyepiece cylinder. That's where I got cold feet - I didn't want whatever that piece is to start moving around inside so that I couldn't get it back together. I was wondering if it is part of the internal optics.
I appreciate the offer to help.
Hey Sam-
I'm also a retired engineer (Materials) with a eye towards recreational surveying. Just a guess here as I've no experience with David White transits, but the presence of 4 circumferential screws would lead me to wonder if the screws center (ala a four jaw chuck) an optical element. A reticle springs to mind. A more dire situation may be that the loose piece may be an cemented optical element which has come loose which may explain the cloudiness.
Cool looking transit- good luck with it!
Thanks, Anvil. To be clear, I'm not sure anything was loose that isn't supposed to be when I started to remove the 4th screw. But I guess it could be. I've read elsewhere about optics where two lenses are glued together, I think maybe to correct for chromatic aberration. As you suggest might be the case, with time the glue degrades and the pieces separate.
The brass rim of the eyepiece is serrated, suggesting it's meant to be unscrewed. Don't know how hard I dare to twist to loosen it.
Shooting from the hip without proper study of your pictures.
Four screws near the eyepiece end could be holding the frame of the reticle (cross hairs). Those would be very fine spider web strands. Tightening the screws too much could stretch and break them. The screws would be loosened to rotate the hairs into vertical/horizontal alignment and then top vs bottom and left vs right screws would be loosened/tightened to center them.
Bill93,
I was thinking that, too. But the two capstan screws visible farther from the eyepiece look more
like the reticle adjustment, to me anyway.
Though I would expect to see 4 capstan screws for that.
I don't think the four screws are for adjusting a reticle. They are tightened all the way down to the cast body of the transit, as opposed to adjustment screws that would have some play in both directions. They seem to be holding something inside the scope cylinder in place, but as I said, whatever that thing is, it is not rigidly attached to the brass eyepiece cylinder.
The screws might be holding a prism that flips the image to look "correct". Without such a prism, a refracting telescope will show an inverted image.
Someone in an astronomy forum said the same thing - thanks.
