Getting objective in the shed

[Michael G]

I recently found an old measuring microscope (ex USAF) that I want to use in the shed. It has a 10x eyepiece lens and at the moment there is a 2.5x objective fitted to it (total magnification = 25x). That magnifies things way too much for the sort of thing I want to use it for (eg looking at threads). The objective thread is the standard 20mm one. I'm thinking something between 0.8x and 1.2x would be ideal. If anyone has experience in microscopes for toolmaking work, can you suggest a useful magnification?
I'm looking for ideas where to get a cheap objective lens (say sub $50)? eBay has failed me as they don't seem to have anything much less than 2.5x (where this came from) for a reasonable price.

Michael

[Anorak Bob]

Michael,

I've just had a look through some old ( 1932 and 1947, real old ) Bausch and Lomb brochures. They offered a 5X eyepiece and a 2x objective. I have a 5X eyepiece in my mid forties B&L monocular scope. The barrel diameter is 23.2mm They should be easy enough to locate if the size is the same.

Who made your scope?

BT

[Stustoys]

I've been thinking along the same lines as BT, and thought changing the Ocular be an easier find. Didnt come up with much. Though I did find another piece of stuff to try from China lol

Stuart

[Anorak Bob]

I've been thinking along the same lines as BT, and thought changing the Ocular be an easier find. Didnt come up with much. Though I did find another piece of stuff to try from China lol

Stuart

China? What happened to Jena Stu? Those German optics getting too pricey?

So tell us, what's the latest acquisition?

[Stustoys]

I haven't pulled the trigger on the Chinese "optics" yet BT, but I do have some Japanese optics on the way(the guy took a week to post it!), you'll just have to wait lol.Stuart

[Michael G]

The 'scope is a US made Gaertner. It's engraved with a USAF number, so I guess was used at some stage for something highly secret...
It has a measuring feature (the rectangular bit by the eyepiece) with a dial set up that can measure thou's*. There is also a hole in the front tube that I have been told was used for internal lumination. I'll probably plug that unless I really need it.
The plan was to make up a bracket so I could mount it in a lathe tool holder. If I get the balance point right I should have a solid base as well as something that I can mount in the lathe to examine circular items (pitches of small threads for example)


242027242028

Michael
*assumption based on having the right objective

[Stustoys]

:( I dont have one like that.

Whats its measuring range?
whats its focal length and field of view?
If the measuring is spot on, wouldnt it be a shame to stuff it up?

Stuart

[Michael G]

(Small frisson of gloat - I have one that Stuart doesn't (I know nothing of it but...))

Most of the information I have is from here -
Gaertner Scientific Corporation - Microscopes - Basic Modular Microscope M101A (http://www.gaertnerscientific.com/microscopes/m101b.htm)

If I can get the 'scope doing say 10x then measuring is not such an issue. If not then I may just have to calibrate it against a steel rule and have a conversion factor. It's a 168mm tube, so from the table the current working range is 67mm and the field of view is diameter 4.
Measuring range is tricky but I have 40 marks inside the tube and each is 1 rev of the dial (ie 100 graduations), so I can do 4000 'units' - if I can get 1 unit = 1 thou or even 1 unit = 0.1 thou that would be great.

Michael

I just measured a 1/100th steel rule I have. One division on the rule (1/100th ") is 250 units - so is 25 units per thou - let's say that one division is equal to a micron. If I had a 1x objective instead of the 2.5x objective that would be 10 units per thou - that is, the graduations on the barrel would be in 1/10th of thou. Interpolating from the Gaertner table, that would give a working length of 170mm and a field of view of around 10mm. I'd keep the 2.5x so that I could pretend that I could work to microns but would prefer a 1x so I could work in thou as well.