Travelling Microscope Query

Our friendly courier dropped me a parcel off this morning.
I spotted an interesting item up for sale, and had an offer accepted, so I've ended up with a measuring microscope, as in this photo; micrometer head and scale is metric.
I've not taken any pictures of it myself yet, so this one is from the original advert, just to show the layout.
It will stand as shown, on its back, or on one end.

Everything appears to work as it should, though a clean and polish will be in order soon, but I have a query regarding focussing, as I'm no expert on microscope/telescope optics.
Though not obvious from this one photo, the microscope tube works like a draw telescope, and extends to a marked scale, up to 200mm.
The closest I can get it to focus with the current optics, is about 13" from the objective with the tube at full draw, well beyond the 200mm marking on the top tube; I really need to get it down to about 2½", to be in the same plane as the table on which it would stand.
The eyepiece is marked up as 7.5, so I assume this is the magnification, as per my other binocular microscope(s); the eye lens itself screws into a tube with a pair of cross hairs at the bottom end, along with a second lens.

The objective is marked up as "Telescope" which would seem an accurate description, as I can focus on the buildings opposite with the draw tube fully compressed.
I don't have any other objective lenses to try as both my other binocular scopes are designed for benchwork/dissecting etc and have combined dual lens slide in units; their eyepieces work OK in this scope, but they don't bring the focussing any closer.
The objective's thread seems to be a nominal 0.8" or a shade over 20mm
I've not tried to measure the pitch yet.

Any thoughts about an easy solution please?

At the moment, I'm guessing I need something like this 4x lens, which appears to be the correct thread, though, as above, I've not checked the pitch yet; That might be easier if only I had a suitable microscope.
https://www.ebay.co.uk/itm/134641718804

Cheers
Bill

Edited By peak4 on 18/07/2023 21:02:49

My guess is it's meant to focus on a somewhat distant object, not close-up like a microscope. Possibly it's not meant to look down unless there's a hole on the table and the item is on the floor: normally the scope looks sideways; does it swivel through 90°?

On end, with the instrument measuring height, the item could be a foot or more away. Bit like a vernier height gauge, except cross-hairs instead of a physical pointer.

If it's for somewhat distant objects, 13"+ across a table, then it's probably working correctly.

Dave

Sorry, Bill... I can’t do it just now, but if you search the old forum threads you will find a discussion about mine.

MichaelG.

The postman came earlier with a second hand Union 5x objective, so now I don't have to place objects on the garden fence to view them.
Focus is now a bit close at about 15mm ish, but far more useable.
I've not tried to do much with it, but did try measuring a 4BA thread, by counting ten pitches and came up with a sensible answer, only about 0.02mm out, so it will do for its intended purpose.

It looks like the slot in each end casting is to hold some sort of a stage, so I'll try and find a length of ¼" Perspex, frost it and arrange some back lighting.
Screenflashlight as an Android app on the mobile should do that bit nicely.
https://play.google.com/store/apps/details?id=com.eduardo_rsor.apps.linternapantalla&hl=en&gl=US

Used on its own you can see the individual pixels, but out of focus and behind a bit of frosted plastic, it should be fine.

Bill

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Please see the penultimate post on this page, Bill: **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=89940&p=2

You, of course, have the great luxury of a nice big micrometer  head.

MichaelG.

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Edit: __ direct link to the Album: https://www.model-engineer.co.uk/albums/member_album.asp?a=29450

Edited By Michael Gilligan on 25/07/2023 05:18:16

In case any readers not-acquainted with these instruments have missed it …

Their big advantage is that [subject to the optical resolution of the lenses] they can take very small measurements at long distances. Hence the inclusion of the ‘telescope’ objective.

What other arrangement would allow you to so accurately measure the size of a bolt-head from across the room ?

MichaelG.

Cheers, I had read that post; as you have spotted, mine only came with the telescope objective, and my workshop is of limited size.
I really picked it up, largely on a whim as it was a good price, for measuring smaller things close up, such as identifying threads etc
7.5x eyepiece and 5x objective is just a bit to magnified for some things, so I might seek a lower powered eyepiece and a 4x objective, but there's no rush for that.
Whilst my long distance vision is fine with glasses, and now hopefully better following a replacement lens in one eye, I still sometimes struggle reading/seeing small things close up, or matching threads and gauges.
I'll have to see how I get on after I've been back to the optician for a post cataract surgery eye test and new prescription glasses.

I already have a binocular dissecting microscope for working on PCBs, pulling splinters etc.

Bill

Just curious … Does your 7.5x eyepiece have cross-hairs, Bill ?

MichaelG.

so accurately measure the size of a bolt-head from across the room

Same problem here as you highlighted in the Platinum wire thread!

Straightness of the traverse beam would be just one fly in the ointment.

Ian P

The advantage of optics is that light beams don't sag as much as physical ones!

Hence the use of lasers

Howard

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That’s why they were made so heavily and finely … the one shown in my Album would make a very good lathe-bed.

MichaelG.

Another lens fitted on top of the objective would shorten the focussing distance, but what strength would have to be found by trial and error.

I saw that on ebay and was tempted myself just out of curiosity, but overspent on other things and just managed to resist it.

Edited By old mart on 25/07/2023 19:13:58

Yes, on a separate graticle retained with a threaded collar.
If/when I pick up a lower powered eyepiece, I'll likely add a cheap(ish) set of crosshairs off ebay or similar.
No point yet though as I won't know the diameter of any future eyepiece.
I do have a couple of other pairs of eyepieces off my binocular scopes, but they are 10x & 17x, as well as missing the cross hairs.
I even have several random spare spotting scope eyepieces form birding scopes, but they start at 15x and go up to about 35x

Bill

Is one name for this device "cathetometer" ?

Best regards,

Swarf, Mostly!

RMS standard eyepieces are 23.2mm ‘insertion’ diameter, or thereabouts

… but of course the reticle diameter varies between types.

MichaelG.

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A close relative, I would say.

MichaelG.

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I thought it interesting, Ian, that you chose to not quote the question that I asked of the world in general

… instead, you highlighted the potential shortcomings of this method.

Fair enough … but the question remains.

MichaelG.

Well, I'm not good at answering questions aimed at the world in general.

My point was related to you saying that the travelling microscope could 'accurately' (your words) measure a bolt head across the room.

I just thought there were many factors that came between theory and practice, especially in the home workshop

Ian P

My words were in fact “so accurately” … which is not an absolute but a relative expression.

If, just for example, it’s accuracy was +/- 5% then I was asking what else could do so well

Equally if it’s demonstrable accuracy turned out to be a different percentage; the same question applies.

MichaelG.

Edited By Michael Gilligan on 26/07/2023 11:56:15

I wonder if it was to align the head on an RF30?