Working Distance, Low-Mag Objectives

[Tycho]

Hi,

I’ve just acquired an old Meiji ML2000 microscope which is fitted with 2 Meiji objective lenses;

Meiji S.Plan M 10X 0.25 P/N 15291
Meiji S.Plan M 40X 0.65 P/N 18377

And using those lenses, everything is perfectly fine.

I’ve also tried to use two objectives of smaller magnification, these being x4 and x1.3. These were supplied with the microscope but are not Meiji components.

The stage of the microscope cannot be raised sufficiently for either of these two objectives to be used and obtain a focused image – this can only be achieved by holding the specimen close up under the lens. The stage has an auto-stop mechanism, but even with this is the dis-engaged position, the low-mag objectives are still unusable.

Could anyone explain what the problem is here?

Thanks
T

[Scarodactyl]

They are likely designed for a different tube length, or are a different barrel length. Not every objective will work with every stand.

[MichaelG.]

[…] The stage of the microscope cannot be raised sufficiently for either of these two objectives to be used and obtain a focused image – this can only be achieved by holding the specimen close up under the lens. ...

I find that rather surprising; and therefore very interesting
... it seems contrary to the usual difficulty, where low-mag objectives need more working distance than a particular ‘scope can provide.

Photos of the troublesome objectives might aid recognition.

MichaelG.

.

Edit: presumably this is the instrument
https://meijitechno.com/meiji_old/pdfs/ ... %20PDF.PDF

[MicroBob]

At which distance between object and objective flange do you get a sharp image?

Bob

[Tycho]

Attached is a picture of three of the lenses; the two Meiji lens X10 and x40 which work perfectly. The working distances of those two are ~7mm and ~1mm.

The x4 was recently bought off eBay and won't focus on the microscope, and similarly, a x1.3 (not shown) which was provided when the microscope was newly supplied, will not focus, i.e. cannot get close enough to specimen.

The microscope was bought new by a friend of mine, who has since passed away. He used it to look at corrosion test specimens. It was originally supplied by a local company sometime around 1999, but they have since gone out of business. Please note that my expertise with microscopes is very limited.

Thanks
T

[Scarodactyl]

There's your problem--you have a finite (160mm) tube length objective on an infinite system. The 160 is designed to have 160mm of empty space between it and the eyepieces, and there's a big tube lens in the path instead.
The 4x is a common and inexpensive objective, but lower-mag objectives actually tend to be rarer and more valuable in general. So you may be able to liquidate it and fund some better-fitting infinity objectives. Parfocality will still be a concern for a non-Meiji objective but not to this degree.

[MichaelG.]

Hi,

I’ve just acquired an old Meiji ML2000 microscope […]

Scarodactyl has the answer
... and my first assumption about the model of microscope was wrong.
The version that I linked uses 160mm objectives, but yours must be infinity corrected
[which would make it not old, but nearly new, by my standards]

Here’s some useful reading : https://www.microscopyu.com/microscopy- ... al-systems

Enjoy what should be a very fine instrument.

MichaelG.

.
Edit: Looking at your photograph ... ‘Your two Meji objectives are not only ‘infinity corrected’ but also ‘Metallurgical’ ... so are you sure about that Ml2000 model number ?
https://meijitechno.com/catalogsearch/r ... serch_btn=

[Hobbyst46]

The 4X/0.1 objective almost certainly is DIN standard so its parfocality distance is 45mm. And its working distance large, ca 2cm as far as I remember.
It will be usable (not great) on many 160mm tube length microscopes, new or old (except for some very old microscopes that accepted 33-37mm parfocality distance objectives).
Such objectives are sold new for around 20 USD including postage...

Please note also that your 10X and 40X objectives are marked ".../0" so designed to be used WITHOUT coverslips.