Objective hits the glass

[Boart66]

Hello. My problem is the following. When i try to turn from 40x to 100x the tip of the oil ojective hits the coverglass, do i have to have the microscope adjusted some how? The microscope is a Breukhoven BMS E1, and im a 55 year old rookie

[BramHuntingNematodes]

100x usually is an immersion lens and as such will be nearly touching the coverslip when in focus. Also, the oiling process precludes fast switching from 40x-100x anyway. I wouldn't worry very much over it if the 20x and 40x are parfocal

[Boart66]

Thank you for your answer, i dont understad all of it, is the stem from 40x to 100x to big? And yes im using oil when i use te 100x objective, do you rekomend buing a 60x objective to?

[BramHuntingNematodes]

The step is not so big, but there is very little clearance for the 100x. Also, you should not oil non oil objectives. So when you switch to the 100x you will naturally be racking the nosepiece up so as to allow for a drop of oil on the coverslip to be applied.

A 60x objective some people find useful. Oil 60x are excellent. I don't like the dry 60x as they are finicky and often don't look great but some people seem to really like theirs

[75RR]

.
If you are using a wet mount (i.e. observing Pond life) then you may have too much water under the cover slip.

https://www.youtube.com/watch?v=yxTFgDe5CEE

[carlh6902]

If you wear glasses, but are using the scope without your glasses, you may be compromising the proper working distance of your scope to accommodate your vision. If so, try it with your glasses on.

Then there are the two classic beginner mistakes:

1) Not using a proper .17mm cover glass. If too thick, this will happen.
2) The slide is upside down, so you're viewing through the slide, rather than a cover slip.

Carl

[apochronaut]

Are the 40X and 100X objectives original to the microscope? If the parfocality is sufficiently different between the two, such a collision could occur when revolving to the 100X. It would not take much.
Another possibility is that some objective series are designed to have the parfocality adjusted between the objectives.

[Boart66]

Thank you for all the tipps, I will try them tomorrow.

[Dubious]

Your 100x objective not being parfocal with the 40x objective is not really a problem because, as other here have suggested, you should not be switching casually between them anyway. You don't want to get oil on the non-oil objectives, so can't easily use them together on the same slip cover--that's why people who routinely use a 100x oil objective often have a lower powered oil objective to use with it.

Some people really like oil objectives--I never have. Most of what I want to see (mainly pond life) can be seen adequately with a 10-40x objective. But of course it all depends on what you want to observe.

[Javier]

On my first monocular scope, the 40 x objective used to hit the cover slip very often. I though it was my fault, but it wasn't. Since I upgraded my microscope, I have never had that issue again. It is worth mentioning that the 40x was the original objective of that microscope. What a nightmare of an instrument it was!

[apochronaut]

Your 100x objective not being parfocal with the 40x objective is not really a problem because, as other here have suggested, you should not be switching casually between them anyway. You don't want to get oil on the non-oil objectives, so can't easily use them together on the same slip cover--that's why people who routinely use a 100x oil objective often have a lower powered oil objective to use with it.

Some people really like oil objectives--I never have. Most of what I want to see (mainly pond life) can be seen adequately with a 10-40x objective. But of course it all depends on what you want to observe.

It is always a good idea to have a lower magnification oil immersion objective but few amateur microscopists do. Obviously , one does not want to rotate out of 100X oil immersion back to a dry 40X but I believe the question was about a problem of the 100X hitting the slide going from the 40X to the 100X. The working distance difference between the 40X and 100X oil is very small, so if parfocal the 100X should rotate in easily. Yes, you can get away with backing off the 100X and then lowering it into the oil but rotating the 100X in and delivering the oil just as it positions over the slide has some benefits. Parfocality exists for a reason, one of which is quick and easy maintenance the object's registration.
If your 100X is hitting, either there is a parfocality problem or, if you are using prepared slides; some with thicker than normal coverslips might just be within spec. for the 40X but might be just slightly thick for the 100X, with it's .03 or so closer w.d.

[Boart66]

Lots of great tips. Wat is the ideal distance between the glass and a 100x objective, i have the ability ti messure down so 10 um.

[BramHuntingNematodes]

It's between .13 to .18mm so about the same thickness as another coverslip

[dtsh]

Lots of great tips. Wat is the ideal distance between the glass and a 100x objective, i have the ability ti messure down so 10 um.

Different models of objectives can have different working distances, but I believe 0.1mm is what most of mine are designed for. It also depends on the thickness of the coverslip and how far down into the mountant the structures you're looking at are.

[75RR]

Different models of objectives can have different working distances, but I believe 0.1mm is what most of mine are designed for. It also depends on the thickness of the coverslip and how far down into the mountant the structures you're looking at are.

That (in bold) is the point. Objectives are designed (optimum resolution) to assume the sample is pressed up against the bottom of the correct thickness cover slip.

If, when using the 40x, your sample is not pressed up against the cover slip, (due to excess mountant - usually water) and you then have to focus deeper (i.e. raise the stage) - changing to the 100x at that point (given that the 100x has a shorter Working Distance (WD) would inevitably place the 100x and the cover slip in collision.

[Boart66]

I appreciate you sharing your knowledge and taking your time to answer me. I will have to experiment a bit with this and hopefully learn how to use it. Thanks and Cheers from Sweden.