Oil immersion objective on old microscope?

[Even]

I just recently bought an old, used Karl Kaps microscope from a retired doctor. It does not have a model number, just marked with "Asslar/Wetzlar Nr. 9553". The 100x objective is marked with "170/0,17 100/1,30". There are no indications, that I can find, that the objective is an oil immersion objective.

I also see from most articles and videos on the internet that the 100x objective typically is an oil immersion objective. Is it possible that 100x objectives is to only be used dry (without oil)? Can I destroy the objective if I try to use oil?

At the moment the objective is useless as I am unable to get clear pictures with that magnification. I am thus hoping to get some answers.

[zzffnn]

Welcome to the forum.

What you have is indeed an oil immersion objective.

That 1.30 number indicates that it is an immersion objective (anything more than 0.95 requires immersion). Common immersion types are oil, water and glycerine. Unmarked ones are almost always oil immersion.

[apochronaut]

Interesting brand. A new one to me but there must have been a lot of smaller makers out there. Any objective with an N.A. over 1.0 but in practice, .95 must be an immersion objective. This can take the form of water, glycerin or oil, as well as a few other exotic substances but it would be highly unlikely that such an objective working at 1.3 would be water or even glycerin, since oil is essentially the default immersion medium.
Looks like it could be a really good microscope.

Using the objective without oil will provide you with an image but it is too full of spherical aberration to have much in the way of resolution. Try some immersion oil , or if you have to wait for that, clear vegetable oil will get you part way to 1.3 N.A., certainly better than dry.

[apochronaut]

Welcome to the forum.

What you have is indeed an oil immersion objective.

That 1.30 number indicates that it is an immersion objective (anything more than 0.95 requires immersion). Common immersion types are oil, water and glycerine. Unmarked ones are almost always oil immersion.

sorry, Fan. must have been typing at the same time.

[Even]

Thank you very much for such fast and clarifying replies! I will order some immersion oil and try with vegetable in the mean time.

I think I made a bargain with the microscope. The brand seems to be going strong under the company name Kaps Optik, but is focusing more on optics for medical/dental and rifles than standard microscopes now.

[zzffnn]

Best oil immerse your condenser top lens as well.

Apo, funny how our wordings are so similar. Yours are more precise.

[Even]

Let me post another newbie question, while we're at it:
Have you ever experienced the 40x objective being oil immersion as well? The frontal shape of my objective is very similar to the 100x previously mentioned and I have problem getting a good focus with that too, even when observing flat objects. I see that the aperture is below 1..

[Peter]

Hi Even,
My 40x objective is oil however it is NA 1. Your 40/ 0.65 will not be an immersion objective.
Peter.

[Even]

Best oil immerse your condenser top lens as well.

Is this a practical joke, or is it true? I have never heard of that before - must be a lot of mess.

[75RR]

Nice looking microscope. Looks to be in very good condition.

Is this a practical joke, or is it true?

It is true but it is not that messy.

Here is a link to a booklet on maintaining a clean microscope which includes removing immersion oil:

http://microscopy.duke.edu/downloads/Th ... scsope.pdf

I have problem getting a good focus with that too ...

The higher the objective magnification and the NA (Numerical Aperture) the more demanding the objective is.
Small things can make a big difference, is your cover slip 0.17mm or very near to it?

[apochronaut]

Thank you very much for such fast and clarifying replies! I will order some immersion oil and try with vegetable in the mean time.

I think I made a bargain with the microscope. The brand seems to be going strong under the company name Kaps Optik, but is focusing more on optics for medical/dental and rifles than standard microscopes now.

It looks to be in very good shape. The 40xobjective appears almost unused but if you are having trouble getting an image, it is possible that the previous user allowed some of a sample or even immersion oil to dry on the front lens. Even though, as Peter points out, your objective will not be an oil immersion type, at N.A. .65, one of the biggest mistakes microscope users make when changing objectives is to forget how close the focus is with the dry 40x objective and accidentally dip it into immersion oil that has previously been put on the slide for the 100x objective.....it is nice , often to get a wider view again, after visiting with the high power objective and the combination of dry medium power and oil high power makes the possibility of contaminating the front lens of the 40x , quite high.

Have you looked closely, at the front lens of the 40x? If, not invert one of your eyepieces as a magnifer, and looking into the bottom lens, bring the top lens close to the front lens of the 40x, while holding it at an angle towards a window or light. At some angle you will get a nice reflection off of the front lens of the 40x and focusing the eyepiece on it you can see if it is nice and clean. If it is fouled, clean it with a little rubbing alcohol and a cotton swab. You will need several new swabs in progression to clean it well, likely. Your inverted eyepiece will give you a very good view.
Report back about this because, you should easily obtain a good clear image with the 40x.
Don't worry about oiling the condenser at this point. That is only necessary for very critical imaging, using the 100x objective. You will get an excellent image with the 40x and a dry condenser, if the 40x does not have some problem.

[IanW]

Evan, in order to get a clear image at X40 and upwards its important to set your scope up properly for Koehler illumination.

[billbillt]

I find it strange it is using the older 170mm tube length... Leica stopped using it years ago.. They work fine, just thought it would be the more popular 160mm tube length...

BillT

[Even]

Here is a link to a booklet on maintaining a clean microscope which includes removing immersion oil:
http://microscopy.duke.edu/downloads/Th ... scsope.pdf

Thank you for the link! I will try to obtain the necessary equipment.

The higher the objective magnification and the NA (Numerical Aperture) the more demanding the objective is.
Small things can make a big difference, is your cover slip 0.17mm or very near to it?

I am using low cost cover glass from China with thickness specified to be in the range 0.13-0.17 mm. How much a difference will it make if it is 0.13 mm? Should I get better slides and cover glass?

[Even]

Evan, in order to get a clear image at X40 and upwards its important to set your scope up properly for Koehler illumination.

Thank you for the suggestion. I looked into Köhler illumination, but I think it is not possible to retrofit this microscope based on previous discussions on this forum.
Oliver, 2012:

Koehler illumination does not only need a field diaphragm but also collector lenses.

My microscope is missing both.

[apochronaut]

None of the varying specifications for cover glass thickness or kohler illumination will make enough of a difference with a .65 N.A. objective to be all that noticeable or so as to elicit a comment that " I am having trouble getting good focus". Good focus should easily be obtained, irregardless of whether the coverslip is .14 or kohler has been established. Kohler, is more of a factor in the evenness of the background illumination.

You need to assess if the objective is in fact working properly. I assume the 10x is working well?

Is it possible for you to take a picture with a phone through one of the eyepieces, of what your 40x is imaging? That way, a better evaluation of the problem, could be made by those on the forum.

[apochronaut]

My concern is that the objective is fouled in some way. It is not uncommon for oil to get into the internals of 40x objectives accidentally, and that will definitely destroy the focus.

[75RR]

Thank you for the link! I will try to obtain the necessary equipment.

I find that a blower, Chinese bamboo sticks, cotton wool and isopropanol alcohol is sufficient for most cleaning.
If you can obtain petroleum ether to make up the Zeiss 'L' Cleaning Solution on page 12 do so.

I am using low cost cover glass from China with thickness specified to be in the range 0.13-0.17 mm. How much a difference will it make if it is 0.13 mm? Should I get better slides and cover glass?

At a Numerical Aperture of 0.65 which is what your 40x objective has you should be ok within the 0.13 - 0.17mm range as long as that is the actual thickness.
As you increase the NA above that then the closer you are to 0.17mm (either just below or just above) the better.
If you can get your hands on a micrometer at some point, it is worthwhile confirming that.

As mentioned, incorrect lighting and an unclean lens are among those things that can interfere with obtaining a good image.
If you can not achieve Köhler do not worry too much - Critical illumination will also give you a clear image in both your 40x and 100x
Make sure that the condenser is up high - it should be just a couple of mm below its full height.
Light intensity should be controlled solely by the illuminator dial (rheostat).

Introductory booklet from Zeiss: http://www.its.caltech.edu/~bi177/priva ... inning.pdf

[75RR]

Came across this by accident on ebay (was searching zeiss - it was among the sellers other offerings), anyway thought I would let you know about it in case you did not have a 20x objective.
The fact that it is a phase objective should not be a problem - a lot of microscopists use phase objectives in brightfield as well.

Curiously it does not mention the tube length so I am not sure if it will work on your microscope.
It might be worth contacting Karl Kaps as to its suitability if you are interested.

http://www.ebay.co.uk/itm/Karl-Kaps-Len ... SwPhdVBuxq

[Even]

None of the varying specifications for cover glass thickness or kohler illumination will make enough of a difference with a .65 N.A. objective to be all that noticeable or so as to elicit a comment that " I am having trouble getting good focus". Good focus should easily be obtained, irregardless of whether the coverslip is .14 or kohler has been established. Kohler, is more of a factor in the evenness of the background illumination.

You need to assess if the objective is in fact working properly. I assume the 10x is working well?

Is it possible for you to take a picture with a phone through one of the eyepieces, of what your 40x is imaging? That way, a better evaluation of the problem, could be made by those on the forum.

I did my first attemt at taking photos with my mobile phone through the eyepieces. The sample is part of a wing from a queen ant and I moved the stage a little bit to find more high contrast/interesting parts. I used a wet mount with destilled water, moved the condenser to a position close to the class where the illumination seemed the best, used fully open condenser diafragm and the rheostat set to lowest position for all photos. I have two set of eyepieces: 8X and 12X and used the 8X for the setup.

I was actually surprised to the sharpness of the photos. I found the image to be more blurry when looking with contact lenses through the eyepieces. It might also be that the wing I used was thin in comparison to other things I have looked at. Should I expect even better focus at 40X?

[Even]

Came across this by accident on ebay (was searching zeiss - it was among the sellers other offerings), anyway thought I would let you know about it in case you did not have a 20x objective.
The fact that it is a phase objective should not be a problem - a lot of microscopists use phase objectives in brightfield as well.

Thank you for telling me about this. I do not have a 20X and actually have a free slot in the revolver. What is the difference of a phase objective in comparison to the objectives I have? What can is it used for?

Curiously it does not mention the tube length so I am not sure if it will work on your microscope.
It might be worth contacting Karl Kaps as to its suitability if you are interested.

I tried contacting Kaps to ask some other basic questions, but they only forwarded me to some other german microscope specialist. I therefore don't have any high hopes for getting info about the suitability of the objective. I will see what I do.

[zzffnn]

For 40x objective to work, you need to have a very thin mount with cover slip laying perfectly flat, without excessive mountant.

Ant parts may be too thick for 40x objectives to view properly. Please try a blood smear or cheek cell smear.

For plain brightfield, your condenser iris should be around 80%-90% of your objective back focal aperture size, going over too much will reduce contrast.

Looking at your 4x objective image, your light is not even enough. Maybe missing diffusion, adjust condenser height and centration?

[75RR]

Your 4x, 10x and 40x all look nice and sharp. Less movement when you take a photo will improve it a little more.
Light is a little uneven (particularly noticeable in the 4x) though present in all three.
If your microscope did not come with a diffuser (usually a round frosted glass filter) that goes on top of the light housing - then you need to get one.
Measure the diameter of the light housing to make sure you get the right size.
You can pick one up one on ebay or at a microscope shop near you.

Have a look for microscopy clubs in your area - they are a good place to learn and source bits and pieces.

I tried contacting Kaps to ask some other basic questions, but they only forwarded me to some other german microscope specialist.

That might do - if they can confirm that Karl Kaps only made 170 tube length objectives then your question has been answered. It will work on your microscope.

[Even]

Amazing! I am learning so much from you: The diffuser trick evened out the light and got me a better image. Reducing the iris also improved the 40X contrast.

The funny thing is that the light was the first thing I looked at. I put a piece of a sheet of paper on the stage and adjusted the condenser height until the light was most concentrated. When doing this I could see that the center spot is brighter 2/3 on the left side. I am unable to take a photo of this, but I believe this has to do with the light being reflected via a mirror in the base of the microscope up to the condenser and that the mirror or bulb might be slightly tilted/offset. Trying to center the condenser is not working out. Any tips?

[75RR]

Images improving!

Found this: http://pdf.medicalexpo.com/pdf/karl-kap ... 99641.html

I am unable to take a photo of this, but I believe this has to do with the light being reflected via a mirror in the base of the microscope up to the condenser and that the mirror or bulb might be slightly tilted/offset.

Turn microscope on its side - take a photo of its innards.

[Even]

I am a total newbie: After opening the bottom cover of the microscope and seeing that there was no adjustment for the mirror it suddenly made sense what the two screws on the back of the microscope were for, light adjustment. Now I don't even need the diffuser to make well lit and clear images

[75RR]

That is pretty neat.

What is the difference of a phase objective in comparison to the objectives I have? What can is it used for?

It is used for Phase Contrast - a useful lighting technique. You need a Phase condenser to achieve it.
See page 4 in link: http://pdf.medicalexpo.com/pdf/karl-kap ... 99641.html
A Phase objective can be used for brightfield as well - there is no perceivable loss in image quality.

Note also that the leaflet shows that there is a trinocular head for your model - you should keep an eye out for one.

If you have a blue filter you should use it - it will turn your light whiter - which will improve the image.

http://www.microbehunter.com/what-are-t ... icroscopy/

[apochronaut]

None of the varying specifications for cover glass thickness or kohler illumination will make enough of a difference with a .65 N.A. objective to be all that noticeable or so as to elicit a comment that " I am having trouble getting good focus". Good focus should easily be obtained, irregardless of whether the coverslip is .14 or kohler has been established. Kohler, is more of a factor in the evenness of the background illumination.

You need to assess if the objective is in fact working properly. I assume the 10x is working well?

Is it possible for you to take a picture with a phone through one of the eyepieces, of what your 40x is imaging? That way, a better evaluation of the problem, could be made by those on the forum.

I did my first attemt at taking photos with my mobile phone through the eyepieces. The sample is part of a wing from a queen ant and I moved the stage a little bit to find more high contrast/interesting parts. I used a wet mount with destilled water, moved the condenser to a position close to the class where the illumination seemed the best, used fully open condenser diafragm and the rheostat set to lowest position for all photos. I have two set of eyepieces: 8X and 12X and used the 8X for the setup.

I was actually surprised to the sharpness of the photos. I found the image to be more blurry when looking with contact lenses through the eyepieces. It might also be that the wing I used was thin in comparison to other things I have looked at. Should I expect even better focus at 40X?

sorry for not responding earlier but I am never in a position to on Sat.

The sharpness of your objectives is normal for their type. I am going to make a guess and suspect that your initial concern was over the lack of sharpness over the entire field, or what is in fact, lack of depth of field, something that diminishes generally, as the magnification rises.

Stacking programs allow one to overcome this optical deficiency of lenses. Since the emergence of digital photograpy and the burgeoning of millions of photographer hopefuls, electronic systems to improve the performance of lenses to meet the requirements of photography have arrived in the thousands.
Microscopists have traditionally worked around the problems of depth of field , primarily by pulling focus( adjusting) and registering the data in the brain, making drawings( for which there are many inexpensive useful tools available) or making a series of images.
What I see regarding the performance of your lenses, is fine.

[Even]

It is used for Phase Contrast - a useful lighting technique. You need a Phase condenser to achieve it.
See page 4 in link: http://pdf.medicalexpo.com/pdf/karl-kap ... 99641.html
A Phase objective can be used for brightfield as well - there is no perceivable loss in image quality.

I am wondering whether it is possible to retrofit a microscope such as mine with a phase contrast objective and a opaque sheet in the filter holder, similar to the kits available for darkfield microscopy?

If you have a blue filter you should use it - it will turn your light whiter - which will improve the image.

I actually experimented a bit with the blue filter included after being adviced about the diffuser and came to the conclusion that it was giving better images, too.

[Even]

The sharpness of your objectives is normal for their type. I am going to make a guess and suspect that your initial concern was over the lack of sharpness over the entire field, or what is in fact, lack of depth of field, something that diminishes generally, as the magnification rises.

I knew that I should expect a shallow depth of focus at higher magnification, but initially could not seem to find anything that had a clear image. Thanks to the feedback from you at this forum I have learnt so much about samples/mounts, light and optics that the microscope has turned from useless to useful.