Problem with choosing the patch stop size for the 40x lens

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ewieckow
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Problem with choosing the patch stop size for the 40x lens

#1 Post by ewieckow » Wed Dec 22, 2021 5:32 pm

Good afternoon,
I have recently been the owner of the OLYMPUS BH-2 microscope from the 1980s. In order for me to be able to take full advantage of what it offers (a powerful illuminator), I added a condenser insert (made of a plastic folder), on which I was able to select and paste the appropriate patch stop size ( for DARK FIELD) to the lens with a 10x magnification. Unfortunately, despite many attempts, I failed with the 40x lens. In the case of the 10x lens, I got the Dark Field. However, I have doubts about it, because sometimes you can see strange shadows, I do not know what they come from, e.g. browns. Both lenses are SPlanApo Olympus. I attach photos. I am asking for help.
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josmann
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Re: Problem with choosing the patch stop size for the 40x lens

#2 Post by josmann » Fri Dec 24, 2021 1:44 am

ewieckow wrote:
Wed Dec 22, 2021 5:32 pm
Good afternoon,
I have recently been the owner of the OLYMPUS BH-2 microscope from the 1980s. In order for me to be able to take full advantage of what it offers (a powerful illuminator), I added a condenser insert (made of a plastic folder), on which I was able to select and paste the appropriate patch stop size ( for DARK FIELD) to the lens with a 10x magnification. Unfortunately, despite many attempts, I failed with the 40x lens. In the case of the 10x lens, I got the Dark Field. However, I have doubts about it, because sometimes you can see strange shadows, I do not know what they come from, e.g. browns. Both lenses are SPlanApo Olympus. I attach photos. I am asking for help.
Yoooooo, welcome to the BH2 club! Looks like you're starting out with an exceptional complement of lenses!

I don't think you'll have much luck using patch stops with the .95 NA SPlanApo 40x. It's a fantastic lens, but beyond around .70 NA, patch stop dark field is no longer really feasible. Fortunately, the Amscope oil immersion darkfield condensers with a dovetail of 42mm work perfectly with the BH2 and really do create a very dark background. This eBay seller has a bunch for a good price right now: https://www.ebay.com/itm/403317128296?h ... SwFdVhnzH-

If you come into possession of one of the 100x SPlanApo objectives with the adjustable iris, that condenser will also allow you to achieve 100x darkfield.
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Greg Howald
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Re: Problem with choosing the patch stop size for the 40x lens

#3 Post by Greg Howald » Fri Dec 24, 2021 5:19 pm

Josmann gives the best advice I know concerning this subject. Dark field above 20x is critical and difficult to achieve. The adjustable iris on the 100x objective is the only way I have been able to tweak things in to a dark field image, and I was unable to make a stop for 40x. This seems that the distance from the filter holder to the top condenser lens is too great and difficult to impossible to overcome.
Unfortunately the most satisfying solution I have found is to purchase the necessary accessories.
Good luck, Greg😃

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Re: Problem with choosing the patch stop size for the 40x lens

#4 Post by ewieckow » Sat Dec 25, 2021 7:47 pm

Oh, thank you!
In my spare time I will have a look at it, Thank you very much!

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Re: Problem with choosing the patch stop size for the 40x lens

#5 Post by apochronaut » Sun Dec 26, 2021 1:06 pm

One of the problems with patch stops when compared to dedicated DF condensers is that they need to be in focus with the top of the slide, so the condenser focus needs to be precise and knowable. A 10X stop doesn't require a super degree of precision but at 40X, the depth of field is much less and any variance in illumination at the periphery more magnified. Blurring of the edge of the light funnel is not desirable and centering more difficult. So attention to precise details is really important with DF, as important as with phase or DIC.
With a dedicated DF condenser when used properly , the focus is predetermined whether it is dry or immersion and guaranteed to cast a precise and sharp light funnel at the top of the slide. In most cases a specific slide thickness is required and either marked on the condenser or available from the condenser's specifications. In the modern world, the default thickness is 1mm but with a modified BF condenser unless careful experiments are undergone one wouldn't know if the condenser is casting a focused image or not with any particular slide thickness. Using a piece of thin paper on top of the slide as a screen would probably help but the focused stop also needs to be the correct size, so a complicated juggle of stop size , slide thickness, condenser height and stop to condenser distance ensues. Locking down some of the variables allows for more accurate attention to the others.
So, start with the slide thickness and peg it at 1mm. Don't rely on the box. Measure it. Then oil the condenser and fix it's focal point. All 1.25 abbe condensers are meant to be oiled for optimum performance anyway, so why not? Using one dry is probably o.k. but you will need to use the upper limit condenser stop in order to accurately position the dry condenser's focal point for repeatable performance. Whichever is good for you, it just needs to be pegged down. Iris wide open for now. So now those are fixed variables, as well as decent centering, which you can refine as you go along. You just need to find the correct stop to bottom condenser lens distance and it's correct diameter.

The relationship to N.A. of the objective is one of matching requirement only. The objective N.A. needs to be in the range of .20 -.30 below the minimum N.A. of the condenser, so all the more reason to oil the condenser when you have a high N.A. objective. That one seems to have a correction collar not an iris, so at a fixed N.A. of .95, it is unlikely that you can get D.F. with a conventional condenser ; or is yours a higher N.A. achromat ? Typically there is a roughly .20 difference between the maximum and minimum N.As of a DF condenser funnel. A 1.25 Abbe condenser for instance , when accurately coordinated with the largest stop possible would be 1.25 - 1.0 or thereabouts, so as Josmann says, not a possible match with your 40X planapo. It is very hard to get any .95 N.A. objective to yield DF unless you are lucky enough to find one of those rare, really high N.A. condensers that were occasionally made. Zeiss Winkel made one of 1.52 N.A. The lower N.A. would have been 1.25 or so.

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Re: Problem with choosing the patch stop size for the 40x lens

#6 Post by ewieckow » Sun Jan 16, 2022 4:32 pm

Dear Achronaut,

I have read your description many times carefully, thanks for your input.
I just don't fully understand what's going on in "; or is yours a higher N.A. achromat?" but it probably doesn't matter.

Can I use immersion oil (40x) in my lenses, even though they don't have "oil" written on them?

Can immersion oil get into / between the lens of the objective?

How do you clean your lenses of oil?

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Re: Problem with choosing the patch stop size for the 40x lens

#7 Post by ewieckow » Sun Jan 16, 2022 4:40 pm

Dear Olympus BH-2 / BHSU users:

How to use Rheinberg lighting? - since setting the dark field for the 40x objective is only possible with an oil condenser? The situation is similar here too?

Is the above-mentioned oil condenser that you recommend (AmScope) will allow me to view the same place on the preparation in the polarization technique, excluding the dark field? as I understand no and I will have to replace the condensers quickly? I understand it this way because I imagine that the above-mentioned oil condenser only has such a possibility, due to the shape of the light that enters the lens?
Sorry for the stupid questions.

Sorry for my English

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Re: Problem with choosing the patch stop size for the 40x lens

#8 Post by deBult » Sun Jan 16, 2022 8:05 pm

ewieckow wrote:
Sun Jan 16, 2022 4:32 pm
Can I use immersion oil (40x) in my lenses, even though they don't have "oil" written on them?

Can immersion oil get into / between the lens of the objective?

How do you clean your lenses of oil?
You will ruin your 40* PlanApo when using oil between lens and sample/coverglass.

Only use oil on objectives marked HI or “oil”.

You wil require special immersion oil, cleaning using a chamois leather or old linnen towel and a minor drop cleaning fluid.
Each brand of microscope lenses uses a different cleaning fluid, as some cleaners attack the kit used to hold your objective together.

The recommended dark field condenser requires immersion oil between the top of the condenser and the bottom of the slide: NOT on the objective.
Last edited by deBult on Sun Jan 16, 2022 8:17 pm, edited 1 time in total.

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Re: Problem with choosing the patch stop size for the 40x lens

#9 Post by deBult » Sun Jan 16, 2022 8:15 pm

Oil immersion and cleaning instruction

https://www.microbehunter.com/oil-immer ... -at-1000x/

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Re: Problem with choosing the patch stop size for the 40x lens

#10 Post by apochronaut » Mon Jan 17, 2022 4:39 pm

ewieckow wrote:
Sun Jan 16, 2022 4:32 pm
Dear Achronaut,

I have read your description many times carefully, thanks for your input.
I just don't fully understand what's going on in "; or is yours a higher N.A. achromat?" but it probably doesn't matter.

Can I use immersion oil (40x) in my lenses, even though they don't have "oil" written on them?

Can immersion oil get into / between the lens of the objective?

How do you clean your lenses of oil?
My apologies for picking up on your question so late. What I meant by that was in reference to your condenser, not objective. If you had a high N.A. achromat condenser, it would more than likely be 1.4 N.A.. This would allow for a larger patch stop which could possibly create a light funnel between 1.2 -1.4 N.A. You might just be able to use a .95 objective under such conditions but it would require very high precision and definitely an immersed condenser.
A conventional oiled abbe condenser used with a DF stop would run in the range of 1.0-1.25 , so could definitely not produce DF with a .95 objective.

I think your other questions have been answered already.

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