Oil immersion condenser

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Greenfields
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Post by Greenfields »

Although the maximum aperture of the condenser [and so whether it is oiled or not] definitely limits the resolving power of high n.a. objectives, in a paper published in 1952 John Baker found that, in practice. the effect is less than contemporary theory predicted.

http://jcs.biologists.org/content/joces ... 5.full.pdf

[open access]

I guess that this is why some users find the inconvenient messiness of oiling condensers [and probably the stage] not to be worth the effort unless they are compelled to achieve the absolute maximum resolution possible.

Henry
Feel free to edit my images.

iconoclastica
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Post by iconoclastica »

That's interesting reading. I cannot access Hopkins & Barham's (1950) paper, but their "curve" can be extracted from Baker's rho values. It then turns out that for all practical means, the curve can be treated as a linear relationship:

Image

On the x-axis, I used (1 - s) rather than s in order to force the regression line through 0.61

Estimating rho back from the linear equation results in aberrations from Baker of about 1%, which is nothing compared to existing rounding errors and all underlying assumptions.

So, for the system resolving power I find

rho = (0.61 + 0.23(1 - NAc/NAo)) labda / NAo



Which regrettable says nothing about the effect of the refractive indices of the media below, inside, and above the slide...
--- felix filicis ---

Pau
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Post by Pau »

Baker's article seems interesting but I fear that his data must be wrong

- What 0.0 NA does mean?
- Although my limited experience agrees with some of his affirmations like
When this equation is used, it is generally understood that the numerical aperture of the condenser is the same as that of the objective. It is often stated that when the two apertures differ, their mean should be used as the denominator of the fraction in the equation. No practical microscopist, however, would accept this. If it were true, one could get better resolution with an objective of N.A. 0.1 and a condenser of N.A. 1-2, than with an objective of N.A. 0.7 and a condenser of N.A. 0.5. In fact, of course, the latter arrangement
would give quite good resolution and the former very poor.
I think that setting the condenser aperture like 0.2 really kills the resolution of a 1.4 objective, not just diminishes it by a mere 25%

What do you think?
Pau

iconoclastica
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Location: Wageningen, Gelderland

Post by iconoclastica »

It rather looks that Baker is just plain mistaken. The equation he uses to calculate the resolution can be reversed to determine the apparent NA. Doing so, it becomes clear that the performance of both high NA objectives decreases asymptotically to 1.0, even with the worst of condensers.

However, I haven't found rejection of this theory sofar. E.g. Oster & Pollister (Optical Techniques, 2013) write that "even if the illumination aperture is reduced to zero (parallel beam illumination), the resolving limit in representative cases is only increased by a factor less than 1.5 (Hopkins & Barham, 1950"

If anyone has access to the original text of Hopkins & Barham: I am getting increasingly curious.

BTW, the issue has been discussed here before: https://www.photomacrography.net/forum/ ... p?p=145277
--- felix filicis ---

Sumguy01
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Post by Sumguy01 »

Hi Guys
I have a Nikon Universal condenser that I use on an Optiphot 2.
It has Achr - Apl 1.4 on it.
It does not say oil on it.
Does anyone know if it is safe to use oil on this one?
Has anyone tried it and is it worth the mess for the results you got?

Pau
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Post by Pau »

Sumguy01 wrote:I have a Nikon Universal condenser that I use on an Optiphot 2.
It has Achr - Apl 1.4 on it.
It does not say oil on it.
Does anyone know if it is safe to use oil on this one?
Has anyone tried it and is it worth the mess for the results you got?
Yes, it's for oil (dry condensers have a maximum NA of 0.95, in most cases they are labeled 0.9)
If you use that condenser dry, again its max NA is 0.95

Is worth oiling it?
See the former discussion, when you want maximum resolution with oil objectives yes, in many other cases no.
Pau

enricosavazzi
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Post by enricosavazzi »

Sumguy01 wrote:Hi Guys
I have a Nikon Universal condenser that I use on an Optiphot 2.
It has Achr - Apl 1.4 on it.
It does not say oil on it.
Does anyone know if it is safe to use oil on this one?
Has anyone tried it and is it worth the mess for the results you got?
Only oil (and a couple of exotic types of immersion fluids) allow NA of 1.4, so you can safely say that this is a condenser for oil immersion.

I have done some occasional work with oil immersion on the subject side, and even less with oiled condenser. It is potentially messy, and some old types of immersion oil can be toxic and you should not get them on your fingers. Most of the modern oils are not so toxic, but some special ones are.

You also need objectives for oil immersion, and if you need DIC also DIC condenser prisms designed for the oil objectives.

Basically, one should use oil only as a last resort, in cases where you cannot get enough resolution with air objectives and condensers. It is not used just for the fun of it.
--ES

Sumguy01
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Joined: Mon Jan 28, 2013 11:05 pm
Location: Ketchikan Alaska USA

Post by Sumguy01 »

:D Hi guys
Thanks for the info.
Someday I may try oil on the condenser with my 60x 1.40 obj.

viktor j nilsson
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Location: Lund, Sweden

Post by viktor j nilsson »

enricosavazzi wrote:
Sumguy01 wrote:Hi Guys
I have a Nikon Universal condenser that I use on an Optiphot 2.
It has Achr - Apl 1.4 on it.
It does not say oil on it.
Does anyone know if it is safe to use oil on this one?
Has anyone tried it and is it worth the mess for the results you got?
Only oil (and a couple of exotic types of immersion fluids) allow NA of 1.4, so you can safely say that this is a condenser for oil immersion.

I have done some occasional work with oil immersion on the subject side, and even less with oiled condenser. It is potentially messy, and some old types of immersion oil can be toxic and you should not get them on your fingers. Most of the modern oils are not so toxic, but some special ones are.

You also need objectives for oil immersion, and if you need DIC also DIC condenser prisms designed for the oil objectives.

Basically, one should use oil only as a last resort, in cases where you cannot get enough resolution with air objectives and condensers. It is not used just for the fun of it.
Can't say I have been using oil objectives a ton, but it's worth mentioning how nice it is that oil objectives are so tolerant to cover slip thickness and sample preparation. I have a Nikon CF Fluor 40x 1.3 oil and a CF Plan Apo 60x 0.90 Dry. Looking at the same slide, the oil objective immediately delivers pretty much the crispiest image imaginable as soon as you swing it in. The 60x PlanApo is a lot more finicky. Adjusting the correction collar is really critical. And even when you get it properly optimised, the image quality is never as good. So I'd say that it depends on what you want to do. If you accept the clean up afterwards, I'd say that I can something be a lot quicker getting good photos with oil.

JohnyM
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Joined: Tue Dec 24, 2013 7:02 am

Post by JohnyM »

Agree. My set is 10x PA, 20xPA, 20xPF, 40x1.3 PF
Exactly because of coverslip correction. Another downside of it is that on stacking you need to constantly readjust it to maintain IQ... and then the focus shifts.

houstontx
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Joined: Fri Jul 31, 2015 1:07 pm

Post by houstontx »

thanks for the info and link to previous thread. I had been worried about using my high NA objectives with my 0.7NA condenser. Now i can stop obsessing about achieving maximum resolution! Haha...I mean who needs it...right :?

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