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
Oil immersion condenser
Moderators: rjlittlefield, ChrisR, Chris S., Pau
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- iconoclastica
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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:
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...
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 ---
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
What do you think?
- What 0.0 NA does mean?
- Although my limited experience agrees with some of his affirmations like
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%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.
What do you think?
Pau
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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
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 ---
Yes, it's for oil (dry condensers have a maximum NA of 0.95, in most cases they are labeled 0.9)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?
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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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.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?
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
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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.enricosavazzi wrote: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.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?
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.