DIC - Plan Fluorite or Plan Apo?

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benjamind2014
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DIC - Plan Fluorite or Plan Apo?

Post by benjamind2014 »

I've got a couple of quotes regarding a DIC microscope setup, but they are quite expensive, and include Plan Apo objectives. I've spoken to a couple of guys who say that Plan Fluorites are just as good for the purpose of video recording of DIC observations.

Can anyone chime in with further information as to the differences between these two objective types when using DIC transmitted light? I was under the impression that there isn't much difference, but Plan Apo objectives are much costlier in practice (unless you are lucky enough to find them second hand).

Scarodactyl
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Re: DIC - Plan Fluorite or Plan Apo?

Post by Scarodactyl »

This will probably vary contextually--fluorite isn't exactly rigorously defined, and some are more apo-like than others. But I'd guess you probably wouldn't see an enormous difference. I have a couple Olympus fluorites which don't give me any trouble, but I got a GE-branded objective which was marked as a fluorite but has pretty rough CA. It varies.
Who are you getting the quote from?

PeteM
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Re: DIC - Plan Fluorite or Plan Apo?

Post by PeteM »

I'd agree that the Plan Fluorites are the sweet spot in terms of price-performance.

Since DIC has a sort of optical sectioning capability, the ever-so slighly fuzzier edge from an objective corrected chromatically at two or three points versus one corrected at three or four doesn't amount to much. And the Plan Apos, with their additional lens elements, are more likely to lose contrast and possibly introduce strain.

The only exception to this, in my experience with Nikon, Olympus, and Zeiss finite and Nikon and Leica infinite objectives, would be the 60x Plan Apo DIC objectives with oil immersion and a 1.4na available from most major makers. If you want the ultimate in resolution, there often isn't a near-equivalent Plan Fluor readily available on the used market.

I would warn that I've seen some Chinese objectives marked as plan fluorites which are plan achromats at best. I've also found that the Motic and AccuScope plan fluorities seem a half step behind the optical quality of the Leica-Nikon-Olympus-Zeiss equivalents. I'd want to compare and contrast quality, if possible, if you're thinking of buying a new Chinese DIC scope versus assembling a used top brand DIC scope. With Zeiss there's also the delamination issue to watch for.

Macro_Cosmos
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Re: DIC - Plan Fluorite or Plan Apo?

Post by Macro_Cosmos »

Yes, FL is just as good as apochromats... if not... better (sometimes).
- Greater contrast
- Equal levels of CA correction unless you pixel peep, ONLY applies to oil immersion objectives
- Way cheaper, an FL is a third or quarter of an apochromat, unless it's some very exotic objective such as Olympus' A-line 20x phase contrast objective which is nearly $10k

My recommendation is 10x apochromatic objective, 20x and 40x, have one apochromatic depending on what you want, and a 60x oil immersion fluorite, it doesn't hurt to get the 100x instead.
If you're doing video, I don't see much of a reason to go with apochromatic objectives at least on the higher magnifications. You'd be doing VEC (video enhanced contrast), specimen preparation is far more important than whether your objective has that fancy lettering or not. I have some solid objectives but my videos are still bad due to shoddy technique and lacklustre specimen preparation skills.

Lou Jost
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Re: DIC - Plan Fluorite or Plan Apo?

Post by Lou Jost »

Yes, FL is just as good as apochromats... if not... better (sometimes).
I agree. In addition to the advantages given, there is another one. Because FL objective designs are less constrained by color correction, they can have more uniformity of sharpness across the field, and/or larger image circles of good quality.

it doesn't hurt to get the 100x instead.
Here I'd disagree, if both have the same NA and both are infinity corrected. The lower-powered one has a larger image circle and can be pushed to 100x if needed. The reverse is not true.

Scarodactyl
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Re: DIC - Plan Fluorite or Plan Apo?

Post by Scarodactyl »

One can also buy fluorites and save a lot of dough, then acquire used apo objectives to try as deals appear. If it's a Nikon or Nikon standard system the cheap used 20x apos give you a good head start on that.

PeteM
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Re: DIC - Plan Fluorite or Plan Apo?

Post by PeteM »

Another plus for a 60x over a 100x - when both have the same 1.4na numerical aperture - is that the 60x will often see deeper below the cover slip. So, the ultimate resolution is the same, but the ability to deal with a slightly thicker specimen is often improved.

Macro_Cosmos
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Re: DIC - Plan Fluorite or Plan Apo?

Post by Macro_Cosmos »

Lou Jost wrote:
Tue Sep 07, 2021 10:56 am
Here I'd disagree, if both have the same NA and both are infinity corrected. The lower-powered one has a larger image circle and can be pushed to 100x if needed. The reverse is not true.
Absolutely true, but we're talking about a microscope here so I don't think it works (well). In general, I'll recommend your practice but not with microscopes.

Both the 60x and 100x are well pass "empty magnification" regarding modern consumer cameras boasting over 45 megapixels. 60x objectives are scarce compared to 100x, the DIC prism for 60x and the objective itself is often more expensive than the 100x if it's Olympus.

How would one intuitively push an objective mounted to a microscope further with a 300mm tube lens? Most need the trinocular head for viewing leisure, it's possible to mount a longer focal length tube lens to a microscope, but is there a tube lens that can function well with all the stuff placed in front of it? ie, nosepiece, slider prism, analyser, maybe a fluorescence turret as well, you'd also lose the binoculars. Best bet is a 300mm achromatic doublet, those DSLR/Mirrorless lenses likely won't work well. My microscope with the fluorescence turret installed produces heavy vignetting if I want to use direct projection which is a shame, I have to use a projection eyepiece now. Used to be fine without that extra component in front of the tube lens.

I never use my 100x objective despite the higher NA (1.4 for the 100x, 1.2 for the 60x). The 60x is far nicer to have, that is absolutely true.
For sensor coupling, a 60x with an NA of 1.4 resolves a 24MP monochrome sensor at 550nm green light (18 MP for NA 1.2). The 100x... well, it drops to 9MP since NA is the same. Olympus even offers a 40x with an NA of 1.4 now, but that's another can of worms, the U-DICTS must be used for it, very unergonomic, that's the least of concerns since the 40x NA1.4 XApo is like $12k new. :shock: :shock:

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