Abbreviations on objectives

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morfa
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Abbreviations on objectives

Post by morfa »

Hi everyone!

I'm putting together a list with the most common abbreviations found on microscope objective barrels. I'll add this list to a flickr post I've made about the use of microscope objectives in photography. My intention is that this article should serve as a guide for "micro-curious" photographers. In other words, I want to keep it relatively simple and with a photographer's perspective.

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The rest of the article can be found here: http://www.flickr.com/photos/johnhallmen/5379235010/
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AchromatAchromatic The objective is corrected against color aberrations. According to the definition an achromatic objective should be able to bring two wavelenghths into focus at the plane. See Apo.

ApoApochromatic The objective is highly corrected against color aberrations. According to the definition an achromatic objective should be able to bring three wavelenghths into focus at the plane. See PlanApo.

BD Brightfield / Darkfield. Sometimes called HD (German: Hell / Dunkel). Objectives designed to work with an illumination system where the subject is lit by light through the barrel of the objective. These objectives have a special hollow chamber surrounding the optical elements through which subject illumination can be provided using specialized illumination equipment. For regular use this hollow compartment needs to be covered/stuffed with something in order to prevent light from leaking in but otherwise they are just like their non-BD counterparts. Nikon's highly regarded series of objectives marked "M Plan" have optically identical BD versions marked "BD Plan" which work just as well for photography. At least provided that the outer barrel is unscrewed and removed (otherwise the working distance can be compromised), that no light is allowed to pass through the hollow chamber and that the (often larger than normal) mounting thread isn't a problem.

CFChromatic aberration Free. Nikon has used this abbreviation to describe their finest objectives. The CF-objectives make most necessary corrections in the objectives themselves which sets them apart from most other objectives that typically need to be used with designated eyepieces in order to deliver a well corrected image. Because of this feature the Nikon CF objectives has a well deserved reputation for being among the best objectives for photography. Note that only some CF objectives are marked as such which makes identification a task for the experienced users.

DICDifferential Interference Contrast. An illumination technique for enhancing contrast in transparent specimens. Sometimes called NIC (Nomarski Interference Contrast). The glass elements of DIC objectives are made of "strain free" glass. For regular photography this does not matter and they behave just like their non-DIC counterparts. More info: en.wikipedia.org/wiki/Differential_interference_contrast_...

EPI – The objective is designed to work well with a certain type of lighting system where the subject is lit by light rays coming through the objective itself (via a special epi-illumination accessory containing prisms and/or half reflecting mirrors inserted into the optical path of the system). When an epi-illumination system is not used these objectives behave just like regular objectives. Also see BD.

ELWDExtra Long Working Distance. Also see LWD and SLWD.

FlourFlourescence. The objective is designed to work well in a flourescence imaging system. Flourescence is a technique where the electrons in the subject are excited using high intensity illumination. When they relax back into their normal state they send out a photon and this light is captured by the Flourescence imaging system. By separating the excitation light from the light transmitted from the subject the result is an image where the light is coming from the subject itself rather than from a separate source of light. Flour objectives are highly corrected against aberrations (almost on par with Plan Apo). Alternative meaning: Flourite The objective has elements made from flourite glass – more expensive than regular glass but with some desirable properties in terms of aberration resistance. objectives with flourite elements often have shorter than usual working distance.

HD Hell/Dunkel. See BD. In some cases it stands for High Definition but I've only seen this in optics other than microscope objectives.

HMCHoffman Modulation Contrast A microscopy technique intended to increase contrast in low contrast areas using modulation filters inserted at the rear end of the objective. I'm not sure how HMC objectives behave when for regular photography when the HMC modulation filter is removed but I'm guessing they then become very similar to a non-HMC objective (please correct me if I'm wrong!). More info: www.olympusmicro.com/primer/techniques/hoffman.html

LWDLong working distance. The objective is constructed in a way that allows more room between the front element and the subject. Also see ELWD and SLWD.

NANumerical Aperture. The number following this states the brightness of the objective (much in the same way as the F-number of a camera lens). The higher the NA, the higher the potential resolution which the objective can deliver is. The equivalent F-number on a standard camera lens (the widest aperture) is approximately F=1/(2*NA)*M/(M+1) where F is the widest aperture (for instance 1.8 for a "50mm f/1.8" lens), NA is the numerical aperture on the objective (for instance 0.25 for a "10x NA=0.25" objective) and M is the rated magnification of the objective.

NICNomarski Interference Contrast. See DIC.

MMetallurgical. The objective is intended for use in metallurgical applications. This generally means that it's corrected for use without a cover glass.

Oil - Oil immersion, sometimes Oel (german). Objectives intended to be used with a drop of immersion oil between the front element and the cover slip. These objectives usually have higher NA than usual and often very high magnification. They don't work well without the oil and their working distance is very short so they are not very useful for regular photography.

Plan – The objective offers a flatter field than a semiplan or non-plan objective.

Planachromat – A chromatically corrected objecitive with a flat field. Also see Plan and Achromat.

PlanapoSometimes Plan Apo. A highly color corrected objective with a flat field. Generally an indication of a high end objective. Also see Plan and Apo.

PhPhase contrast. A microscopy technique used to reveal certain structures/details. This abbreviation is i often followed by a number (i.e. Ph 5.) indicating the size of the contrast ring to make it easier to match with the appropriate condenser. Looking through one of these objectives you can clearly make out what looks like a darker ring shaped area somewhere in the light path. For regular use this Phase Contrast feature is not desirable. Phase contrast objectives are far from useless but given a choice it's probably better to avoid them for regular use. Charles Krebs has made a nice comparison revealing the effect of phase contrast objectives in regular use.

Semiplan – Indicates flatter field than regular objectives but less flat than Plan. See also Plan.

SLWDSuper Long Working Distance Used by Nikon to identify objectives designed to give maximum working distance. More often than not, the extra working distance comes at the cost of a somewhat lower NA. Also see LWD, ELWD, ULWD

ULWDUltra Long Working Distance Used by Olympus to identify objectives designed to give maximum working distance. More often than not, the extra working distance comes at the cost of a somewhat lower NA. Also see LWD, ELWD, SLWD

WIWater Immersion The objective is designed to be partially immersed in water. Since water have different optical properties than air it's likely that they perform better when used with water between the front element and the subject. However, in at least some WI objectives the front cone-shaped piece can be screwed off, leaving an objective well suited for regular photography (as shown by David Millard here).

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A similar list of abbreviations is available on Nikon's site here: www.microscopyu.com/articles/optics/objectivespecs.html or at Olympus' site: http://www.olympusmicro.com/primer/anat ... tions.html
I'm sure there are a lot of things to add, correct and improve here. Any help in this regard is deeply appreciated!

One confusing thing is "Flour". Looking at Nikon's own list of abbreviations it's supposed to mean "Fluorite aberration correction". However reading about their "Plan Flour" series it doesn't say a word about flourite: http://www.nikoninstruments.eu/Products ... uor-Series and instead I get the strong sense that it refers to the flourescense technique.

Again – any help and input appreciated!
Last edited by morfa on Thu Feb 10, 2011 9:56 am, edited 3 times in total.

Pau
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Post by Pau »

Fluorite objectives, also called semiapochromats, are better color corrected than achromats but a bit less than apochromats. Most makers mark them Fl

some more abbreviations from classic West German makers:
(please note that all these objectives need correction in the eyepiece, or in Zeiss newer infinite models in the tube lens)

Neofluar (Zeiss): Fluorite objective (usualy semiplan)

Plan Neofluar (Zeiss): Plan Fluorite objective

Fluotar (Leitz) Fluorite objective

NPL (Leitz) flat field corrected up to 20mm (older Pl objectives are equivalent)

Pl (Leitz) flat field corrected up to 28mm.

EF (Leitz): "eben feld", equivalent to Semiplan achromats

Pv (Leitz): Phase contrast with the special Heine condenser.
Pau

Tom Jones
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Post by Tom Jones »

Reichert, Austria: "Ph A" is Anoptral Phase Contrast, primarily for Zetopans.

Tom

Blame
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Post by Blame »

" The equivalent F-number is approximately F=1/(2*NA)"

Arrrgggggg. How many times has that got to come up?

F numbers on a camera are measures as "focal length to camera/apature".

That formula gives "focal length to subject/apature".

To get the equivalent F-number you need F=M/(2*NA), where M is the actual magnification (not rated magnification for objective).

rjlittlefield
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Post by rjlittlefield »

Blame wrote:" The equivalent F-number is approximately F=1/(2*NA)"

Arrrgggggg. How many times has that got to come up?

F numbers on a camera are measures as "focal length to camera/apature".

That formula gives "focal length to subject/apature".

To get the equivalent F-number you need F=M/(2*NA), where M is the actual magnification (not rated magnification for objective).
Blame, try calming down and think about what John is actually saying.

The formula F=M/(2*NA) gives the effective f-number (working aperture). It's a good direct indication of how much diffraction might be affecting your image.

But John said "equivalent", not "effective". I believe he's addressing questions like "How does a 4X NA 0.1 objective compare to an f/whatever macro lens?"

One way to answer that question is to figure out what the f-number of the objective would be, if it were rated the same way that camera lenses are. In other words, "What is the equivalent f-number of the objective?"

In that case, F=1/(2*NA) is not a bad approximation. A better approximation would be F=1/(2*NA) * M/(M+1), where M is rated magnification.

John's formula is saying that a 4X NA 0.1 objective is roughly equivalent to an f/5 macro lens (f/4, using the better approximation), while your formula is saying that at 4X the objective will give effective f/20.

Of course at 4X an f/4 macro lens will also give effective f/20. That's why the NA 0.1 objective and the f/4 lens are "equivalent".

--Rik

realjax
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Post by realjax »

John, great idea!. You might find some more in this list, at the Olympus microscopy resource centre.
Jacco

Alan Wood
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Post by Alan Wood »

This sort of list can become extremely long. I have some tables of old Olympus objective designations:

http://www.alanwood.net/photography/oly ... tives.html

Please change "flour..." to "fluor..."

Alan Wood

Blame
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Post by Blame »

rjlittlefield wrote: Blame, try calming down and think about what John is actually saying.

The formula F=M/(2*NA) gives the effective f-number (working aperture). It's a good direct indication of how much diffraction might be affecting your image.

But John said "equivalent", not "effective". I believe he's addressing questions like "How does a 4X NA 0.1 objective compare to an f/whatever macro lens?"

One way to answer that question is to figure out what the f-number of the objective would be, if it were rated the same way that camera lenses are. In other words, "What is the equivalent f-number of the objective?"

In that case, F=1/(2*NA) is not a bad approximation. A better approximation would be F=1/(2*NA) * M/(M+1), where M is rated magnification.

John's formula is saying that a 4X NA 0.1 objective is roughly equivalent to an f/5 macro lens (f/4, using the better approximation), while your formula is saying that at 4X the objective will give effective f/20.

Of course at 4X an f/4 macro lens will also give effective f/20. That's why the NA 0.1 objective and the f/4 lens are "equivalent".

--Rik
Damb. Your right. I never thought about looking at it that way. I always convert both of them to F/20.

rjlittlefield
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Post by rjlittlefield »

Blame wrote:
rjlittlefield wrote:Of course at 4X an f/4 macro lens will also give effective f/20. That's why the NA 0.1 objective and the f/4 lens are "equivalent".
Damb. Your right. I never thought about looking at it that way. I always convert both of them to F/20.
Yep, they're just different ways of looking at the same issue. I'm glad to see that we now agree about that.

--Rik

morfa
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Post by morfa »

Thank you guys!

I will make some changes and additions to the list based on this input. At first I thought I'd limit myself to the most common abbreviations but now I'm not sure. Alan makes a good point – this sort of list can become very long and at some point it will defeat the purpose of being something easily digestible.

I'm still not sure what to make of "Fluor". I don't doubt that it means Fluorite in some cases. But I wonder if it doesn't refer to the "fluorescence technique" in Nikon's later models? Reading the brochure (PDF) the description of the "CFI Fluor Plan" objectives I don't see "Fluorite" mentioned anywhere but I see lots of references to "flourescence"...

Also, I'm not sure if these modern "Fluor" objectives are really to be considered one step below Apo. These are Nikon's own words: "Nikon Fluor Series microscope objectives rely on the chromatically superior, proprietary CFI60 infinity optical system, so their performance is on a par with Nikon's legendary Apochromats." Source: http://www.nikoninstruments.com/Product ... Objectives

Blame: I'm glad the NA thing cleared up and just to clarify why I chose this way of looking at it here: I'm trying to translate the NA printed on the objectives into something similar printed on regular camera lenses. Your post reminded me that using the term "F-number" for this, instead of "maximum aperture" can be confusing since it's sometimes used to mean other things such as effective f-number. As long as camera lens manufacturers keep printing a highly significant number preceded with an "F" on their lenses I think we have to accept the fact that this is going to be referred to as the F-number by a large group of people. And sometimes you have to pick you poison – if I had written MaximumAperture = 1/(2*NA) it is VERY easy to make the classic mistake of forgetting that Maximum Aperture actually represents the smallest numerical value. The built in illogicality of this makes "Maximum Aperture" a quite unfortunate term to use in a formula I think.

rjlittlefield
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Post by rjlittlefield »

morfa wrote:if I had written MaximumAperture = 1/(2*NA) it is VERY easy to make the classic mistake of forgetting that Maximum Aperture actually represents the smallest numerical value. The built in illogicality of this makes "Maximum Aperture" a quite unfortunate term to use in a formula I think.
Hhmm... How about "Widest Aperture"? And maybe add the M/(M+1) factor, so that it gives the right number (ignoring pupil factor)?

BTW, there's a glitch in the definition of Apo -- it says "achromatic" where should be "apochromatic".

This is a very helpful list!

--Rik

Bob Topp
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Post by Bob Topp »

How about moving this to the FAQ- it's very useful to a novice like me. Thanks for the effort.

BT
2011- I am building my first tube microscope from a commercial 4x 160mm DIN objective.

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Post by gpmatthews »

ICT is used on Leitz objectives for interference contrast (DIC) objectives (also on substage condensers)
Graham

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