Comparison of optomechanical design of immersion objective tips of Zeiss, Olympus, Nikon

[microcosmos]

Lately I have been cleaning oil immersion objectives from Zeiss, Olympus and Nikon on inverted microscopes, and experienced the following:

Zeiss Plan Apo 63x/1.4 oil

- spring-loaded tip is smaller-diameter than the barrel below so any oil flowing down will get inside the barrel, necessitating the pink hair band to absorb any excess oil.
- the circular groove around the circumference of the tip helps to catch excess oil but only if there isn't too much of it.
- there is a circular depression around the front lens, which I think is meant to catch excess oil and stop it from spreading, but it doesn't seem to work and sometimes traps bubbles under the slide. It also makes the objective very difficult to clean because dirt that accumulates in the depression keeps getting dragged onto the lens when lens paper is pulled across or moved in a circular motion. This causes the use of a lot of lens paper and more wear and tear on the lens caused by repeated cleaning attempts.

Olympus UPLSAPO 60x/1.35 oil

- The spring-loaded tip is larger-diameter than the barrel, so overflowing oil doesn't get into the barrel but could still make its way down to the nosepiece.
- Easier to clean than the Zeiss because of the relatively large area of flat circular glass that extends beyond the actual front lens. However, at the circumference of the circular glass seems to be a black cement ring that is starting to disintegrate after years of heavy use. The black particles are sticky and adhere onto the front lens or produce streaks across it if the lens paper is pulled across.

Nikon Plan Apo 60x/1.4, 100x/1.45, 100x/1.49 oils



- completely flat front tip with no grooves or disintegrating cement, very easy to clean (cleaning these objectives actually feels therapeutic)
- pronounced ridge around circumference of tip is able to catch a good amount of excess oil without having to add hair bands

I am interested to learn from others' experiences on these and other makers' objectives, ways of getting around the difficulties, and reasons for designing the tips in different ways.

[Hobbyst46]

Important information to inverted microscope users. Those are probably features that the manufacturer/seller never mentions... Dripping oil is really nuisance in those cases. I have even heard of pumps or other devices for catching the overflow.

[Phill Brown]

I'll leave oil immersion on an inverted.
Doesn't that mean the condenser also has to be oiled?

[PeteM]

Another relevant feature is that many oil immersion lenses have an "up" locking position to keep them from transferring oil. Typically you push up and rotate to lock the nose of the objective a few mm above the focal plane. Reverse the action to have a normal spring-loaded action. I have a couple Zeiss finite that do this, my 60x Plan Apo oil Leica does as well.

[josmann]

Curious - are you guys using Type B im-oil for this?

[microcosmos]

I'll leave oil immersion on an inverted.
Doesn't that mean the condenser also has to be oiled?

The inverteds I was cleaning are optimized for epifluorescence and confocal laser scanning of cell culture dishes, so the objective is the condenser. There is a diascopic condenser but it has very low NA.

[Phill Brown]

I'll leave oil immersion on an inverted.
Doesn't that mean the condenser also has to be oiled?

The inverteds I was cleaning are optimized for epifluorescence and confocal laser scanning of cell culture dishes, so the objective is the condenser. There is a diascopic condenser but it has very low NA.

Thanks, good luck with the project.

[apochronaut]

Use type B, heavy viscosity oil. That is it's design intent mostly. It can be difficult if working at cooler temperatures but has very low runoff.
The actual front lens design difference between the 3 designs is due to the Olympus lens having an embedded front lens. This is a physical embedment. There is no cement. There is some possibility of oil creep making it's way between the lenses but I have not heard of much if any of that. Sometimes the embedded lens will just fall out since it is very difficult to embed without cement. This is the cause of the occasional objective being encountered with a depressed hole in the middle, which can be mistaken for a concave front surface.

[microcosmos]

The actual front lens design difference between the 3 designs is due to the Olympus lens having an embedded front lens. This is a physical embedment. There is no cement. There is some possibility of oil creep making it's way between the lenses but I have not heard of much if any of that. Sometimes the embedded lens will just fall out since it is very difficult to embed without cement. This is the cause of the occasional objective being encountered with a depressed hole in the middle, which can be mistaken for a concave front surface.

So far we have had no problem with oil getting into the lens. As mentioned earlier, the problem with the Olympus lens was with sticky black particles from the disintegrating ring of black material around the front glass:



This zoomed-in image of the Olympus oil lens shows the large circular front glass with the small front lens visible through the middle part of the glass, and a ring of black disintegrating material between the glass and the metal. If it is not some kind of cement or adhesive, what is it? You can see some of this disintegrating/melted material smeared on the lower right of the glass. It is sticky and can't be blown off. I think it is too black and sticky to be just dirt, and it keeps producing this stuff no matter how many times it is cleaned (well, not enough times to completely remove it!)

Here's the 60x/1.20 UPlanSApo beside the oil lens. It also has this black ring of sticky disintegrating material around the circular front glass:



Interestingly, it is the Nikon objectives that look as if they are embedded with no cement (see photos earlier).

[Macro_Cosmos]

It depends on the objective in Olympus' case. Those older specialised W/LSM and newer silicon oil immersion objectives are similar to Nikon's in that there is a ridge to catch running immersion media.
For normal immersion objectives, Evident offers some kind of black cap that covers the front, sealing it from running immersion oil.

[apochronaut]

The actual front lens design difference between the 3 designs is due to the Olympus lens having an embedded front lens. This is a physical embedment. There is no cement. There is some possibility of oil creep making it's way between the lenses but I have not heard of much if any of that. Sometimes the embedded lens will just fall out since it is very difficult to embed without cement. This is the cause of the occasional objective being encountered with a depressed hole in the middle, which can be mistaken for a concave front surface.

So far we have had no problem with oil getting into the lens. As mentioned earlier, the problem with the Olympus lens was with sticky black particles from the disintegrating ring of black material around the front glass:



This zoomed-in image of the Olympus oil lens shows the large circular front glass with the small front lens visible through the middle part of the glass, and a ring of black disintegrating material between the glass and the metal. If it is not some kind of cement or adhesive, what is it? You can see some of this disintegrating/melted material smeared on the lower right of the glass. It is sticky and can't be blown off. I think it is too black and sticky to be just dirt, and it keeps producing this stuff no matter how many times it is cleaned (well, not enough times to completely remove it!)

Here's the 60x/1.20 UPlanSApo beside the oil lens. It also has this black ring of sticky disintegrating material around the circular front glass:



Interestingly, it is the Nikon objectives that look as if they are embedded with no cement (see photos earlier).

The black doughnut around the central active part of the lens is a light block. Over time some disintegrate and wear or flake off. That is indicative likely that it is an embedded front lens. An embedded front lens does not mean embedded in the front lens housing, it means a tiny plano convex lens embedded in a cavity in the front lens. Then a black surround or sometimes stippling or frosting is applied to the surrounding glass of the main front lens to stop scattered rays entering the embedded lens obliquely, lowering contrast a bit. It works as an achromat doublet but with extreme curvature so that high N.A. can be achieved.
The embedded lens is a plano convex precision cementless doublet patented by Arthur Shoemaker as part of an objective patent for AO in 1972. The design has been referred to as a milestone in objective design and was immediately adopted by most manufacturers of high N.A., highly colour corrected objectives.
https://patents.google.com/patent/US3700311A/en I think this is it but there might be an earlier patent for the embedded front lens.

[microcosmos]

Here's an Olympus silicone objective with a similar ring of black substance that seems to melt/disintegrate into sticky particles (I already cleaned them off the glass with some difficulty).

[apochronaut]

One never knows what abuses a second hand objective has sustained. The light block covering the surround of an embedded front lens is outside the N.A. of the lens and not part of the image forming optics. It's absence shouldn't affect the resolution of the objective but some contrast likely . I have a couple of early issue AO 20X .50 planachros in a very old 7 colour coded ring shroud used going back to at least 1950. Most of those objectives are in the single colour code ring fat barrel used into the late 90's. They date from about 1967 or thereabouts and each has a different method of blocking light in the peripheral part of the objective. One uses a darkening, which causes the glass to look like dark smoke glass. The other has a sort of enamel on the surface, similar to what the Olympus has. This AO objective is dry.
Maybe Olympus hadn't enough information regarding the coating they were using in the presence of silicone?

[microcosmos]

Maybe Olympus hadn't enough information regarding the coating they were using in the presence of silicone?

It does seem at least that they didn't have information on how this material would degrade over long-term use, and this kind of information was probably unimportant for selling the objectives. It also seems that this material degrades whether silicone, water or oil is the immersion medium. It is of course possible that the wrong immersion medium is sometimes used on a given objective, but these incidents should be quite rare (confusion between our same-magnification water and oil objectives probably being more common among such incidents).