MicrobeHunter.com Microscopy Forum

I came across an offer today for a Nikon 100x NCG oil objective. I feel little inclined to buy it, but it made me wonder what these lenses are intended for. It's 160mm tube length, so I presume it was to be used with transmissive lighting - the incident lighting of Nikon's adds 50mm tube length. So, immersion oil is applied on top of something that then doesn't swim away. The only thing I can think of is very thin mineralogical slides. Is that correcty worked out?

Blood smears?
I have a Nikon 40 NCG (dry)which I had some reason to believe was for blood.
A path lab might use oil objectives for diagnosis where they don't need to keep the slide?

no cover glass. not normally used for transmitted light microscopy but they are sometimes for smears, thin sections of hard materials.
I've seen vet technicians put oil right on temporary dried smears.

yuk, that's unhygienic ! Thanks, so many micoscopic applications beyond the ones I am familiar with.

Smears are fixed with methanol or heat, so if done "properly" it shouldn't pose as a biohazard.

P.S. Another story, but I would be careful with second-hand counting chamber slides since they use cells/blood in a raw state...

Almost all clinical labs use standard 100x 0.17 oil immersion objectives, with oil and without cover slips, for blood smears, body fluid smears, or gram stains for that matter. Lower power objectives are used with a thin film of oil substituting for the cover slip there as well. Cover slips are costly, slow to use, and quite unnecessary in this application. The desiccation and staining processes pretty much kill everything, so the infection potential is pretty low, too. Besides, clinical lab folks treat everything as potentially infectious anyway. We use the cover slips for urine.

In 40 years I've only seen one person use a cover slip on a blood smear, and that was a pathologist reviewing the slide to ID malignant cells. And that was on top of a drop of oil to fill the void above the dried smear and eliminate diffraction. I'm pretty sure it was only to keep the oil off of his high dry objective!

The oil has nearly the same refractive index as the glass so it really isn't necessary. Occasionally you might find a lab using an No Cover Glass/No Cover Slip objective, but there are not many. That's why you don't see many NCS objectives on the used market. The biggest user of oil 100x biological objectives are clinical labs. The NCS objective will give better results at the extreme end, but they're pricier and not considered necessary as clinical work doesn't generally involve structures requiring extreme resolution.

I'm pretty sure I have a nice 160 Oly NCSPlanAPO 100x 1.40 oil if someone is interested.