Do I need to add immersion oil to the condenser too?

[ke6igz]

I have a Olympus CHBS microscope. The manual recommends adding immersion oil to the slide and condenser when using the 1000x objective. How important is it to add it to the condenser?

[DrPhoxinus]

If you use the condenser without oil you can still get an image but the resolution will be less than what you would get with oil.

[apochronaut]

Not oiling an abbe 1.25 condenser lowers the N.A. of the condenser to it's dry (air space) N.A. of about .90 and the N.A. of an oil immersion 1.25 objective used with it to about 1.13 + -. This translates to a difference in resolution of about 1/20 of a micron or 50 nanometers.

[Greg Howald]

Easy answer. YES.

[Tom Jones]

It's generally not important.

For a little perspective, in clinical labs we used a LOT of oil. Every single WBC differential slide, and every single gram stain, was examined under oil immersion at the objective only. Unless the slide had be coverslipped and stored for later pathology review, we didn't use coverslips either, even though the objectives called for them. If you needed to go back to 40x from 100x oil, and didn't have a 40x or 50x oil objective, you simply wiped the oil off of the slide with a glass rod and looked through the remaining oil film substituting for a coverslip. It works fine. Oh, yeah, we almost never cleaned the oil off the oil immersion objectives either. Sometimes, if you could see a few random RBCs or other junk floating around, liberated from the surface of preceding slides, you might gently wipe it off with gauze or a cotton ball, just to clear up the field. The trauma center I worked at processed as many as 500 WBC diffs slides per day prior to current automation. It's only a hundred or so today that need review. Grams stains on cultures or patient specimens might number 100 per day. That means many tens of thousands of hematology slides and gram stains are being processed across the country every day without using oil on the condenser.

In 40 years, I've actually never seen an oiled condenser used in a clinical lab. You just don't gain enough to make it worth the time and trouble.

Not using oil with the condenser does limit the NA. The real question is whether that causes a meaningful loss of resolution in the sample in question. Most generally, the answer is no. At least not to the extent it is normally worthwhile to oil the condenser with all the time, difficulty and mess it causes. If you're looking at really fine structure in a diatom, or some other subject where you need absolutely the best resolution you can get, use oil and deal with the mess.

The best suggestion I can give you is to take the kinds of specimens you normally look at, look at them without oil on the condenser, then repeat the observations using oil. Just drop the condenser and add a drop of immersion oil, return it to the correct position and take a look. You don't even need to move the slide. Then clean the oil off the condenser and try the same process with the next specimen. You can assess for yourself whether it is worth the trouble, or even provides a better view of the kinds of things you normally look at. Unless you're doing really critical work, I'd bet you almost never oil the condenser again!

Tom

[apochronaut]

That makes an enormous amount of sense in a production facility. On the other hand , having handled a hundred or so condensers over the years, most of the used ones had a considerable amount of oil on them, right up to some being saturated and invaded. Many of those would have been prior to 1980. Maybe due to ever increasing time constraints, the more precise practice of oiling the condenser became increasingly a timewasting pain?
Until the later 70's , dedicated dry higher N.A. condensers were not common and into the 80's, dry achromat aplanats of .90 became de rigeur, providing only a smijeon less resolution but an overall better field correction.