Silicone immersion objectives - any experience?

[viktor j nilsson]

Happy to report that both the 40x 1.00 and 100x 1.25 silicone objectives has now arrived safely and in good condition. Based on the reputation of the grease Olympus used on their classical microscopes, which tends to turn solid with age, I have been rather surprised by how smooth the iris mechanisms has been on all the three iris-equipped short-barrel objectives that I now own.

I tested the 40x 1.00 Apo a bit yesterday.
A couple of notes, based on visual observation only.

I used a sloppily prepared water mount, mostly looking mostly at some bundles of filamentous algae and a dead mite. Both subjects were quite deep and challenging for high NA work - exactly the conditions I hope will benefit from silicone immersion.

I used a 50:50 water:glycerine mixture (based on volume) as immersion medium.

Under ideal condition (algae sitting just under the cover slip), the 40x 0.95 dry PlanApo (with perfectly adjusted correction collar) clearly outperform the 40x 1.00 Apo.
The Planapo was more contrasty, had less longitudinal CA, and showed better contrast.

A little deeper into the slide (halfway down the body of the mite), the difference between them becomes less clear. With its collar perfectly adjusted, the Planapo still provides a decent image, but the image from the Silicone Apo is almost as good.

When focused at the lowest part of the mite (a claw), the PlanApo cannot form any clear image at all. But the Silicone Apo still produce a fairly sharp and contrasty image.


Conclusions:
Water:glycerine definately works, and is extremely easy to clean up.

The Apo showed a bit more CA than I had expected. Maybe the Dispersion characteristics of Water:Glycerin differs from that of silicone oil, as suggested by Wes. I will pick up some silicone oil to try. I was also not very careful in preparing the water:glycerine mixture, so I may be a bit off on the RI.

Later long-barrel silicone objectives are likely much better than the non-plan Apo 40x. It is sharp in the center, but fall off quite a bit outside FN 14 or so. But I mostly see this as an objective I would use for deep stacks of water mounts.

In all, I thought it felt quite promising and I look forward to trying this out more, and taking photos. Being able to focus deeper into water mounts without adjusting the collar might be very useful indeed for some subjects. I will try to compare it with my Nikon 40x 1.30 oil objective, to see how they both handle deep water mounts.

[Rossf]

Hey viktor j Nilsson,came across this post and realised I’ve got the same 100x objective!-I got it mainly for the iris-mine is super smooth for its vintage as well-I haven’t used silicon oil yet but this is the objective that proved to me that oil immersion was something worthwhile! Using oil (hope it’s not detrimental) i imaged a marine protist that took up the whole view and was pretty stunning in detail-it also proved to me the size of the front element has no direct bearing on the quality of the image! I’ve seen and have 100x objectives with quite larger front elements but this is the one that really works for me-not really into immersion except for my Leitz water objectives-now I really want to try it with silicon oil- I think my solution to the messiness is to consider the slide and coverslip as disposable so at least that cuts down the work! And maybe not use my beautiful ach/apl condenser..actually I wonder if you have to use silicon oil on the condenser or just the coverslip?
Regards ross

[viktor j nilsson]

Hey viktor j Nilsson,came across this post and realised I’ve got the same 100x objective!-I got it mainly for the iris-mine is super smooth for its vintage as well-I haven’t used silicon oil yet but this is the objective that proved to me that oil immersion was something worthwhile! Using oil (hope it’s not detrimental) i imaged a marine protist that took up the whole view and was pretty stunning in detail-it also proved to me the size of the front element has no direct bearing on the quality of the image! I’ve seen and have 100x objectives with quite larger front elements but this is the one that really works for me-not really into immersion except for my Leitz water objectives-now I really want to try it with silicon oil- I think my solution to the messiness is to consider the slide and coverslip as disposable so at least that cuts down the work! And maybe not use my beautiful ach/apl condenser..actually I wonder if you have to use silicon oil on the condenser or just the coverslip?
Regards ross

That's wonderful!
Don't use silicone on the condenser, it is corrected for oil (if anything), so silicone oil won't improve things there.

Interesting to hear that you liked the image with immersion oil.
I have now tried silicone oil (NA = 1.40), pure water (NA = 1.33), 50:50 water:glycerol (NA ~1.40), and pure glycerol (NA = 1.47) with my 40x 1.00 apo.
I thought that it was pretty clear that 1.33 and 1.47 was quite some ways off. The 50:50 mix at NA 1.40 performed quite well, but I think that the real silicone oil was slightly better.

However, I must emphasize that everything you heard about the horrors of silicone oil is true.
I definately think that it is smart to treat cover glasses as disposable if you use silicone oil. But that's not the only problem!

I thought that I had cleaned off the silicone oil from the 40x 1.00 objective after I finished using it the other night.
But the next day, when I was testing my DIC setup using my Klaus Kemp test slide, I accidently switched over to the 40x 1.00 (which I thought was clean and dry).
Evidently, there was some silicone oil left on the 40x apo, which immediately left a blob on the test slide.

I first tried to clean it with ether on a q-tip, but this just spread it out into a thin layer of micro beads:

silicone.JPG (27.48 KiB) Viewed 1242 times

Eventually I got the slide clean with ethanol and kimwipes.

But then, as soon as I started to look at the test slide again, new blobs of silicone oil showed up on the slide. It turned out that I had also managed to get silicone oil on the dry 40x planapo AND the 20x planapo.

It took me a while before everything was clean.

If you try silicone oil - be very careful. Much more careful than I was.

[Rossf]

viktor j nilsson that’s a hideous story to any microscopist! Did all this happen at night when you were probably too tired to be experimenting with silicone oil? I’ve done some really stupid things late at night-even ruining one of my favourite objectives Glad to hear you got the 20x Plan Apo for the Vannox-the silicone oil intrigued me when you mentioned it can image deeper into samples than oil-I bet it was used for time lapse video because of its stability especially if the camera is shooting all night.
Regards ross