American Optical 50x Iris Oil

[rnabholz]

I just picked up one of these to add to my darkfield scope after having a favorable experience with the 100x iris.

This one presents a bit of a challenge to use.

I am finding the working distance is pretty large, making maintaining the oil contact bothersome. Between that and the different focus point, not nearly parfocal, it can be a pain.

I am using Cargille A oil. Would B help me maintain the oil connection better? I have heard it is a bit of a bother to clean up vs A?

Any tips or tricks are welcome.

Thanks

[zzffnn]

Yes, type B is much better than type A in maintaining contact between low power oil objective and cover slip. And yes, it is much hard to clean up. You can use a cover slip to scoop away the oil, or use cotton swaps wetted with alcohol.

Parfocal issue can occur between different catalog numbers series, but I have not met that with modern AOs. You can always use shim/parfocal rings.

http://cynmar.com/accessories/25702-par ... it127.html

http://m.ebay.com/itm/Set-of-14-Par-Foc ... 2056116672

[lorez]

I am finding the working distance is pretty large, making maintaining the oil contact bothersome. Between that and the different focus point, not nearly parfocal, it can be a pain.

What you describe are the symptoms of an objective that is full of oil. Nothing short of a rebuild is going to help.

lorez

[rnabholz]

Thanks zz

I am finding the working distance is pretty large, making maintaining the oil contact bothersome. Between that and the different focus point, not nearly parfocal, it can be a pain.

What you describe are the symptoms of an objective that is full of oil. Nothing short of a rebuild is going to help.

lorez

Is there a way to confirm that diagnosis, I still have time to return it if it turns out to be the issue.

Thanks

[lorez]

You may be able to see the oil meniscus by using your phase telescope to look at the various lenses in the objectives. The symptoms are a 100% key in my experience. Send it back.

lorez

[rnabholz]

Let me add one more data point.

While I thought it was part of the oil viscosity issue, when I was able to finally achieve the best focus, I still felt as though there was "movement" in the image. Very subtle, but definitely there. I was not able to get what I would consider to be a really sharp focus.

Perhaps more support for your diagnosis?

Thanks very much

[lorez]

What you described at the top of the discussion is all I need.

lorez

[rnabholz]

Thank you.

Rod

[zzffnn]

Maybe a clumsy previous owner used too much lubricants, when (s)he tried to free the iris?

Lorez, have you ever seen such a problem, in an objective without iris or correction collar? I wonder how an immersion objective can be filled fluid, unless fluid went in from the back end (the immersion tip should be oil or water proof).

[lorez]

Sadly, the oil immersion objectives are not impervious to oil penetration. Improper use and care allows the oil to accumulate on the barrel of the objective and eventually seep between the lens elements. The seals erode and the oil gets in. I have a pile of damaged objectives.

lorez

[apochronaut]

AO didn't use a seal. They machined and assembled them very precisely. I'm pretty sure there would have been torque specs. on the front cap, which seats the front lens housing. The oil is supposed to be in contact with the front lens element and only the front lens element. However, in many actual situations, where the user is an employee, doesn't own the equipment and wants to expedite tasks, oil can get loaded on without adequate removal and ends up getting into the space between the front housing and the locking ring or cap. Often on those and the 100's a pointed tool like a scibe or needle run around that seam will pile up a big stack of hardened black goober. If that is there, then the oil could have slipped around the housing. The 50X is no more prone than any other, though. OIl seepage is a fact of oil immersion lenses, no matter who made them.
Cleaning them out is easy, as long as the oil hasn't caused element separation. Sounds like that isn't the case, if the image is close enough not to be that noticeably defective.

[rnabholz]

Thanks for the guidance everyone.

While the fix may be doable for someone with the skills and experience, I have neither, so I will exercise my right to return this one and find another that is in better shape.

Thanks again for the benefit of your experience.

Rod

[rnabholz]

Just a note to say that my replacement for the defective 50x Iris arrived today. It works wonderfully well, and just as you would expect with regards to parfocality and working distance.

Thanks for the diagnosis lorez and Apo.

[apochronaut]

I'm curious, Rod. Do you find that you have to stop this one down at all, to effect a good dark background?

[zzffnn]

I am guessing if Rod only photographs mounted diatoms, he may not need to stop down NA 0.8 iris 50x at all. If he still continues on shooting some big fat living ciliates (Stentor, Vorticella, ect, as he did before), then he would need to stop down that iris sometimes.

At least that was my experience using my LOMO 30x iris NA 0.6-0.9.

[rnabholz]

I'm curious, Rod. Do you find that you have to stop this one down at all, to effect a good dark background?

Wide open the darkfield was good. I did play around with it some, closing it a bit at times and convinced myself the view was better, but in the first session with it I can't say that I did any critical evaluation.

I hope to do more with this weekend.

Thanks

Rod

[rnabholz]

I am guessing if Rod only photographs mounted diatoms, he may not need to stop down NA 0.8 iris 50x at all. If he still continues on shooting some big fat living ciliates (Stentor, Vorticella, ect, as he did before), then he would need to stop down that iris sometimes.

At least that was my experience using my LOMO 30x iris NA 0.6-0.9.

It will be fun to try this out on those big targets. Darkfield at NA .6 and higher was a bit fiddly with masks, but the DF Condenser and this objective should be easier.

[zzffnn]

It will be fun to try this out on those big targets. Darkfield at NA .6 and higher was a bit fiddly with masks, but the DF Condenser and this objective should be easier.

Rod,

Here is what those ciliates look like under NA 0.65-0.95 darkfield:

viewtopic.php?f=6&t=3292

1st video was shot under NA 0.95 (dry 40x apo).
2nd video was likely shot under NA 0.9 or 0.95 (water achromat 30x or dry 40x apo, cannot remember).
3rd video was likely shot with a dry NA 0.65 achromat.

With that Vorticella type of ciliate that I videotaped in the 1st video, I did try a dry 0.65 achromat first. But its image was less resolving (no cilia could be seen, for example), although with less halos. In the end, I prefer the more resolving and more halo image of NA 0.95, and published only that one. If you want, I can upload the NA 0.65 video and did an enhanced still frame capture, just for you.

I also found that with wet mount living ciliates, I have to compress the cover slip sometimes. That Vorticella, for example, could not be focused well even at a low darkfield NA of 0.65, without compression (removal of more water and pinning/compressing the ciliate down flat).

Overall, with ciliates, I personally prefer oblique over darkfield. Some key internal details for identification (such as mouth part or surface cilia) could be obscured in darkfield, though easily visible in oblique/brightfield. Ideally, I would start with oblique then supplement with darkfield. Many ciliates are texturally not translucent enough for very high NA darkfield, at least not as much as mounted diatoms.

[apochronaut]

I'm curious, Rod. Do you find that you have to stop this one down at all, to effect a good dark background?

Wide open the darkfield was good. I did play around with it some, closing it a bit at times and convinced myself the view was better, but in the first session with it I can't say that I did any critical evaluation.

I hope to do more with this weekend.

Thanks

Rod

There is no real reason to have a mid magnification oil objective for DF. A quality high N.A. dry objective would be just as good as long as the N.A. was high enough to produce maximum resolution and low enough or could be lowered enough to effect DF .
However:
The idea of having an oil, higher N.A. mid magnification objective suits the purpose of DF well in actual practice, where one can reduce the magnification, after going to high power oil immersion without fussing with an oil problem. When needing to change back down to a lower power objective in lengthy DF sessions, this is often the case and is one of the most annoying instances in microscopy. I have found the .80 barrier to be borderline with that 214F condenser but generally, the iris turns out to be unnecessary. The iris seems to be there, to accommodate other applications, most notably fluorescence, where the # 1016 objective was widely used. Leading up to the production of the # 1016 objective, they produced a 44X dry .85 achromat with iris, 43X .85 L.W.D. dry achromat, 50X .95 oil achromat all for 160mm tubes, then a 50X .85 oo oil achromat with iris and then this 50X .80 oo oil planachro with iris. Later for the 400 series they tweaked the # 1016 into a 45mm barrel as a 50X .80 oo oil Neoplan with no iris. The iris objectives all work for DF, those without do not except for the last objective on the list . It seems that .80 is pretty close to the cuttoff. The iris in the case of the # 1016 is probably not necessary for DF.
Bausch & Lomb was the main competitor in the market, at the time the 34mm parfocal objective based AO microscopes were in their heyday. There was a significant market for DF microscopes, which by the early 90's, became dominated by Olympus. B&L also issued a 50X .80 oil objective pitched at the DF market but in that case it was an oil planfluorite without iris. B & L did not make a fluorescence microscope, so perhaps that is why the iris was unnecessary for that objective.
This is all affected by the individual condenser employed. Some condensers work at a higher minimum N.A. The later AO condensers, seem to be of the latter type.

[rnabholz]

It will be fun to try this out on those big targets. Darkfield at NA .6 and higher was a bit fiddly with masks, but the DF Condenser and this objective should be easier.

Rod,

Here is what those ciliates look like under NA 0.65-0.95 darkfield:

viewtopic.php?f=6&t=3292

1st video was shot under NA 0.95 (dry 40x apo).
2nd video was likely shot under NA 0.9 or 0.95 (water achromat 30x or dry 40x apo, cannot remember).
3rd video was likely shot with a dry NA 0.65 achromat.

With that Vorticella type of ciliate that I videotaped in the 1st video, I did try a dry 0.65 achromat first. But its image was less resolving (no cilia could be seen, for example), although with less halos. In the end, I prefer the more resolving and more halo image of NA 0.95, and published only that one. If you want, I can upload the NA 0.65 video and did an enhanced still frame capture, just for you.

I also found that with wet mount living ciliates, I have to compress the cover slip sometimes. That Vorticella, for example, could not be focused well even at a low darkfield NA of 0.65, without compression (removal of more water and pinning/compressing the ciliate down flat).

Overall, with ciliates, I personally prefer oblique over darkfield. Some key internal details for identification (such as mouth part or surface cilia) could be obscured in darkfield, though easily visible in oblique/brightfield. Ideally, I would start with oblique then supplement with darkfield. Many ciliates are texturally not translucent enough for very high NA darkfield, at least not as much as mounted diatoms.

Thanks zz

In general I do find that I enjoy the 10 and 20x darkfield views of ciliates much better than higher magnifications. First those levels of magnification generally frame those relatively large targets better, and tracking a moving ciliate at higher mags is just frustrating.

Add to that the complication of oil on a loose cover slip and you are quickly reaching the HFC level (Hassle Factor Critical).

Not likely to be a regular regimen, but fun to try.

Thanks

[zzffnn]

Rod, sorry for the diversion. But I have to ask apo here:

44X dry .85 iris objective for 160 mm tube?

I may want one of those in the future. Any brand would work, though short objectives are highly preferred. What is the catalog number and how do I find one? Thank you, apo! I would consider an infinity AO too, if it is a dry iris at around 0.6-0.8.

[zzffnn]

Rod,

In that first video that I referred you to, the cover slip was pressed down so much that it tightly adhered to slide and
did not float at all. That compression immobilized the ciliate too, which almost fully filled the 40x objective field (and would be impossible to film if not immobilized). I also had to carefully add water to prevent complete dry-out (though too much water can flood away the subject).

Coupled with immersion objectives, especially my water immersion (which can leak into under cover slip), it is quite fiddly. That is why a dry iris objective at NA 0.65-0.85 range would be nice for DF.

Definitely not a regular regimen, more like pushing the limits.

[rnabholz]

Thanks for the info Apo.

The oil issue alone was a driving consideration for me. I found myself regularly fouling my 40x dry. Now I scan with a 20x high and dry above the oil and can swing in 50 or 100x without missing a beat.

The cost of the 50x Iris Oil was about $10 bucks higher than a 40x dry, I figure I will save that much in lens cleaning tissue in the first month. ;^)

[apochronaut]

Thanks for the info Apo.

The oil issue alone was a driving consideration for me. I found myself regularly fouling my 40x dry. Now I scan with a 20x high and dry above the oil and can swing in 50 or 100x without missing a beat.

The cost of the 50x Iris Oil was about $10 bucks higher than a 40x dry, I figure I will save that much in lens cleaning tissue in the first month. ;^)

For sure. It makes life so much easier but you can see that both AO and B & L purposefully kept the maximum N.A. on the oil objectives down below the much more common .85 that had almost become an industry standard for higher N.A. mid magnification objectives. Finding an AO .85 40X oo corrected dry objective, is like looking for a needle in a haystack anyway. They made one but not a lot of them. I know of a few around but they are mostly in the hands of those that don't actually use them. They just like them because they are rare, they can keep them out of the hands of those that would actually use them, and they can stare at them from time to time.