MicrobeHunter.com Microscopy Forum

The B&L paraboloid condensers they're great but don't really work so well after .85. The cases they came in originally included three or four funnel stops of various configurations.

To get 1.1 you would need to start with a condenser of 1.3-1.5 A Cassegrain DF condenser can work at a full 1.30 objective aperture.

It seems odd that there were almost no .95 apos with iris diaphragms during the first 50 or so years that those fairly standard apochromat series that everyone made existed. Zeiss had a 60X 1.0 apochromat with iris and Bausch & Lomb briefly listed a 61X 1.4 with iris. Maybe Leitz too but I don't know about that.

Somebody here was playing around with internal reflection darkfield I seem to recall. Got decent results. A cassegrain condenser seems to be hard to track down affordably or at all even.

BramHuntingNematodes wrote: ↑

Tue Jan 18, 2022 4:16 pm

The B&L paraboloid condensers they're great but don't really work so well after .85. The cases they came in originally included three or four funnel stops of various configurations.

The thing about DF is that the quality of the image is not totally dependant on N.A. and the usefulness of any objective's N.A. is also affected by magnification. There are a lot of problems in many DF images that I have looked at which are caused by scatter from all kinds of sources. Scatter causes flare which occludes details and diminishes contrast. A surprising amount of detail is available at .85 N.A. if all the ducks are in a row. Sure it would be nice to open up the objective to a fuller aperture but you are possibly allowing in a bunch of incoherent light that will diminish the quality of imaging, plus if you are viewing at 400X as opposed to 1000X , your eyes become a factor in resolving detail.
An N.A. of 1.2 theoretically allows one to resolve down to 261nm with green light. An N.A. of .85 theoretically allows one to resolve down to 370nm. Only .1 of a micron difference. If you are using a 40X objective at 1.2 and a 100X objective at .85 , which would allow you to see details better?
It seems counter intuitive to expect high resolution below 1 micron at .85 but it is there, assisted by sufficient magnification and a highly colour corrected objective to reduce incoherent rays.
The Balplan 1.25 with iris and one of those paraboloid condensers yields awefully sharp DF.

I couldn't access any images to describe what I am referring to at the moment due to them being on an inaccesible hard drive but remembered some I had posted some time ago. 6 years it seems . The following link goes to a thread of images taken through a 100X 1.32 planapo in DF, obviously stopped down to achieve DF. It is hard to determine just what the functional N.A. was because the Reichert objectives do not have any graduations on the iris control ring but based on the condenser being used , the degree of darkness in the background , and minus too much in the way of corona ; I would guess in the neighbourhood of .95.

viewtopic.php?f=6&t=1253

Thank you, apochronaut.

I ended up buying a Nikon plan (CFN 45mm parfocal) 50x 0.85 oil iris, as its price is quite good and I realized I was using too high of darkfield NAs in my previous videos (I saw too much halos and not enough depth).

I hope that works for you tell us how it is I see that lens p. freq and have wondered at it

BramHuntingNematodes wrote: ↑

Fri Jan 21, 2022 1:24 am

I hope that works for you tell us how it is I see that lens p. freq and have wondered at it

Will do, once I set up everything. I moved not long ago and still have my main scope parts in storage. This is for my 2nd rig.

@apochronaut

Do you know what is the difference between AO (214F) funnel stops 214-79 and 214-127? They look totally identical to my eyes.

I got them from what looks like AO 214F 214F darkfield condenser (whose box has red velvet inside). The darkfield condenser fits on my AO series 4 perfectly, though I haven't used it yet.

I am guessing the 214-79 funnel is for the cat# 1079 100x 1.25 achro inf 34mm parfocal, while the 214-127 is #1127 97x 1.25 achro inf 34 mm parfocal?

Maybe I can use them for other finite objectives having 160TL ~34mm parfocal height at ~90-100x NA 1.25?

Thank you very much.

My manual states:
"No. 214-79 Funnel Stop fits No. 1079 100x objective; No. 214-127 Funnel stop fits No. 127 97x objective".

Yes. -79 for the infinity objective and 127 for the 160mm objective of which there were also a few 100X made. the threads are different so they cannot be interchanged.

Got it, thank you!