Types of Phase Contrast and when to use which type

[Scoper]

I would like to see a discussion concerning the types of phase contrast and which types are most appropriate for for different studies.

My particular interest is which type is best for observing pond life.

Links to various examples of different phase contrast in terms of pond life would be appreciated.

And a question…when a manufacturer offers phase contrast for a viewing option, which type of phase contrast is most likely offered?

Thanks for any insight into this subject.

[apochronaut]

In the 1940's Zernicke's original concept was taken up by numerous companies. Zeiss, who originally had the rights to the patent didn't really do much with it but no doubt they were inhibited by activities during and after the war. Between 1946 and 1950 a slew of refinements to the original concept were invented and patented ; the rotary multi-diaphragm phase condenser , improved techniques for depositing the annulus on glass and a number of different phase types.
Several manufacturers developed phase systems for various applications but it was likely AO , Olympus and Nikon that offered the largest array of phase types. Reichert and PZO offered anoptral phase, maybe Zeiss too eventually.
I know of 4 phase types. Dark, Bright, B-Minus and Anoptral. There is also the advancement of apodized phase, which Nikon refined I think.
AO did quite a bit of early research and the primary research team published a book ; Phase Microscopy : Bennet, Jupnik, Osterberg and Richards. 1951.
In the late 40's AO started compiling data and user impressions on the capability of their various phase systems with various objects and materials, publishing it in a chart form.
It is here in this thread as of 1948.
https://www.microbehunter.com/microscop ... php?t=5032

https://www.microbehunter.com/microscop ... hilit=1948

[patta]

I fear that all this beautiful variety of phase contrast methods has disappeared, and today ony standard "bright" setups are normally available - with no indication wether is High, Medium or Low like in the table linked above.

The trouble with pond life, is that there is a bit of everything; I have only a "standard bright" phase microscope to compare (Leitz Phaco I), it is excellent to highlight tiny bacteria, whereas for large organisms, the complex inner organs get messed up by phase halo.
I believe the "standard bright" has been selected as simple jack of all trades, for routine jobs like counting colibacteria and sperm cells, rather than for aesthetic enjoiment.

See also this book for some (old) photos that compare the different phase contrasts:

https://www.microbehunter.com/microsc ... t=10527
My impression looking at those image is: the phase methods that give more contrast, give also stronger halo and lose details in complex subjects.
And the other way around.

[apochronaut]

The default phase contrast that is supplied simply as phase, is dark phase or also known as positive phase more recently. Some mfg. also produce bright or negative phase still. There are generic negative phase objectives available from sources such as Boli optics. They are probably Motic. I am not sure what diaphragm is supposed to be used but that may be becoming somewhat standardized with Chinese manufactured 180mm reference length microscopes.

In the past, Dark, Brght and in the case of AO B-Minus, were divied up into low , medium and high contrast levels. Dark L, Dark M and Dark H for instance. High contrast was little used and only a few objectives marked with H exist and only in certain magnifications. AO only ever catalogued 3 high contrast objectives : Bright H as 43X .66 and 95X then later 97X 1.25 and a 10X .25 B-Minus H. High contrast is usefull in order to highlight inclusions, so it is understandable that only two higher magnifications of Bright contrast exist as H. The lone low magnification objective, a 10X B-Minus H, probably works best for scanning certain samples for inclusions. B-Minus presents more as a contrast enhanced BF. There was an uncatalogued 43X Dark H, which seems to have a whole other use intended.

Japanese companies , notably Nikon further subdivided contrast levels, such as DLL, or Dark low low etc.

[Scoper]

Thanks for the info and the link.

It sounds like if one wants the variety of phase constrast techniques, one will need to collect older sets of phase objectives/condensers and be locked into using the older frames that they fit.

Any suggestions as to which brand to focus on? My immediate interest is pond life but tomorrow..who knows?

[apochronaut]

My experience is heavy with AO and less so with the others. I have trialled some 32mm parfocal Lomo phase objectives in a 160mm AO stand without success.
In general , phase objectives require a system apporoach and certain objectives were little used and quite rare, so hard to find. After AO shifted to infinity development , they reduced the total # of phase objectives from 27 in 9 types to 13 in 3 types, then just 4 dark phase when they introduced 45mm parfocal objectives. There are 4 planachro dark phase for each infinity system. Reichert 45mm parfocal infinity objectives will work on an AO/Reichert 45mm stand with an eyepiece switch and there are Plan Fl. and Plan Apo versions available which are wonderfull, although not common. AO were the only company that offered B-Minus phase., and I think also Dark high contrast. In my experience, AO phase has less halo than some others but I don't know why.

Olympus had 16 objectives in 4 types for their 36.65mm parfocal system. Bausch & Lomb also used a 160mm 36.65 parfocal system for most of their history, so those objectives may be compatible with Olympus. Olympus also produced the Galen I for B & L so objectives for that, marked B & L are Olympus. I don't know whether there was more than the default 4 medium phase for the Galen or whether there is any compatability between Olympus and B & L short objectives. To my knowledge, B & L only produced dark phase. When Olympus switched to a 45mm parfocal system, they continued with the 4 phase types as achromats, including at least one as a planachromat : positive low. They slso added relief phase contrast for inverted microscopes.

Nikon has offered 8 types of phase that I know of but not all in all magnifications. They have previously used the term dark and bright on their 160mm short 33mm parfocal objectives but more recently positive and negative. They offer a dark apodized phase as an achromat , which reduces the halo and shading off effects that phase exhibits.

Anoptral phase is a unique type invented by Alvar Wilska, an under appreciated Finnish inventor. I am sure he id appreciated in Finland, though. In it's purest form the phase annulus is much wider than standard phase and the optical retardation material different, so that the background is brownish andvthe depth of field great. It is a relief phase contrast. Reichert made a very good version, Meopta not quite as good. PZO slso made a good one, Lomo and Jena as well but I know less about them. It had a heyday in the 1950's but seems a bit forgotten now. Strange, since the depth of field can be extreme with high magnifications, 2 microns.

[BramHuntingNematodes]

The Galen phase lenses are not compatible with either the regular B&L phase or the flat field. The regular and flat field phase lenses/ diaphragms are close, except the 10x.

The Galen lenses are pretty good looking plan dark medium phase achromat lenses! It is uncommon to see the proper turret, particularly by itself and for a reasonable price. Some intense improvisation can produce ok results in some cases.

[apochronaut]

Galen Olympus or Galen Kyowa?

[BramHuntingNematodes]

Ah right, I meant the kyowa ones. I have seen that I miller has some of the Olympus lenses but I have never handled one, nor have I even seen a photo of the Galen Olympus turret.

[apochronaut]

The older Kyowa I am pretty sure are JIS, so 36mm parfocal and a 170mm tube.

[BramHuntingNematodes]

Hmm well they're marked 160. In any case, they're pretty good but not worth going out of your way to accommodate.

[apochronaut]

Hmm well they're marked 160. In any case, they're pretty good but not worth going out of your way to accommodate.

Not JIS then. Maybe the very old ones were. Are yours the ones with the black base? I think the same as on Bristolscope.

[BramHuntingNematodes]

Yeah the black knobbly base. Some are Bausch and Lomb, some are Leica.