Thank you so much for reply, Apochronaut.
Do I understand correctly, that modern achromat objectives are “flat field” in older B&L models?
No. Read again what I wrote. The information relates only to B & L microscopes designed to use objectives marked flat field, planachromat, flat field fluorite, planfluorite or flat field apochromat.
[/quote]I’m attaching pics of both microscopes and lenses - newer on the left, older on the right in all images. (newer and older - is a judgement based on level of visible traces suffered abuse and performance.) there is no model number on the older scope.[/quote]
Just because a microscope is newer, it doesn't mean it is carrying the newest objectives. The oldest objective you have there is the large barreled 40X .65 flat field
[/quote]Any useful parts you see I should keep from the older scope?
As far as objectives - you’d change 4x and 40x to planachromats, correct? [/quote]
Might as well but the flat fields with the large middle grip ring are probably the same optics as the plans
Other way around.
The planachromats seem a marked advancement over the 1960's flat field objectives.
I did some tests a number of years ago and found the colour correction of the planachromats to be so good that in one case at least, outperformed the same magnification flat field fluorite made for the Dynoptic. It's not surprising that they stopped production of the flat field fluorites when the planachromats were released. They did subsequently release a 50X .80 planfluorite oil objective.
The transition from the flat field achromats, which arrived with the Flat Field Dynoptic in the mid-60's to the planachromats seems to have begun around 1973 or 74 or so, maybe a little earlier.
In the earliest catalogue I know of to base a reference on, an early 1975 price list, all of the objective line from 2.5X to 100X show new catalogue numbers, from 31-12-20 to 31-12-26, except the 20X, which is still listed as 31-10-61 and the only one pictured as the older blocky straight sided type. By Dec. 1976 the 20X was listed as 31-12-23 and the picture shows the slimmer profile of the newer objectives, rather than the blocky type with the adjustable outer shroud. The earliest objectives with the new catalogue numbers and barrel formats were still marked flat field and the 2.5X seems never to have been marked otherwise, so there are two different series of flat field achromats distinguished by cat.#, barrel type and performance and as well flat field optics and plan optics out there with the same cat.#, similar or identical barrels and equal performance.
Oddly, everything in all catalogues I have seen are described in general as plano and specifically as planachromats. Even the three flat field apochromats that they catalogued for the Balplan, are described as planapochromats, when in fact the barrels say Flat Field Apochromats.
At some point, they must have stopped using the term flat field in literature. The phase contrast objectives were the last series to be converted from flat field to plan. In the 1975 catalogue, they picture the straight sided shroud type Flat Field phase objectives 31-10-51 to 31-10-54 but in 1976 they picture those in the turned brass barrels, marked planachromat cat. #'s 31-12-40 to 31-12-43. In the text though, both series are called "plano phase contrast".