The first ones were for the Dynoptic and Dynazoom but only for those microscopes with
the words Flat Field printed boldly across the front of the head. I've
seen a 100x 1.30 Flat Field Fluorite, that was physically similar to the
last U.S.A. made 160mm objective series from B & L, just larger, with no
160 written on it and Flat Field clearly marked. There were most likely
achromats like that too but B & L may have had trouble with people
understanding that the Flat Field and 160mm objectives were for mutually
exclusive instruments, so the physical format of the barrels was dramatically changed early on.
The first clearly different Flat Field objectives were those with large
straight sided barrels but with a small knurled ring near the base.
Polished chrome barrels for the achromats and fluorites and polished
brass for the apochromats. For DF you have to replace the rear diaphragm
with one of smaller diameter for the high N.A. objectives.
I know of 4x .09, 10x .25, 40x .65 and 100x 1.25 oil as achromats : 50x
.80 and 100x 1.30 oil as fluorites and 7.5x .20, 12.5x .30, 25x .65, 75x
1.2 oil and 125x 1.40 oil as apochromats. I'm pretty sure there were also
40x .85 and 100x 1.30 oil apochromats as well.
Some of those Flat Field objectives were carried forward into the Balplan
> program and some were not but they are all made with the same
> corrections, so any work fine. I think what happened , is that they decided to
> upgrade the program and deleted those that either weren't in their plans
> or needed technical upgrading.
> To complicate things further, they changed the barrels into ones with a
> more convoluted shape with a large central knurled ring, yet retained the Flat Field
nomenclature. B & L has always had an internal parfocalizing adjustment,
so with the newer barrels they incorporated an internal cam,
actuated by a small screw in the side.
Some of those , mainly in lower magnifications; 10x and 20x with the newer
barrel shape can be found still marked Flat Field, while others are marked
It's possible that for some objectives they just brought some of the same
designs forward into the newer barrels and decided that Flat Field was no
longer as useful a marketing nomenclature and switched to Planachromat instead
but it seems likely that two newer style barrels exist, one as a Flat Field and
one as a Planachromat.
> I have never seen a 100x in the newer shaped barrel that is marked
> Flat Field and in tests, the 100x 1.25 oil Planachromat, is a noticeably
> better objective than an older 100x 1.25 oil Flat Field Achromat. However,
I see that you have both a Flat Field and a Planachromat in the newer barrels.
albeit , slightly different ones.
I would be interested to know your impressions of the differences in them.
> At the time that the newer barrels came out they also seem to have
> deleted the older straight sided fluorites. One re-engineered fluorite I
> know of for sure is a 50X .85 oil planfluorite in the new style barrel,
with parfocalizing cam.
> The newer planachromats are so good that they are better than the earlier
> straight sided Flat Field fluorites, displaying very little if any chroma
> in tiny, normally diffractive spaces. The 50x Planfluorite must have been
considerably inproved, in order to fit well with the Planachromats and indeed it is.
> However the reason for the deletion of the higher magnification Flat
> Field Apochromats is probably somewhat different because they are all
> excellent, displaying very fine flat field apo quality. The N.A.'s alone ,
The dovetail for the condenser of the Balplan is distinctly
> different from that of the Dyna series and they had not yet redesigned a
> high N.A. achromatic/ aplanatic condenser yet for the Balplan. It was
> probably left to near the end of the development list. I'm pretty sure
> that they had plans to refine the Flat Field Apochromat series originally
> for the future but by the time they had refined the bread and butter
> stuff, the entire program was in jeapardy due to new ownership and an
> entirely different consolidated stocklist. First for Cambridge
> Instruments and later the Cambridge/Wild-Leitz merger. The Balplan just
> wasn't needed. All they ever listed in the 70's catalogues as apochromats
for the Balplan were the 7.5x .20, 12.5x .30 and 25x .65 and seemingly
entirely unchanged from the objectives that were made for the Dyna series.
The pictures look identical to the objectives made for the Dyna series but
they are listed as Planapochromats. I suspect that they are the Flat Field Apochromats
> rebranded. I have never seen a Planapochromat, except in the catalogues.
All of mine ( 7.5x,25x,75x and 125x) are marked Flat Field Apochromat.
> In later literature the apochromats are not mentioned at all. They possibly did
> not sell well, due to cost; another nail in the Balplan coffin.
> Another omission in catalogues is the is the 50X .85 oil planfluorite.
I have one of those and have seen one other but it shows up in not one of the
6 trade catalogues or price lists printed between 1975 and 1986 that I have,
devoted to the Balplan. Beginning in the Oct.1 1977 price list cat.# 31-12-25,
a 50X .85 planachromat shows up but it is gone by 1986. I have not ever seen one of those.
> So, it is safe to say that the more slender design Planachromats 2.5X
> .06, 4X .09, 10X .25, 10X .25 L.W.D., 20X .50, 40X .65, 100x 1.25 oil and
> 100X 1.25 oil with iris are of superior performance, with resolution and
> contrast noticeably better than the older straight barreled Flat Field
> Achromats. I have trialled two entire sets; 4x,10x,40x and 100x against
each other and the Planachromats are superior in all ways , visually.
Presumably the 50x Planachromat oil would be as well and of course
50X .85 Planfluorite. Personally, I wouldn't bother with older Flat Field
> Fluorites( if you can find one), although for a good price, one or more
> would certainly be better than the older Achromats.
> All of the Flat Field Apochromats are worth while but scarce as scarce
> can be. I'm still in the design stages of working an achromatic high N.A.
> condenser into a Balplan housing for the 75X 1.2 and the 125X 1.4 oil
Flat Field Apochromats.