AO/Reichert 50X 0.80 and AO 50X 0.85 Objectives

[Charles]

Attached are pictures of some AO-Reichert 50X Inf Oil Imm with iris objectives with a little confusion...maybe Phil can clear up?
On the left is an AO Plan Achro INF 50X Oil Imm objective with an NA of 0.80 CAT number 1016.
On the right is a Reichert Plan Achro INF 50X Oil Imm objective also with an NA of 0.80 CAT number 1016.
In the middle is what looks to be an older AO Achro INF 50X Oil Imm objective but with an NA of 0.85 CAT number 1026.

Both the AO 1016 and Reichert 1016 seem to be optically identical and both made in the USA. The only difference is that the AO one has embossed etched lettering and the Reichert has printed on lettering. On Steve Neeley's site: posting.php?f=5&mode=post he says the CAT number 1016 are Advanced Plan Achros and the 1026 is just an Achro. Question is, why is the Achro have a higher NA than the Advanced Plan Achros. Seems the the advanced plan achros would have the higher NA?

He also mentions a 1029 50X Achro which I have never seen.

AO-AO-Reichert 50X INF Iris

AO-Reichert INF 50X 0.85NA 2 CAT 1026 1016.JPG (36.08 KiB) Viewed 7076 times

The other side

AO-Reichert INF 50X 0.85NA CAT 1026 1016.JPG (35.63 KiB) Viewed 7076 times

[apochronaut]

The switch to painting objectives was one of those minor cost cutting moves, that seemed like a good idea at the time. The paint they used improved over time but it still wore off or was removed by reagents , even from the latest production objectives. The practice is now ubiquitous. I guess when you think about it, engraving an objective body would take quite a bit of effort.

I don't know 100% why there was an N.A. reduction with the plan design, nor have I ever read anything official, as to what constitutes an "advanced" plan achromat but in testing various objectives, it seems that planarity is one of the measures, if not the prime measure. In this regard, the 1016 is good but not great.

Here is a guess, however , why the # 1016 would be deliberately made as a .80, when the 1026 and the briefly made 1029 were .85 and the earlier 160mm C125 50X oil was .95! The #1016 50X .80 plan achro was designed to be used for oil dark field( so the user could go back and forth from 100X to 50X with ease) and for D.I.C. and fluorescence too. In use the .80 N.A. is directly usable for dark field , whereas .85 offers a little less contrast and needs adjustment. In the period when the 1026 and 1029 were designed, there was much less consideration for those techniques so the higher N.A. was deemed desirable and no doubt the performance of the 1016 was sufficiently better than those two( which were identical, except for the iris) that the extra .05 N.A. was insignificant.

When they came to design the D.I.N. objective range for the series 400, most of the objectives, 4 Neoplans and 6 planachros ( + 3 planfluorites) are the older AO designs, tweaked into longer barrels but with improved coatings, so contrast and colour correction are exemplary. The AO-Reichert cat.#1016 became the Reichert cat. # 1758 50X oil N.A. .80 Neoplan but sans iris diaphragm.They also improved the planarity on those to which it was necessary somewhat, including the 1016, so the # 1758 is in all ways a superior objective to the 1016 but clearly they determined that the iris was not really necessary .... .80 was low enough and high enough too. Later it had the Leica name on it. For anyone building up an infinity corrected microscope with D.I.N. objectives and considering dark field, the 1758 is a great objective and can sometimes be snagged for peanuts. I paid 29.00 for the one I use and it is really nice to be able to back out of 100X oil dark field to 50X oil , for a renewed medium magnification view.

[Charles]

Thank you for your insight Phil.

[apochronaut]

As an aside , Charles, Bausch & Lomb who pretty much commanded the the dark field market in North America with the 100watt Balplan, until Olympus eroded it in the 90's also had an oil 50x .80 ( planfluorite) but did not put an iris in it. The earlier 50x flat field fluorite they made, prior to the dark field market boom was a dry .85, which in many ways would be a very desirable objective but not for high resolution dark field, where A) the N.A. is too high to get adequate contrast and B) it is not oil immersion, so fiddling back and forth between oil and dry would be necessary and about as annoying as accidentally stirring your coffee with the fork you just whisked the eggs with.

[Charles]

Speaking of B&L, I noticed in the AO darkfield condenser sets, where they included funnel stops, they would also put in a funnel stop for B&L objectives. In the picture, there are two stops are for B&L objectives as well as two stops for the AO objectives.

AO DF Condenser with DF Stops

AO DarkField Condenser.jpg (90.38 KiB) Viewed 7037 times

[apochronaut]

I have one B & L funnel stop for a 50's 97X achromat and it looks different. I do have those two short ones, as well. The larger of the two, fits in the 90X N.A. 1.30, Apochromat; the little one, in the older objectives, made between the teens into the 30's. They had the lenses, all in a little unthreadable nose section, with the diaphragm at the top of that section. That little funnel stop just fits into the diaphragm port and the flat flange on top of it just rests on top of the port.
That long skinny one, I don't recognize. Perhaps it is for the 44X .95 apochromat, which would also need a funnel stop, to work in dark field?
I am guessing that condenser might be for a series 4? It looks like one for a 10 too, but all of the above mentioned objectives would work on a 4, so they covered all eventualities.

[zzffnn]

Interesting and informative read. Thank you Phil.

[Charles]

Hi Phil,

All four funnel stops are for oil immersion objectives (97X). The smallest one is used in objectives with serial numbers under 400,000 and the long fat one is for serial numbers above 400,000. For B&L, the short fat one is used in the B&L objective which unscrews in the middle and the long skinny one is for use in B&L objectives which can't be separated in the middle. The two silver rings (adapters) are for different types of fork mounts. I think this AO DF was made before the infinity scopes started coming out so probably fits the grey 1-4s as well as the 15-35s.

[apochronaut]

I'm curious where this information comes from, Charles. Was there a note or pamphlet with the condenser?

I own all of the Spencer oil immersion objectives, that were made between about 1905 and the end of production, with the exception of a couple. They only made 2, 97X objectives in that period, that I know of. One was the C 127, 97X 1.25 N.A. achromat, made for the later black microscopes like the series 15 and 35 as well as the series 2/4. The funnel stop used in that objective is a similar one to the one you picture with the threaded flange on top. It has the cat.# 214-127 stamped on it. The funnel stop you picture is for the previous series of objectives cat.# 127, which was a 95X 1.25 N.A. There is likely no part # stamped on that funnel stop. Even though the two stops have the same thread and can be screwed into either the C127 or the 127, the aperture diameter is slightly smaller on the older design. Dark Field imaging requires absolutely precise adjustments to optimize imaging, so using an aperture slightly too small or too big would not be ideal. The other 97X objective they made, is a very uncommon, early infinity corrected objective, made before they upped the infinity oil immersion to a 100X. The infinity corrected objectives take funnel stop 214-79, which has a different thread. None of those stops fit B&L.

The short fat funnel stop fits the Sprencer 90X 1.3 apochromat and the 90X 1.4 apochromat perfectly. They are separable objectives. Unthreading the objective and dropping the funnel stop into the lower section, allows it to seat into a machined relief, just above the back lens. The wide top portion, snugly fits into the upper section barrel, to maintain alignment. I tried to fit this into the divisible Bausch & Lomb 97X objective as suggested, made between 1925 and when they switched to an undivisible design, with no luck. It rests ON the back lens, which is unacceptable and there is nothing to stop it from flopping around and being off centre.I did manage to make it fit a very old divisible 1/12" 1.32 N.A., made about 1895 and it seems to fit o.k. Whether the aperture is correct would have to be tested. That funnel stop is designed for the Spencer apochromats.

The very short funnel stop with the flange on top is for the Spencer separable objectives made between about 1900 and 1932 or so.They had an aperture diaphragm built into the back of the front lens section of the objective. That funnel, just slips into that aperture and the flange rests on it, reducing the N.A. I have one in a 1.8mm 1.30 N.A. achromat, made about 1905, serial # 40905. It also works in the slightly later 95X 1.25 N.A. objectives and the 113X 1.25 N.A. objectives. There was a different stop, you do not picture, made for the separable objectives ,made after 1932. They did not have that low, rear diaphragm, so the funnel for them is a small 8mm X 8mm tube which fits into a machined collar, just above the back lens. Your very slender, long funnel, if you measure it will likely be 8mm in diameter. The separable lens sections , sometimes become seized, so that long funnel, could be inserted through the back of the objective body, drop down in, and seat into that collar just above the back lens, and work as well. Spencer obviously realized this problem , after the fact and made an extra long funnel for the late 30's objectives. My little short one came from the 1930's.
As for it's use as a funnel for the Bausch & Lomb 97 X undivisible objective, as suggested. The long tube section of it, below the flange would have to be less than 1", otherwise it would rest on the back lens,as well. The 97X B&L does not have a precise 8mm collar behind the back lens, to receive a precise fit and stop the funnel from flopping around. The original part # for the B&L funnel for that 97X objective, which threads into the back of the objective is 31-50-15 and your Spencer item , looks nothing like it.

I can send pictures, if you like. Phil.

[Charles]

Phil, It is the instructions which is with the condenser. The condenser can be used with objectives with NA 0.85-1.25.

See attached:

AO Condenser Instructions

AO Condenser Instructions2.jpg (58.07 KiB) Viewed 6976 times

[apochronaut]

I assumed you had some kind of pamphlet but it doesn't make any sense. The funnel marked with the part # 04109, looks identical to the one mounted in my 90X 1.3 apochromat......unless the dimensions are slightly different. Mine, doesn't work in any of the B&L divisibles , I have here but fits the apochromats like a glove.

Could you measure the long one? 04110. It could work in a B&L undivisible , if the length was right.
Oddly , there is no mention of the 8mm x 8mm funnel that is fitted in a Spencer objective I have with a serial # 308,XXX, one which according to your pamphlet , should take the little T shaped drop in one but doesn't. Spencer made a dedicated dark field objective for some time, with a built in restrictor diaphragm, bringing the N.A. down to .85, so they might have had a period of time when they didn't need to have and didn't produce a funnel stop and then started again when they discontinued the .85 version. Perhaps that little 8mm x 8mm was produced briefly , in order to satisfy a gap and the one marked 04110 , as I earlier thought, could also be a duplicate for that, if 8mm in diameter.

Magnification has no bearing on dark field efficiency, it is the N.A. that determines the contrast level. Typically, .85 is the cuttoff but some condensers, allow a little more. That's why I don't think using the 214-127 funnel is a good idea, even though it fits, for the 127 objective. It might bump the N.A. up too high.
You do see, quite a few older Spencer's with B&L objectives and visa versa, so it was obviously deemed necessary to accomodate that possibility. They were both 160mm, after all.

[Charles]

Phil,

The funnel stop measures 31mm long with about 6mm diameter. I have a few 160mm AO objectives and B&L objectives, so will try them tonight.

I wonder if this AO DF condenser could also be used on B&L scopes with the two different ring adapters for the condenser mount? I will need to try it on some black stand B&Ls I have.

[apochronaut]

The older Bausch&Lomb non-divisible objectives( with a single black ring) have a little circular relief cut into the top of the rear diaphragm plate, which is probably there to engage with the top flange on your long thin funnel stop, and center it. The newer ones( with a single red ring) do not have that. They receive a threaded funnel stop instead. The older ones have serial #'s beginning with a letter, which corresponds to a year, the newer ones have no serial #.
I tried the broad funnel stop in every divisible B & L objective , I have. It looks to me like there is needed a keeper of some sort, in them, otherwise they flop around, easily. The best fit was in an older 100X 1.30 fluorite but the fit in the 97X 1.25 achromats is problematic , however the system probably does work.Maybe there was a spacer that was intended to be used with them or perhaps there was an assumption that the objective being in a vertical position , would cause the funnel stop to orient correctly. This sort of thinking was what prompted Spencer to make a dedicated dark field objective, with a machined in .85 N.A. diaphragm stop. They mention in the late 20's catalogues that mis-aligned funnel stops were a problem. Later , the systems evolved to be positively threaded in, or alternately have precise machined collar fittings. Bausch & Lomb did embrace iris diaphragms, very early too. It took Spencer a while, probably into the late 30's to make those available. The 1930 catalogue , they offer no objective with an iris diaphragm, and the objective with a restrictor is no longer availaable. They do mention that objectives made by other mfg. can have custom made funnel stops made for them but the objective needs to be sent to the factory for this work to be done. In the 1945 Blue book they offer an iris diaphragm , for the achromat as well as the apochromat. Again the note regarding the possibility of having funnel stops made for objectives of other manufacture is found at the bottom of the page. Possibly, the unit you have was a custom made set? It occurs to me that the broad funnel stop, made for the apochromats, might have been found to be adequate for the B&L 97X achromat, either as is or with a slight modification, hence the close similarity between the two.