Bausch & Lomb 4.3mm 1.00 fluorite oil working distance

[hans]

It came with the extender pictured which adds exactly 1/4" as accurately as I can measure, within a few mils. I have not been using the extender on the Dynoptic, way too long with it installed, not sure what it is for. Parfocality is off ~200 um from the other objectives, which normally I would consider a bad sign, but maybe is just the adjustment apochronaut mentioned recently. What I find strange is that the working distance seems very long for an oil objective, a bit hard to judge, but pretty sure it is more than 1 mm above 170 um cover glass. I was having trouble getting Cargille 300 to bridge the gap. Tried again with B and it works but the oil contact still seem a bit precarious. Otherwise the image looks nice, crisp with good contrast, and an obvious improvement in axial CA fringing over the 4mm 0.65 phase objective used in brightfield. (I don't have a non-phase 4mm achromat to compare with.)

It the long working distance normal? There is no cover glass spec marked anywhere, just "BAUSCH & LOMB / ROCHESTER, N.Y. U.S.A." on the other side.

[BramHuntingNematodes]

B&l lenses all require .18mm cover glass, but thicker can be substituted without compromising optical quality when using immersion.

[BramHuntingNematodes]

Also if you ever get some of those hyperplane eyepieces they pair exceptionally well with the high na fluorites.

[hans]

I have been using it with ~0.17 cover glass so far and I suppose the working distance could be a nice benefit with with thicker homogeneously-mounted specimens. I just thought it might indicate a problem with the objective, but the image is nice so I guess I should not worry too much and just use the Cargille B which better resists draining out of the gap.

Yeah, I did get a pair of the 10X hyperplane and the improved planarity is definitely noticeable. With this objective there is a little lateral CA around the periphery, maybe because it is right on the edge between where hyperplane vs. compens are recommended?

[apochronaut]

I have a couple of them. The earlier 4mm fluorite I have is a dry .85, from around W.W. I. The parfocality of the two 1.0 N.A. objectives I have is quite different but the w.d. very similar , 250 and 265 microns, measured by bringing the objective in contact with cover slip and then backing off to focus. The slide used was 1.03mm and 1.21 across the cover glass. There is a difference of 130 microns in parfocality and it is evident due to the difference in the gap at the top of the shroud. It looks like one has been lengthened quite a bit, perhaps to be parfocal with 37mm objectives? Your adapter seems like it might have been used to parfocalize with 45mm objectives, Hans.

Objectives from that era have a relatively small image circle and achieved good lateral ca reduction over a fairly small field. The Hyperplane and Planoscopic eyepieces ( B&L and Spencer respectively) could correct for field flatness some but not too widely inclusive of lateral ca control; especially with a fluorite. Typically, compens eyepieces provided the desirable field flatness as well as ca control across the entire field with apochromats but the f.o.v. possible for that level of performance was smaller than the accepted f.o.v. using huygens or curvature correcting eyepieces. A 10X compens for instance usually gave an 11mm f.o.v. in comparison to non-compensating types that could be 13 or a little more, with lateral ca. The narrower f.o.v. was something that research oriented microscopists could mostly live with. First, in research, detail is paramount not spectacle and second the actual f.o.v. is not usually that relevant when the field is being captured photographically. Thirdly, in order to increase the apparent f.o.v. one could always utilize 15X eyepieces.
With 15X eyepieces , the apparent f.o.v. can be made greater than with 10X, giving a flatter field due to the larger lenses employed. Within any design type, the apparent f.o.v. of 10X eyepieces is physically restricted by the tube diameter. Thus the real f.o.v. of 15X eyepieces is only slightly less than with 10X and in certain cases as wide. For this reason, due to the higher N.A. of the better colour corrected objectives, 15X eyepieces are a better choice for default eyepieces than 10X. Some companies made fractional apochromatic objectives to adjust for the higher resulting magnifications when using 15X eyepieces ; 7.5X, 12.5X etc. and of course if lower magnifications were required , a microscopist can always slip in any eyepiece they need. Compens eyepieces were typically available in 5X, 10X, 15X, 20X and 30X and all of them got used. You might wonder at a 30X eyepiece but using a 30X eyepiece with a 10X .30 or higher N.A. objective is pretty much the same thing as using a 10X eyepiece with a 30X l..w.d. objective. 30X eyepieces were limited in application to use with no more than a 20X objective, where a 60X l.w.d. type of performance could be achieved, if needed.

[hans]

The parfocality of the two 1.0 N.A. objectives I have is quite different but the w.d. very similar , 250 and 265 microns, measured by bringing the objective in contact with cover slip and then backing off to focus.

Yeah seems like parfocality adjustment moving the whole objective together should not have much effect on working distance due to the short focal length relative to the tube length. I will check working distance again more carefully once I have a better and less precarious illumination setup for the Dynoptic.

Your adapter seems like it might have been used to parfocalize with 45mm objectives, Hans.

A little too short for that I think, with the extender it is about 41.5 mm shoulder to the tip of the objective. Could it be related to vertical illumination?

Thirdly, in order to increase the apparent f.o.v. one could always utilize 15X eyepieces.
With 15X eyepieces , the apparent f.o.v. can be made greater than with 10X, giving a flatter field due to the larger lenses employed. Within any design type, the apparent f.o.v. of 10X eyepieces is physically restricted by the tube diameter. Thus the real f.o.v. of 15X eyepieces is only slightly less than with 10X and in certain cases as wide. For this reason, due to the higher N.A. of the better colour corrected objectives, 15X eyepieces are a better choice for default eyepieces than 10X.

This makes a lot of sense, so far I have 10X Huygens, wide field, and hyperplane pairs plus single 5X and 7.5X hyperplane. No 15X or compens but I have been keeping an eye out.

[apochronaut]

If you add the w.d. + the coverslip plus a bit of parfocality extension it might get pretty close. Since it came from a Dynoptic, perhaps the previous owner didn't understand the dramatic difference between the flat field objectives and the 160mm objectives and was trying to parfocalize it with the longer flat field objectives?

[BramHuntingNematodes]

Both the 15x compens and hyperplane eyepieces are very good and will give considerably more relief than the Huygens. The 12.5x compens (although NOT the 12.5x hyperplane) I consider the best compens lenses, with relief comparable to contemporary eyepieces and a good view. Some of the Huygens eyepieces I can't even look through as my eyelashes conflict with getting as close as needed.

The wf-22 eyepieces are also very good. Don't be fooled by the wf-23.

[hans]

Since it came from a Dynoptic...

Actually no idea what it was on originally. Seller didn't say and was selling a wide variety of surplus, no other B&L stuff.

Both the 15x compens and hyperplane eyepieces are very good and will give considerably more relief than the Huygens. ... Some of the Huygens eyepieces I can't even look through as my eyelashes conflict with getting as close as needed.

Good to know, I have gotten a bit better about the eyelash thing with practice. Usually people talk about eye strain using microscopes but the Huygens give you facial strain trying to keep your eyelids stretched fully open for extended periods of time...

The wf-22 eyepieces are also very good. Don't be fooled by the wf-23.

The ones I have just say "WIDE F.", photo attached, is this what you're talking about? And I just noticed they are actually 15X. (eBay listing said 10X.) I have only used them briefly (hadn't cleaned them up yet when I was doing all the messing with the phase contrast a few weeks ago) but they seemed nice.

[hans]

Oops here's the photo:

[apochronaut]

Those are the early W.F. eyepieces that had w.f. but very poor ca correction. Those 22mm and 23mm designations on the later ones are eye relief . Both have been marketed on ebay as though it is f.o.v. The 23mm actually has a narrower f.o.v. than the 22mm.
The 23mm are actually compensating eyepieces, quite w.f. ones...about 18 or so.

[hans]

Thanks for the ID help, while we are on the subject, these were in an AO 10 stand I bought for parts. No markings other than 10X W.F. shown in the photo. I haven't tried them in the Dynoptic, assumed they were for something newer (one of the StereoZooms?) due to the styling, but I see the -22 and -23 also have somewhat newer styling.

[BramHuntingNematodes]

I got some like that and they work OK basically the same as the old school wide field eyepieces with a larger field. Not ideal for fluorites and apos but pretty decent and very comfortable with achros.

Apo can correct me if I am mistaken, but I believe he meant to say the -22s are compensating, rather than the 23s. The -23s perform about like the ones you got. The 22s are longer and about 15 grams heavier.

[apochronaut]

I hit the wrong number. Yes, 22 are long and compensating. They work pretty well to give the apochromats some extra field. B & L also made some high eye relief compensating eyepieces, with funny rubber cushions around the eyelens, so eyeglass wearers don't slam lenses. For some reason they remind me of bumpers on loading docks.