Afocal finite tube Bausch and Lomb eyepiece thoughts and comparison

[BramHuntingNematodes]

One thing I didn't figure out about afocal photos is that with the 1/2 sensor I needed a half power eyepiece to get a good image without blurriness and with about the same FOV as the 10x eyepiece with my eyeball. If you're using old timey fixed tube, non-plan B&L lenses like I got there are two good choices of eyepiece: the compens which is the compensating eyepiece for apo lenses, and the Hyperplane, which sounds cool because it is. It intorduces planar corrections and is described by B&L's catalogs as having corrections between the Huygens and Compens eyepieces. I wondered about it so I used the Dynoptic's eyepieces and matched them with my NA=0.85 fluorite lens(I would have used a NA=0.95 Apo but both my examples have pronounced separation) and my 1.4 Apo. The corrections become more critical as the NA increases, or so I thought. I think the Hyperplane did pretty well. It's pretty difficult to discern a loss of sharpness. On the other hand, it's difficult to tell how the planar corrections help also. The images with the pronounced red fringe are the Compens eyepiece.

First some diatoms using the fluorite



For comparison, here is a picture of these diatoms I took with the Dynazoom using direct imaging and the NA=0.65 B&L Planachromat for the Balplan.


and some fan scales of I believe Culex sp. with the 1.4 Apo. I would have used the same slide but coverslip thickness is important with the 1.4 Apo as the WD is incredibly small!



Some things to consider if you have one of these old black beauties: they are still pretty effective at seeing the smol things and the low power eyepiece might be useful for afocal photography. Another nice thing about these scopes of days gone by is that B&L made eyepieces in just about every power from 5x to 33x (! the highest I seen).

[apochronaut]

Quite interesting, Bram. I haven't done that much of this sort of thing with B & L optics but in the past, played around with similar Spencer stuff quite a bit. For most of the first 1/2 of the 20th century, the two companies had pretty comparable product lines. Spencer's version of the hyperplane was the planoscopic.
A couple of comments and questions.
One of the technical aspects of the design of the apochromat/compens system was to provide as flat a field as they could along with maximized corrections, within the confines of the glass available. To do this and provide maximum flatness and corrections at the field stop, they had to compromise the f.o.v. with , in the case of a 10X compens, a smaller field stop than a 10X huygens eyepiece would have. I believe the hyperplane may have a wider field too, so offered an improved field flatness and better lateral ca correction than a huygens with fluorite and achromat objectives.
One of the big differences between the compens and the other eyepieces is that compens have undercorrections where huygens and the planar types are overcorrected. In order to get both lateral ca and spherical aberration under control in the old apochromat systems, they had to overcorrect ca in the objective and undercorrect it in the eyepiece. This shows in the case of the 1.4 N.A. objective ( 61X ?), where the lateral ca begins to be a bit severe, when used with the corrective hyperplane.
I think the forte of the hyperplane was to control the curvature of field of the achromats and fluorites and in doing so it also helps correct for lateral ca and particularly makes the 40X fluorite shine. With the hyperplane, it probably approaches apochromat performance but less so with the compens.

I'm wondering why the field stop is hazy with the compens?

What was the eyepiece used for the 40X planachromat shot?

[BramHuntingNematodes]

I agree the Hyperplane looked very nice with the 40x fluorite-- crispness obtained was remarkable. The 1.4 NA was the 90x. I can probably still get some better performance from it-- it's finicky about the slide and the light. I am not sure about the red hazy margin, whether or not it is an artifact of the camera setup. It's 1/2 sensor with a small telefoto lens to reduce vignetting. I don't think the haziness was present with my 12.5x Compens eyepiece, though, and I used the same setup. More experimentation is warranted.

The planachro shot was taken through the camera port directly, or rather, through a 1/2 reduction lens. I admit I get a little excited with the zoom feature, and there may be a little empty magnification with it turned all the way up using the 40x 0.65.

The other eyetube on the Dynoptic has the W.F. --22 eyepiece on it and gives an excellent view with my left eye (the one without astigmatism). I would take some shots with it, but the magnification factor of 10x is so far from the (near as I can tell ideal) 5x it's hard to compare.

[hans]

Yeah that first one looks really nice. Is this using the Raspberry Pi camera you have mentioned in the past? What lens?

I am not sure about the red hazy margin, whether or not it is an artifact of the camera setup.

Might try angling the camera so that the center of the camera FOV is pointed more toward the eyepiece field stop, and see if you can see the field stop sharply?

[BramHuntingNematodes]

Is this using the Raspberry Pi camera you have mentioned in the past? What lens?

The picture taken directly from the Dynazoom was using the Raspberry Pi. The first picture was taken using a board-mounted Aptina MI5100 sensor and an S-mount lens at 12mm f/2 of somewhat mysterious Chinese manufacture. About as cheap as I could manage. I like the board-mounted sensor format and wish there were a few more easily navigated options to acquire some as I don't need most of the geegaws that typically come with cameras.

I think the red haze comes about because the sensor lens should be just a tiny bit closer to the Compens eyepiece. The relief is only about a mm different for the two, but the eyepieces also come with a ring of spring steel around them to adjust the tube length. I just now noticed that the one on the Compens is about half the width of the one on the Hyperplane.

[BramHuntingNematodes]

Yeah that first one looks really nice.

Oh yeah, and thanks!

[apochronaut]

Those eyepiece collars never show up as a feature in catalogue images of the systems. At least not that I have seen, so not much anyway.
They may be a convenience thing but they would for sure affect the eyepiece's p/u point enough. I call them the Cyrano de Bergerac accessory.

[hans]

I am having a hard time seeing much different in lateral CA between the hyperplane and compens, especially paired with the fluorite. With the apochromat it looks like the image through the hyperplane has higher contrast, which is maybe emphasizing the lateral CA a bit?

Also curious, how are those diatoms mounted, and what type of condenser are you using?

The first picture was taken using a board-mounted Aptina MI5100 sensor and an S-mount lens at 12mm f/2 of somewhat mysterious Chinese manufacture. About as cheap as I could manage.

A nice demonstration, consistent with various articles about theoretical intermediate image resolution, that objective is the critical part of the system and the requirements on the camera lens/sensor are not too severe. 16 megapixel APS-C I have been using is clearly overkill so far, since downscaling the images 2:1 or even 3:1 there is not much loss of resolution. Although with Bayer sensors it is nice to have plenty of margin for at least 2:1 downscaling, so that the demosaicing algorithm is not critical and artifacts are not noticeable.

[BramHuntingNematodes]

The diatom slide is more than a century old, and so I believe it must be mounted in oriental styrax. The condenser is B&L's achromat 1.4.

I think the subject used in the 90x Apo comparison was not ideal. No permanently prepared slide I had on hand had a coverslip thin enough so that the lens could focus well within its 70 micron working distance. I had been looking at some mosquito larvae and had a previously wet mount that had dried together that focused OK. In fact, I think these are pecten spines rather than comb scales as the body had desiccated. I may append some additional pictures in this thread for my own reference.

In looking at the old marketing literature, B&L even goes so far as to recommend the Hyperplane eyepiece over the Compens for the high-dry fluorite lens. I assume for the reasons suggested by Apo.

[apochronaut]

I agree the Hyperplane looked very nice with the 40x fluorite-- crispness obtained was remarkable. The 1.4 NA was the 90x. I can probably still get some better performance from it-- it's finicky about the slide and the light. I am not sure about the red hazy margin, whether or not it is an artifact of the camera setup. It's 1/2 sensor with a small telefoto lens to reduce vignetting. I don't think the haziness was present with my 12.5x Compens eyepiece, though, and I used the same setup. More experimentation is warranted.

The planachro shot was taken through the camera port directly, or rather, through a 1/2 reduction lens. I admit I get a little excited with the zoom feature, and there may be a little empty magnification with it turned all the way up using the 40x 0.65.

The other eyetube on the Dynoptic has the W.F. --22 eyepiece on it and gives an excellent view with my left eye (the one without astigmatism). I would take some shots with it, but the magnification factor of 10x is so far from the (near as I can tell ideal) 5x it's hard to compare.

I'm a little confused about where the objectives are. The 40X planachro is on a flat field Dynazoom? The 160 objectives are on a 160 Dynoptic? Correct?

[BramHuntingNematodes]

Yes, that's right. The Dynazoom is trinocular and the Dynoptic binocular with the afocal setup on the left eyetube.