Leica/Wild: any special advantage in different tube+optic combinations?

[fufluns]

For their M stereoscope series, Wild used an elbow tube (404891 or 18057), a 304490 tube with a Wild 10x/21 photo eyepiece, plus an eyepiece tube (404207) with a relay 0.32 lens (370759) mounted within a camera lens adapter (162226). The system was using two lenses, for a final enlargement at the film/sensor of 3.2x. It is my understanding that the Wild 404207 eyepiece tube plus 10x/21 photo eyepiece could be substituted by a Leitz Tube TL 160mm plus a Leitz Periplan 10x18 lens but I have no direct experience with this.

In his MZ series, Leica firstly used the same approach, with the same eyepiece tube (10404207) and relay lens (10445541 mounted in 10162226), but changed the photo tube (10445932) and the photo eyepiece (LEICA 10445304) to adapt them to the new 37 mm elbow tube (10446174 or 10446194). Final enlargement at the film/sensor was still 3.2x.

Using the same Leica/Wild elbow tube, Scientific Diagnostic choose another approach, using only one lens: a Olympus photo lens 2.5x, mounted on a short photo tube, plus a longer tube (PA1-35A) with no lenses to the camera. In this way they only used a single projection lens, instead of two lenses. Final enlargement at the film/sensor was 2.5x.

With their newer video/photo tubes, Leica still adopted a two-lenses system, but with a different configuration. A tube (10445930) including a 1x projections lens is now attached to the phototube (type 10450301, 10450302 or analogue), and from there a longer photo tube camera adapter (10446175) including a 2.5x relay lens goes to the camera. Final enlargement at the film/sensor is 2.5x.

LMScopes also uses a two-lenses-system, with a C-mount port 1x plus a LM Digital SLR Universal Adapter, which for the full-frame sensor includes a plan achromatic lens with a factor of 2.2x (final enlargement = 2.2x).

Now, I would be interested in understanding if there is any intrinsic advantage in using a two-lenses-system versus a single-lens-system, considering the optical interferences that any lens introduces to the system.

Thank you in advance for your comments.

[apochronaut]

I don't know these systems very well but I can see that it was probably a lot more economical for Wild to use a reduction lens in concert with an existing 30mm 10X eyepiece design, rather than engineer a 3.2X photo eyepiece. That might be the rational for the way that system was designed.
With Leica, the necessity was possibly different, since it may well be an infinity corrected system due to Leica inheriting a bunch of infinity corrected systems from at least 3 of the partners of the merger and some were stereos. I know from other systems that sometimes the telan lens serves only the eyepieces , so they had to include a 1X telan lens in the photo tube as well as the photo eyepiece/lens.

[PeteM]

I don't know what, if any, eyepiece corrections Wild (Leica) used in its M series stereo microscopes. Just judging by how well a generic eyepiece works, once cut down to reach deeper in the tubes and be parfocal, not much.

So, you'd think a single photo relay lens would make sense. This is the case for a Leica .70x C-mount adapter which will work (different sensor size) for either the stereo or compound scopes. It provides good images with a 1" Sony sensor camera.

However, on the Leica infinity microscope side, Leica had two different generations of optics (Delta and HC) and eyepiece corrections. Ideally, you'd want a correcting eyepiece in the path.

It apparently made sense for Leica to use a correcting eyepiece followed by a .32x lens to get around the 2.5x magnification wanted for film cameras. My incarnation of this, found after a long search, is an 8x Leica widefield photo relay optic, followed by a .32x lens (commonly buried in a 35mm photo adapter) to get 2.56x magnfication. Even with the extra glass, this provides a better image for the compound scope than going with an uncorrected optic in place (such as LMScopes likely provides). I suspect, but don't know, it wouldn't offer readily visible advantage chroma-wise for a lower power stereo microscope.

Leica also spec'd a 10x Leica relay eyepiece with a .32x adapter (3.2x) - the situation you have. My recollection is that it didn't have as wide a field number.

We also have users who have directly projected, by getting a sensor closer down the stereo accessory tube - without corrections. If memory serves, there's a thread somewhere on this site showing the quality of images obtainable that way.

[Scarodactyl]

It is my understanding that the Wild 404207 eyepiece tube plus 10x/21 photo eyepiece could be substituted by a Leitz Tube TL 160mm plus a Leitz Periplan 10x18 lens )

Mechanically yes, but optically the results would be poor. Wild stereo eyepieces are essentially neutral while Wild/Leitz compound eyepieces are decidedly not.

In short, yes there are advantages. The eyepiece plus reduction lens combo on wild never gave very good results, maybe OK for film but noticeably degraded on a modern camera. This approach generally makes sense if a) your eyepieces have specific corrections that are needed for the image to be good and b) you don't want to design a suite of special projective eyepieces. By designing one or two specially corrected photo eyepieces and changing the focal length of the lens above the eyepiece you can make the image suitable for a range of formats.

This approach in short makes sense for compound microscopes with correcting eyepieces. It does not make sense for a stereo microscope that does not need those corrections. It makes even less sense to use a viewing eyepiece that adds aberrations of its own, which your eye will mostly filter out in viewing but your camera sure won't. Why did they do it that way? I assume it was to have complete compatibility in their microscope camera system across compound and stereo microscopes. An unfortunate shortcut from a company that usually didn't stop at 'good enough.'

Presumably the dedicated photo eyepieces were a later attempt to improve the situation some with better optics while maintaining compatibility.

So with that in mind, the main benefit was that it made the stereos compatible with a completely obsolete line of cameras. So for a company like Lmscope making an adapter for newer digital cameras it makes sense to take a different approach. I don't know how well the olympus PE eyepiece plays with Wild scopes in specific but I suspect the results would be at least good. No guarantees though--you would think any vendor with products priced this way would always be amazing but I have bought a couple (from one of the other expensive third party adapter sellers, also with a sterling reputation) that had Olympus nfk 2.5x projective eyepieces built into them that would not have been at all optically appropriate on any system they would have mechanically fit.

One problem with projective eyepieces is they always crop the image a lot since they're one-size-fits-all and have to work with objectives with more limited field coverage. They don't have to be designed that way but they always are.

The Leica system with the separate 1x adapter is a genuine innovation, allowing a true one-lens option. What you describe as a two lens system (eyepiece plus reduction lens) is actually a three lens system, because the intermediate photo adapter also has a lens in it (the 'tube lens') to converge the infinity focused light coming out of the zoom body. The new system removes the tube lens from the intermediate attachment (or trinocular head) and has it as an interchangeable part, so you can resize the image for any sensor by just swapping that one lens for one of a different focal length*. Better yet as a hobbyist it is easy to get a good achromat of whatever focal length you want and to 3d print an adapter to thread into the tube, allowing you to ideally adapt whatever camera you want for peanuts with great image quality.

*well, except for the 2.5x configuration you mentioned which does stack a 2.5x adapter on a 1x. The reason for that is likely that the 2.5x is a teleconverter which reduces the physical height of the assembly. Other magnifications like 1.6x, 0.33x etc generally at least have a 1 lens option, while the 1x maintains compatibility with their line of 37mm adapters.

[fufluns]

Here I post a couple of images in order to compare the photo-sistems we were discussing.

The first photo is the ventral view of the pollinarium of a Polycycnis gratiosa orchid.

Pollinarium 1.jpg (237.62 KiB) Viewed 1645 times

I used the same magnification on a Leica M80 stereo microscope (two images on the right, 2.5x with a 0.8x Achromat, total magnification = 2x) and on a Leica Z16 APO macroscope (image on the left, 1.6x with the Planapo 1x, to be corrected at 1.25x due to the Y tube, total magnification = 2x).

Photos were taken through a trinocular head with a 1x photo-lens + a 2.5x relay-lens (Leica Microsystems, left), and through a Wild elbow phototube (404891) fitted in one case with a Diagnostic Systems tube (center, which only use a 2.5x photo lens), and in the other case with a Wild 10x photo lens + 0.32 relay lens (right), respectively.

Both the systems by Leica and by Diagnostic Systems gave on the sensor the same magnification of 2.5x. When photographed through the Wild 10x photo lens + 0.32 relay lens, the total magnification of the phototube is 3.26x and the image on the sensor is larger. See scale bars in the image.

I would say that the the images produced by the 2-lens systems by Leica and by Diagnostic Systems are marginally better, but the Wild 3-lens system holds on its own, also due to the greater enlargement of the image on the sensor at the same microscope’s magnification. Should I compress the image on the right to the same size of the two on the left, the differences would be still more negligible.

Photo 2 is showing the pollinarium of the orchid Huntleya burtii.

Pollinarium 2.jpg (285.42 KiB) Viewed 1645 times

Here I used the M80 stereo with a 1x Planachromatic lens at 2.5x magnification, to compare the results of the Leica Microsystems phototube (1x = 2.5x relay lens, on the left) with those of the Wild elbow phototube (with Wild 1x photo-lens and 0.32x relay lens, on the right). For the latter image I set the magnification of the scope at ca 1.9x in order to obtain images of comparable sizes on the sensor.

Even though I can see an edge on the Leica system, the difference is not substantial in my opinion, and I would be quite happy also with the classic elbow phototube by Wild, both with Wild or Diagnostic Instruments solutions.

[jfiresto]

Thank you for those images. I gather the very last image shows the chromatic aberration I have read about, that the Wild photo system never fully got under control. What amuses me, and I have come to much appreciate, is that the Wild phototubes (directly) project the best image on to the receiver that probably didn't need it: a one-inch video camera. I could well believe that came from adapting existing designs. I have an older Wild phototube that adds what could have been a second observer, vertical eyepiece.