When using microscopes with a finite (eg. 160 or 170 mm) mechanical tube length, there are roughly two ways to perform microphotography:
1. Afocal method. With this method, there is a lens or camera objective between eyepiece and camera sensor. The camera lens acts as a relay optic and captures the image that is corrected by the eyepiece.
2. Projection by means of a special projective or photo-eyepiece. Here there is no (camera) lens between the eyepiece and sensor and the image is projected onto the sensor by the respective eyepiece or projective.
For a long time I have used the afocal method, but after a lot of experimenting with eyepieces that can serve as projection eyepieces, I have become convinced that the latter method produces better images. With the afocal method, there is extra glass between the eyepiece and the sensor. It is certain that this will never improve the image in the center of the microscope field. Any additional optical element in the optical path can potentially degrade the image. And on any additional glass surface, disturbing dust speckles can settle.
Projectives are special eyepieces that correct the image formed by the objective and project it onto the sensor. For photography with DSLR cameras, projectives with low magnifications are particularly suitable. A highly wanted projective is for example the NFK 1.67x, to be used with the Olympus BH2 microscope system. However, the price for this projective on the second-hand market is often absurd.
Not all microscope manufacturers have produced useful projectives in the past. Carl Zeiss, for example, went the afocal path at one point and because of this, photography with Zeiss microscopes with 160 mm mechanical tubelenght was and is mainly done with a relay lens between eyepiece and sensor. If you want to photograph with for example a Zeiss Standard microscope without any relay optics, an ordinary observation eyepiece (e.g. a Kpl10x) can be used as a projective when the position of this eyepiece in the photo tube is raised a few mm. However, the results with this are variable and there is often a clear chromatic aberration at the edges of the image when photography is done this way.
I own a fairly large collection of eyepieces and at one point I wondered what would happen if I would combine two different Zeiss eyepieces and used them as a projection eyepiece for photography. So, I exchanged the eye lens of a Zeiss Kpl8x eyepiece with the eye lens of a Kpl10x eyepiece. I had only expected a bad image, but the result was surprising. Not only did the image on the camera appear parfocal with the visual image, there was also very little chromatic aberration at the edges. The result was significantly better than when using a raised Kpl10x eyepiece. I got the best results when I screwed both lenses from a Kpl10x eyepiece onto the barrel of a Kpl8x eyepiece. The fact that it works better this way than raising a normal eyepiece is probably caused by the increased distance between field lens and eye lens. Apparantly, the eyepiece is functioning like a projection-eyepiece this way. With some photo-eyepieces, like for example the Carl Zeiss FK10x, it's also possible to vary the distance between the two lenses. In any case, the chromatic aberration is largely canceled. I also experimented with Leitz and Olympus eyepieces. The results of this are shown below.
If you want to experiment with this method, it is important that an adapter is used with which the distance between camera sensor and eyepiece can be varied.
I tested the combination of a Kpl8x and Kpl10x eyepiece with a stage micrometer on a number of different Zeiss objectives. Both lenses of a Kpl10x eyepiece were screwed onto the barrel of a Kpl8x eyepiece and some results of this are shown below. This ‘hybrid’ eyepiece gives considerably less chromatic aberration than when a normal Kpl10x or Kpl W10x is used at an elevated position. There is a slight pincushion distortion, but this is within an acceptable range. Satisfactory results were achieved with all Zeiss objectives that I tested, including various (plan) achromats, Neofluars and (plan) apochromats. The tests were done on a Zeiss Standard 16 with trinocular tube. The hybrid eyepiece was not raised and the distance between camera sensor and eyepiece was adjusted until the image on the camera was parfocal with the visual image. Both an Olympus PEN E-PL1 and a Canon 600D camera were used.
Combination of a Zeiss Kpl8x and Kpl10x eyepiece in use as a projection eyepiece with the Zeiss Standard and Canon 600D camera. The field lens and the eye lens of a Kpl10x eyepiece were screwed onto the barrel of a Kpl8x eyepiece.
Stage micrometer photographed with a Zeiss Plan 10/0.25. Eyepiece projection with a hybrid Kpl8x-Kpl10x eyepiece.
Stage micrometer photographed, from top to bottom, with Carl Zeiss Plan 25/0.45, Neofluar 25/ 0.60 and Planapo 25/0.65. Projection with hybrid Kpl8x-Kpl10x eyepiece.
Stage micrometer photographed with Zeiss Plan 40/0.65 (top) and Zeiss Planapo 40/1.0 (bottom). Projection with hybrid Kpl8x-Kpl10x eyepiece.
Comparison between eyepiece projection with a hybrid eyepiece (top) and a raised Kpl W10x eyepiece (bottom). Chromatic aberration is clearly visible with the normal eyepiece. Objective: CZ Plan 25/0.45.
Arachnoidiscus, photographed with Carl Zeiss Plan 25/0.45 objective and hybrid Kpl8x-Kpl10x eyepiece. This is the complete section as it was captured by the sensor of the Canon 600D.
Left: a moss photographed with a Zeiss Planapo 25/0.65 and hybrid Kpl8x-Kpl10x eyepiece. Right: The orange rectangle indicates the portion of the microscopic field of view that is photographed using this eyepiece and a Canon 600D camera. The circle refers to an eyepiece with a field number of 18, such as a Zeiss Kpl W10x/18 eyepiece.
I tested different eyepiece combinations with the Leitz Dialux-II and Laborlux-12. For example, with Leitz NPL Fluotar objectives on the Laborlux-12 I get good results with an eyepiece that is composed from the parts of 3 different eyepieces: a Leitz 6x field lens, the metal barrel of an Olympus 5x eyepiece and the eye lens of a Periplan 10x eyepiece. Quite exotic, but it works well with NPL-Fluotar objectives. With the the Leitz EF achromats this combination produces slightly more chromatic aberration. The combination of an Olympus 5x barrel with both lenses of a Leitz Periplan GF10x also works well for both EF achromats and NPL Fluotars but the part of the field of view that is captured will be smaller.
The most recent and best combination that I have tested sofar consisted of the field lens and eye lens of an older version Leitz Periplan 8x eyepiece, screwed onto the barrel of an Olympus 5x eyepiece. This hybrid eyepiece worked well with all Leitz 160 mm objectives on the Leitz Laborlux-12 and 170 mm objectives on the Leitz Dialux-II. Several achromats, planachromats, NPL Fluotars and planapochromats were tested. With this hybrid eyepiece, the image of the camera was parfocal with the visual image. There was no significant pincushion distortion detected.
All experiments were done with a Canon 600D.
Hybrid eyepiece composed of 3 different eyepieces. Right: Stage micrometer photographed with this eyepiece and a Leitz NPL Fluotar 25/0.55 objective on the Leitz Laborlux-12.
Dracaena epidermis photographed with Leitz Fluotar 25/0.55 and hybrid Leitz6x-Olympus5x-Periplan10x eyepiece. Microscope: Leitz Laborlux-12.
A: Hybrid eyepiece that was constructed by screwing the field lens and eye lens of a Leitz Periplan 8xB eypiece onto the barrel of an Olympus 5x eyepiece. B: Original Leitz Periplan 8x eyepiece. C: Hybrid eyepiece with a lenght of 54 mm. D: Ihagee adapter attached to the photo-tube of the Leitz Dialux-II. E: Connection of the Canon 600D to the photo-tube.
Stage micrometer photographed with hybrid Leitz Periplan 8x/Olympus 5x eyepiece. Upper image: Leitz Plan 25/0.50. Lower image: Leitz Pl Apo 25/0.65.
I exchanged the eye lens of an unbranded 5x eyepiece with an Olympus P7x eye lens. It turned out to be a great find. This combination worked very well with different Olympus objectives of 37 mm and 45 mm parfocal lenght. There is no pincushion distortion. Good results in combination with the Canon 600D camera were achieved with the following 37 mm Olympus objectives:
Plan 10/0.25, Plan 20/0.45, Plan PL40/0.65, 40/0.65 and F40/0.65
The normal achromats with low magnifications (4x and 10x) without plan correction are overcompensated, which leads to chromatic aberration. This is because the hybrid eyepiece contains the eye lens of a compensating P7x eyepiece. As for the 45mm Olympus objectives, in theory they should require a different correction than the 37mm lenses because they were used with different eyepieces and projectives. Nevertheless, good results were achieved with the following 45 mm objectives:
EA 4/0.10, EA 10/0.25. EA 40/0.65, A 10/0.25, A 40PL 0.65, D Plan 50/0.90, S Plan 20/0.46 en Splan 40/0.70
I performed the tests using both a Zeiss microscope and an Olympus BH2 microscope. The reason for using a Zeiss stand is the normal 23.2 mm tube it contains, which makes it possible to use an Ihagee adapter and to adjust the distance between eyepiece and camera sensor. The distance between the eyepiece and the camera sensor was set in such a way that no more vignetting occurred and the sensor of the Canon 600D was just fully exposed. With the Olympus BH2 I could not set this distance freely and I used a temporary set-up with which the results were still quite good. The only objectives that gave lesser results were the 100x objectives (both of 37 and 45 mm length and both without plan correction). Fortunately, this objective is not very popular among many microscopists.
Hybrid eyepiece consisting of the lower part of a no-name Huygens 5x eyepiece and the eye lens of an Olympus P7x eyepiece. Total lenght of this hybrid eyepiece is 59 mm. At the right, in orange, the part of the field of view is seen that is captured by the sensor of the Canon 600D. The area that is captured without vignetting is as large as it can be when using eyepieces with field number 18 (e.g. Olympus WF10x).
Stage micrometer photographed with a 37 mm Olympus Plan 20/0.40 objective and hybrid eyepiece. Camera: Canon 600D.
Stage micrometer photographed with 37 mm Olympus Plan 20/0.40 objective. Here, an Olympus FK2.5x projective was used in combination with the Olympus OM-Mount Photomicro Adapter L. It is clear that a smaller part of the field of view is captured compared to the hybrid eyepiece. Camera: Canon 600D.
Leaf of a moss taken with a 37 mm Olympus Plan 20/0.40 objective and hybrid eyepiece. Camera: Canon 600D.
Stage micrometer (left) and pollen (right), fotographed with Olympus S Plan 40/0.70 and hybrid eyepiece.
The original eyepieces
Anyone who owns a collection of eyepieces from different brands can make many combinations. There is a good chance that a combination can be made that works well as a projection eyepiece. At the moment I am testing other combinations than the ones discussed here. The following image shows the original eyepieces that served as the basis for the hybrid eyepieces.
The original eyepieces that were used and combined with each other. From left to right: Zeiss Kpl10x, Zeiss Kpl8x, Leitz 6x B, Olympus P7x Bi, no-name 5x (metal part: 54 mm), Olympus 5x (metal part: 49 mm) and Leitz Periplan GF10x.
Conclusion and comments
Combinations of different eyepieces can give good results as a projection eyepiece. Considerably less chromatic aberration occurs compared to an ordinary eyepiece that is raised. Apparently, by increasing the distance between field lens and eye lens, some of the color artifacts are eliminated. Slight pincushion distortion may occur which will not be visible in most slides. The degree to which chromatic aberration occurs may be slightly more or less compared to the afocal method. With the combinations I tried, the chromatic aberration was minimal. It is recommended to try out different combinations of eyepieces.
The results were satisfactory with both the Olympus PEN E-Pl1 and the Canon 600D camera. It should also work with other cameras, but it cannot be ruled out that certain cameras give less optimal results.
With certain combinations, like the Kpl8x-Kpl10x hybrid eyepiece, the part of the field of view that is photographed may be slightly smaller compared to some afocal setups. On the other hand, with the 5x-P7x hybrid eyepiece, a very large part of the viewfield with field number 18 was captured.
I personally find it not that disturbing when a smaller part of the viewfield is recorded. And apart from histological slides, I usually don't see a reason to capture the most of the field of view. The quality of the image will always be best in the center of the field of view. My reasoning is always: what you want to photograph is usually located in the middle and not at the edge of the microscope field. And if the entire sensor area is used for a smaller part of the microscope image, the photographic resolution of that part will be better.
The advantage of this method compared to the afocal method is the simple and compact camera setup and the lack of extra glass between eyepiece and sensor. Moreover, there is no need to invest in a camera lens or an expensive and hard to find projective or photo-eyepiece.
Sometimes it is good to do some crazy experiments instead of sticking to the usual 'rules'. I can recommend it to everyone.
It would be great receiving feedback from people who are going to try this method. Please refer to this website when the method is going to be mentioned elsewhere.