How to Add a Camera to a BH2 Microscope
In order to attach a digital camera to the BH2, you will need a BH2-TR30 or BH2-SWTR30 trinocular head (or one of the alternatives listed below) and a phototube adapter which meets the following criteria: 1) The lower mount is compatible with 38mm NFK port on the trinocular head. 2) The upper mount is compatible with the camera body you wish to attach. 3) The adapter is the proper length for parfocality between the camera and the eyepieces. 4) Allows for the required NFK photo eyepiece to be installed in the NFK port on the trinocular head. Listed below are several methods by which you can correctly couple a camera to the BH2.
Regardless of the method by which you mount a camera onto your BH2 scope, it is imperative that the camera be parfocal with the eyepieces (i.e., the eyepieces and the camera must both be in sharp focus at the same focus setting). If you find yourself having to significantly re-adjust focus when switching between using the eyepieces and the camera, this indicates improper geometry of the camera mount, and this is adversely affecting the quality of your camera’s imaging. So, what’s actually happening when you refocus a microscope to correct a non-parfocal camera image? Let’s start with the obvious. When you change the focus setting from the position where the eyepieces are sharply focused, to favor the camera, you’re moving the stage (either up or down) away from its proper position. In other words, you’re changing the working distance of the objective from where the optics were designed to operate to some other position. This change in working distance affects the position within the optical tube where the objective projects its intermediate image. By mucking around with the plane of focus of the intermediate image, you are in-turn changing the plane of focus of the final image presented to the camera by the NFK photo eyepiece. When you get the plane of focus of the final image to land on the image sensor within the camera, the image is “in focus”. You are in effect focusing the camera by forcing the optics to operate at a different optical tube length than that which they were designed to operate, and this introduces spherical aberration to the camera image. The BH2 is a very nice scope with very high-grade optics. Do not mess this up by using an improper camera mount!
The Photomicro L Adapter was the official Olympus solution for attaching an Olympus OM SLR camera body to the BH2 microscope. The lower end of the Photomicro L attaches to the 38mm NFK port on the trinocular head, while the upper end accepts the Olympus OM-mount camera body, placing the film or image-sensor of the camera the proper distance from the NFK photo eyepiece for parfocal imaging. The design of the system is such that when one of the Olympus NFK photo eyepieces is placed into the top bore of the trinocular head before the Photomicro L is attached, the resulting optical configuration projects a fully corrected image of the specimen under observation directly onto the film plane or image sensor of the attached camera. The total magnification of the resulting image, as projected onto the film plane or image sensor, is the mathematical product of the magnifications of the objective lens and the NFK photo eyepiece. For example, a 10X objective lens and an NFK 2.5X photo eyepiece will produce a total magnification of 25X at the film or sensor plane (i.e., the image projected onto the film or digital image sensor will be 25X life size). When using a standard DSLR with an APS-C or ASP-H image sensor, the NFK 1.67x is the correct photo eyepiece to use. Unfortunately, the NFK 1.67x is very rare and is therefore quite expensive (often in the range of $600 to $1000 on eBay). If, instead of an APS-C or APS-H camera, you use a full-frame DSLR (which has an image sensor the size of a 35mm film frame) then the much cheaper NFK 2.5x is the correct photo eyepiece to use. The problem with this approach is that full-frame DSLR bodies, even in used condition, are about as expensive as the NFK 1.67x. If you’d like to add a camera to your BH2 without breaking the bank, you can simply do what many people do and just use an NFK 2.5x with your APS-C or APS-H camera and live with the resulting reduction in the field of view. The Photomicro L was designed for use with Olympus OM-mount SLR cameras, but it can also be used with Canon EOS (EF mount) DSLRs or older Canon FD mount SLR equipment by adding a very inexpensive OM-EF or OM-FD adapter (available from Amazon or eBay) to provide a fully parfocal solution for Canon SLRs and DSLRs. Other camera types may or may not be adaptable to the Photomicro L, so be careful. Some (such as Nikon) will not provide proper positioning of the image sensor relative to the NFK photo eyepiece to provide parfocality with the eyepieces. In general, the following DSLR camera types can be mounted onto the Photomicro L using the appropriate lens mount adapters, to provide parfocal imaging for the BH2: Canon EOS cameras, Sony NEX cameras, and the various 4/3 or Micro 4/3 cameras. When using a Canon EOS, use the NFK 2.5x photo eyepiece for camera models utilizing full-frame sensors, and use the NFK 1.67x for camera models utilizing APS-C sensors. When using a Sony NEX, use the NFK 1.67x projection lens. For 4/3 or Micro 4/3 cameras, the best results will be obtained using the NFK 1.67x projection lens, but even then, the field of view of the resulting images will be noticeably restricted, as compared to the view through the eyepieces. For cameras using 4/3 sensors, better results would be obtained with an MTV-3 or U-PMTVC adapter, rather than the Photomicro L, since the MTV-3 / U-PMTVC contains an integral 0.3X reduction optic to increase the field of view.
The MTV-3 adapter was the official Olympus solution for attaching C-mount cameras (such as a video cameras) to the BH2 microscope. Like the Photomicro L adapter, the MTV-3 adapter connects to the 38mm dovetail port of the trinocular head, along with a suitable NFK photo eyepiece, and allows the resulting optical configuration to project a finished image of the specimen under observation directly onto the image sensor of the attached C-mount camera. As an alternative to the MTV-3, the very similar Olympus U-PMTVC adapter (made for later BX microscopes) can also be used to attach a C-mount camera to the BH2. The black U-PMTVC has one advantage over the cream-colored MTV-3, in that the design allows for a slight adjustment of the optical length to tweak the parfocality of the attached camera. An NFK 2.5X photo eyepiece, when used with an MTV-3 with the accompanying 0.3X reduction lens, projects an image of approximately 16mm diameter onto the image sensor plane, thereby requiring a C-mount camera with relatively large image sensor. This requirement for a large sensor-size unfortunately excludes most of the modern C-mount cameras out there today. The Nikon J1 and V1 cameras have a CX sensor of the proper size, and with a suitable C-mount adapter, should work well with the MTV-3 (I have not actually tried these cameras with the MTV-3, so take that for what it’s worth). The C-mount port and the 0.3x reduction lens are integral to the removable top piece on the MTV-3, which is held in place by a single thumbscrew. The fact that the C-mount / reduction lens can be easily removed from the MTV-3 is kind of a mixed blessing. On the negative side, a great many of the MTV-3 adapters available on eBay these days are missing this critical piece. Many potential buyers of the MTV-3 (and likely many sellers, as well) do not know that many of these adapters are incomplete. Be sure to look for this critical piece if you intend to buy an MTV-3, since you cannot attach a C-mount camera without it. If, on the other hand, you would like to buy an MTV-3 for the sole purpose of installing a T-mount camera to the BH2 (as described in this video), you will only need the outer tube. The MTV-3 outer tube was used for this project because the MTV-3 contains an elegant and well engineered mounting mechanism which will not mar the 38mm NFK port on the trinocular head. Whatever you do, please do not pay full price for a bare MTV-3 tube. Point out to the seller that what they have is only half of an MTV-3 and pay accordingly.
The Diagnostic Instruments (more recently, Spot Imaging) PA1-10A camera adapter was a third-party alternative to the Olympus Photomicro L adapter, which, while no longer manufactured, can often be found on the used market at a lower cost than the PM L. As with the Olympus solution, the PA1-10A provides a camera mount that’s parfocal with the viewing oculars and produces fully corrected images. Like the Photomicro L, the PA1-10A attaches to the 38mm dovetail on the BH2 trinocular head and must be used with a suitable NFK photo eyepiece in place. The PA1-10A differs from the Photomicro L in that instead of an Olympus OM mount on the top, it features T2 threads (42mm x 0.75mm), to allow various camera body types to be attached using the appropriate T2 T-ring adapters. Diagnostic Instruments sold the EOSC-T2 T-ring adapter to allow Canon EF-mount camera bodies (e.g., EOS) to attach to the PA1 10A, and the CANC-T2 T-ring adapter to allow standard Canon FD-mount bodies to be attached. The Diagnostic Instruments EOSC-T2 and CACN-T2 adapters are very hard to find these days, but fortunately, generic T2 to EF and T2 to FD T-ring adapters are readily available at low cost on eBay or Amazon which can be used to attach Canon cameras to the PA1-10A. It should be noted that there are two distinct variations of this Diagnostic Instruments adapter that can be found in the wild. Both are marked as “PA1-10A”. One variation has a circular dovetail on top with female T2 threads internal to the dovetail, while the other variation has male T2 threads. I recently asked Spot Imaging (formerly Diagnostic Instruments) about the adapters other than the PA1-10A that they used to sell, which were advertised as compatible with the BH2. They responded that these adapters do not include correction for residual chromatic aberration, and based on this response, I would not use any Diagnostic Instruments adapters other than the PA1-10A on a BH2 scope.
Olympus made no provision for attaching a T-mount camera to the BH2. The Empire of Dirt Workshop has developed a simple 3D-printable adapter which allows a bare MTV-3 tube to be used to attach to the NFK port on the trinocular head, along with a helicoid focus and a few adapters, to provide a parfocal T-mount for the BH2. Once you have a T-mount, you can then adapt to a great many camera types using the appropriate T2 T-rings. See this video for details of building and using this adapter on your BH2.
Since neither the Olympus Photomicro L nor the Diagnostic Instruments PA1-10A adapter are currently manufactured, a better option might be the Olympus 38mm to T-Mount adapter manufactured by Richard Kinch, at http://www.truetex.com/olympus-38mm.htm. Like the Olympus Photomicro L and the Diagnostic Instruments PA1-10A adapter, the Kinch adapter secures to the 38mm dovetail on the trinocular head, along with an NFK photo eyepiece, and through the use of a suitable T-mount adapter, accepts a compatible DSLR (e.g., Canon EOS) to provide a parfocal solution to produce fully corrected images.
“So, what about those little drop-in USB cameras sold by companies like Swift and Amscope, that replace one of the eyepieces. Surely those will work?” No, unfortunately they will not work properly on the BH2. Since the optical design of the BH2 relies on the eyepieces or the NFK photo eyepieces to provide some of the required correction for chromatic aberration, replacing an eyepiece with one of these little cameras will produce images with significant uncorrected lateral chromatic aberration. This will be visible in the resulting images as color fringing which gets progressively worse the further you get away from the optical axis (i.e., the center of the image). Now, if you were to replace the Olympus LB objectives on your BH2 with Nikon CF (Chromatic-aberration Free) objectives from the same era (or some other fully compensated objectives), the little eyepiece camera would drop in and work just fine, since all the compensation for chromatic aberration would be provided within the objectives themselves. But Nikon optics on a BH2 feels like giving up.
The Photomicro L Adapter and the MTV-3 / U-PMTVC setups described above can be rather expensive, especially when you factor in the cost of the NFK photo eyepiece and the upgrade from a binocular to a trinocular head. One way to lower the total cost of these solutions is to eliminate the viewing head from the setup entirely. Olympus offered a BH2-PT vertical phototube, which is essentially a vertical monocular tube for the BH2. This phototube can replace the traditional binocular or trinocular viewing head and, when used with the PM-ADF adapter, provide the required 38mm NFK camera port. The Photomicro L or the MTV-3/ U PMTVC adapter attaches to the 38mm NFK port on the PM-ADF, along with a suitable NFK photo eyepiece. You of course lose the ability to directly view the image through the ocular lenses, but when using a suitable camera with live-view functionality, this can be a workable option for many people. The BH2-PT can occasionally be found on eBay. But be careful. There was a version with a shorter top tube that is non compatible.
In addition to the BH2-PT described above, Olympus also made IMT2-PT phototube, which was intended for the IMT2 inverted scope but also works well on the BH2. Like the BH2-PT, the IMT2-PT can replace the traditional binocular or trinocular viewing head and provide a camera port. The Photomicro L or the MTV-3/ U PMTVC adapter attaches to the 38mm NFK port on the IMT2-PT, along with a suitable NFK photo eyepiece.
A time-honored approach to photomicrography is to simply position the lens of a camera to shoot afocally through one of the eyepieces of the microscope. When done correctly, the resulting images can be of very high quality. The problem with this is that it is rather awkward to position a camera to shoot down one of the eyepieces on the BH2, since the BH2 eyepieces are inclined (i.e., not vertically oriented). Additionally, the presence of the camera on one eyepiece makes it difficult to look through the remaining eyepiece. Because of this, it is tempting to instead just drop an eyepiece into the NFK slot of the trinocular head and proceed that way. The problem with this approach is that it doesn’t work well, since the NFK bore in the photo port is too small to accept the normal Olympus WK 10X or WHK 10X eyepieces. They will go in part way, but they will not seat to the proper position to be parfocal with the regular eyepieces. If you’re using the BH2-PT phototube, the solution is simple. Just remove the PM-ADF adapter and drop your 10X eyepiece directly into the ocular tube. A WHK is better here than WK, since it has a higher eyepoint, but either of these can be made to work. Another lesser-known option is to use a WHK15-L eyepiece in the NFK slot. So long as you use the regular “-L” version and not the “-H” helicoid version, it will drop right into the NFK bore just fine. It will provide a reduced field of view as compared to 10X (very similar to using an NFK 2.5X with an APS-C or APS-H camera) but that may still be an option for you. Another way to take the occasional image without spending a lot of money is to take images afocally using your smartphone, by simply holding the phone up to one of the eyepieces and snapping the picture. You have to be careful to make sure that the camera is properly aligned with the optical axis of the eyepiece before taking the shot, but the results can be very good. There are inexpensive adapters available to allow a smartphone to mount onto a microscope eyepiece, which allow the camera to be properly aligned with the optical axis of the eyepiece.