Olympus microscopes and photomicrographic equipment

Attaching a digital SLR camera to an Olympus BH, CH or IMT microscope

Introduction

Olympus produced equipment for connecting their Olympus OM 35 mm film cameras to trinocular versions of their BH (BHA, BHB and BHC biological models, BHF fluorescence model and BHM and BHMJ metallurgical models) and CH compound microscopes and IMT inverted microscope for photomicrography. These accessories can either be adapted or replaced to allow Canon EOS, Four Thirds, Nikon, Pentax, Sigma, Sony and other digital SLR cameras to be used instead of OM cameras, with the digital sensor located in exactly the same plane as the film.

Starting from the top, you need the following 6 items:

Camera body
Lens adapter
Photo tube
Photo eyepiece
Eyepiece adapter
Trinocular head

The BH microscopes were discontinued around 1980, and so most of the items referred to on this page (including the Photomicro Adapter L, the FK photo eyepieces, the PM-ADF eyepiece adapter and the BH-TR45 trinocular head) are also discontinued. The best places to find them are eBay and microscope dealers who sell used equipment.

Camera bodies

You do not need a lens on the camera, because the photo eyepiece is designed to project an image directly onto the sensor. The best digital SLRs to use as replacements for an Olympus OM have a 36×24 mm full-frame sensor, for example the Canon EOS 5D Mark II, allowing you to carry on using the same FK 2.5× photo eyepiece.

A cheaper option is a digital SLR with an APS-C sensor, such as the Canon EOS 7D, 40D, 50D, 600D (Rebel T3i) and 1100D (Rebel T3), but the smaller sensor results in a substantially smaller field of view.

It is possible to use digital cameras with a Four Thirds sensor, but the camera’s field of view is even smaller than with an APS-C sensor.

Vibration from the camera’s mirror and shutter can be a problem when taking photographs through a microscope. Traditional solutions include electronic flash, long exposure times, mirror pre-release, and stands that support the camera independently of the microscope.

Canon EOS digital cameras from the 5D Mark II, 7D, 40D, 450D and 1000D onwards have a Live View Silent Shooting mode that makes them particularly suitable for photomicrography. In this mode, vibration is almost eliminated, because the exposure is started electronically while the mirror is already raised and the shutter is already open. This is also referred to as EFSC or electronic first shutter curtain. EOS cameras also come with EOS Utility software that allows the camera to be controlled via a USB connection from a computer, allows the computer screen to be used for checking focus and composition, and allows images to be saved directly to the computer.

The camera body is connected via a lens adapter to the photo tube.

Lens adapters

The lens adapter connects the camera body to the photo tube, and ensures that the digital sensor is located in exactly the same plane as the film in an OM camera.

For Canon EOS camera bodies, new lens adapters are readily available on eBay to enable these bodies to be fitted to the top of the Photomicro Adapter L instead of an Olympus OM camera. These adapters convert the OM bayonet on the Adapter L to an EF bayonet, and exactly compensate for the 2.0 mm difference in registration between OM and EOS bodies.

For Sony NEX, Four Thirds and Micro Four Thirds camera bodies, new lens adapters are readily available on eBay to enable these bodies to be fitted to the top of the Photomicro Adapter L instead of an Olympus OM camera.

For Minolta AF/Sony α camera bodies, there are new adapters on eBay that might be suitable for use with a Photomicro Adapter L. The adapters are thick but they include a lens, so they might allow OM lenses to focus to infinity; if this is the case, then they probably are suitable.

For Canon EOS, Minolta, Nikon, Olympus E, Panasonic, Pentax, Sigma, Sony α and other camera bodies, new T-2 lens adapters are readily available on eBay to enable these bodies to be used with the photo tubes made by Richard J. Kinch, which have a T-2 fitting on top.

Photo tubes

Olympus produced the Photomicro Adapter L to allow their Olympus OM 35 mm film cameras to be used for photomicrography with trinocular versions of their BH compound microscopes. Lens adapters are easily available on eBay to convert the OM rear lens fitting on the top of the Adapter L so that Canon EOS, Four Thirds and other shallow-bodied cameras can be used instead of OM cameras, with the digital sensor located in exactly the same plane as the film.

The bottom of the Adapter L clamps on to the circular dovetail on an eyepiece adapter.

The Adapter L was originally finished in grey to match the BH microscope. The finish was later changed to cream to match the BH-2 microscope.

If you want to use a Nikon, Pentax or other deep-bodied digital SLR, it is not easy to convert the Adapter L, so Richard J. Kinch (Making Digital Camera Microscope Adapters) makes alternative photo tubes that use a T-2 mount and that maintain the proper 150.0 mm distance from the lip on which the top section of an FK eyepiece rests to the plane of the sensor.

Photo eyepieces

To project the image produced by the objective onto the sensor in the camera body, special photo eyepieces that sit inside the circular dovetail on the eyepiece adapter are used, not the viewing eyepieces.

The FK photo eyepieces were designed for photomicrography with the short barrel objectives that were supplied with the BH microscope, including the Plan, PlanApo, MPlan and Neo Plan ranges. These objectives have a 36.65 mm parfocal distance.

For digital SLRs with a full-frame sensor, such as the Canon EOS 5D Mark II, the most appropriate photo eyepiece is the FK 2.5×.

For digital SLRs with an APS-C sensor, such as the Canon EOS 7D, 40D, 50D and 550D, the most appropriate photo eyepiece is also the FK 2.5×, but the field of view is substantially reduced because of the smaller sensor.

Camera image areas with Olympus FK 2.5× photo eyepiece

Camera image areas with Olympus FK 2.5× photo eyepiece, relative to Bi WF10× viewing eyepieces (F.N. 18)

For digital SLRs with a Four Thirds sensor, the most appropriate photo eyepiece is also the FK 2.5×, but the very small sensor means that the camera’s field of view is even smaller than with an APS-C sensor.

Olympus did not make an FK photo eyepiece with a lower magnification than 2.5× that would have compensated for sensors smaller than 35 mm film.

Olympus did not make a photo eyepiece that can cover the field of view through the BH-SWTR superwide trinocular head.

Eyepiece adapters

The trinocular heads for the BH microscope have a plain vertical eyepiece tube with a 25 mm external diameter

They need the PM-ADF eyepiece adapter that clamps on to the vertical tube and provides the circular dovetail for attaching a photo tube and holding the photo eyepiece.

Trinocular heads

Trinocular heads have a pair of inclined tubes for binocular viewing plus a third vertical tube that takes an FK photo eyepiece.

Four trinocular heads were made for the BH microscope. They all have a plain vertical eyepiece tube and need an eyepiece adapter in order to provide the circular dovetail for attaching a photo tube. The common trinocular head is the BH-TR45, and there is also a BH-TR30, a strain-free BH-PTR30 and an uncommon and expensive superwide head, the BH-SWTR.

BH-TR45 trinocular head

Olympus BH-TR45 trinocular head

On the BH-TR45, BH-TR30 and BH-PTR30 trinocular heads, both viewing eyepiece tubes are adjustable. To make the viewing eyepieces parfocal with the camera, first focus the image from a low-power objective seen through the camera. Then, without touching the microscope’s coarse or fine focus knobs, adjust the left and right viewing eyepiece tubes to bring the images seen through the eyepieces into focus.

On the BH-SWTR superwide trinocular head, both eyepiece tubes are fixed but the superwide eyepieces incorporate dioptric adjustment. To make the viewing eyepieces parfocal with the camera, first focus the image from a low-power objective seen through the camera. Then, without touching the microscope’s coarse or fine focus knobs, adjust the left and right viewing eyepieces to bring the images seen through the eyepieces into focus.

Trinocular heads for the BH-2 microscope can be used on the BH. They incorporate the circular dovetail and so the PM-ADF eyepiece adapter is not necessary.