Olympus microscopes and photomicrographic equipment

Attaching a digital SLR camera to an Olympus CH-2, CK2, CK40 or CK40M microscope

Introduction

Olympus produced equipment for connecting their Olympus OM 35 mm film cameras to trinocular versions of their CH-2 compound microscopes, CK2 and CK40 inverted biological microscopes and CK40M inverted metallurgical 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 CH-2, CK2, CK40 and CK40M microscopes were discontinued several years ago, and so most of the items referred to on this page (including the Photomicro Adapter L, the PM-ADF eyepiece adapter, the NFK photo eyepieces and the BH-TR45-W and CH3-TR45 trinocular heads) 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 NFK 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 unless a very expensive NFK 1.67× photo eyepiece is used.

It is possible to use digital cameras with a Four Thirds sensor, but even with an NFK 1.67× photo eyepiece the camera’s field of view is substantially smaller than the viewing eyepieces.

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, Sony NEX 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 CH-2 compound microscopes and CK2 and CK40 inverted 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 NFK 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 PM-ADF eyepiece adapter are used, not the viewing eyepieces.

The NFK photo eyepieces were designed for photomicrography with the LB or long barrel objectives that were supplied with the CH-2, CK2 and CK40 microscopes, including the DPlan, SPlan and SPlan Apo ranges. These objectives have a 45 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 NFK 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 the NFK 1.67×. Unfortunately, these are uncommon and expensive. The NFK 2.5× can be used, but the small sensor substantially restricts the field of view.

Camera image areas with Olympus NFK 1.67× and 2.5× photo eyepieces

Camera image areas with Olympus NFK 1.67× and 2.5× photo eyepieces, relative to CWHK 10×/18 L or NCWHK 10× viewing eyepieces

For digital SLRs with a Four Thirds sensor, the most appropriate photo eyepiece is also the NFK 1.67×, but the small sensor means that the camera’s field of view is substantially smaller than the viewing eyepieces.

Eyepiece adapters

The trinocular heads for the CH-2, CK2 and CK40 microscopes 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 NFK photo eyepiece.

The trinocular head normally supplied with the CH-2 and CK2 microscopes was the BH-TR45-W, a cream version of the BH-TR45 head that was made for the BH microscope. The trinocular head normally supplied with the CK40 and CK40M microscopes was the CH3-TR45. Both of these heads have a plain vertical eyepiece tube and need an eyepiece adapter in order to provide the circular dovetail for attaching a photo tube.

On the BH-TR45-W trinocular head, 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.

With the CH3-TR45 trinocular head, the image seen through the right viewing eyepiece should automatically be in focus at the same time as the image on the sensor of the digital camera. The viewing eyepiece tube for the right eye is not adjustable. The viewing eyepiece tube for the left eye is adjustable, so that the image seen through the left eyepiece can be brought into focus with the view through the right eyepiece.

Trinocular heads for the BH-2 microscope can be used on the CH-2 and CK2. They incorporate the circular dovetail and so the PM-ADF eyepiece adapter is not necessary.

Summary and further reading

The following table summarises the best options for various combinations of cameras and microscopes.

Camera	EOS 5D Mk II	EOS APS-C	Four Thirds	Nikon APS-C
Adapter	OM/EOS adapter	OM/EOS adapter	OM/Four Thirds adapter	Nikon T-2 adapter
Tube	Adapter L	Adapter L	Adapter L	Richard J. Kinch
Eyepiece	NFK 2.5×	NFK 1.67×	NFK 1.67×	NFK 1.67×
Adapter	PM-ADF	PM-ADF	PM-ADF	PM-ADF
Head	BH-TR45-W	BH-TR45-W	BH-TR45-W	BH-TR45-W

For more information, see the following pages:

Send comments or questions to Alan Wood

Olympus microscopes and photomicrographic equipment

Olympus OM system close-up and macro equipment