Adapting Cameras to Microscopes

 

Adapting the Canon Powershot S50 to my microscopes

The adapter is in two main pieces: a top plate and a base plate that has the circular ring to fit the bayonet ring. The two plates are held together by fixing screws with large washers and the top plate has oversize holes through which the screws pass. This enables the top plate to "float" for centring purposes. Once centred the screws can be tightened. Centring is achieved by observing the hard edged circular image produced by the camera at minimum zoom.

I use an Asahi Pentax adapter with a home turned bayonet fitting that is a tight fit to a home-built camera holder constructed of polystyrene sheet. It may look crude, but it is functional. The internal diameter of the mounting ring for the bayonet fitting is also a tight push fit around the Wild M8 eyepiece, hence the camera can be mounted on any of my microscopes. I find that for general use, the Watson x8 Compensating eyepiece works well and gives a reasonable sized field which just sits inside the disc of the full field as seen by the eye. A Zeiss KPL-W 10/18 also works well, especially with Zeiss objectives, but requires a different adapter to take this higher eyepiece. I improvised an adapter from brass tubing.

In all cases it is important to get the camera in the optimum position at the ocular eyepoint. This can be found by trial and error and is often easiest with high eyepoint oculars such as the KPL. The eye-circle should be visible in the digital viewfinder and should be a circle with hard, not out of focus, edges.

Once in position with the eye-circle central in the digital viewfinder the zoom on the camera can be used to ensure the image fills the field. I usually use maximum optical zoom because it is a known amount of zoom and this facilitates calibration of image dimensions.

Adapting a Canon Powershot G9 to my Microscopes

I wanted to try a more modern camera and settled on the Canon Powershot G9. This camera cannot be mounted in the same way as the S50 because of the high zoom ratio lens. It turns out that the optimum position for the microscope ocular is somewhere inside the camera lens!

This means that a dedicated commercial adapter is needed. I decided to use a Zarf Enterprises adapter. The results were generally acceptable, but there was some chromatic aberration noticeable at the field edges. Presumably this is because the adapter is not specifically designed for use with my Zeiss or Leitz objectives and does not offer the same corrections that a dedicated microscope ocular would.

The image opposite shows the Zarf adapter with the G9 in situ on a Zeiss Standard microscope.

The G9 has a flash hotshoe and this can be used to couple to my flash system. It fires a Vivitar 283 via a Wein Safesync. The use of a Safesync is advisable because older flashes such as the Vivitar 283 may present high voltages to the camera hotshoe. Modern digital cameras are not designed to work with high voltages and damage may result. The Safesync effectively isolates the camera from any unwanted high voltages.

Adapting a Canon EOS 500D to my Microscopes

As I was not getting the quality of pictures I really wanted from the G9 setup, I decided to move to a DSLR. This involves a different approach to producing an image for the camera.

Whereas with both the S50 and the G9 there is a fixed lens that cannot be removed from the camera, a DSLR has a removable lens. Whilst it would in principle be possible to use a camera lens in the same way as with the S50 and G9, which uses the virtual image produced by the microscope ocular as does the human eye, I wanted to try forming a real image projected directly on the DSLR sensor by the ocular, without additional camera lenses. (It is also possible to directly project using an objective only, but this loses the advantage of the corrections provided by a microscope ocular.)

This was the normal way 35 mm SLR cameras have in the past been used and there are photo eyepieces intended for just this purpose. Unfortunately, other than top of the range DSLRs, most DSLRs have smaller than full size 35 mm sensors. This means that if used with a standard photo eyepiece, only a small area in the centre of the field will be captured. For this reason, the few oculars that will work are projection eyepieces (i.e. that are designed to project a real image) of low magnification (~2.5x) that now command a very high price.

An alternative is to use a conventional eyepiece designed to produce a virtual image, but raised in the microscope tube to produce a real image. This uses the ocular outside of its design parameters, thus risking unpredictable aberrations. I experimented with a range of different oculars to find one with acceptable aberrations and eventually decided upon the trusty old Zeiss KPL-W 10/18. The resulting setup is shown below.

Here is the KPL-W eyepiece shown in position inside the camera adapter adapter, and below that shown removed so that the method of raising the eyepiece can be seen. The total distance raised was 11 mm. This is sufficient to produce a real image within the adjustment capabilities of the phototube, so that parfocality can be achieved with the camera and the binocular image seen by the observer.

The microscope adapter used is the Asahi Pentax microscope adapter which has an M42 thread, so a further EOS to M42 adapter ring is required. This is the wide black ring that can be seen directly below the camera body in the image below.

 

 

Overview of DSLR setup

 

Above is an overview of the complete setup. The DSLR chosen was the Canon EOS 500D. This has the advantages that it can shoot HD video clips as well as having live view. In live view mode it features electronic first curtain shutter, so that when not using flash shooting can be free of vibration caused by shutter release.

Describing the setup L-R:

Left foreground: Netbook used for controlling the camera remotely. Behind that can be seen a Vivitar 283 flash on a stand with the termination of one leg of fibre optic in front of the flash. This is the silvery cable with the yellow collar seen beneath the flash. On the right of the flash is a stack of boxes. These are, at the bottom a resistive control box to control flash duration. The method for setting this up can be found on Charles Krebs' Krebsmicro website (The other articles accessible from the Krebsmicro home page provide much valuable information). Next up is the control box for the continuous illumination and above that the Luxeon K2 LED continuous light source with fibre optic plugged in. Finally there is the Zeiss Standard microscope with the camera mounted.

 

 

Software

For each of the three cameras described above, I use Breeze software for controlling all camera functions from my netbook. I find this software superior for photomicrography to the Canon software and have no hesitation in recommending it.

 

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