Richard J Kinch

Description:The C-mount to digital camera adapter mechanically and optically couples C-mount instruments to small digital cameras such as the Canon Powershot A-series (see current list of compatible models in the specifications below). Many other brands and models of smaller digital cameras with small lenses and filter thread mountings or adapters may also work with this adapter.

The adapter assembly consists of a cylindrical, custom-machined adapter which provides standard male filter threads (52mm M52x0.75 thread, or 58mm M58x0.75 thread) on one end, and a female C-mount threaded receptacle (1"-32 thread) on the other. Other filter thread sizes may be fitted via standard camera step-up or step-down rings. Inside the adapter is a three-element, antireflection-coated, optical assembly which coverts the focal C-mount image (which the camera cannot use) to an afocal image (which the camera can use). This custom adapter attaches to a stock conversion lens adapter for the Canon camera, which is a thin tube providing a bayonet adapter on one end and female filter threads on the other end. The custom adapter and stock adapter screw together via the threads to complete the assembly. One end then attaches to the camera and the other end to your C-mount instrument interface.

The conversion lens adapters for certain Canon models provide an additional threaded ring. This ring extends the conversion lens adapter to accommodate the longer extension of the Canon camera lens in the mid- to telephoto-range of zoom. The adapter assembly is normally used in the widest wide-angle zoom setting, or slightly zoomed in, without the extension ring. Other Canon models, and non-Canon makes, do not provide this ring; instead one adjusts the tube length by threading the C-mount adapter further in or out of the conversion lens adapter.

Removing the Canon ring: Lens accessories attach to the Canon A-series cameras via a conversion lens adapter which in turn attaches to the camera via a bayonet fitting. To expose the bayonet receptacle on the camera at the base of the lens, remove the lens ring from the Canon camera by pushing the release button and turning the ring. Refer to the Canon manual for your camera for further details on removing the ring.

Attaching the adapter to the camera: Insert and lock the bayonet end of the adapter assembly to the camera. A bit of play exists normally with this attachment.

Attaching the adapter to the instrument: Screw the C-mount instrument into the adapter. The standard C-mount male threads should not project more than 4mm into the adapter; if you have a non-standard coupling with longer projection, take care that it does not bottom out on the optical assembly inside the adapter. Screw the adapter and instrument together until the shoulders are firmly mated. Take care when mating the adapter threads, as they are very fine and fragile, and easily cross-threaded or otherwise damaged.

Starting the camera and setting the zoom: When first turned on, the Canon camera will set the camera lens in the widest angle zoom setting. This maximum wide-angle setting is the normal setting for photography with the adapter, because the circular instrument field just fills the camera field up to the top and bottom of the rectangular edges ("inscribed" crop), and the corners are dark. Thus you need take no action to adjust the camera for this choice of image cropping. You may also zoom the camera's lens just a bit from the widest angle, to obtain an "outscribed" crop, where the corners of the image are just inside the circular instrument field, the entire camera frame is imaged, and crescent portions of the instrument field are cropped out of the camera image.

To zoom in any further with the camera lens, you must first insert the extension ring to prevent the camera lens turret from bumping into the adapter. If you attempt to zoom too far without the extension ring, the camera will shut down while displaying a "lens error" message. To correct this error, insert the extension ring and restart the camera.

Using the automatic camera focus, aperture, and exposure time: You may find that the automatic mode of the camera works with your instrument, which makes everything very easy. In this case, the camera will automatically focus on the instrument image, and select an appropriate aperture and exposure time. Many instruments are compatible with this "point and shoot" convenience.

Setting manual focus, aperture, and/or exposure time: If the automatic mode of the camera does not produce suitable results, or you want precise and repeatable control of photographic conditions, use the manual settings to set the camera properly. C-mount instrument standard and adapter optics should provide an image that appears to the camera to be at infinity, not close up, so you should normally be using a fixed manual focus at infinity. Different manual settings of aperture may improve or degrade resolution, contrast, and vignetting of your instrument's image.

Consult the Canon manual for using the custom "C" mode of the camera, which will allow you to save a manual setup of the camera for quick and consistent use.

Adjusting and calibrating for parfocality: The adapter is designed and delivered for "parfocal" operation. In practice, this means that the camera will take a well-focused photograph whenever a trained operator sees a properly calibrated and focused instrument view. That is, one need not be concerned about adjusting a different focus for photographing with the camera versus the normal visual view of the instrument. This assumes that the instrument correctly follows the C-mount optical interface standard, and is in good calibration and adjustment. In optical terms, parfocality means that the digital camera will focus at infinity when the instrument provides a image at the precise location specified in the C-mount standard. Parfocality is designed to be established when the last face of the optical assembly is positioned coplanar to the threaded end of the adapter.

To calibrate the parfocality of the adapter, you can adjust the axial position of the optics in the adapter by loosening the setscrew (using a 1/8" hex key) and moving the black cylindrical lens assembly in and out very slightly. This will change the focus and can be used to compensate for non-standard instrumentation that may be out of focus. If you want to check or return the adapter to standard parfocality, loosen the setscrew, and use a flat surface to locate the end of the optical cylinder to be coplanar with the threaded end of the adapter body. Take care that if adjusting the optical cylinder in too far towards the camera, that the camera lens turret does not bump the cylinder in the zoom ranges you will be using; use the extension ring to extend the range if this occurs.

Cleaning the optics: Cleaning the optics should not normally be necessary, as they are protected within the adapter. The exposed lens face nearest the camera can be cleaned without disassembly. If cleaning of the internal optical surfaces should become necessary, proceed as follows.

Separate the custom adapter from the conversion lens adapter. Loosen the setscrew holding the optical cylinder in place and remove the cylinder. Unscrew the two parts of this cylinder, a narrower and wider end, from each other. Remove the two lenses and one spacer ring. Take care to note the orientation of the lenses and spacer ring in the assembly so that you do not reassemble them backwards, which would degrade image quality. Carefully clean the lenses and remove any dust, as you would for a microscopic instrument.

Warranty: We manufacture these adapters to high mechanical and optical standards, and guarantee the performance will be in accord with the specifications. Please contact me via email ( should you have any difficulties we can correct.

Specifications (April, 2008)
Input interfaceC-mount detector standard:
18mm circular focal image
1"-32 UN-2B thread (female)
0.69 inch (17.5mm) flange distance
Output interface37 degree circular afocal image
M52x0.75 or M58x0.75 male thread
(52mm or 58mm camera filter thread)
(Step-down rings to 46mm and 37mm available)
19mm exit aperture
18mm exit pupil relief
Weight150 grams
(58mm lightweight version)
(Does not include weight of conversion lens adapter)
Overall length58mm (2.3 inches)
Canon camera models compatibilityCanon A510, A520, A540, A570, A580, A590IS,
A610, A620, A630, A640, A650IS,
A710IS, A720IS
Optical elements3 elements in 2 groups, fully coated
ManufactureMade in USA