When using film cameras it is usual to express the magnification obtained by a lens in terms of the size of the image on the film. On 35mm film the image size is 36x24mm, so a life-size image (1:1 magnification) will be obtained if the camera lens can be focused on a subject of dimensions 36x24mm so that the image fills the viewfinder frame and so occupies all the image area on the film.

If a subject of double that size is used (72x48mm) then the image will be half the size and the magnification will be 1:2. Similarly, if the image is 18X12mm (half the size of the film frame in each dimension) then the resultant image will be two times the size of the object and the magnification ratio will be 2:1.

The magnification ratio = negative (image) size / size of the area of coverage in the focal plane (- in focus). Both these are linear measurements, of length rather than area.

For a digital camera, the situation is similar, although unlike the case with the film camera, you never see the raw  image at its original size as you could with a film negative or slide. The image is always enlarged, be it on the camera's LCD screen or on a computer monitor.

The camera specifications state that the Olympus 2100 has a 1/2 inch CCD. I have not been able to confirm the dimensions of the image area on this device, but a search on the web has indicated that the image area on other 1/2 inch CCD's appear to have dimensions of around 6.5x4.8mm.

The Olympus specifications state that the camera lens, with its 7-70mm zoom is the equivalent to a 38-380mm zoom on a 35mm camera. Since the latter produces an image of 36x24mm on 35mm film, it is reasonable to suppose that the 'film area' on the Olympus CCD is in proportion to the scaled down lens sizes. Using the ratio 7/38, this would give the Olympus image size as 6.63x4.42mm. This is in close agreement with the figures I saw during the web search, although the proportions are slightly different. The discrepancy may be accounted for by the simplification of the figures used by Olympus for the zoom lens specifications.

This means that if I can 'fill the frame' with a subject that measures around 6.6x4.4mm it will produce an near to life size image on the CCD, which is very close to what is obtained when I use my 50mm Rodenstock Rodagon enlarger lens on the camera.

A footnote:

The word macro has become synonymous with all close-up photography as camera manufacturers use the term as a selling point for their cameras. I don't know of any current digital cameras (other than Digital SLRs) that actually have true macro capability, and the Olympus 2100UZ is no exception.

To have good close-up capability the camera should be able to work at ratios of 1:10 down to around 1:4 magnification, .

Macro capability comes in when the camera can handle ratios from around 1:4, through 1:1 (true macro) down to about 4:1, by which time the depth of field will be down to .01inches (.25mm) or less.

Beyond 4:1 you reach the realms of microphotography, where the camera really needs to be linked to a microscope that can give the necessary control over focusing and image movement.