Leica Telescope-Ocular To-R
The Ocular To-R (Leica order no. 14234) is an adapter that makes it possible to use standard, telephoto, or zoom-lenses as telescopes. It attaches to Leica R-lenses via the bayonet mount. The Ocular contains a Schmidt-Pechan-prism that rotates the image by 180°, so that it appears upright and correctly sided, as well as an eyepiece with a focal length of 12.5mm. It has a -3 to +3 diopter adjustment. Focus is achieved via the focusing mechanism of the lens. The adapter is no longer in production, but can be found pre-owned in excellent condition for 300-500 USD (check here for current offers on ebay).
The effective magnification achieved by attaching the Leica Ocular depends on the focal length of the lens. It is calculated as the ratio between the focal length of the lens and the focal length of the Ocular. For example, a 90mm lens would achieve a magnification of 7.2 (=90mm/12.5mm), and a 400mm lens a ratio of 32.
Ocular TO-R Specifications
The body of the adapter is a solid, all metal construction with the eyepiece cover being of high-quality rubber. It's core specifications are the following:
- optical construction with 3 elements;
- focal length of 12.5mm;
- eyepiece magnification of 20x;
- exit pupil diameter of 3.78mm;
- usable aperture of 1/3.3;
- field of view diameter of 12mm;
- weight of 100g (3.5 oz).
The Leica Telescope-Ocular works rather well and can quickly turn a telephoto lens into a spotting scope. In good light, it can also be used in combination with Leica's 1.4x or 2x APO-Extenders. With long focal lengths, it achieves magnification ratios that are generally beyond those of binoculars, but the setup tends to require a tripod for comfortable use due to the heavy weight of the lenses. Also, some photographers report that it takes some time to get used to the "tunnel perspective" that the Ocular To-R provides as a result of a field of view diameter that is smaller than the display in a camera viewfinder. It might, hence, be desirable and useful to try out the Ocular To-R, if possible, before buying it in order to avoid disappointment later on.
The Leica Ocular works well with many of the R-series lenses, including the APO-Telyt telephoto optics. It can also be used in combination with Leica's tele-converters, if the light is good enough. Moreover, if you are more generally interested in the now discontinued Leica reflex system, you might want to check out the comparison of Leicaflex and Leica R cameras.