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Fitting a Schneider-Kreutznach Xenoplan 17 mm f:1.7 CCTV lens on an Olympus OM auto bellows:
For a number of reasons alternatives to the Zuiko 20 mm bellow lens may be considered. I.e., it may be hard to acquire, it is not inexpensive, and perhaps one would like to get even higher magnification levels. Alternatives that could solve all this are CCTV lenses. These comes in focal length from just a few mm (e.g. 5 mm), can be quite cheap (i.e. less that 100 US$), and should be easy to acquire. Using a 5 mm CCTV lens on the OM auto-bellows should yield something like 60X magnification.
When I first posted for a used CCTV lens on a bulletin board to test this idea I was offered a Schneider-Kreutznach 17 mm f:1.7 Xenoplan CCTV lens for free. While it would not provide much more magnification than the 20 mm lens, it would be suitable enough to try out the idea.
To achieve the best possible image quality the lens should be mounted in reverse, as with any lens not specifically designed for macro purposes beyond 1:1 magnification. Creating a reverse mounting adapter for CCTV lenses turned out to be simple. I acquired a Swift OM-T-mount adapter, which turned out to have an internal diameter of 49.1 mm when the T-mount insert is removed. General Brand xx to 46 step-up rings (outer diameter 48.2 mm) fits snugly enough into the OM-mount part, and thus it is just a matter of selecting a step-up ring that also fits the lens - a 40.5 to 46 mm in this case.
Comparison of two lenses:
To the left the Zuiko 20 mm f:2.0
To the right the Schneider-Kreutznach 17 mm f:1.7 Xenoplan CCTV lens
Parts for the CCTV lens adapter:
To the left the Swift T-mount adapter for OM with the T-mount insert laying on top.
In the middle a General Brand (B&H) 40.5 to 46 mm step-up ring
To the right the CCTV lens.
The CCTV lens mounted:
The front of the bellows fitted with the Schneider-Kreutznach 17 mm f:1.7 Xenoplan CCTV lens.
It is a somewhat cumbersome setup, as one has to focus before stopping down the lens, and it is all to easy to alter the focus while stopping down the lens. Ideally, the focusing ring on the lens should be locked, i.e. by a drop of glue or by adhesive tape.
The front of the bellows fitted with the Olympus 20 mm f:2.0 bellows lens.
Compared to the Xenoplan a far more workable solution due to its ability to be stopped down using a remote release cable fitted to the bellows. But, the Xenoplan also gets the job done.
January 19th, 2006