Continuing on the subject of adapting Enlarger Lenses and using them beyond their original intent (darkroom printing/enlarging), here’s the newest member of the family: Bogen Voss 25mm F/3.5.
By poking on the web, I was able to gather some information. Bogen enlarging lenses weren’t and still aren’t getting much love (which in my opinion is totally baseless), and weren’t known to be anything spectacular or outstanding (like Schneider-Kreuznach, Rodenstock, Nikkor or Minolta). From tiny bits of info collected here and there, Voss lenses were bundled with entry level Bogen enlargers, and this particular enlarger lens was primarily intended to be used for enlarging miniature (16mm) film formats.
It is quite possible and easy to adapt this lens to DSLR (for macro only) but infinity focus is only possible with mirror-less cameras (for infinity focus, lens needs to be seated close to the sensor and won’t clear the mirror on DSLR, however once mounted on macro-bellows or focusing helicoid wide enough to clear the lens from the mirror, macro magnification of greater than 1:1 can be achieved). As a side note: any Enlarger Lens with focal length 75mm and above can achieve infinity focus on DSLR and can be easily converted into a regular taking lens.
So, what do we need to convert this lens into a regular taking lens? Nothing too expensive that will break the bank. Basically the only thing we need is what is missing on all enlarging lenses – the almighty focusing mechanism. But before we go looking for focusing substitute, we’ll need to figure out the distance between the lens mount and the camera mount for infinity focus.
Here’s one simple method: with lens removed from the camera, we place the camera on flat surface, make sure the surface is clean and chances of dust and dirt getting on the sensor are minimal. Turn on the camera, make sure the LCD is on too. Next, we align the enlarger lens in front of the sensor so it projects the image directly onto camera sensor (be extra careful not to bump into the sensor with the end of the lens) and slowly move the lens outwards until furthest away object (preferably 20 or more meters away) appears sharp on camera’s LCD screen. And final step, we measure the distance from lens’ mount to the camera’s mount. This will give us approximate size for focusing helicoid needed for infinity focus. As a precaution, we’ll use focusing helicoid 3-5mm shorter than the distance measured. Rough example, if measured distance equals 29mm (from lens mount to camera mount) for an object 30 meters away, the obvious starting size for focusing helicoid should be 25mm.
Now that we know the minimal focusing helicoid size, we can start looking for one. There are vast varieties of focusing helicoids in various mounts available at amazon or ebay. There are some that can directly mount to your camera (preferred), or those that have universal mounts (M42, M39) and will require additional adapter to be mounted onto your camera. Depending on the female (lens side) mount of the helicoid, you might also need additional adapter to mount the lens onto helicoid. The ideal choice for mounting M39 enlarger lens onto Sony Alpha Nex for instance, would be M39 to E-Mount focusing helicoid (in my case, parts that I’ve used to adapt Voss 25mm F/3.5 to Nex are listed under the picture on top).
Technical details (curtesy of SubClub.org):
Focal length: 25mm
Aperture Max: F/3.5
Aperture Min: F/16
Number of Aperture blades: 6
Optical Formula: Tessar type (4 elements in 3 groups)
Optimal Print Magnification: 10X
Lens Mount: M39 (LTM or Leica Thread Mount)
Country of origin: Japan
Year of manufacture: unknown.
Classification: Enlarging various 16mm film formats.
Additional notes: Imported and distributed by Bogen, original maker of the lens is unknown.
Some sample images (minor editing, re-sizing, no cropping):
Even though, the lens vignettes throughout the entire focus range (except extreme macro) on Sony Nex (1.5 crop factor) sensor, it’s nothing a simple cropping wouldn’t fix. Vignetting should be very minimal to none on micro 4/3 mirror-less cameras. On the positive side of things, lens offers excellent fine-detail resolution (from center to the edge), very good color transmission, contrast, flare resistance and swirling bokeh – enough said. A real keeper and definitely fun lens to play with. Obviously, posted samples do not do proper justice to this lens, but I’m willing to remedy it by posting more and more pictures taken with this combo.