The lens, a long-time favorite with vintage enthusiasts for its compact size, metallic build, and pleasing rendering, especially for portraits and controlled telephoto work, was introduced in 1974.
The solid all-metal and glass compact (multi-coated if it comes with an MC designation) is a 4-element in 3 groups construction, has a minimum focusing distance of 0.12 meters, takes 52mm filters, weighs 410 grams, and enjoys a rating of Sharpness at 9.0, Aberrations at 8.7, Bokeh at 8.7, Handling at 8.1, and Value at 9.5 on PentaxForums.
The lens also carries the designation "-A" to denote that the lens has a removable shank and can be installed in other camera lens mount systems. Variants of the lens include a multi-coated "MC" version and a "K" version with a PK mount.
On the Pentax K-m, the Jupiter-37A 135mm f/3.5 is equivalent to a 202.5mm lens on a full-frame camera. The focal length, categorized as a medium telephoto, offers a balance between magnification and perspective compression, with a narrower field of view ideal for portraiture, street photography, and isolating subjects.
In use, pre-setting the lens to its designated aperture opening, and closing the aperture to the setting before taking the shot, whilst framing and focusing is done at full aperture, is the way forward.
To set, first turn the aperture ring to its smallest opening (f/22), press the aperture ring down towards the body of the camera, and turn it to the required aperture setting. Release the ring and turn it slightly to the right to click the lock into place, and you are ready to go.
In manual mode on the Pentax, you still have the advantage of using the green button (the Exposure Compensation button on the K-m) to quickly set the shutter speed and aperture for proper exposure. Do this by pressing the button before releasing the shutter.
