Optomax 35 mm f/3.5
This lens branded Optomax seems to be identical in optical scheme, and is mechanically very similar, to the Kyoei type 2. It differs in the preset ring being thick like in the Photax, instead of thin like in the Kyoei type 2. The M42 lens mount is provided by a removable adapter that attaches to a proprietary V-groove at the bottom of the lens barrel. The adapter attaches to the lens via three set screws.
The front element diameter (as exposed at the lens front) is approximately 23 mm. The filter mount thread is 46 mm. The coating of the front lens element displays bluish reflections, unlike the Kyoei type 1 and 2.
The sprinkling of white dots visible around the perimeter of the front element in Figure 1 is not molds or dust, but a good example of "Schneideritis", called in this way because this fault is especially common in several legacy lens models made by Schneider Kreutznach. In brief, this is caused by black paint on the lens perimeter lifting off from the glass (though not necessarily flaking off, which is a more serious problem). This fault can be corrected by cleaning and repainting the lens perimeter, but on the other hand the effect of Schneideritis is usually a minor, often undetectable reduction in lens contrast. Loose paint flakes, instead, may potentially be more troublesome and should be cleaned out.
The UV performance of this lens is discussed more in detail here.