Soligor 35 mm f/3.5
One of several incarnations of the Soligor 35 mm f/3.5 is shown above. Like some of the Noflexar specimens, this lens has a projecting rear element that is easily damaged by placing it with its rear down on a table. A rear lens cap of sufficient depth should always be used to avoid risks. This is not a problem, of course, if the lens is always kept mounted on a focusing helicoid or adapter for a mirrorless camera. Second-hand specimens should be visually inspected for this fault - a small worn-out spot in the rear lens coating does not substantially affect image quality, but should lower the price of a lens.
35 mm f/3.5 Soligor lenses of this type have serial numbers that begins with KA (which I interpret as a likely abbreviation of Kyoei Acall). Sometimes they come equipped with Acall-branded lens shades, other times with similar but unmarked lens shades. It is very likely that Kyoei produced these lenses for Soligor, as well as for other brands.
The original cardboard boxes of these Soligor lenses display a sketch of an optical scheme, shown at the left, that seems to use 6 elements in 5 groups. However, thanks to the fact that these lenses are easily disassembled without tools (only a rubber cork is needed to unscrew the front retaining ring), I found that these lenses use a different optical formula than the one in the sketch at the left.
The actual formula consists of 5 elements in 5 groups, of which 3 are placed in an outward position before the diaphragm and two at the rear of the diaphragm. The thickness and curvature of individual elements does not correspond to the sketch at the left. There are no cemented elements, and this is very likely one of the factors that allow these lenses to perform well in UV photography.
The Soligor model illustrated on this page has a 23 mm front element diameter and a 46 mm filter mount. It appears optically identical to Kyoei ones and uses many of the same internal mechanical details, but this Soligor has a bluish optical coating, unlike the golden coating of the Kyoei shown on this page. The adapter attached at the base of the lens and carrying the M42 thread is not a T adapter, but instead a proprietary adapter with three set screws that engage a V-shaped groove on the base of the lens barrel.
The UV performance of this Soligor lens is discussed more in detail here.
Aside from three specimens of the Soligor model illustrated above, all with serial numbers beginning with KA, I have seen other Soligor 35 mm f/3.5 lens models with 4-, 6- and 7-digit serial numbers, as well as serial numbers that begin with H (possibly meaning Hanimex) followed by 6 digits, or M followed by 4 digits. Some have large front elements, others small ones. Lenses with both large and small front elements are mounted in barrels with preset apertures, as well as automatic apertures.
The above Soligor 35 mm f/3.5 is mounted in a barrel mechanically different from the one in Figure 1. In particular, the aperture rings are mounted behind the focus ring and closer to the lens mount. Internal mechanical differences are also present, but the rear of the lens with the characteristic retaining ring of the rear element remains the same. This lens model may be more modern than the one in Figure 1, and carries a 7-digit serial number with no letters. However, the optical scheme and its UV performance remain the same.
There are several models of Soligor 35 mm f/3.5 lenses. Some of these models have a different diameter of the front element and obviously use a different optical formula. The scarce available information seems to indicate that at least two optical designs, and perhaps more, are used in Soligor 35 mm f/3.5 lenses. Thus, this brand is perhaps the most difficult, among those discussed in this group of pages, when it comes to deciding without testing whether a specific lens is suitable for UV photography. If considering the purchase of one of these Soligor lenses, choose a model with a front element diameter of 23 mm if you have a choice, because these are likely among the earliest models.
A Soligor 35 mm f/3.5 model has been reported to display a lower UV transmission than the known-good Kyoei lenses. Unfortunately, the source at the above link provided no information on which of the several existing Soligor models was tested.