Vivitar made a few 24mm lenses. At least one of them was a TX mount. This particular version I have is a fixed M42 mount, made by Tokina (serial starts with 37). For an old lens, it's pretty sharp, although the far edges on full frame is bad, even stopped way down. Mount it on a crop-body, this will make a nice mini-wide angle without the mushy edge. Unusual for a wide angle, this lens has 8 aperture blades.