I own SIGMA SA-7 and a couple of YASHICA lenses: YAHICOR Y503 Telephoto and YASHICA Y504 wide lens, both seem to be 55 mm wide. I would like to use them with my SIGMA original lenses, 70-300 and 28-80. I need an adapter but I do not know what brand and exact size. What kind of adapter do I need?
You have not provided enough information (pictures) to identify the mounts on your lenses.
The "lenses" you mention appear to be conversion lenses that screw onto the filter threads of other real lenses. Look for a symbol that looks like a circle with a line crossed through it (∅) on the lens you wish to use them with. The number following the symbol is the filter size of the lens in millimeters. You will need a step-up or step-down ring from that size to the size of the conversion lenses, which you have indicated is 55mm.
Such conversion lenses are essentially toys that significantly degrade the quality of the image. They cannot even be given away for the price of shipping. You are better off seeking better real lenses for your camera.
If the Yashica lenses you describe are not conversion lenses, there is likely no existing adapter to use them on Sigma SA mount because the SA mount is not popular enough. Only two adapters are returned when searching a popular auction site for SA mount adapters:
- M42-SA adapter
- Hasselblad V-SA tilt-shift adapter
Neither appears suitable for Yashica lenses.