I have this lens that came with a Ricoh Singlex 35mm film camera I bought very cheap - just to get the Rikenon 1.4. The Singlex will take any Nikon F mount lens, but a Nikon F body will not accept a Rikenon lens .Hi, I just saw this now as I bought exactly the same lens on ebay a couple of days ago. Man who sold it, claimed he used it on f mount as it is made for nikon. But for the love of God I cannot mount it on my nikon d300s or on the ftz adapter. If you read this could you please let me know if there was any trick that makes it work? Thank you!
Daniel
Rikenon lenses of this style have one attachment ear on the flange that is longer than the other two - so it won't fit. It can be filed or ground down to fit, but I haven't seen one done yet.
I would like to know too !
Very good article here:

The Ricoh that's a Nikon made by Mamiya - Welcome to the Ricoh Singlex
Ricoh developed a bit of a reputation for good SLR bodies and lenses using the M42 & Pentax K Mount. The company still makes K mount dSLR under the Pentax brand. But weirdly their first
