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Oh Pentax, you have let me down....not in an earth shattering way, but very slightly in your backward compatibility. I started with a Pentax SV in 1964, upgraded to a Spotmatic then went through practically all the 35mm Pentaxes bar a couple - didn't bother with a K1000 or an MX. Finished off with the ultimate Pentax 35mm SLR IMO - the LX - before changing my allegiance to Canon - partly because I started working for them in 1987 and I subsequently got a great staff discount on both cameras and lenses, but also because the EOS system had just been introduced. It was only natural to continue with Canon when their FF DSLR's came out because all my Canon EF lenses continued to fit. I still hankered after a Pentax FF DSLR though. Anyway, one accessory I purchased somewhere along the Pentax way (probably the 1960's) was a Pentax right angle finder. It fitted every Pentax I ever owned right up to the LX. However, my beef is that it does not fit the K1!
To praise Pentax on one aspect of backward compatibility however, I have to say that all the 4 Pentax K lenses I still have that I purchased after buying a Pentax K2 around 1975, fits and works perfectly on the K1 II - except in having to use manual focus of course. I also bought, in the 60's, an M42 screw fitting Bellows II/Slide copier unit, which I later adapted to fit my subsequent K camera purchases. I adapted it to fit my K2 years ago by purchasing the M42 to K adaptor - which allowed all the K bodies I purchased later to be fitted to it as well. However, one small problem with the arrangement back then was not finding an adaptor to fit a Pentax K bayonet lens to the M42 screw fitting on the bellows, which would allow me to use the bellows for close ups and also to continue using the slide/neg copier. I overcame that by making one myself....by mating an M42 T adaptor with a suitably modified K lens cap (see photos - but bear in mind everything attached to the K1 II is between 40 and 55 years old and is obviously showing it's age. It all works however!) Anyway, just one more moan about my big disappointment. I'm disappointed that ,after fitting every Pentax I've ever owned before the K1 II, the right angle finder does not fit the eyepiece of the K1 II body! OK, it won't kill me, but to rub salt in the wound, it fits all my Canons!
For anyone interested in fitting a K bayonet lens to M42 screw fitting item such as old bellows units or old screw fitting extension tubes etc.) the following photos show how I did it. The first image is of the complete assembly - K1 camera with a K/M42 adaptor fitted (readily available from many outlets,) the bellows, then the home made M42/K adaptor (which can also be used together with the M42/K adaptor as a manual 22mm extension tube BTW), followed by the lens and finally the slide copier. The second image shows how the camera and lens can be used together for extreme close ups, image 3 is of the lens and home made adaptor on their own and 4+5 shows the home made adaptor on it's own. Of course everything is manual except that I have found the K1 II will show in LV a correctly exposed image with the aperture closed down. Any question on making the adaptor, please ask.