I decided to make Pentax 67 lens adapters to use with my astro cameras. There were several reasons to use the Pentax lenses. I have Canon EOS lenses, but it is a pain to set and change the f-stop, so I wanted to use a completely manual lens with the astro cameras. Also the Canon cameras make it difficult to use a filter wheel because of the backspace available, which is only 44mm. I also wanted some quality lenses, the Pentax 67 lenses can be bought on Ebay for a very good price and they are completely manual, they have a ton of backfocus (85mm), they are good quality and they have a very large flat image circle, more than enough to illuminate the entire ccd, as they are made for a 6x7cm image field! I bought some EOS to Pentax 67 adapters from Ebay, I cut them down and had Precise Parts make some adapters to the astro cameras and then joined the two pieces. As for adapters to Pentax lenses, do not get the Cirrus Adapters unit, it is cheap and worthless, I tried one. Get the ones with the small tripod adapter like the one from "buyitjnow" (seller on ebay). These are much better adapters.