Bingo, you have entered into the wonderful M42 adapter controversy. Here's the deal:
1) Some will argue to only get the genuine Pentax adapter, like me. Much more expensive, but a better machined piece of "equipment," and easy to remove. Have you tried to remove YOURS yet? The 3rd party ones can be a nightmare, and the trick is to remove the screw and spring thingie so that it's only held on by friction. People have shed tears trying to remove the discount ones with the locking clip attached.
2) Believe it or not, Pentax didn't make this adapter available for a period of time, so I suggest you get one now while it is.
3) I bought a Bower from B&H that wouldn't even FIT in the mount. Another Bower did. And gee, aren't experiences like THESE loads of fun!?
4) With the Pentax adapter, the Pentax M42 lenses fit fine, but she may find that with the 3rd party lenses (Vivitar, etc.), the aperture ring doesn't line up correctly at 12 o'clock when the lens is fully tightened. It may be toward the SIDE of the lens, but it is still totally functional like this.
5) To reiterate what was said above, it asks you for focal length (FL) only to tell shake reduction how to operate. For a zoom lens, set it for the FL you think you're going to be using, or turn SR off.
6) I guess you've already discovered the F-- display. With a manual lens, the camera doesn't know what you're doing as to aperture. This is also why aperture info is not included in the EXIF data. (It hurts me big time, but what can you do?)
7) Is she shooting in Aperture Priority (Av) or Manual? Tell her that with M42 Taks, Av has been known to consistently underexpose up to 2 stops!!! So tell her this is to be expected. Some people just set the compensation. I prefer to shoot in M mode and use the green button. (On the K-x, I can use the ev button, but that's another story.) M mode meters wonderfully for me for all of my Taks, EXCEPT THE SMALLEST APERTURE WHICH UNDEREXPOSES. In addition, she may find that with certain lenses, when you get down to F22, F16...depending on the lens...you won't get focus confirmation. So, you focus wide open, and then stop down to the aperture you want.
Just wanted to let you know some of these quirks, but they're all tolerable, and the joy of using the old classic glass more than make up for them.
Last edited by Ira; 06-01-2010 at 08:36 AM.