I wrote about the travails of getting the SMC Lens Correction Adapter M -3 from Pentax here in the USA. In the end PentaxUSA Corporate stepped up and sent me one and its now on my camera.
I can't tell you what a positive difference this little piece of plastic makes for me!
My prescription is -3.5 in my camera eye
The built-in viewfinder diopter adjustment goes from -2.5 to +1.5 on the K-x and K-r. That's just a wee bit too little for me
And that does make a difference. With the information at the bottom of the viewfinder and glasses on I had a choice, I could view the image or shift and view part of the image and the data. Now that I have installed the -3 adapter and set the built-in viewfinder adjustment I can shoot without glasses for the first time since I was in high school
I can get my eye right up to the cup and see the entire field of the viewfinder all at once!! I've tried a couple of MF shots and its easier, far easier, for me now too.
I wish I knew who at PentaxUSA Corporate stepped up and had this sent to me, I'd like to thank them personally.