I recently found my Dad's old SLR, It's a Pentax MZ-50 with a Sigma 28-80mm zoom lens. Is this a good lens at all? I'm thinking of buying an adapter so I can use it with my Canon 20D. I mainly want to do it because 80mm with the crop factor would be like 128mm and that would be cool.
One more question, does the adapter effect the focusing distance at all? I haven't read much in to using adapters, and I'm quite new to photography so I'm not sure if it's even worth doing.