I have purchased all of the parts i need to make a 35 mm adapter, however i am finding it impossible to get the correct spacing between all the parts. I am using a lens from an old Olympus OM-1 35mm camera. So if i understand correctly, if i can get the correct amount of space between the lens and my focusing screen, it will exactly simulate the range that i can focus on with my OM-1. No matter what distance i use, however, i cannot get the same range. Is there something else thats going on inside of the OM-1 that i dont know about? Any suggestions on building this would be appreciated.