Converting Old Lenses For Use On Digital SLRs

I first discovered this unique and often overlooked aspect to the hobby some time in 2006. I had gone fully digital a couple of years prior with the release of the first generation Digital Rebel (300D), and I had some old Olympus OM and Canon FD glass that was sitting unused. At the time there weren't too many adapters out there (now the market is overflowing with them), but I did find an OM-mount to EOS-mount adapter, and that's how it all started.

Hopefully, if you're interested in getting started with adaptation of older lenses to a newer format, something in this post will be useful to you.

How Extension Tubes Work

There seems to be a lot of misconceptions out there regarding extension tubes and how they work, and if you're just getting started with them, it can be a little frustrating when you're not getting them to behave how you might expect.  I've talked a few people through it to clear up questions they had, so hopefully by writing up a post about it, it will help someone else one day.

Extension Tubes Are Just Spacers

An extension tube

Some years back, I ran across several product reviews for a set of extension tubes that were unnecessarily negative. The main reason was because the users expected to be able to "zoom in" farther with these tubes to allow the subject to better fill the frame. What they were probably thinking of was a teleconverter, which introduces additional lens elements to effectively increase the focal length of the lens it's attached to.  Extension tubes are different.  They have no optical elements at all; their only purpose is to add additional distance between the lens and the film plane. If you really wanted to, you could actually make your own extension tube with a cardboard toilet paper tube! That's how simple they are.