Why won't my Canon 100 mm L lens stay focused in close up shots.

Question

My 100 mm canon L lens won't stay focused when i focus on close objects. Even with IS off & lens set on manual focus. It acts like it can't decide where/what to focus on.

Answer 1

I also own this lens and use very frequently for taking macro shots.  It is easy to be closer to the subject than the lens is designed for, about 11 inches.  Actually, when shooting things like bugs it is within the bug comfort range, and the subject flys away before you can shoot.  To be able to get closer than the minimum focus distance you can add one or a series of extension tubes.  These tubes actually extend the mm of your lenses lenth by a precise amount.  This does not give you any more magnification, but allows you to photograph with your 100mm macro lens closer to the subject than the minimum focus distance.  These tubes are placed between the body of the camera, and the lens.  The tubes are hollow, and have no glass installed in them.  Some tubes do have electrical connections to the body of the camera and lens through the tubes.  This allows the auto focus to operate.  You may have to manual focus a touch to achieve pin point focus on the subject.  But the outer element of the lens will be much closer to the subject.  Canon makes these tubes, but you will pay a high price for them.  Sets are available from third party companies like Kenko, which are very good.  The set includes 3 tubes, in various lenths, my set has 31mm, 21mm and 13mm, and will allow the electronic focus to function.  I hope this information is helpful.  The Canon EF 100mm 2.8L IS USM is one of their best lenses.