Cap'n 100m L lens

[Andyzem]

Why won't my 100mm W/ macro (L lens) stay focused on close ups. I have the IS-off and the focus on manual. After focusing, the focus mechanism acts like it is searching and goes in and out of focus and does not settle on anything.

[trulandphoto]

---

@Andyzem wrote:
Why won't my 100mm W/ macro (L lens) stay focused on close ups. I have the IS-off and the focus on manual. After focusing, the focus mechanism acts like it is searching and goes in and out of focus and does not settle on anything.

---

I'd guess either the switch isn't really on manual or there's something wrong with the lens. It shouldn't focus at all if it's really on manual. 

Try disengaging AF start from the shutter button and using back button focus only. That way when you go to release the shutter it won't start AF again and you can leave the lens on AF.

[Bill-Emmett]

The Canon EF 100 f2.8L IS USM lens will not focus closer than 11.5 inches from the subject. The problem you have is being within the minimim focus distance.   If you want to get closer you will have to add a extension tube.  Extension tube will allow you to focus on subjects closer than the minimum focus distance, depending on the tube you use.  You will be actually extending the lenth of your lens from 100mm to the value of the tube.  This allows you to get closer from the front lens element, to the subject.  Be sure when you look at extension tubes you buy a set that will allow you auto focus to work. The EF will get you in the ballpark, and you can trim the focus to pin sharp using the focus ring on the lens.  Good luck, and enjoy your lens.

[Skirball]

---

@Bill-Emmett wrote:

The Canon EF 100 f2.8L IS USM lens will not focus closer than 11.5 inches from the subject.

---

Just a point of clarification:  that's the minimum focus distance (MFD), a term that I find to be somewhat misleading.  Far more useful is the Minimum Working Distance, the distance between the front element of the lens and the subject.  For the 100mm macro it's about 6 inches, which is quite close.