Canon EF100/2.8 AF hustle

Just started shooting underwater with a 20D and 100/2.8 Macro in an ikelite housing. I found that it failed to lock on focus most of the time. Just wondering if the EF-S60/2.8 Macro will do better than the 100/2.8 on that. I tried to use the model light on the DS125 but still cannot make the lens hit the focus. Just also wondering if some other model light(e.g. those from the L&M, fisheye...etc) will help.

Need more details. What distance and subject size are you trying to shoot.

The 100/2.8 is one of the best macro lenses at AF out there. That said, it is a more difficult lens than a 50 or 60 which is why we usually recomend you start with a 50 and then move up to a 100 as your skill increases.

If you are trying to shoot small subjects near 1:1, AF that is very hard at this range on all lenses but the 100 is one of the best in this area.

If you are after fish portrait type shots of medium to larger fish, you are probably too far away. If the subjet is more than 3ft away, it is too far, you need to get closer which may mean you need a wider lens like the 60.

I found the 60 to be fairly forgiving. It focuses most of the time without a modeling light. It will hunt in low light conditions, like any lense.

I always carry a focus light. The 100 is a great lens but the low light situation on a lot of dives requires the light to help it distinguish the key aspect for focus.