Issues IS and AF on 70-200mm f4 IS USM

im purchasing this lens, later this week and i will mainly be shooting mountain biking (very fast moving action) with my old lens, (a kit 18-135mm) i had trouble finding focus during video, i mainly just used manual focus because the auto focus did terrible, on a high quality lens like this i would like to know if the AF will capture sharp focus with fast moving subjects such as a mountain bike rider, MF isnt bad it would just be alot easier if the AF was capable in situations like that, if you have any type of input that would help me, please let me know, thank you.

Trying to capture video images of fast moving subjects using AF on a dSLR will be difficult with any USM lens. It's not an issue with the lens, but with the method of auto focus used by the camera. You may have a little better luck with a STM lens, but probably not enough for the type of subject you are shooting.

For still images, though, the AF performance of the 70-200 f/4 IS is superb.

jonathanheierle wrote in post #16200582
im purchasing this lens, later this week and i will mainly be shooting mountain biking (very fast moving action) with my old lens, (a kit 18-135mm) i had trouble finding focus during video, i mainly just used manual focus because the auto focus did terrible, on a high quality lens like this i would like to know if the AF will capture sharp focus with fast moving subjects such as a mountain bike rider, MF isnt bad it would just be alot easier if the AF was capable in situations like that, if you have any type of input that would help me, please let me know, thank you.

No DSLR focuses quickly on action or any other subject. If you want a quick focusing camera for video, you'll need a camcorder designed for that task.

(The jury is still out on he claims of improved video autofocus wih the Canon 70D, because the camera is not available at retail yet.)

The AF problem isnt with the lens, its with the body. Its just not designed to be a great focusing system for video action.

For clarification, I added the bold text above. That lens and many of the cameras are perfectly capable of tracking and capturing very fast action for still photographs using the viewfinder and the phase detection array of sensors. The limitation is on AF tracking when shooting video, specifically, with contrast detection focusing method. We'll soon know if the 70D is truly faster focusing in video mode. Canon claims something like 5X as fast as the earlier DSLRs.

jonathanheierle wrote in post #16200582
im purchasing this lens, later this week and i will mainly be shooting mountain biking (very fast moving action) with my old lens, (a kit 18-135mm) i had trouble finding focus during video, i mainly just used manual focus because the auto focus did terrible, on a high quality lens like this i would like to know if the AF will capture sharp focus with fast moving subjects such as a mountain bike rider, MF isnt bad it would just be alot easier if the AF was capable in situations like that, if you have any type of input that would help me, please let me know, thank you.

it won't help that any at all

getting a 70D might help though since it has dual-pixel phase AF during movies

amfoto1 wrote in post #16201097
For clarification, I added the bold text above. That lens and many of the cameras are perfectly capable of tracking and capturing very fast action for still photographs using the viewfinder and the phase detection array of sensors. The limitation is on AF tracking when shooting video, specifically, with contrast detection focusing method. We'll soon know if the 70D is truly faster focusing in video mode. Canon claims something like 5X as fast as the earlier DSLRs.

Thanks for the clarification.

thanks! i dont think i can afford a 70d though haha ill most likely end up buying a 7d and make do, with the 70-200 and a 24-105 f4, i can only put $950 towards a body...if anyone wants to sell my a 70d body for 950 let me know haha