Some questions about focusing while filming

[nelwell01]

So recently I've been planning on filming a snowboarding video with my T2i although I'm not completely sure how I am going to keep focus on the other rider. I'll be on a snowboard following another snowboarder and I won't be able to keep my eyes on the camera and continue to try to focus. So basically, how do I get the entire frame in focus? Is that possible?

For some help, I looked at the BTS (this video) of a longboarding video by Devinsupertramp on YouTube and they used a similar camera rig to the one I'm planning on using (they talk about it around 4:30). In their video, they had one rider hold the camera on the low angle rig while filming the other riders. Because the rider filming still had to stay in control, they never touched the focus or anything. How would I set up my camera to do this? As for lenses, I have the regular kit lens and a 50mm Prime.

There are other YouTube channels out there that I know film snowboarding with DSLR's but even when a rider comes flying past the camera, they stay in focus.

Overall:

How do I get a lot in focus?

How do I focus quickly while still snowboarding?

[Tim]

Hello Newlwell01,

With regards to using the EOS Rebel T2i for snowboarding shooting, we'd recommend the manual focusing method.  The EOS Rebel T2i cannot continuously auto focus while movie recording like camcorders can.  In this way it would be difficult for me to recommend a specific AF mode, as they would always interrupt the Live View while they attempted to catch focus. 
My recommendation is, in addition to manually focusing, to use a wider angle lens and small (narrow) aperture values.  This does two things; one, the wider angle lens has a shallower depth of focus, so critical focusing is lower.  Two, the use of a small aperture will allow for greater depth of field, which will retain more of the image in focus.

[nelwell01]

Thanks for the response! So will I be able to do this with my 18-55mm lens or should I get a wider one like a fisheye?

[Mykolas]

nelwell01,

The EF-S 18-55mm f/3.5-5.6 IS lens should be sufficient.  However, if you want a wider angle lens, you may consider the EF-S 10-18mm f/4.5-5.6 IS STM or the EF-S 10-22mm f/3.5-4.5 USM lenses.

[TCampbell]

Depth of field is naturally more generous when you use wide-angle lenses.  

If you were to use a 10-18mm lens set to, say, a 14mm focal length... then the hyperfocal distance at f/4 is 8.5'.  Manually focused to 8.5', everything from about 4.5' to infinity will be focus.   At f/16 you can focus the camera to about 2.5' and the whole world is in focus.  At longer focal lengths and lower focal ratios you'll need to focus to your subject, but at short focal lengths (ultra-wide angle lenses) you really don't need to worry about focus because depth of field is very large.

GoPro cameras are popular for this sort of thing, but they use a fixed wide-angle lens and a tiny sensor size.  That results in a very generous depth of field so the camera really doesn't have to focus.

If you'd like to check focal lengths and f-stops that you want to try, go to DOFmaster.com and use their online depth-of-field calculator. 

For any given focal ratio (f-stop) and lens focal length combination there is a value called the "hyperfocal distance".  That is the magic distance at which the lens will have the highest possible depth of field for that combination of camera body + lens focal length + f-stop.     You can then switch off the lens' auto-focus, manually focus the lens to that distance, and as long as your subjects are farther than the minimum focus range in the hyper-focal distance those subjects will be acceptably focused.