Best Infinity style lens for DSLR filming?
 

I know that this defeats the purpose of a DSLR, but I was looking for the possibility of the best solution for Infinity type filming on my Canon T2i (cropped sensor).
My current crop of lenses is limited, currently stock Canon 18-55 lens (crap), Canon 50mm 1.8, and Tamron VC 2.8. Of all the lenses the Tamron is obviously the best and the 50mm 1.8 a great photo lens, but sucks for filming as it won't hold focus when you move.

I was thinking that the Sigma 30mm 1.4 would definitely be a decent choice as it will be more of a true 55mm perspective (on a cropped lens). And as such give more latitude for greater focus.

As I said, I realize that the reason DSLRs are fantastic is the DOF, but since I will be building an arsenal of lenses for particular situations, I am after a lens with more latitude and less DOF for situations like dancing footage at a reception, or even some sports shooting (I also do some infomercial style videos for my daytime job and we film some of our sponsored Triathletes and swimmers for products). I figured it would be easier to take a DSLR (with a couple lenses) or two on a remote shoot rather than video gear for simplicities sake.

Also taking along a DSLR for sporting filed use, would give me an opportunity to take both video and photo (for our printed pieces, ala Fusion) at the same time for these sporting events.

Shooting at infinity really limits your focus options and is not the best solution for what you are trying to achieve (I think) check out this thread and I think it will help you.

http://www.dvinfo.net/forum/canon-eo...steadicam.html

also check out this site and I believe it will also be useful.

Online Depth of Field Calculator

So I take it according to that thread, it's best to shoot with a lens that's 24mm equivalent.
Keep in mind I'm not trying to shoot in total infinity, just enough where I can move around slightly without having to adjust my focus constantly.

I gather the wider the focal length, the more latitude I will have.
By wanting a 24mm focal length on a cropped sensor, I should be looking at a 15mm or equivalent style lens?

So I guess I should look into something like the Tokina 11-16 2.8.

Not really, you can shoot at what ever focal length you want. I use my 17- 50 the most out of all my lenses when using my Black Bird (usually at 17mm on my 7D). But, you must take into consideration f, focal length, and distance from your subject. Read Charles' post again and you will see what I'm talking about. Just setting it to infinity does not always give you the most latitude for movement from your subject. Punch in some settings into the DOF calculator and you will see how these things work together.

If deep focus is what you need just stop down. If you want it to be even deeper than that then stay at 17mm on your Tamron, a combination of shooting at f5.6-8 and being wide will give you plenty of DOF for those deep focus shots. It's pretty much true for any lenses the more stopped downed you are the deeper your dof becomes. You're not really gonna find a fast lenses with deep dof, that's not the nature of fast glass.

Evan is right, stop down will give you deep focus, but the problem is if you stop down at a reception your picture will be dark as hell, and so deep focus with large sensor camera under low light doesn't mix, if this is what you are looking for you are using the wrong camera, either learn how to focus manually with shalow dof or use small 1/3 chips video camera that will give you deep focus even at f 1.6

Yes, stop down as much as you can, shoot as wide as you can, and don't let the subject of interest get to close to the camera. Even a wide lens has shallow DOF when focused close. Back away from your subject and things become much deeper.

With a 17mm lens at f/4 on a crop sensor camera, here are some examples:

* Focus at 1 foot: roughly one inch is in focus.
* Focus at 3 feet: 1.5 feet are in focus. (2.43 ft to 3.93 ft)
* Focus at 5 feet: 4.7 feet are in focus. (3.58 ft to 8.28 ft)
* Focus at 12.6 feet: everything from 6.3 feet to infinity is in focus!

So, rather than stop down to darkness. sometimes the answer is to simply back up.

And just to be the token nerd... I believe the concept you're describing is actually the 'Hyperfocal distance'

Hyperfocal Distance

Useful on smaller-chipped cameras, harder to achieve as the sensor increases in size and requires a longer focal length to cover it. Returning you to the non-nerdish debate...

I'll add to the previous comments; use whatever lens you want, but shoot at a higher ISO, that way you'll have to stop down to maintain correct exposure. Stopping down equals deeper focus.

Thanks all for the useful input.

Just for the record I know how to manually run a photo and video camera in full manual, as I prefer this method. The issue I was running across, especially on the cropped sensor, was using a lens like the Canon 55mm 1.4 works great in low light, but your subject, especially when moving can move out of focus rather easily. I also have a Tamron 17-50 2.8 that holds focus well, but is obviously darker in low light.
I figure using a lens like the Sigma 30mm 1.4 would work better in low light as the lens essentially becomes a 55mm lens and would hold focus a bit better. And going to an even faster wider lens would work even better for low light. I still plan on using video cameras for the bulk of my filming and use the DSLR for specialty beauty shots and photos, as it was untended for.

It's just that I would also like to use the DSLR for some reception dance shots, and was looking for the best all around solution that would work in low light and hold focus better for longer periods on moving subjects.

Thanks again for everyone's input. I think that I have some good ideas on work arounds. Especially since I use supplemental lighting anyway, off camera, and some on camera.

Check out post #3 on this thread:

http://www.dvinfo.net/forum/canon-eo...-opinions.html

Stan thanks, I remember seeing this thread which confirmed my decision to want to pickup the Sigma 30mm, as one of my next lenses.