I've been asked to photograph (video, actually) kids in a gymnasium, and they want the whole room to show at once. If I am standing in a corner, what kind of lens do I need to capture the whole 90 degree range? What do I need to worry about DOF?
Any advice is greatly appreciated as I have no experience with such a project.
On a 1.5 crop factor DSLR like your Pentax K-30, theoretically a 12mm lens will give you exactly a 90 degree horizontal field of view.
However, given you may want to correct for lens barrel/pincushion distortion, and that focal lengths are often rounded up or down by manufacturers to suit their marketing, if getting in absolutely the full 90 degrees is required, I'd recommend a zoom lens starting at around 10mm, which you would probably use at around the 11-12mm setting.
I don't believe Pentax have a lens in that focal length range natively (the Pentax 10-17mm is a fisheye lens, almost certainly not what you want!), so you'll be looking at lenses by other manufacturers. I like the Sigma 10-20mm f/4-5.6 lens as a good performing and affordable ultra-wide lens, although there are other lenses (including other models by Sigma) you could consider.
You will not have to worry greatly about depth of field, because the lens has such a wide angle. At 11mm, if you set the aperture to f/8 and set the lens to the hyperfocal point (around 2.5 feet), then everything from 1.4 feet away from the camera to infinity will be in focus. Even if you set the lens to f/5.6 (for better light gathering), and set the focus to infinity (for simplicity), anything that's more than about 4 feet from the lens will be in focus.
While this hopefully answers your question, and this is something that you've been asked to do specifically in this way, I have to say that I'm not sure that the resultant video from such a wide-angle lens in a large space will be particularly engrossing to watch -- any time the kids are more than a 15-20 feet away from the lens I suspect they will be pretty tiny in the video, and look a bit lost in a vast empty area of floor and ceiling.
@houser934@abirkill As Alexis suggests, video at extreme wide angle will really not show well at all. No human interest will show. What sport are they playing? If basketball, you can, fairly simply, get nice goal shots from behind the basket shooting straight out. but not with a wide angle lens.
There is a class of wide angle, even fisheye, still photographs showing, for instance, the whole basketball floor and surrounding crowd and stadium, but you need to correct them with something like the adaptive wide angle filter in Photoshop, so necessary especially for fisheye to pull the curvy lines straight. Sometimes the Adobe lens Correction profiles are adequate to do it automatically, but I find I have always had to go with the filter in Photoshop. I doubt, though, that this translates to video readily. And not being a videographer I don't know if such corrections can be applied globally to a video anyway, moving as it is.
Anyway, good luck and let us know how it goes.
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However, given you may want to correct for lens barrel/pincushion distortion, and that focal lengths are often rounded up or down by manufacturers to suit their marketing, if getting in absolutely the full 90 degrees is required, I'd recommend a zoom lens starting at around 10mm, which you would probably use at around the 11-12mm setting.
I don't believe Pentax have a lens in that focal length range natively (the Pentax 10-17mm is a fisheye lens, almost certainly not what you want!), so you'll be looking at lenses by other manufacturers. I like the Sigma 10-20mm f/4-5.6 lens as a good performing and affordable ultra-wide lens, although there are other lenses (including other models by Sigma) you could consider.
You will not have to worry greatly about depth of field, because the lens has such a wide angle. At 11mm, if you set the aperture to f/8 and set the lens to the hyperfocal point (around 2.5 feet), then everything from 1.4 feet away from the camera to infinity will be in focus. Even if you set the lens to f/5.6 (for better light gathering), and set the focus to infinity (for simplicity), anything that's more than about 4 feet from the lens will be in focus.
While this hopefully answers your question, and this is something that you've been asked to do specifically in this way, I have to say that I'm not sure that the resultant video from such a wide-angle lens in a large space will be particularly engrossing to watch -- any time the kids are more than a 15-20 feet away from the lens I suspect they will be pretty tiny in the video, and look a bit lost in a vast empty area of floor and ceiling.
There is a class of wide angle, even fisheye, still photographs showing, for instance, the whole basketball floor and surrounding crowd and stadium, but you need to correct them with something like the adaptive wide angle filter in Photoshop, so necessary especially for fisheye to pull the curvy lines straight. Sometimes the Adobe lens Correction profiles are adequate to do it automatically, but I find I have always had to go with the filter in Photoshop. I doubt, though, that this translates to video readily. And not being a videographer I don't know if such corrections can be applied globally to a video anyway, moving as it is.
Anyway, good luck and let us know how it goes.