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Non-wide angle lens with deep focus?

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Terry Nutkins
Non-wide angle lens with deep focus?
on Jun 27, 2014 at 5:29:49 pm
Last Edited By Terry Nutkins on Jun 27, 2014 at 5:36:43 pm

Hi there,

I am currently shooting a documentary and am wondering if it is at all possible to achieve deep focus with a non-wide angle lens? It has proven difficult in certain circumstances to maintain focus/perform focus pulls in a verité environment and I would like to find a lens (if this at all possible technically) that has a deep depth of field without producing a wide-angle/fisheye effect. (or maybe shooting an external interview scene with a wide-angle might be okay if not?)

Thanks!


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Todd Terry
Re: Non-wide angle lens with deep focus?
on Jun 27, 2014 at 5:40:33 pm

Obviously the wider the lens the easier it is to achieve deep focus... but you can increase the depth of field on any lens simply by closing the iris (shooting at a higher f-stop).

At something really high like f/22 you'll get a reasonably deep depth of field, even with a longish lens.

Of course that will radically affect exposure, and might limit you to sunny exteriors, or high ISOs.

Also your choice of camera (or rather, imaging size) will affect the appearance of the DoF. A tiny-sensor camera (like a little HDV camera with a 1/3" sensor) will have a much much deeper DoF, even at long focal lengths, than a 35mm-sized sensor camera.

The easiest/best/usual way of increasing depth of field is simply pouring on enough light that you are able to stop the lens way down. That might not be the answer you're looking for (or what would work well in a verité environment), but that's just the way lenses work. They are rules of optics and physics that you just can't easily break.

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Rick Wise
Re: Non-wide angle lens with deep focus?
on Jun 27, 2014 at 6:01:44 pm

[Todd Terry] "Also your choice of camera (or rather, imaging size) will affect the appearance of the DoF. A tiny-sensor camera (like a little HDV camera with a 1/3" sensor) will have a much much deeper DoF, even at long focal lengths, than a 35mm-sized sensor camera."

That's because a smaller-chip camera needs a wider lens to achieve the same field of view. A 10mm lens has the same depth of field no matter what camera you use it on. Note that depth-of-field tables only specify: focal length, f/stop, and distance from subject. They never include chip size since it's not a direct factor. The consequence of a small-chip camera is you end up using shorter focal lengths.

Also, if you leave the iris the same and go to a wider lens, you will not get more depth of field if you move the camera closer to achieve the same framing of your main subject(s). On the other hand, if you go to a wider lens and let the framing be looser, you do get some more depth of field.

The dance never ends.

Rick Wise
Cinematographer
MFA/BFA Lighting and Camera Instructor Academy of Art University
San Francisco Bay Area
http://www.RickWiseDP.com


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Todd Terry
Re: Non-wide angle lens with deep focus?
on Jun 27, 2014 at 6:19:54 pm

[Rick Wise] "That's because a smaller-chip camera needs a wider lens to achieve the same field of view."

Yes technically I should have said equivalent focal length, but Rick is absolutely correct in that it is really the field of view.

I've actually seen some lenses on small sensor cameras where the focal lengths were actually marked as if they were 35mm-format focal lengths, when I know they were actually not. I'm thinking "There's no way that medium-shot is really a 50mm on a tiny-sensor camera"... in actuality it was probably more like 10mm or less... but the lens barrel was marked with what people expected to see, not what it really was.

And yes, the dance goes on...

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Rick Wise
Re: Non-wide angle lens with deep focus?
on Jun 27, 2014 at 5:41:46 pm

Depth of field depends on 3 factors: f/stop, distance from the subject, and focal length of the lens.

  • f/stop: The more you close down the iris, the greater the depth of field. Usually to increase depth of field you will need to add more light so you can stop down. On cameras with variable ISO, you can increase that setting up to the point the image degrades too much for your taste. The higher the ISO, the more you can close down the iris.


  • Distance from the subject: The farther away the subjects are, the greater the depth of field. The closer, the more shallow the depth of field.


  • focal length of the lens: Given the SAME distance to the subjects and the SAME f/stop, the wider the lens the greater the depth of field; the longer the lens the more shallow the depth of field.


  • Those three variables apply to all lenses. There are no special lenses with greater depth of field. In your situation, figure out what lens you want to use, then increase depth of field by either adding more light or increasing ISO, and, if necessary, move the actors a bit farther from the camera.

    Rick Wise
    Cinematographer
    MFA/BFA Lighting and Camera Instructor Academy of Art University
    San Francisco Bay Area
    http://www.RickWiseDP.com


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    Terry Nutkins
    Re: Non-wide angle lens with deep focus?
    on Jun 27, 2014 at 6:25:50 pm

    Thanks very much for the info. We're using a large sensor camera FYI.

    Does this scene (with the cop at 9m) look like it was shot with a wide-angle? Or maybe its just a small-sensor camera? We've been in some similar situations (although most much more cramped) and trying to perform focus pulls for objects at different distances has proven difficult.
    https://www.youtube.com/watch?v=_BqFkRwdFZ0#t=539


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