Depth of field machine for DV

dof

The small footprint of a CCD makes it hard for digital video cameras to emulate the short depth of field of film cameras. You’ll notice depth of field in movies when they have one actor close to the camera and you see the second actor over the shoulder; the actors will alternate being in focus because of the short depth of field. Here are some examples. To emulate this using a DV camera you have to change the size of the target area.  A smaller image is projected on a clear screen in front of the camera which is then recorded. This project uses a clear CD blank for the screen. The CD is rotated using an old CD player; otherwise the camera would pick up the grain of the plastic. Pretty easy, right? I haven’t even mentioned that the resulting image is upside down.

[thanks Angstrom]

Comments

  1. josh says:

    first post!!!

    i never even noticed that with DV cams. Will look and see if i can do that for mine.

  2. bird603568 says:

    You could always film in stero and make the people wear the funny glasses

  3. eski says:

    That would require 2 cameras as well, bird. Kind of defeats the purpose. :)

    Thanks for this hack! I may very well use this on my nzxt shoot…

  4. blah says:

    One thing these people are forgetting is that most DV cameras have zoom lenses. The reason why 35mm cameras have a shallow DOF is because it is a a normal angled lens aka 50mm. take a DV camera with the equivalent lens size of 17-20mm well that gives you a large depth of field.

    I don’t know why it does this, I’m just a film student. If you want a shallow depth of field with a DV camera, get further away from your subject and zoom in on them. You’v probably noticed in someone’s home movies that the camera has a hard time auto-focusing on a subject if you’ve zoomed in on them. That’s because the margin is very narrow and hard to evaluate.

    Remeber:
    Wide-angle= deep DOV
    Telephoto= shallow DOV

  5. furtim says:

    Depth of field is completely different from 3D. For an actual alternative, folk are working on a camera that stores information about parallax so that depth of field can be chosen later in software. It’s pretty crazy stuff. Engadget had a story on it, but I’m too lazy now to look it up.

    These recent camera hacks here are pretty badass, though.

  6. furtim says:

    I broke down and found the link: http://digitalcameras.engadget.com/entry/1234000370066585/

    It’s got nothing to do with parallax across the image sensor, as I had misremembered, but instead operates by simulating smaller apertures by inserting a “microlens array” between the true aperture and the image sensor. As such: “The light field camera decouples aperture size and depth of field. The microlens array harnesses the additional light to reveal the depth of each object in the image and project tiny, sharp subimages onto the photosensor.”

  7. Scott says:

    if you put a second spinning CD in, won’t that flip the picture again? will that effect the picture?

  8. micah buckley-farlee says:

    blah: wrong.
    focal length does not affect depth of field at all, only aperture.
    if you want more information, well, it is explained in the article, you might start there.

  9. micah buckley-farlee says:

    scott: the cd isn’t the part that flips the picture, the lenses do. all film and photo lenses project an inverted image.

  10. ombligotron says:

    Micah: Wrong.

    http://www.dpreview.com/learn/?/Glossary/Optical/Depth_of_Field_01.htm

    Not only is it affected by focal length, but subject distance as well. In fact, this is related to the reason DV has such a huge depth of field. 1/3-inch sensors (DV sensors, as in the Panasonic DVX and Canon XL1/1s/2) have a field of view (FoV) crop of 7.2x. This means that you need a 7mm lens to cover the same angle that a 50mm would cover on a normal film camera. Like Blah said, wider equals more depth of field, so in turn you get the same coverage as a 50mm lense, but much more is in focus, which is generally not preferred. If you put a 50mm lense on a DV camera, you would get the same depth of field as a 50mm film (the optics are unchanged), but it is much less useful because it would seem to you like a 360mm lense (7.2 x 50). Look up Canon’s wide angle lens for the XL2. Normal wide angle for film is a 35mm lense for pretty wide, 24mm lense for “Wes Anderson wide” and anything below 24mm for shockingly wide. Canon’s XL series wide angle for DV goes down to 3mm. Three. The entire frame is usually in focus, and it’s only about a 24mm equivalent field of view.

    Blah’s second paragraph is correct. One more reason why DV film makers should try and write their stories outside, during the day. The outdoors will give you more space with which to use the telephoto effect to blur out backgrounds, less competing lines in the aforementioned background blur, and the daylight will reduce noise because you can run at a lower sensitivity.

  11. I think what Micah meant to say was RTFA.

    furtim, I fixed your link

  12. Scott says:

    thanks for the reply micah. so since its the lenses that flip the picture, i guess if flipping the picture was easy enough as adding an extra lens, it would have been done already, huh?

  13. micah buckley-farlee says:

    scott:
    well, it’s hard to only invert the picture without affecting it in other ways as well. it requires relatively costly parts, so with the nature of this hacking project, it’s much easier to just view the viewfinder with a mirror and flip it in post.

  14. Redrock says:
  15. edg says:

    if anyone has tried this, I want to know something, does the lens vertically flip AND horizontally flip the image?

  16. Brian says:

    Yes, the lens flips the image Vertically and Horizontally, So if you use a mirror in front of you viewfinder in an angle it will flip it back only Vertically but NOT horizontally.
    To flip it back both ways (so it looks totally normal), you would have to use a “Pentaprism” but they are very expensive and hard to find, but if you have an old 35mm SLR camera that you can take apart you could use the one inside it (yes, all SLR cameras have a “Pentaprism” built in) it’s a tedious job and gotta be creative in how to adapt it.
    Hope this was helpful.

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