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IRAY: Enhancing DOF? (Making the blur blurier)

ScavengerScavenger Posts: 2,674
in New Users

Is there a way to make the blur area when using DOF on a camera more blurry? I've narrowed the f-stop area as much as I can.

I'd rather not have to do a back plane render and then use photoshop.. any settings to blur-ize stuff in the camera more?

Comments

  • BeeMKayBeeMKay Posts: 7,019
    edited April 2016

    That depends on your setup. Is there anything, like the floor or other items, in the scene that interact with your field of blur? Or are you intending to make a fully blurry picture?

    If you just want a fully blurry picture, return the fstop to something regular, and then move the focal point towards the camera, until the result suits you.

    The only other option would be to render the surroundings with the intial blur, and the without the figures, then render just the figures, moving the focal point closer to the camera, and save that as a png. Here's combining the pictures in Photoshop required, so it kind of defies your request... wink

    EDIT: Just re-read the question. Hiro Protagonist is correct that the DOF is accurate.

    If you want really blurry color spoths, then maybe simply using a low-res lighting HDRI will serve your purposes? They are very fuzzy to begin with, and if you add DOF to the mixture, they get even fuzzier.

    Post edited by BeeMKay on
  • Hiro ProtagonistHiro Protagonist Posts: 699

    To me DOF in Iray seems to be pretty realistic (in terms of modelling a physical camera). To get a very blurry background will mean narrowing depth of field so much that not all of your subject may be in focus, though. You can see this in this stock photo of a dog. I get pretty much the same result in Iray. The attached was using a 35mm lens, focal distance 100 and F/Stop 8.

    We don't know what degree of  blurriness in the background you are looking for relative to the focus on the subject, though. Perhaps it's not a physically based one, in which case it would have to be faked.

    dof.jpg
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  • ToborTobor Posts: 2,300
    edited April 2016

    Using only the f/stop to control DOF loses half of the physics. The other half is the focal length of the lens. A short lens exhibits less DOF at any given aperture than a long lens. This is how it works in photography, and D|S reproduces this pretty well (though the aperture/focal length metrics don't seem to correlate with real-world numbers, so don't expect DOF charts for photography to work in D|S). 

    See the attached images. The lens focal length (not "focal distance") is 50mm and 200mm. For a 35mm film frame, a focal length of 50mm approximates natural perspective. Note that the background (the Pixar Campus HDRi, for those interested) with a 200mm lens is far more blurry, even at the same f/stop, in this case f/13.

    I've also attached a comparison between 50mm at f/13 and 50mm at f/80. Despite the very steep difference in aperture size, the DOF is similar. This is due to the relatively short focal length of the lens. A "wide angle" lens for 35mm film may have a DOF of just a couple feet to infinity, even with the aperture all the way open.

    Obviously, if you use a long focal length, you need to move (dolly) the camera further away in order to get the same figure size in the frame. This is how it works in real-life, as well.

     

    DOF-50mm.jpg
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    DOF-50-perspectiveview.jpg
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    DOF-200mm.jpg
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    DOF-200-perspectiveview.jpg
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    DOF-50mm-stoppeddown.jpg
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    Post edited by Tobor on
  • BeeMKayBeeMKay Posts: 7,019

    Nice explanation, Tobor. Thank you! smiley

  • ScavengerScavenger Posts: 2,674

    Tobor, the exact kind of info I was looking for! Thanks!

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