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f/stop / focal distance

MoogooMoogoo Posts: 136
in The Commons

So i set the f/stop with what ever I want to be crystal clear in it and things outside are blurry, simple enough.

My question is without changing the f/stop is there a way to increase the drop off to blury so like changing the scale factor so it drops off more blurry faster?

thanks

Comments

  • Matt_CastleMatt_Castle Posts: 3,009

    Not within Iray itself, as Iray tries to emulate realistic optics, but does not currently have tilt-shift available as an option.

    However, one could render out a depth canvas and use that to do a depth of field blur in post.

  • MoogooMoogoo Posts: 136

    Thanks Matt.

  • bytescapesbytescapes Posts: 1,905

    In a real camera, placing the camera close to the subject will result in shallower depth of field (i.e. shorter focal distance will result in a shallower depth of field, otherwise known as things getting blurrier faster). Longer lenses also have a shallower depth of field, and conversely wide-angle lenses have a greater depth of field. At least this is how things work in the real world, and I believe Iray simulates this more or less correctly.

    Just like a real photographer, you can try to juggle the combination of aperture (f-stop), lens focal length, and camera placement to get the effect that you want. Sometimes, like a real photographer, you'll find that some combinations you want aren't achievable: if you place the camera very close to the subject and use a long lens, you'll only be able to frame a small part of the subject.

    Incidentally, there's something a bit weird about the aperture numbers in Iray. I quite often find myself forced to use something like f/64 or f/128, apertures that simply do not exist on any camera or lens I've ever owned. I'm not sure that the apertures in Iray map sensibly to real-world apertures.

  • cridgitcridgit Posts: 1,765
    edited May 2022

    Redacted

    Post edited by cridgit on
  • Matt_BrownMatt_Brown Posts: 177

    cridgit said:

    bytescapes said:

    Incidentally, there's something a bit weird about the aperture numbers in Iray. I quite often find myself forced to use something like f/64 or f/128, apertures that simply do not exist on any camera or lens I've ever owned. I'm not sure that the apertures in Iray map sensibly to real-world apertures.

    Totally agree; Sometimes I have to use bothersome small numbers or even silly things like 222 or 444. It gives my OCD a little itch but not yet enough to scratch.

    I felt the same way at first. However, once I realised that I could achieve almost any depth of field with any focal length the fact that the numbers were silly ceased to bother me. Now I just wish that I could set my SLR or F2.347 occasionally! Also as Iray doesn't use APS-C or 35mm the numbers probably don't really mean anything anyway.

  • Richard HaseltineRichard Haseltine Posts: 108,063

    Matt_Castle said:

    Not within Iray itself, as Iray tries to emulate realistic optics, but does not currently have tilt-shift available as an option.

    I thought til-shift was moving the backplate, to avoid parallax? Iray in DS has an offset option on cameras to do that.

    However, one could render out a depth canvas and use that to do a depth of field blur in post.

  • solisphotographysolisphotography Posts: 43

    The Lens Radial Bias setting in your Camera can help with the DOF drop-off. It's at 0.5 by default but changing it to 1 or 2 increases the DOF drop-off. I almost always use 1 unless I'm really tight on a subject with a long lens (greater than 100), then I use 2. 

  • DripDrip Posts: 1,237

    You could alter the focal distance? So you may combine the f/stop you have with different focal distance, and adjust your camera position to match. A higher focal distance should result in (slightly) slower blur drop-off behind, and faster blur drop-off in front of the subject.

  • Matt_CastleMatt_Castle Posts: 3,009

    Richard Haseltine said:

    Matt_Castle said:

    Not within Iray itself, as Iray tries to emulate realistic optics, but does not currently have tilt-shift available as an option.

    I thought tilt-shift was moving the backplate, to avoid parallax? Iray in DS has an offset option on cameras to do that.

    Iray as currently implemented in DS has shift - which is translating the backplate and lens relative to each other, which does correct for perspective - but it's the tilt part - rotating the lens and backplate relative to each other that really gives the additional control over your focal plane, allowing it to be diagonal through the image. This is often used to do fake "miniature photography" where the angle of the focal plane is used to mimic the often very shallow DoF you'd get when photographing a small object with a (comparatively) large aperture.

    Mind you, this is all stuff that involves lenses that are too expensive and niche for me to justify owning in the real world, so my understanding is more theoretical than practical.

    I would have liked to have experimented with it for this piece (although that would have been a very extreme tilt beyond the limits of real-world lenses, but when you're in the virtual world, that's not so much of an issue), but I instead ended up faking a split-diopter effect by rendering each half of the image with a different focal distance and merging them in post:


    Gallery Link

  • Richard HaseltineRichard Haseltine Posts: 108,063

    Matt_Castle said:

    Richard Haseltine said:

    Matt_Castle said:

    Not within Iray itself, as Iray tries to emulate realistic optics, but does not currently have tilt-shift available as an option.

    I thought tilt-shift was moving the backplate, to avoid parallax? Iray in DS has an offset option on cameras to do that.

    Iray as currently implemented in DS has shift - which is translating the backplate and lens relative to each other, which does correct for perspective - but it's the tilt part - rotating the lens and backplate relative to each other that really gives the additional control over your focal plane, allowing it to be diagonal through the image. This is often used to do fake "miniature photography" where the angle of the focal plane is used to mimic the often very shallow DoF you'd get when photographing a small object with a (comparatively) large aperture.

    Mind you, this is all stuff that involves lenses that are too expensive and niche for me to justify owning in the real world, so my understanding is more theoretical than practical.

    I would have liked to have experimented with it for this piece (although that would have been a very extreme tilt beyond the limits of real-world lenses, but when you're in the virtual world, that's not so much of an issue), but I instead ended up faking a split-diopter effect by rendering each half of the image with a different focal distance and merging them in post:


    Gallery Link

    Ah, I see - thank you.

  • FishtalesFishtales Posts: 6,212

    As someone who uses camera settings and tone mapping settings based on my DSLR camera settings I fail to see where there is a problem.

  • cgidesigncgidesign Posts: 442
    edited January 2022

    @Matt_Brown

    ... Also as Iray doesn't use APS-C or 35mm ...

    I think it does. Frame Width (mm) in camera parameters seems to define the sensor size.

    @solisphotography

    Thanks for your tip  yes

    DOF-scene_1.png
    1365 x 824 - 380K
    DOF-scene_2.png
    1361 x 609 - 533K
    DOF-scene_3.png
    1362 x 607 - 550K
    Post edited by cgidesign on
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