Camera DOF

tonyg3d

Curious now how the depth of field works in Daz Studio.

Here's my process. Set up my scene. Position the perspective view pretty much where I want the camera.
Ensure that nothing is select.

Create new camera ---> Copy active view.

Thing is, when I select the DOF ON, the F/Stop is always set to 22. 
Why does the visual guide for DoF vary? Sometime the space is huge, sometimes is tiny.
What's causing this? I love the DOF but the small version makes it really difficult to focus on an area.

Does the created camera project to the nearest polygon object and make a decision there? 

jbowler

tonyg3d said:

Thing is, when I select the DOF ON, the F/Stop is always set to 22. 
Why does the visual guide for DoF vary? Sometime the space is huge, sometimes is tiny.
What's causing this? I love the DOF but the small version makes it really difficult to focus on an area.

DAZ does it correctly but it is not as easy to use as the old, lower resolution, 35mm cameras I'm used to.  Depth of field depends on both the focal length and the f/stop; well, actually, it depends on the camera "aperture", the size of the hole in the lens, but because aperture is traditionally expressed as a number dividing the focal length DOF depends on both; f/stop is focal-length/aperture.

So if you take the actual camera focal length and divide it by the f/stop number the result should be the same for any given physical depth of field - any specific distance between the DOF planes.  The number is the inverse of the DOF; DOF gets reduced with higher focal lengths and increases with higher f/stops (smaller aperatures).

Unfortunately if you look carefully you will see that for things like 4K renders the DOF planes are perhaps slightly out of focus.  That's because DOF also depends on the resolving power of the film; high resolution films produce lower depth of field.  "High resolution" in a film means the size of the silver grains that capture the light; smaller grains make for higher resolution.  In digital imaging it is the size of the pixels produced by the render, so you have much more DOF on a smaller pixel size image.  Another way of lookinig at it is that lower resolution, smaller pixel size, images have to be physically smaller to avoid the lack of resolution being obvious, so they have to be viewed from further away, so our eyes are less able to see the lack of resolution caused by something being out-of-focus.

I'd like to see a different way of specifying DOF.  The old film camera model is fine for us old photographers, but for digital imaging the DOF measure I care about is when the camera starts to produce dots that are bigger than the pixel separation.  So I want to have the DOF planes tell me this; I want those planes to be set at something like 1.5 pixel size.  Anything which is in focus within a pixel (so a point produces a circle of diameter close to to the pixel separation) is in focus.  I.e. instead of f/stop I want image resolution; the height in pixels of the image (width doesn't matter, DAZ doesn't use that in the lens calculations); I want to see where those limits are.  This is much, much, much more useful than the current antiquated measurement.