How do you make the plans in the "focus" area match the real focus?

tcassat

I think the title is a bit confusing, so I'll try to explain it better:

In the camera parameters, you can turn on Depht of Field. By doing so, you have access to the "focal distance", which is the plane where the camera's focus will be.

After positioning the focus correctly, you can also change the "F/STOP", and by doing so, you see the visual representation in the viewport of the area that will be in focus. Theoretically, everything within the two white planes associated with F/Stop will be in focus, and anything outside will be blurred.

However, in many cases this visual representation simply doesn't match reality at all. You can have the F/Stop planes super close together, indicating that only a few centimeters of the image will be in focus, but when you render, you discover that the focus area actually extends for tens of meters.

In 99% of cases, I have to completely ignore the F/Stop planes and go with trial and error, using numerical values usually between 80-400 to achieve the desired effects. Is that really how it works? Is there something wrong with what I'm doing?

Thanks.

Chezjuan

Generally I find that the planes give an idea of the focus area, but I have had times where something gets weird with the camera and things don't work as desired. Also, it sort of works like a SLR camera in that the smaller focal length setting the deeper the focal plane will be. The camera defaults to a FL of 65 mm, and going to f/1.95 gives a very slim focal plane. Change the FL to 25 and the the focal plane is deeper.

That said, when setting DoF, I usually put the planes about where I think I want them, turn on Iray preview in the aux viewport with the camera selected, and then mess with both the focal distance and f-stop until I get the look I want, and don't really look at the numbers.