Trouble with DOF

[tomsdesk]

The difference in focus between the background image and the back model elements in my last render (see top detail) seemed too strong, so I did another render setting the focal point at the face of the front house wall (not the porch) and the f-stop set at "4" (see lower detail and settings image)...doesn't seem to be any difference? What am I doing wrong, thanks?

(Sorry about the red tinted sky in the first image...how that doesn't hinder comparison.)

Oh yeah...the field of view in SU is set to "20", if that makes any difference(?).

[Chris]

Try setting F-number to 1. You might also try to increase the focal length to 150 - 200 mm (which will change your view!)

[Fletch]

Tom,
What specifically is the effect you are expecting to achieve?
Do you have much experiencing with achieving DOF on real cameras with similar scenes in real life?

[tomsdesk]

Fletch,
None at all...I just want to blur the bushes in the far background of this image a bit so they fit better with the background image.

[Fletch]

might be challenging to do with a real camera/similar scene. I'm no photography expert... but I believe the foreground will also blur in your scene.

You should render a depth mask (renders very very fast)
then use the depth mask to drive the depth of field.

This will render much quicker because renderings with pinhole cam will render much more quickly than with F-number.
Then rendering the depth mask takes about 5 seconds...

In photoshop, go to "Filter>Blur>LensBlur" and drive the blur with depth mask.
tutorial link (scroll half-way down the page)

[Ecuadorian]

Tom, it seems to me that the real problem is that your background image has very low resolution. Try finding a better one in a stock photography site, such as Fotolia.com or Dreamstime.com. The price is right and there's plenty of selection.

Anyway, if you want to keep the current background and blur the more distant bushes and trees, the effect you're trying to achieve is called "fake miniature". In real photography this is done with special lenses or with post-production, but with a 3D model you can simply scale your model so it's actually a miniature in SketchUp. Try scaling your scene by 1/100 and remember to set again your focus point.

[tomsdesk]

Thanks a bunch, Guys...lots of info to play with. Couldn't immediately find anything similar to the depth mask in PSP, but will give it a good look later. Changing the F-# to 1 did indeed blur the foreground too much (even after moving the focal point to the middle foreground); tried 2, but not much difference than 4; but 1.4 gave me just what I was looking for, thank you very much (but also blurred the middle background trees a bit more than I wanted originally, so maybe I'll have to do this in PSP afterall since I still had do some desat back there to make the original render better).

BTW didn't have much going on the 'puter this weekend so let this cook for something like 520 passes at interior+...surprised how the stuff in the shadows kept getting better and better.