DoF with high F/Stop causes blur in non blur area ?

phcriado_50d0961ab5

Sometimes I want to use depth of field but I want to get a large number of objects in focus (sharp) so to do this I have to increase the F/Stop value from 22 to 40 or even 60. Whenever I do this it seems I loose some of the sharpness of the objects in focus.

I was wondering if there's a ratio between F/Stop, Focal Distance and/or Focal Length that I need to watch in order to avoid this ? I usually set the Focal Length to 55mm or 45mm.

I have noticed this doesn't happen when I leave the F/Stop value alone at 22.

I'd appreciate any tips or ideas.

Thanks.

JimmyC_2009

DOF in the real world has a much greater depth with a smaller aperture (higher number), DS does the same.

It doesn't sound as if you are using the DOF guides in DS which show you what will be in focus? You need to go to the Default Camera settings (or whatever camera you are using) and turn on the near and far planes visibility. In the Camera settings in the Parameters pane, make sure that 'Depth of Field' is switched on.

There is a DS guide available here which may help : http://docs.daz3d.com/doku.php/public/software/dazstudio/4/userguide/start

phcriado_50d0961ab5

I am using the guides and I see the objects inside the focus area, but when the depth is too great, things are not equally sharp inside the focus area, they loose focus gradually as you move away from the camera, even if they are inside the focus guide planes. I read somewhere that in real life you can't just increase the F/Stop madly, it will get messed up at some point. I was thinking I might be doing something wrong in DS.

wiz

awz4158 said:

I am using the guides and I see the objects inside the focus area, but when the depth is too great, things are not equally sharp inside the focus area, they loose focus gradually as you move away from the camera, even if they are inside the focus guide planes.

That is true. It's exactly the way real life cameras work, too. DAZ does that part of the physics correctly.

There is only one "plane of focus" where you have maximum resolution. As soon as you start moving away from that plane, even a mm, you start adding very small amounts of blur. The "near DoF plane" and "far DoF plane" are not "brick walls" separating a "sharp zone" from an "unsharp zone". They simply indicate where the blur has increased to some value that photographic experts from around 1890 declared to be "no longer sharp". Even today, the photographic experts don't agree on that criterion, which is why two different lens manufacturers might draw the DoF marks on their lenses differently.

Imagine placing a figure at 500cm from the camera, and adjusting the "focal distance" to that value.

Now place three more figures, 50cm, 100cm, and 200cm behind the first figure. Now you have four figures, 500, 550, 600, and 700cm from the camera.

Tweak the aperture so that the far DoF plane goes through the third figure.

Now render it. The first figure, at the focal plane, is sharp. The third figure, at the rear DoF plane, has the amount of blur allowed by the "ancient and mystical DoF criterion". The second figure, being half way between the focus plane and the rear DoF plane, has half the blur of the DoF criterion. The last figure, being twice as far away from the focus plane as the rear DoF plane, has twice the blur of the DoF criterion.

If you want several things that are at different distances to all appear razor sharp, and a background at a different distance to not be sharp, you have to composite it, because physics says it can't be done. (Real photographers use a compositing technique called "focus stacking" to get around this).

I read somewhere that in real life you can't just increase the F/Stop madly, it will get messed up at some point. I was thinking I might be doing something wrong in DS.

It's true you can't increase DoF too much in real photography.

That's called "diffraction", and it's part of physics that DAZ can't do (thank God). If you were shooting real stuff with a real camera and you stopped down to f32, diffraction would start to make everything, even things at the plane of focus itself, softer. Since DAZ doesn't do that, you can turn the aperture down to something silly, like f2200, and still get a good render. If you did that to a real camera, your image would be one big blur.

wiz

How do you attach pictures on this antique forum? I just did the DoF experiment, and now I can't attach the screen caps.

JimmyC_2009

Thanks for answering wiz, it was a bit late for me, long past bedtime :)

To post an image on the forum, just click on the 'Browse' button just below where you write your post, and browse to where the image is on your system. Don't worry about resizing it, the forum software does that.

Richard Haseltine

You need to use Post Reply, not Fast Reply, to get the options including the image attachment button.

Jaderail

If you look VERY VERY closely at the DoF camera LINE of sight, Between the two Fields is a X on the line of sight. THAT point and only THAT point is perfectly in full focus. All in front and all behind that point will have SOME DoF applied to it just as it would in a real Camera.

phcriado_50d0961ab5

Thank you all for the replies. I think it would be nice if some future update could include the option to force a certain region to be sharp instead of making the progressive blurring.

wiz

I quite agree. What you describe is so useful a result that some of us who work in the real world ™ in addition to CGI master some very complex photographic procedures to do it.

Unfortunately, that's something that DAZ simply passes on to the renderer, and as far as I can tell, 3Delight cannot support this. It looks like it should be possible to break the pipeline and alter the depth map (or whatever they call what I call a depth map) and make it non-linear, before the pixel filter that spreads points based on depth.