depth of field controlling horizon

[cneville]

Hi all.

I'm having trouble making the horizon look realistic.

I'm working with a boat model I am using a large disk waterplane as shown on several tutorials with materials maps etc. I am also using the Vray camera.

The edge produced between the water surface and the horizon is in too fine of focus. It reproduces the "fall of the edge of the earth effect". I tried manipulating the f-stop and film speed controls but could not see an appreciable effect. that edge should have a much softer focus but I cannot seem to achieve it.

My understanding is that the depth of field controls don't work with the Vray camera.

I'd appreciate your wisdom....

chuck

[fooprobe]

Re: depth of field controlling horizon

Depth of field does work with vray's physical camera. However I find that I often have to set the aperture to be extremely wide - sometimes to f-numbers below 1 - in order to get the desired blur. You're probably better off using zdepth and getting the blur in post. It's faster and easier and should work very well for a simple model such as a horizon.

[fpedrogo]

Re: depth of field controlling horizon

Depth of field does work with vray's physical camera. However I find that I often have to set the aperture to be extremely wide - sometimes to f-numbers below 1

DOF actually works with the physical camera. When you have the physical Camera enable you have to control the amount of DOF using the F-Number. As you did. That is the only way to control the DOF when you have the Physical camera. Lower values, produce more DOF while larger values produce less DOF. The F-Number also control the exposure of your scene, so you have to correct the exposure using the shutter speed and/or the Film ISO.

[andybot_cg]

Re: depth of field controlling horizon

Another trick to get higher DOF blur is to increase your film size (similar to going to a larger format camera) I forget now if you have to adjust your field of view to compensate, I'll double check (i.e. wider angle to cover larger "film" area)

[Micha_cg]

Re: depth of field controlling horizon

I have the impression the DOF effect works like in the real world only if the unit and scale of the modell is right. A wrong setup and strange F-number values must be used.

Disable exposure and the F-number can be free used without a new exposure adjustment. The shutter isn't needed, since we have no motion blur.

[fpedrogo]

Re: depth of field controlling horizon

The shutter isn't needed, since we have no motion blur.

Right, the shutter isn't needed to control the motion blur, because we don't support motion blur yet, but the Shutter also control the exposure of the scene. So to control the exposure, you could use the Shutter Speed or the Film ISO.

Disable exposure and the F-number can be free used without a new exposure adjustment.

This is a good trick, but if you had a proper exposure using the physical camera, and then you decide to use DOF, you have to readjust the multiplier of all the lights in your scene included the HDRI multiplier if you disable the exposure option.

[cneville]

Re: depth of field controlling horizon

HI Thanks all,

Thanks for the information. I have not tried film size suggestion yet.

The image I have is using the Vray Sun so I am also using the vray physical camera. I tried lowering the f stop number from the default f 8 as suggested. I lowered down as low as f 0.5 with shutter speed adjusted to suit. I still couldn't see a significant effect.

I dont's have ZBrush though I probably could figure out how to blur the horizon in PhotoShop. That said I hate to hitting problems that I have to fix in post. ... unless I have to.

I went back to the V-Ray for Rhino manual. It said as I had recalled and as had been referenced here that "In order to properly use the sun, it is a necessity that it be used in conjunction with the Physical Camera." I'm not really sure why that is.

But since I could not achieve results with the physical camera, I tried to mimic the book's tutorial with the tea cups. I had to reduce the sun's intensity dramatically, but I did soften the horizon to a point that looked reasonable. I will admit it was difficult to determine whether the front and back end of the boat were, in fact, both simultaneously in focus. I only tried a handfull of different settings in these tests.

Seems harder to achieve than you'd think it should be for something that's a pretty common occurrence when doing images of things outside.

Thanks again. Any other suggestions will be appreciated.

chuck

[fooprobe]

Re: depth of field controlling horizon

use the zdepth image as a channel in PS, then use the lens blur filter with that channel as the source for the depth map. very easy. i also like getting as much as i can out of the rendering itself, but post is inevitable anyway, and it's so much faster. in-camera DOF is also just not practical, time-wise, with animations.

andy, i hadn't heard about the film width trick, and i'm trying it but increasing the size doesn't have much if any effect? doesn't seem to affect the FOV so no adjustment needed there.

micha - i always build models to full scale, real units, and always have this issue with needing a really low f-number. I can get much more blur if Idon't use the physical camera.

any chance these can be disconnected in the next release? that is, can the blur use the aperture setting in the DOF section rather than the f-number? disable with a check box?

[cneville]

Re: depth of field controlling horizon

Hi,
I watched a tutorial about using zdepth and it looks interesting. Unfortunately at this point I don't think my old version of photoshop has that feature.

I'll keep it on my list of things to try, however, when I can.

Thanks.
chuck

[fooprobe]

Re: depth of field controlling horizon

just use the zdepth image to help you select the region you want to blur and use the gaussian blur filter. use "color range" in the "select" menu.

[Micha_cg]

Re: depth of field controlling horizon

Disable exposure and the F-number can be free used without a new exposure adjustment.

This is a good trick, but if you had a proper exposure using the physical camera, and then you decide to use DOF, you have to readjust the multiplier of all the lights in your scene included the HDRI multiplier if you disable the exposure option.

Right, that's why I use a disabled exposure allways.

@cneville: What is your scene unit and is the size of the objects right? If I remember me right custom units can cause problems.

[cneville]

Re: depth of field controlling horizon

Hi Micha,
I am workin in inch units.

The size of the surface element was part of my problem. The other thread that I have going about map size contained a poit from VisaV showing how he set up a water plane. The water disk size that he used was significantly larger than the one I had created arbitrarily after watching Fernando's tutorial.

Making that disk similar to the 900m he used made a big differrence. I also lowered the f-stop a bit and seem to be getting acceptable results.

[cneville]

Re: depth of field controlling horizon

One other related physical camera question.

I did a second setup using the Rhino camera instead of the physical camera. I had to decrease the suns intensity to about 1/20th. There are no other lights in the scene. That seemed to produce a similar image plus allowed me to usd the DOF controls if I choose to do so.

Does the use of the Rhino camera impact anything beyond the exposure of the scene?

One other DOF question.

Placement of the focal distance can easily be measured from the scene. Aperture controls the blur, but is more trial and error. Is there a way to know how far in front of and behind the focal distance things will be generally in focus? I understand generally is a vague term. It seemed difficult to keep the bow and stern of the boat in sharp focus with a reasonable blur at the horizon. Understanding the fall off or focal radius would be helpful (and less trial and error).

Thanks again.

[andybot_cg]

Re: depth of field controlling horizon

Hey again. I had a little time to do some test images to show what film with and focal length do for DOF. Here are two examples, both using F-Number of 1.5 and focal distance of 30. Note that the field of view is not exactly the same between the two images, I had to do a little trial and error to get them to be approximately the same FOV.

focal length: 80
film width: 50
F-number: 1.5


focal length: 12
film width: 8
F-number: 1.5



Also, here is a depth of field calculator online. As you can see, it all depends on your focal length and film/ sensor size to determine the total depth of field.
Hope that helps!

-Andy

[Micha_cg]

Re: depth of field controlling horizon

Placement of the focal distance can easily be measured from the scene.

Easiest - at the forum tutorial section you find my toolbar post with a button scrip that allow to set the focus per mouse click at the viewport. I hope once a day McNeel or ASGvis add it as standard tool.