questions about camera's perspective, frame width and focal length

function

First, I'm asking for DAZ software camera, not a Real world camera.

Here are 3 mysterious camera options: perspective, frame width and focal length.

For camera perspective on/off, if turn off, the camera view turns to a weird position, so what is the purpose for the perspective off? Why leaves this option there?

For frame width and focal length, I tried many times, they have same function, just change the actual view area, can not find any difference! So, is one of them redundant?

Gordig

Turning "perspective" off puts the camera into what's called orthographic view, meaning that things don't change size depending on their position relative to the camera. It's mainly used for architectural renders, and I can't really think of a use case for it outside of that. Frame width and focal length change the field of view of the camera.

dijitul

As Gordig said, perspective turns perspective on and off -- the effect which normally shows farther objects as smaller.  Orthographic is the opposite where everything is shown as 2D rather than 3D so it's flattened like a CAD or Visio drawing (useful for lining up objects not on the same plane).

As for the other settings, frame width and focal legth have essentially the same effect but measured differently.  Use focal length to change Field of View and/or Depth of Field effects as you would with a zoom or wide-angle lens on a real camera (smaller FL causes more of a fishbowl effect, longer FL causes larger/flatter appearance of distant objects).  If you enable Depth of Field, focal length is where the sharpest focus point will be and everything increases blur as you get away from the focal point.  

On a side note and as a tip (related to focus), when enabling the Depth of Field feature for blur effects, you can set a Plane as a child object to a camera and then zero the plane's translate & rotate transforms.  Use it as a DoF guide from the Camera view this way: Rotate the plane on the X-axis to 90 degrees, and then slide its Z-translate (towards the negative or left slide) to move the plane to the exact point you want sharp focus (such as the model's iris).  Next, take the Z-translate number and copy/paste it into the camera's Focal Distance, then remove the minus (-) sign so it's now a positive number. Last, turn off the plane by disabling it in the Viewport so it's out of view and not rendered.  (Turn it back on if you need to readjust after moving the camera.)   Now, when you render or render preview, the focus is exactly on where the plane is at.  NOTE: You could use a Null instead of a plane, but I find the plane is much easier to pinpoint focus with.

 

Padone

dijitul said:

If you enable Depth of Field, focal length is where the sharpest focus point will be ..

Just to correct @dijitul, it's focal distance where the focus is. Then the depth of field is related to focal lenght but can be adjusted independently. I mean it's not fixed for a certain focal length, not in daz studio nor in a real camera. Specifically, the depth of field depends both on the focal lenght and the camera aperture (aka f-stop). Also no need to setup strange planes or nulls, just activate depth of field and you get it on the viewport.

To match iray with a real camera you have to copy the f-stop in the tone mapping section, since daz studio doesn't. You also need to set the frame width of course.

function

Thanks Gordig, thanks dijitul and Padone, now I seem to understand.

Here is a pic that I found in this forum (forgot the author's name, sorry), it shows different effect by a combined adjustment of Frame width and Focal length, it seems so, but I didn't try. 

dijitul

 

Padone said:

dijitul said:

If you enable Depth of Field, focal length is where the sharpest focus point will be ..

Just to correct @dijitul, it's focal distance where the focus is. Then the depth of field is related to focal lenght but can be adjusted independently. I mean it's not fixed for a certain focal length, not in daz studio nor in a real camera. Specifically, the depth of field depends both on the focal lenght and the camera aperture (aka f-stop). Also no need to setup strange planes or nulls, just activate depth of field and you get it on the viewport.

To match iray with a real camera you have to copy the f-stop in the tone mapping section, since daz studio doesn't. You also need to set the frame width of course.

The plane is to help set the exact point where the sharpest convergence will occur during rendering (when DoF is enabled).  F-stop adjusts the amount of blur beyond this point (in DAZ), it does not change the point of focus that the plane or null is intended to identify.  Depth of Field changes, not focal distance/length, with the F-stop setting.  This phenomenon can also be desmonstrated by enabling the DOF Plane visibility and extending the Focal Point Scale beyond 100%, but the plane is much easier to use from the camera's view IMHO.

Again, this is just a tip to help those who use DoF quite a bit, and to assist in understanding Focal Length vs. Focal Distance.