jonathan.mack

The article in the link is in agreement with my statements and illustrates my point well.

Are we on the same page yet?

BabaJ
Yes it's ‘good’ that you put zoom in quotes, because doing what you describe is not an actual zoom in terms of real camera/film results.

No that's exactly what it is. Zoom is changing the size of the projection. It is equivalent to changing the size of the imaging device. It is expressed in Houdini in terms of focal length and aperture, since these are the values that correspond to the real world. A zoom value would be just as valid, however since it is unitless, it would make relation to physical camera and lens sizes impossible.

BabaJ
In real effects of camera/film a zooming by the camera also has the effect, in addition to the ‘apparent’ change of cropping factor, is the compression or expansion of object sizes relative to their distances to each other.i.e.,

This is not the effect of the lens, but the effect of distance to subject, and the relative distances of subject to subject. Changing the lens or film size only changes the angle of view. The captured image is invariant to focal length or cropping–the same as cropping an image in photoshop.


To get a better understanding, read up on the basics of field of view and imaging.

https://en.wikipedia.org/wiki/Angle_of_view [en.wikipedia.org]

I ran into this exact bug.

Bug: hairgen in mantra fails to find source groom with certain configurations #101315

Use a skin group and density override on the hairgen in mantra generation mode. This causes the descriptive parm to contain a ‘\n’. For some reason the presence of the multi-line descriptive parm causes the procedural to fail to find the source groom. Editing the parm ‘description’ to remove the illegal carriage returns, or editing the python sop to omit this parm returns to normal behavior. The description will only contain ‘\n’ if both a skin group and density override are used.

The work around is to edit the descriptive parm on the node (it's hidden and contains an expression), or to edit the python sop in the groom to omit the decriptive parm from the ifd. (it's not needed to generate the fur).