Hi @all, two questions to Cameras: 1.) There are parameters that change perspective (Perspektive/Focal)... are there any "reference" values for "real world" cameras? Or is every camera different a little bit? E.g. when trying to fit reference photos, one needs proper settings for these parameters right? 2.) How to obtain the projection matrix of a camera object in PoserPython? Thanks, col

'Focal length' is what you're referring to I guess(?) While a 55mm lens on a 35mm (film) camera will cover the same area (or give the same field of view), different focal lengths and different film (or electronic image sensors) sizes give different field of views (or coverage).

I'm not sure what you mean by 'reference photos'. Are these images or renders you make and want to keep as a reference for future work?

I have no idea if either Daz's or Poser's cameras are based on real world optics. I just set them to whatever I feel gives the view I want. I generally use 55mm to start since that's historically a 'normal' view. On a 35mm film camera, a 55mm lens shows the same view as the naked eye (mostly). During the early days of digital, manufacturers gave field of views, or compared them to 35mm cameras. I don't see this much anymore since the pro cameras are pretty much the same size as 35mm film and no one really cares much when using an amateur camera (point and shoot). As a pro I don't bother with numbers anymore. What I see is what I get and that's all I care about. It becomes a factor only for the occasions when I'm doing technical or engineering stuff.

If you're looking for a starting point or want some kind of standard, pick settings that work for you, write them down and go from there.

Does this help or did I miss the point of your question?

Bob

Hi Bob, thanks for thequick reply. Reference Photos I mean is human head reference photos, from 3dsk or lets say screenshots from a movie, whatever image. When trying to sculpt a mesh that matches the reference, using the right camera settings while sculpting seems important. If the "perspective distoration" of the camera used while sculpting is inappropriate, one will not be able to make a mesh that will match all the references. One extreme case example of this is in zbrush, if you sculpt and forget to enable perspective mode first. So I wonder what a "real world camera" perspective is ( and what projection matrix that would be ). In Blender, you have access to the camera projection matrix, and I wanted to check if Poser is using the same by default.

Ahhhhhh, now I get it.

This is quite common with technical photography. You're trying to get an isometric ( https://en.wikipedia.org/wiki/Isometric_projection ) view which is impossible with a camera. You can get fairly close by simply using a long focal length and backing off (moving back from the object). If you're taking the picture, use as long a focal length as possible and move back away from the subject. If you're working from screenshots then you're kinda stuck with what you get. When sculpting, your 3D program will have isometric views. For something small like a persons head, the distortion won't be serious unless it's been taken with a very wide angle lens shoved in very close to the subject (like you see in porn films).

Does this answer your question?

Bob

Hello Bob, it answers almost :). On the other side I am more confused than before because I have not yet heard about isometric projection before. I'm basically looking for settings for a CG programs (blender/poser) camera (perspective mode is fine! - 2d orthographic or other cheated modes are not in focus of interest ) that is the same as the "physical" cameras used to make movies are used for. If that is actually possible, that is. http://www.songho.ca/opengl/gl_projectionmatrix.html In OpenGL (and I think e.g. blender) camera perspective is defined by a projection matrix. But I do not know what the correct projection matrix is that movie makers or photographers use when they use their physical cameras. If the perspective in the CG program is different from the perspective of a photo, one cannot reproduce the mesh by sculpting, I think.

Poser's virtual film is 25.4 mm wide. (1 inch) In traditional 35mm film cameras, the image frame in landscape mode is 36 mm wide. This is roughly (but not exactly) the "crop" you find in APS-C cameras, by coincidence, not design. So the view you get in Poser is much closer to that of a modern cropped-format DSLR vs. the "full frame" which refers to a 36mm sensor.

Poser's virtual film height is variable, while real film is always 24mm in height. (When used in landscape mode) Real film aspect ratio is always 3:2, where Poser's is anything you want. But for purposes of matching field of view and perspective distortion of a real camera, we just need to consider the sensor width.

You can calculate the comparable full-frame field of view using ratios. The ratio 36 / 25.4 is about 1.4173. So in Poser, the 50mm setting would produce an image roughly the same as a full-frame 50 * 1.4173, or about 70.8 mm in real-life full frame.

Go the other way by division. Suppose you want to match a full-frame 50mm field of view -- so you use 50 / 1.4173 = 35.27 mm in your Poser Focal parameter and that will match.

To match a portrait viewpoint, things get tricky. I will forego an explanation of that.

When you ask about movie makers, now you're completely in lala land. Movie makers use "anisotropic" lenses which squeeze a panoramic image into a rectangle on the film of just 24 x 18 mm. Projectors reverse the squeeze for display. I don't think you really mean to match the images on an anisotropic lens, so it isn't worth examining.

bagginsbill,

 Thanks for the info on Poser's 'film' size.  I've always used 50mm as a standard but will (as you recommend) change that to 35mm.

colorcurvature,

 I followed your links and read through the material and I feel you're making this much more complicated than it needs to be.   Set the projection or view in Blender to Isometric and model your heart out.  

Bob

55mm is said to be the focal length of the Human Eye. So if you want things to remain 'natural' in appearance set your focus to 55mm. This is fairly important if you are also setting up V4 to fit the 'Eight Heads' natural natural body scale.