Camera's F/Stop doesn't make sense

rsharp

I recently came to Daz 3D from using Poser (1.0 through Pro 2014).  One of the features I enjoyed was easily setting up a camera to mimic my Canon fullframe along with 50mm f/1.2 lens.

In Daz 3D, I've been attempting to create a similar setup to simulate a fullframe camera at 10 feet from the subject.  And using 50mm at f/1.2.  So settings for my camera are as follows:

• frame width was left at 36mm (default); makes sense as my Canon's sensor is also 36mm wide.
• focal length set to 50mm
• F/Stop at 1.2

Results was that the DOF was way too narrow.  What I then did was to create a white plane (see attached) that had the correct 0.86 foot size (I used a 26 cm plane to get as close as possible) to represent the DOF.  I then modifed the F/Stop value until it got as close to that as possible.  I found that in this particular scenario, I needed to specify 5.6

Also, when doing say headshots and the focal distance is obviously less, I cannot use an F/Stop of say 2.8.  I end up having to use f/22 or even f/32.  In reality, a lens with that narrow an aperature would have the entire model in focus.

Is there something I'm missing about the F/Stop value? Could some of the other values (e.g. frame width or focal length) not be accurately represented? (i.e. the computation of F/Stop is assuming a much smaller/larger sensor)?

Thanks for any tips.  As a workaround though, I'll continue to use a DOF calculator and create a plane with that size and adjust f/stop accordingly.

 

Notes on the attached image: The checkboard area is half-covered by the yellow plane.  Squares are 2 ft x 2 ft on that board.  The yellow plane is 10 ft x 10 ft; represents the distance from the sensor plane on the camera to the focal point of where my subject will be.  White plane, as mentioned above, represents the proper DOF range for 50 mm f/1.2 at 10 feet on a fullframe DSLR.   The green DOF guides represent the setting when at f/5.6

Tobor

In D|S I don't believe the camera f/stop is based on any real-world metric. IOW, just set the DOF visually as you've done.

As an aside, do take note that the camera f/stop does not alter light admittance. It's only for setting the DOF. Exposure control is done in the Render panel.

 

 

rsharp

Thank you for confirming that Tobor.  And yes, I am aware that's for DOF only.  I'll file a bug then to have that value be based on real-world ones.  Poser does that and it was awefully handy.

fastbike1

There's no point in trying to exactly mimic a real world camera or lens. The software just doesn't do that. Iray mimics real world lighting well, but the camera settings in DS are not realistic. Just set the DOF to be what you want. You have probably already seen that focus distiances are not real as well and that focal lengths do not give the field of view you would expect.

chris-2599934

The f-stop doesn't bear any relationship to real world cameras. It'd be nice if it did, but it doesn't. I don't think they'll ever fix this, because if they did it would mess up all the existing scenes that you have.

However, there is something you can do in DAZ that you can't do in the real world...

• Frame up the shot in your camera the way you want it.
• Switch depth of field on
• Change the viewpoint to Perspective view, but leave the camera selected in the Scene tab
• Point your viewpoint to look at your camera and its subject. You'll see a pyramid shape stretching out from the camera that defines the corners of the shot. Within that pyramid there are three planes: one to show the focal plane and two others to show the start and finish of the 100% in-focus area
• Adjust the focal length and f-stop parameters to get these three planes where you want them - they move bacwards and forwards as you change the values. Try to ignore how ridiculous the resulting numbers would be on a real-world camera!

rsharp

@fastbike1, I completely disagree.  I have used Poser (now using DAZ) to render scenes that I composite with real photographs.  The accuracy of field-of-view, lens compression, etc. are are very good.

One experiment I have duplicated in DAZ that I did in Poser was to simulate focal lengths from 15mm up to 800mm of head-shots.  All the math makes sense.  e.g. When doubling the focal length, I would move the camera double its distance.  The focal distance's value was also adjusted and it too made sense.

Furthermore, I have actually constructed that checkered grid you see in the original post above.  I set my DSLR to the same exact position as I had in my scenes.  Both Poser Pro 2012/2014 renders and now DAZ lined up extremely well to the real photo (perspective of the grid squares matched spot on).

My primary usage of DAZ/Poser is twofold.  First, to prototype real world photography projects.   Second, to allow me to easily composite renders and real photographs.  Since I'm able to mimic all settings, this keeps perspective of objects spot on and makes for some very high quality composites.