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Saturday, 6 December 2014

My Answer on Quora: What is the standard lens length in Maya 3D?

I chanced upon a question on Quora:

What is the standard lens length in Maya 3D?

I decided to answer that, and here is my reply. I hope it sheds some light to people wanting to know how to establish a relationship between camera settings in the real world and the virtual counterpart in Maya.


Indeed, many artists with no experience in photography will not be able to easily understand the relationships between focal length and sensor sizes / ratios.

Having worked in the "camera department" on Hollywood films, it has given me great insight into the relationships between the physical camera and the virtual one in Maya.

Maya does not make it easier. What we know in the VFX/Film world as "sensor size" / "film back" / "film format", is known in Maya as "Camera Aperture". This attribute is found in any Maya camera's shape node. In the attribute editor under the Film Back section you will see: Film Gate, Camera Aperture, Film Aspect Ratio, and Lens Squeeze Ratio.

Just like you said there is a relationship between focal length and the sensor size. 
Back in the Attribute Editor for the Maya camera, the way we get the correct sensor size or film format for our camera gate is to set the Film Gate attribute to "35mm Full Aperture". This is actually a preset that sets the "Camera Aperture" attribute to 0.980 x 0.735. 

From the Wikipedia page for Super 35 film formats of printed film strips, (4th para), I quote "If using 4-perf, the Super 35 camera aperture is 24.89 mm × 18.66 mm (0.980 in × 0.735 in)". 

That is exactly what Maya is giving us (in inches, which is frustrating, when we are describing 35mm in millimeters).

From the same Wiki article we also learn of the film dimensions of 35mm Academy format which is  21.95 mm × 16.00 mm (0.864 in × 0.630 in). That is what the Maya Film Gate preset gives us if we switch to 35mm Academy.

However, we are not limited to only the presets found in the Film Gate attributes. Knowing that Maya is just filling in measurement of the film back dimensions now enables us to input measurements from our own camera sensors even if their measurements are non-standard.

In this context, whatever focal length that you now set, will give you the actual framing of a real world camera with the same sensor size / film back. 

We do all these, to make sure that the numbers will all make sense: the dimensions of the sensor size and the focal length.

Moving forward, we are faced with 2 settings, and two different framings when you look at the viewport: one is our camera's film back / sensor ratio, and the render resolution. Maya gives us the flexibility to have both. 

However it becomes wildly confusing if we do not know what we are doing. Without guides we will never know what we are seeing in our viewport is what. Even when you render, you are only seeing framing of your render resolution, not the framing of your film gate.

To see both, this is my standard workflow, for all cameras I want to look through and eventually render:

In the Camera's attribute editor:
- set "Fit Resolution Gate" to "Overscan", 
under display options section 
- turn on "display film gate". This displays our film back /sensor boundary
- turn on "display resolution". This displays our rendering resolution boundary
- turn off "display gate mask"
- set "overscan" to 1.05

All these will make sure you see 2 boundary boxes, one with a solid line, and the other one, drawn with a dotted line. The dotted box defines the film gate / sensor bounds, and the solid box defines your rendering boundary, defining the resolution of your rendered.

I hope this helps.