Camera Film width setting

[Tom]

Hi,

In the CoronaCamera settings, there's one called 'Film width [mm]'. By default, it is set to 36mm, which makes sense since it's the standard width value of old film rolls in analog photography. However, what significance does this have in a digital camera like the Corona camera?

More generally, what's the purpose of this setting, which seems to have a similar influence to the focal length?

Why keep this setting in the CoronaCamera UI if it's redundant?

And if it has a purpose and you use it, in what situations do you use it?

Many thanks,

[romullus]

Analog cameras have films, digital cameras have sensors, both have fixed physical dimensions, which is important factor in determining certain properties of camera's functionality and the pictures it's taking. In virtual camera this parameter is meaningless, unless you need to match its output to the footage taken by a real camera. So yeah, it's not redundant at all.

[James Vella]

A good example of when you need to change this number is when your matching a backplate photograph taken with a full frame camera vs cropped. Full frame cameras are 36mm so its a good default, when you have a cropped sensor (usually cheaper camera), you need to change the factor. You can read about it here but in short:

The sensor is the physical rectangle in the center of your DSLR camera that reads the image from the lens. Generally, the larger the sensor, the more light and detail you are able to capture, and the higher your image quality will be. A full-frame camera has a sensor the size of a 35mm film camera (24mm x 36mm).

A crop sensor is smaller than the standard 35mm size, which introduces a crop factor to the photos these cameras take. This means that the edges of your photo will be cropped for a tighter field of view. For example, if you use a 50mm lens on a crop sensor camera with a multiplier effect of 1.5x, your effective focal length will be the same as a 75mm lens.

“Different camera bodies have different crop factors,” says photographer Whitney Whitehouse. “Canon has a 1.6x crop sensor, while Nikon, Sony, Sigma, and Pentax have a multiplier of 1.5x, and Panasonic and Olympus are 2x.”

[dj_buckley]

I'm correct in thinking you also need to change it when camera matching to a backplate shot in portrait mode?

For example my camera sensor D810 - is 35.9mm x 24mm.

So when I'm matching to a landscape shot I pretty much leave it at 36mm, but if I'm matching to a portrait shot then I'd change it to 24mm

[James Vella]

Yep, actually just realized this has been discussed previously. This covers the topic pretty well:

https://forum.corona-renderer.com/index.php?topic=39928.0

[Tom]

Thanks a lot for your answers and links guys.