Film Back/Film aperture

[Anthony Martin]

Hi all,

I'd like to get something straight as it's been bugging me for ages, namely: in the projection plane tab of a camera, are the "film aperture" settings the same as setting the "film back"?

I've got a scene built to scale (on the assumption that one SU = 10cm). I'd like to have, say, a 35mm camera and I'd like to be sure that when I set the focal length of the camera it really is giving me the composition that a 35mm camera would capture of my scene.

Sorry if this reads as ridiculously simple but I'd like to be able to know for sure that I'm doing it "right".

Cheers,

Anthony

[Christian Gotzinger]

Hi Anthony,

The film aperture in Soft indeed controls the film back or sensor size.
Super 35 has an aperture of 0.980" x 0.735". But keep in mind that you'll have to adjust the height depending on your aspect ratio. When shooting 2.39:1, your effective aperture would be 0.980" x 0.410".

Full frame DSLR photo cameras have larger sensors than that, even though they are also referred to as "35mm cameras". The sensor of a full frame photo camera is about 1.417" x 0.945".

The only reason why these settings exist are so that you can specify a focal length and get the exact field of view that you'd expect. In real life, the film back / sensor size also has a huge effect on depth of field.

Here are a few Wikipedia links:
http://en.wikipedia.org/wiki/Super_35
http://en.wikipedia.org/wiki/List_of_film_formats

Chris

[Anthony Martin]

Excellent! Thanks for clearing that up for me, Chris.

I'd always assumed that this was the case but was confused due to the terminology that Soft uses, i.e. Film aperture, and the doc's description of it.

Thanks again,

Anthony

[Anthony Martin]

Ok, just to get a little more involved with the film back/aperture thing: what kind of math gymnastics do I need to go through if I want to determine the correct settings for footage that's come out of DSLR that *isn't* a full frame model?

Thanks,

Anthony

[Jens Lindgren]

That depends on the model.

If it's a Nikon D90 wich have the DX sensor size, then it's: 23.6 x 15.8 mm. http://en.wikipedia.org/wiki/Nikon_DX_format

But that's a 3/2 aspect ratio and in video mode it uses 16/9 aspect so it doesn't use the whole height.

Easiest is to just type in the width, and the height should be "width/aspect", in this case 23.6/1.7777...8 = 13.275 mm

If it's a Canon 7D then the sensor is 22.3 x 14.9 mm (22.3 x 12.54 mm in 16/9)

 

I'm not taking into the acount that some cameras can crop more in video mode than in still mode, I sugest that you put the camera on a tripod and take a photo, and then a few frames of video and compare the crop of the width.

If the video mode is cropping more, you have to calculate the difference.

 

/Jens

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Jens Lindgren

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Lead Technical Director

Magoo 3D Studios

[Anthony Martin]

The camera I'll be using is a Nikon D90, so that's very useful to know, thank you, Jens.