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Cinema camera focal length incorrect?

Hi, I am not sure if this is a bug, or if I am missing something...

I am trying to match some real camera footage with an augmented overlay in unreal.

I set the cinema camera up to match the settings of the real camera. Object distance, film back and focal length, and it doesn't line up.

The weird thing is, if I double the focal length value, it works perfectly.

I have tried this with different cameras and lenses, and see the same results.

Should this be working? Or is there an equation to get from ue 'focal length' to real world focal length?

Thanks!

Product Version: UE 4.12
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asked Aug 13 '16 at 06:14 PM in Bug Reports

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antithing
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avatar image Matt.Williams Aug 17 '16 at 08:11 PM

Hi antithing,

Could you provide some details on the camera you're using and maybe an example shot so that I can see what you're seeing? Please include the settings that you're using for the cine camera and real-world camera.

-Matt W.

avatar image antithing Aug 17 '16 at 09:48 PM

Hi, thanks for getting back to me. I am using a blackmagic cinema camera, which according to the docs has a sensor of:

22mm x 11.88mm (Super 35).

So I set my film back to match in the cineCamera.

I am using a 24mm lens, so i set my focal to match in the cineCamera.

The resulting images are way off, the Unreal objects look too far away compared to the plate.

If I play with the focal length of the cineCamera, and adjust it to around 42, it looks much better. I will try to upload some images tomorrow.

Thanks again!

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2 answers: sort voted first

Hey antithing,

I wanted to update you on this. I ran a test yesterday shooting with a Super 35 camera and a 24-200mm lens (shot at 24mm) and I'm noticing some discrepancies with the cine cameras. We'll be continuing our tests on this, but it might be a slow process.

-Matt W.

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answered Aug 26 '16 at 07:05 PM

avatar image antithing Aug 27 '16 at 09:04 AM

Ok thanks Matt. Please keep me posted, if you can.

avatar image Matt.Williams Aug 29 '16 at 03:25 PM

I'm marking this as resolved for our tracking, but I'll keep you updated.

avatar image Matt.Williams Aug 31 '16 at 03:49 PM

Hey antithing,

I've been doing some more research and realized that all Super 35's are not created equal. The sensor we plan for in the editor is 24.88999x18.66 (1.33 aspect ratio), the sensor you're using is 22x11.88 (1.85 aspect ratio) and the camera I used(Canon C100) is 24.6x13.8(1.78 aspect ratio). Once I manually entered my sensor width and height in UE4, everything matched up.

Were you just using the Super 35 preset in the editor?

-Matt W.

avatar image antithing Aug 31 '16 at 05:15 PM

I just last night realized the same! seems much better with that change. Sorry to waste your time! I have only tried with the one camera, but please consider this solved. Thanks again.

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Antithing-

Are you using the "Super 35mm" drop-down on the CineCamera, or are you setting the Sensor width/height manually to 22mm x 11.8mm? I ask because the measurements we are using for Super 35 are 24.889mm x 18.66mm.

If I create a camera in Maya with a filmback of 22mm x 11.8mm and a focal length of 24mm I get identical output when compared to a CineCamera with the same settings.

-Michael

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answered Aug 31 '16 at 03:46 PM

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mfg STAFF
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avatar image antithing Aug 31 '16 at 05:16 PM

Found this last night. Alas, i am an idiot. thanks!

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