Camera focal length

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dag
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Camera focal length

Post by dag » Sun Oct 09, 2011 12:23 pm

I'm assuming the focal length (lens_sensor_dist) is calculated on export to match the camera in blender, which is wrong?
Wouldn't it be better, if possible, to switch the blender FL field with a custom blendigo one that does the conversion after you enter a value, instead of at export, so we know what FL we get in indigo, which is correct?
For example if I had 50mm entered in blender, then switched to indigo renderer engine, the FL field would change to 56.25000226875821 :o.
Just take a 100mm lens. That's 18.181 degrees FoV in blender, but it's actually 20.4.

neepneep
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Re: Camera focal length

Post by neepneep » Thu Nov 10, 2011 10:53 pm

I really need help with matching some Blender renders to Indigo renders and at the moment the focal length is giving me so much grief and hassle.

Is there an easy way to match it directly?

neepneep
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Re: Camera focal length

Post by neepneep » Thu Nov 10, 2011 11:31 pm

See attached image for example.

The overlaid lines shows how the Blender camera appears compared to Indigo. Pretty much a showstopper :(
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camera_test.jpg

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dag
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Re: Camera focal length

Post by dag » Thu Nov 10, 2011 11:47 pm

Looks like the blender camera needs an overhaul as it's not matching real world optics.
Try using lens degrees instead of length, since that seems more correct, but that would probably not work either.

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dougal2
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Re: Camera focal length

Post by dougal2 » Fri Nov 11, 2011 12:56 am

Thanks for letting me know, I'll do some testing here and check the formulae.

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OnoSendai
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Re: Camera focal length

Post by OnoSendai » Fri Nov 11, 2011 1:56 am

Indigo is probably displaying an incorrect focal length. We will have a closer look at this and fix it soon.

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dag
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Re: Camera focal length

Post by dag » Fri Nov 11, 2011 2:46 am

Indigo is 100% correct according to http://www.tawbaware.com/maxlyons/calc.htm
Blender is funky.

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OnoSendai
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Re: Camera focal length

Post by OnoSendai » Fri Nov 11, 2011 2:55 am

What Indigo prints out in the GUI (in the focal length spinbox) is not actually the focal length, but the lens-sensor distance. The two are equal only when the focus distance is set to infinity.

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