[TUT] SideFX Houdini - Match Houdini Cameras to real-world Cameras.

How to make sure that your Houdini camera's field of view matches exactly a real-world counterpart like a Canon 5D, or Alexa, or Red Dragon?
Houdini makes this process a bit more confusing than it needs to be. I try to clear things up while conducting a very unscientific test to see if the numbers match the real-world!
If you want to know a particular camera's sensor size, check out the handy chart on this web site which features many popular sensor sizes:
photoseek.com/2...

[@damegamisama]

Thank you a lot! Very useful and visual tutor!

[@vitalie96]

I did the same experiment with my phone. I have Samsung Note 4. According to the online info my sensor size is 6.828 mm. In the properties of the image I read the next data:
focal length - 5mm
35mm focal length - 31mm
The last value in combination with the sensor size gives huge distortion, so I used 5mm value.
I measured the dimensions of a box, the height from the ground to the lens and placed the box 2m away from the phone. Also, I tried to keep the phone perpendicular to the ground.
So I replicated the values in Houdini and they didn't match the image. Do you have any idea what might be wrong?

[@MathiasJ89]

What about the crop factor of the camera sensor? I'm guessing you used a Canon Full-frame for the test, but say you used your new BMPCC 4k, would you have to compensate the focal length for the crop factor? e.g. 50mm * 1.9 (bmpcc 4k crop) = 95mm?
Great stuff though, thanks for clarifying :)

[@RightBrainedTutorials]

No, that's what the Houdini "Aperture" value is for in the Camera View tab. Most CG apps call this value the "film back" but it's effectively the width of your sensor. As long as both your lens number, and the sensor width match in the Houdini camera and real-life, then the resulting renders will match. Having said that, a...say 35mm lens is rarely mathematically exact. In reality it might be a 35.8mm lens, or sometimes even as far off as being closer to 38mm, or 33mm, and this will always cause some slight inconsistencies. My advice would be to use something like fSpy and a good reference still from your camera/lens combo if you want to find out the absolute exact values. Then again, there's also lens distortion...but that's a whole other can of worms!

[@evanrudefx]

if the aperture is the horizontal dimension of the sensor, why would the default be 41.4214. Since full frame is the standard wouldn't the default be 36mm if this setting was the horizontal width? It almost sounds like the documentation says that you can produce a 35mm equivalent focal length when the aperture is 41.4214. Either way this is stupid, lol. Why can't it just be like every other software and have a film back size

[@RightBrainedTutorials]

That is a good question. Diagonal on a full frame sensor is 43.27mm which means that I don't have the faintest idea where that 41.4214 value comes from. Either way, having a diagonal measurement doesn't make any sense either since when it comes to the FoV the only real number the matters is the horizontal size of the sensor (assuming one is shooting horizontally).

[@evanrudefx]

@@RightBrainedTutorials thanks : )

[@evanrudefx]

maybe this is helpful, if you export a camera from maya (default settings for ) as a abc and import it into houdini, the aperture changes to 36. So you must be correct. This just leaves the question how sidefx got there default value. Maya also calls the the sensor size aperture interestingly. But the default is 36, of course as that makes sense.

[@RightBrainedTutorials]

@@evanrudefx Maybe it's a Canadian thing? :-) If the world gets back to normal a bit, I will definitely ask them next time I see the SideFX team at Siggraph or NAB.

[@evanrudefx]

@@RightBrainedTutorials Someone just answered my question. That number (the default value) produces a perfect 45 degree angkle. so they opted to go for perfect 45 degrees instead of 35mm format, which is 36

[@InterdimensionalBruje]

I was expecting a cámara track of real cámaras to houdini keyframes 😓 the títtle is kind of misleading

[@mdsanima]

very nice. keep going