Right, good point on that one. The sensor size you use for tracking should be
the same size the camera used when it captured the footage.
Damn this fancy new technology... :P
-Nathan
From: Diogo Girondi
Sent: Tuesday, May 29, 2012 2:12 PM
To: Nuke user discussion
Subject: Re: [Nuke-users] Arri Alexa sensor size - camera tracking question
Exactly Nathan.
Unless the camera you're using utilizes different portions of the sensor
depending on the resolution you're shooting. RED does this, 4k uses the whole
sensor, other resolutions utilize a smaller portion of the sensor. So if you're
shooting at a resolution that is not utilizing the full sensor you either have
to input the correct size being used by the camera for that specific resolution
or multiply your focal length by some crop factor.
On Tue, May 29, 2012 at 6:02 PM, Nathan Rusch <[email protected]> wrote:
Going back to the origin of this discussion, it really doesn’t matter one way
or another... the reason the tracking software asks for the film back is so it
can calculate the equivalent "cropped" focal length and thus an accurate field
of view. Unless the process has changed significantly in the last two years,
you shouldn’t ever have to include crop factor in your parameters when solving
for a camera.
-Nathan
From: Diogo Girondi
Sent: Tuesday, May 29, 2012 1:47 PM
To: Nuke user discussion
Subject: Re: [Nuke-users] Arri Alexa sensor size - camera tracking question
I'm not familiar with Nikon lenses, but Canon ones even if designed for APS-C
sensors are still named disregarding any compensation for crop factors.
Personally I never heard of lenses that state their focal lengths compensated
by a certain crop factor since that tends to vary from camera to camera and
it's not a characteristic of the lens it self.
Canon EF-S lenses are a good example of this, they are designed to only mount
on EF mounts of bodies with APS-C sensors (1.6x crop factor) but their focal
lengths are still stated "1:1" taking a full frame if you will as base, so you
still have to multiply their focal lengths by 1.6. My EF-S 10-22mm for instance
when mounted on my 7D is becomes a 16-35mm and not the 10-22mm written on the
lens.
On Tue, May 29, 2012 at 5:28 PM, Howard Jones <[email protected]> wrote:
The crop factor was based on the original question. Not my maths. A
100 mm lens on cropped back will give an equivalent lens angle (not actual) of
a longer lens, with the original question this was 1.5.
You are both agreeing with by stating the film back size gives a
different fov (but not focal length - agreed)
However,
1. If you can't get a 100mm lens that is designed for a crop film
back, ie compensates for the sensor size, then you are correct that in this
case the focal length is the same, regardless of sensor size, however the fov
is different.
However if you can buy a lens that has compensated for the sensor
size and gives the same fov as a 35mm lens then there is a discrepancy.
I'm under the (mis)understanding that the latter is available,
however I can quite believe I'm mistaken.
2. We are all assuming nuke behaves correctly in this fashion. In the
back of my mind, if you put the focal length into the camera tracker and then
change the film back, it changes the focal length, but you can then change it
back.
I can't check this last point until tomorrow, but if it's the case
then what does this mean for the solve? If its not the case then it's because
I'm getting on and the mind plays tricks.
Cheers
H
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