Correct If you are in a situation where the footage has been cropped, it's the film back that should change in proportion to the cropping, not the focal length..
-Alex On 29/05/2012, at 5:44 PM, Darren Coombes <[email protected]> wrote: I Should of stated earlier. We are using 1920 x 1080 footage.. so I should still enter the sensor size for horizontal and vertical aperture, and just put focal length as 18mm then? Sorry to confuse. daz. On 29/05/2012, at 5:37 PM, Diogo Girondi wrote: For what I know Alexa has a single capture resolution and any other resolution is just a down convert from that signal. So in theory it should be using the full sensor area to capture at all times even when shooting HD 1080. But I can be wrong on this since I never got any RAW from ALEXA, only 1080, so you better test it. But every time I had to match move things shot with the ALEXA, using the camera sensor size and the actual lens value was enough to get me there. The RED camera on the other hand, changes the sensor area utilized according to the resolution you're shooting, so the crop factor varies from resolution to resolution. And that's why most people I know (to not say all) shoot full and then debayer/down convert to lower resolutions later on. cheers, diogo On Tue, May 29, 2012 at 4:01 AM, Darren Coombes < [email protected]> wrote: > Thanks for the reply Alex, I'll have a look. We have someone here saying > that the 18mm lens would not be an 18mm lens in our tracker settings, I > just want to make sure what they are saying is right. > > Cheers. > D. > > On 29/05/2012, at 4:57 PM, Alex Fry wrote: > > The "crop factor" is described by the sensor measurements you input. > Your 18mm lens is still 18mm, no conversion is necessary, your field of > view has changed, but not your focal length.. > An 18mm lens has a different field of view if its mounted on micro4/3, DX, > super35, 35 stills, 70mm or medium format, but it remains an 18mm lens. > > Have a play with Nuke's camera node, tweaking the focal length, haperture > & vaperture knobs to get a feel for the relationship they have to each > other. > > -Alex > > On 29/05/2012, at 4:27 PM, Darren Coombes <[email protected]> > wrote: > > Hi, we have some plates shot with the alexa on a 18mm prime lens. > I Need to camera track this material. > > On the Arri website, it says the sensor size for the alexa is 23.76 x > 13.37mm when using the ARRIRAW setting with 1.78:1 aspect ratio. > > in the camera tracker settings, would I put the film back size as 23.76 x > 13.37mm? > And then I guess i need to find out the crop factor for that sensor size > and use that when entering the focal length of the lens? > > So if we shot on a 18mm lens, and theoretically the crop factor was 1.5 > (not sure what the actual crop factor is yet), you would times 18 x1.5? and > that would give the right focal length? > > Can someone point me in the right direction with this? and is my theory of > this right? or am i missing something? > > Thanks. > > Darren. > * > * > * > * > * > * > *Darren Coombes* > * > * > *Compositor* > > *www.resolutiondesign.com.au* <http://www.resolutiondesign.com.au/> > > > *resolution: sydney australia* tel: *+61 2 9360 9908* fax: > +*61 2 9360 8908* > *22* burton st: east sydney: *2010* post office box: *614* > darlinghurst: 1300* *abn: *3305 196 1856* > > *2010 Silver One Show Entertainment Award: Online Branded Entertainment * > *2009 Gold Promax/BDA Award: Best Broadcast Design Image Spot * > *2009 Winner Creative Review Hotshop Award: Post Production / VFX* > *2009 Finalist Creative Review Hotshop Award: Broadcast Design* > > > The information transmitted, together with the attachments, is intended > only for the person or entity to which it is addressed and may contain > confidential and/or priviliged material which may be subject to copyright. > Any review, retransmission or other use of, or taking of any action in > reliance upon, this information by persons or entities other than the > intended recipient is prohibited. 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