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Camera Matching


andymaw
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Recently I used the VRay lens analysis tool on a photo I took using a Canon 5D MkII with a Sigma 50mm Prime lens. Weirdly, after analysing fine, it put the focal length as 47.233. Any ideas why that might be? All the tech specs online say that that the lens is 50mm bang on.

 

Then in Max, when I set the VRay camera to 50mm using a film gate of 36mm I'm not getting a perfect result. If I drop the focal length to around 48mm it's a lot better. I really need to get this spot on for the work that I do so any help greatly appreciated.

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I'll be honest, I've never tried camera matching with the native camera. I've always gone for VRay as I like how close it is to a real life camera. I'll have to give it a shot at some point though.

 

Still can't figure this out, trying lots of different settings. Just rendered without the lens file to see if that makes any difference at all though I assume that's purely for the distortion so shouldn't have any noticeable effect.

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Thanks for the link Chris. Interesting read.

 

I've been playing with the renders at different focal lengths and am finding that producing them using the 47.233mm that the VRay analysis tool gave me is working out best. I took a surveyor with me when taking the photographs so I have accurate locations to within 25mm of the camera position and the control points I used (survey rods). That said then, the renders should line up almost perfectly in the panorama using the correct camera settings (i.e. 50mm focal length) so it's very odd that it doesn't. If I render at 50mm the control point rods are too large, but at 47.233 the rods are pretty much the correct scale but positionally not quite right. Very frustrating!

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The panoramas are usually about 4 to 6 frames, but I take them at 20 degree intervals and crop them to the centre 50%. I'm also using a macro lens to minimise distortion (there's almost none on this lens I use). It's expected that they won't line up 100% perfectly in a panorama but the control points I've used should definitely be at the same scale, or very close to, as the photo using the 'correct' focal length wouldn't you say?

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Definitely. I've got another project that I've already taken the photos for so I'll have a test on that one to see if it was project specific.

 

They're not out by a huge degree at all. Maybe it's me being picky and wanting to get it as close to spot on as possible.

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