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Thread: camera lens-default?

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    Question camera lens-default?

    Does anyone know how Accurender controls/sets the default camera lens--
    35mm, 50 mm telephoto, etc.?

    i.e. how to determine / compare camera lens settings to mm size?

    can this be specified somewhere?

    cheers.....

  2. #2
    Revit Arch. Wishlist Mgr. Wes Macaulay's Avatar
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    Default Re: camera lens-default?

    Hey Cliff -- see if this helps you out:
    http://forums.augi.com/attachment.php?attachmentid=5370

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    Cool Re: camera lens-default?

    Wes-

    Thanks!

    Cliff

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    All AUGI, all the time Alex Page's Avatar
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    Default Re: camera lens-default?

    Wes - thanks again - you're too generous!

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    I could stop if I wanted to rmejia's Avatar
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    Default Re: camera lens-default?

    Quote Originally Posted by Wes Macaulay
    Hey Cliff -- see if this helps you out:
    http://forums.augi.com/attachment.php?attachmentid=5370
    Good stuff, thanks!

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    Certified AUGI Addict patricks's Avatar
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    Default Re: camera lens-default?

    Bringing this back up again because I was using Wes's PDF above yesterday to try to match a 3D view to a photo.

    Wes, I don't think you covered it, but what if you have to crop down a photo? Don't you then have to re-calculate the resulting field of view (FOV) of the camera's image? I think I got it after numerous trig and algebraic calculations (glad I paid attention in math class! ), but I'm not 100% sure.

    What I was dealing with yesterday was a photo slightly skewed off of horizontal. So I rotated the image a couple of degrees in Photoshop, but then I had to crop down to remove the white areas left around the 4 corners of the image after rotating. So the resulting image had a narrower FOV than the original image did.

    Also, not sure if you've thought of updating that document, but you might want to mention digital SLR cameras, most of which have an image sensor smaller than the full size 24x36mm film negative (only the most expensive professional digital SLR's have the full frame sensors). You either have to know what size your camera's sensor is, or you have to know the "crop factor" constant, which for many mid-range Canon SLR's is 1.6, and most mid-range Nikons is 1.5. Using that you can convert your digital SLR's lens focal length to the equivalent 35mm camera focal length.

  7. #7
    Revit Arch. Wishlist Mgr. Wes Macaulay's Avatar
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    Default Re: camera lens-default?

    No kidding Patrick -- that doc was created before digital cameras became ubiquitous. Calibration for us is now taking the camera and taking a shot of a extended tape measure 4' away and seeing how much FOV we get

    Low tech calibration for ya, huh?


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    Certified AUGI Addict patricks's Avatar
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    Default Re: camera lens-default?

    haha yeah, you should have seen my notepad with little diagrams and formulas scribbled all over it yesterday.

    But alas, I was working with an image my boss shot with his camera 4 months ago, before we even had the idea of using that image for a rendering. I had to check the image's metadata (thank goodness for that!) to find the focal length used in the image, and then I had to look up his camera model on www.dpreview.com to find the size of the sensor, and then from that I could figure out the field of view on his camera at that particular focal length.

    But THEN! all of that was thrown off when I had to rotate and crop down the image. I had to do a bunch more calculations (perhaps more than necessary) to figure out the resulting FOV, since the focal length didn't actually change when I cropped the image. I suppose I could have said the "equivalent" focal length changed with the cropped image, but oh well.

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