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Author Topic: Question about Calibrating Long Focal Lengths and Focusing Lens  (Read 5373 times)

tdepke

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Question about Calibrating Long Focal Lengths and Focusing Lens
« on: November 03, 2011, 02:51:29 AM »
Howdy all,

I am a masters student working on a terrestrial photogrammetry project for my thesis. I have some photos that I took from oblique angles on cliffs using a 50mm fixed and a 70mm both focused at infinity.

I am trying to calibrate a 50mm fixed a 70-300mm set at 70mm using the checkerboard pattern and a projector, but I cannot fill the entire image with the pattern and focus at infinity.

What would the best option be:

1. Not fill the entire image with the checkboard pattern but keep the lenses focused at infinity
2. Move closer to the projector to fill the image, but have the images blurry
3. Move closer to the projector to fill the image, adjust the focus to keep the images sharp (even though that was not how the lens was focused for the images I plan to create models with)


I am not sure how much the focus will affect the focal length while zooming the lens will obviously change the focal length drastically.

Thanks,

Tyler
« Last Edit: November 03, 2011, 03:33:16 AM by tdepke »

Alexey Pasumansky

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Re: Question about Calibrating Long Focal Lengths and Focusing Lens
« Reply #1 on: November 03, 2011, 04:50:35 PM »
Hello Tyler,

First of all it is recommended to keep lens focused at infinity. If there are only small unpatterned areas you can keep it but make sure that Agisoft Lens has not found any points somewhere apart the checkboard.
Best regards,
Alexey Pasumansky,
Agisoft LLC