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Set focal length to infinity

asked 2017-06-01 02:28:25 -0500

ROSpioneer gravatar image

I don't know where to ask this question but as I'm working with OpenCV I'll do it here.

I'm working with this camera: Blackfly 0.9 MP Color GigE PoE (Sony ICX692) with focal length 2.8-8 mm.

My question is how to set the focal to infinity so as I can see objects near the camera as well as far ones simultaneously without blurring. I don't know if that is possible! When I want to detect a chessboard for example, it works well when the board is on the focal plan but otherwise it appears little bit blurred so it's not detectable!

If it is not possible how you deal with that issue?

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answered 2017-06-01 06:52:56 -0500

pklab gravatar image

1st of all the focal is related to the lens and not to the camera.

2nd your issue is related to "Depth of Field" which is related to aperture of the lens. This is the f-number of your lens and is aperture and not focal !

"Depth of field" is depth range where your objects are on focus (without blurring)

Larger aperture = small Depth of field

So you can close the aperture of the lens to its minimum to get deepest field for your system (cam+lens)

As side effect you will have a darker image because less light comes to the camera trough the small aperture of lens. Remember this simple rules:

  • large aperture, like f/2.8 = lighter image = small depth
  • small aperture,like f/16 = darker image = large depth

You should remember also that large aperture means small f-number

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Okay I confused DOF and Focal length! thanks However, when you say large depth, it means we can see farthest objects better? how about nearest objects? That was my question. I want to see both of them like there is no depth!

ROSpioneer gravatar imageROSpioneer ( 2017-06-01 07:25:59 -0500 )edit

Changing aperture spreads depth of field in both direction but not symmetrically. far can go to infinite near can go up to min focus distance of the lens.

pklab gravatar imagepklab ( 2017-06-01 09:12:20 -0500 )edit
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Asked: 2017-06-01 02:28:25 -0500

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Last updated: Jun 01 '17