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Step 4. Preparing to find the optical center. |
| Every camera lens has an optical center. This is the place in the lens where the light becomes the smallest. For some lenses you can look down the front of a lens and see this spot. It is where the aperture will actually open. Lenses that have variable focal lengths (like 35-70mm or 70-300mm) are called zoom lenses. Very often a zoom lens will have a different optical center for each focal length as it zooms in and out. You will need to decide which focal lengths of your camera lenses you wish to calibrate for. Important Note: In very rare cases a few lens designs will have optical centers that are actually outside the body of the lens somewhere. This can make it very hard or impossible to use the Panosaurus. If you suspect you have a lens like this please contact me so I can keep track of cameras and lens combinations that would not be suitable to use for other users. |
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| There are several methods to find the optical center of lenses. The picture above shows the setup I use to find the optical center of lenses with focal lengths of less than 70mm. I stick a nail through a business card and then place the nail and card on something to raise it slightly higher off a table (I used a stack of more business cards). I then tape a piece of paper onto the wall about 30 inches behind the nail. I draw a dark straight line on the paper. |
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| After leveling the tripod, I then set the camera on the horizontal arm mounted in the landscape position to the rotator arm about 12 inches from the nail on the tripod. (Distances will vary some according to focal lengths) |
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| I position the tripod so that when I look at the LCD screen or viewfinder of my camera this is what I see. The nail in the extreme left of the frame aligned with the line on the paper. This is always the starting point of the proceedure. |
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| I then slowly rotate the landscape table by holding the round turntable with one hand and moving the rotator arm with the other. Do not move the tripod. Note: The picture above does not show the camera attached but it should be. |
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| I move the rotator arm until the nail and line appear in the extreme right hand of the frame. Notice the nail has moved to the right of the line on the paper. This means that I need to move the camera back further toward me on the horizontal arm. |
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| In this picture after aligning the nail and line in the left of the frame by moving the tripod, I then moved the rotator arm and the nail had moved to the left of the line on the paper. This means that I need to move the camera forward on the horizontal arm toward the point of rotation. |
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| Each time I move the camera forward or backward on the horizontal arm I note where the marking is located. |
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| I am striving to achieve the results seen in the picture above. The nail is aligned in the left of the frame and then when I pan the camera using the rotator arm to put the nail in the right of the frame it stays aligned with the line on the paper. This mean I am rotating very close to the optical center of the lens. |
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| Now for the final fine tuning. I proceed to take pictures of the left frame area and then pan and take a picture of the right frame area. I load the two pictures into my image editing software and greatly enlarge them. If they truly are aligned then I have reached the optical center. Otherwise I keep moving the camera mounting block ever so slightly. When success is achieved I make a note of (or even mark) where on the horizontal arm the camera block is sitting. This is where the camera mounting block needs to be each time I shoot with this lens and focal length. |
