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Here is my problem, I Have a scientific camera, a Sony Block FCB-EH6500, which has an automatic focus. The minimum focus distance is 1 cm when completely zoomed out and 120 cm when fully zoomed in. I'm not sure what lens is in the camera but I was hoping someone could tell me what optics I would need to add to the camera to make it auto-focus at maximum zoom to a distance of 75 cm.

Thanks in advance.

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migrated from physics.stackexchange.com Sep 25 '13 at 18:40

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1 Answer

Without knowing the focal length, the exact lens added to the front of the existing one can't be calculated.

However, what you want is called a "closeup lens". These are usually single-element convex lenses that mechanically mount as filters. First you have to find the diameter of the filter mount on the lens. This is usually written on the front of the lens somewhere. You should also be able to look it up from exact lens model.

Once you know the filter thread diameter, you can get a set of closeup lenses that will fit your lens. Closeup lenses are usually specified in diopters instead of focal length. Start with a "+2" closeup lens and see how that does. You can readily find closeup lenses in the +1 to +3 range. +3 is about as far as you want to go for a single-element closeup lens because of abberations.

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From the website the focal length range seems to be f=4.3 mm (wide) ~ 129.0 mm (tele) –  Kaushik Ghose Sep 25 '13 at 23:05
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