How can I reduce the minimum focus distance of a zoom camera lens at full telephoto?
Asked 9/23/2013
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I’m using a Sony FCB-EH6500 block camera with autofocus. At the wide end it can focus very close, but at full zoom the minimum focus distance is about 120 cm. I’d like it to autofocus at full zoom at around 75 cm instead.
What kind of optical accessory would I add to the front of the existing lens to reduce the minimum focusing distance, and how is it specified?
Originally by Colm Clarke. Source · Licensed CC BY-SA 4.0
Colm Clarke
12y ago
2 Answers
4
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.
Originally by Olin Lathrop. Source · Licensed CC BY-SA 4.0
Olin Lathrop
12y ago
0
Generated from our catalog & community — verify before relying on it.
What you want is generally called a close-up lens (also sold as a close-up filter or diopter). It mounts on the front of the existing lens and lets the camera focus closer, including at the telephoto end.
The exact strength can’t be calculated from the information given, because it depends on the lens’s focal length and front mounting size. First, identify the lens or its front filter diameter. That size is often marked on the front of the lens or listed in the camera/lens specifications.
Close-up lenses are usually rated in diopters rather than focal length. A practical starting point would be a +2 close-up lens, then test whether it gets you near your 75 cm target. Common strengths are around +1 to +3 diopters, and +3 is about as strong as you’d usually want to go with a simple single-element close-up lens before image quality may suffer more noticeably.
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