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Ruth Martindale

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Which size F-Ring will be the best fit on my lens?

Each F-Ring can be adjusted to fit different lens diameters. The range of adjustment is quite small, so you need to choose the optimum sized F-Ring that will fit snugly onto your lens. To do this you need to measure the diameter of your lens at the point where you plan to fit the F-Ring – normally this is the focus ring, but it could also be the zoom ring.

The procedure described below shows a simple and effective way to measure your lens diameter.

First cut a thin strip of paper from a sheet of A4.


Now wrap this strip around the lens at the point where you will install the F-Ring.

Mark the point where the paper strip overlaps.

You now have a measurement of the circumference of your lens. So read this off using a rule.

In this instance the circumference measures 242mm.

Now divide the circumference by 3.14 (π) to find the diameter. In this case 242/3.14 = 77. So a 77mm F-Ring is required, which would be part number FS613G -  F-Ring for 74-78mm.


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