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I have a 50mm diameter, 2mm thick unmounted optical glass filter that I want to attach to my camera. I haven't been able to find a resource that describes the size of the optical glass used in standard photo filters. Would a 52mm mounting house a 50mm filter? I could do this by trial and error but I'm hoping someone already knows the answer.

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  • Not posting as an answer since I don't know for sure that it is true, but I'm not sure how a 52 mm mounting would hold a 50mm filter as the filter would not be large enough to reach from one side of the mount to the other.
    – AJ Henderson
    Jan 2 '14 at 19:23
  • From wikipedia..."The specified diameter of the filter in millimeters indicates the diameter of the male threads on the filter housing." So the filter may be a different size, I don't know. Maybe a 49mm would be closer.
    – Mark
    Jan 2 '14 at 19:42
  • Yes, but the filter holder also needs something to hold on to without going in to the field of view of the lens. That's not likely going to happen with a 50mm filter on a 52mm mount.
    – AJ Henderson
    Jan 2 '14 at 19:45
  • What size lens do you want to mount it on anyway? Jan 3 '14 at 12:24
  • I would use it on lenses with the following normal filter sizes, 49mm, 52mm, 55mm and maybe 62mm. Normally the lens will be stopped down enough that I won't care about vignetting or worse. I have step up rings already.
    – Mark
    Jan 3 '14 at 17:10
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For such project, I would use a step-up ring (e.g. 49-52mm to maximize usable filter area, or 46-52mm to have more leeway during mounting). The glass is guaranteed to fit in the 52mm inner thread and slimmer part with outer thread is guaranteed to provide support for the glass. To fix the glass into mount and fill the remaining gap, I'd try out silicone sealant first.

Disclaimer: I have made some DIY equipment, but not fixed glass to metal.

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  • good shout on the step-up ring! i hadnt though of that! Jan 3 '14 at 12:03
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The answer is that a standard 52mm filter holder takes a 50mm diameter piece of glass. I used a 52mm Tiffen UV filter holder and the 50mm glass filter fit perfectly.

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The diameter of the thread on the back of a filter, and the diameter of its front thread (for stacking multiple filters) are almost always the same, however the inner design/diameter of the filter holder ring may differ between manufacturers.

Unfortunately this means it is a matter of trial and error to find a suitable filter mount.

Exact details are not published by manufacturers, because it is expected that a filter will remain in its original holder/frame.

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