So you've been looking for this very special lens that will make your Nikon / Minolta / Canon / Zeiss-Ikon (choose your brand) contemporary-correct camera kit complete, but the only specimen you can find has a bent filter rim? Despair not! For today I'm offering a simple DIY tool to straighten filter rims, provided they are made from metal that can bend back into shape.
a piece of 1-inch (or more) thick wood, preferably tropical hardwood
a circle drill, slightly wider than your filter diameter
a long bolt, 4mm diameter. In my case it has a cross head but it really doesn't matter
a size 4 nut, that will fit the bolt
some elbow grease, but not even that much
Now, I can write a long explanation of how to get to the final product, but it's actually so simple that I don't really want to. Also, if you cannot deduct how to get to it, this might be an out-of-your-league endeavour for you after all...
This is it. In my case, this is made to size for 52mm lenses mostly found on Nikon SLRs. I have a 2.5/105mm Nikkor Ai lens coming with a badly dented front end, bought it just because I didn't own a 105mm Ai yet and it was cheap.
How does this tool work? Dead simple!
Just place it inside the filter rim, grip it firmly and start twisting the bolt end (with a screwdriver in my case). The two halves will be pushed apart as the bolt advances through the nut, that is embedded on the inside of the left half. This will push the filter rim back out, until the pressure on both halves is about equal. Until that happens, pressure is directed towards the metal filter rim parts that protrude the most, i.e. are most bent inwards.
Here is a picture of the two halves being pushed further apart as the bolt advances.
Now, why did I use a circle dril that was wider than then the filter size? Very logical actually, since I prefer to sand some wood off the outsides of the circle to make it fit. I sand until the fit is too lose (need space to clear the bent metal before applying the tool) and the tool can easily move about.
Cut circle of wood
Sand to size
Drill a hole for the bolt from the side, until just past the middle. Do NOT drill through
Sand the whole piece of wood until no splinters remain
Cut the circle in half with a saw
Sand some more
On the inside of the one half that has the hole through the side, widen the exit so that a nut can be hammered into it. Apply force gently or the wood will snap.
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