Robert Hart
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Okay. A techie question. I have two old lenses.
One is a lightly fungussed 28mm prime, a gift becuse it was not economically repairable. It came up quite well after a clean. When I received it, the lens had a "goat's eye" iris. When I opened it, a loose piece of metal was floating inside and it turned out to be part of an iris blade.
The other is a zoom. I've had it from the mid 80s. Its iris blades had become oiled unobserved over a long period of time. The inevitable outcome was that, they stuck, tied together by a substance similar to candlewax and begain to fold. Result. - Three broken blades. Two are recoverable as it is the pivots which have pulled from the blade ends. One blade has parted in the centre. This blade has to be replaced or remade.
It is a product which is no longer supported. Two third-party vendors have some individual blades or complete iris assemblies but delays after several communications suggest they do not really want to part with them or the transworld transaction might not be worthwhile. So it comes down to making a replacement part. The likely raw material shakes down to steel shim or sacrificed feeler gauge 0.04mm in thickness.
Now comes the harder bit, the method. Any attempt to cut shim stock by shears will inevitably distort it beyond recovery. - Not an option. In mass-production, a punch method is likely used.
My imagining is that to make a one-off blade, I will need to make two fairly robust precise profiles of the iris blade shape with two locator pin holes, two locator pins, use the locator pin holes to drill reference holes in a piece of shim stock, clamp the shim stock between the profiles using pins to maintain position of the shim stock, then cut and dress the shim stock to the profile shape, dress the edges carefully so they do not bind in assembly, install the replacement rivet pins into the holes, fit all the blades into the iris assembly and pray.
Why fix the lenses and not go the eBay route. It is a bit like the road and the chicken, because the task is there.
Any tech advice will be appreciated.
One is a lightly fungussed 28mm prime, a gift becuse it was not economically repairable. It came up quite well after a clean. When I received it, the lens had a "goat's eye" iris. When I opened it, a loose piece of metal was floating inside and it turned out to be part of an iris blade.
The other is a zoom. I've had it from the mid 80s. Its iris blades had become oiled unobserved over a long period of time. The inevitable outcome was that, they stuck, tied together by a substance similar to candlewax and begain to fold. Result. - Three broken blades. Two are recoverable as it is the pivots which have pulled from the blade ends. One blade has parted in the centre. This blade has to be replaced or remade.
It is a product which is no longer supported. Two third-party vendors have some individual blades or complete iris assemblies but delays after several communications suggest they do not really want to part with them or the transworld transaction might not be worthwhile. So it comes down to making a replacement part. The likely raw material shakes down to steel shim or sacrificed feeler gauge 0.04mm in thickness.
Now comes the harder bit, the method. Any attempt to cut shim stock by shears will inevitably distort it beyond recovery. - Not an option. In mass-production, a punch method is likely used.
My imagining is that to make a one-off blade, I will need to make two fairly robust precise profiles of the iris blade shape with two locator pin holes, two locator pins, use the locator pin holes to drill reference holes in a piece of shim stock, clamp the shim stock between the profiles using pins to maintain position of the shim stock, then cut and dress the shim stock to the profile shape, dress the edges carefully so they do not bind in assembly, install the replacement rivet pins into the holes, fit all the blades into the iris assembly and pray.
Why fix the lenses and not go the eBay route. It is a bit like the road and the chicken, because the task is there.
Any tech advice will be appreciated.
