Good filters may often help to protect lenses from scratches or abrasive dirt impact. It's easier to replace damaged filter comparing to replacing damaged lens, and personally I experienced both scenarios. Though filters are bringing extra light reflections, adding weight and slightly increasing lens size. In this article I'm showing customized option of minimalistic filters.
Many people are using lens caps instead of filters, lens cap may also protect sensor from direct sunlight through the lens. Though the cost of that can be missed good shot while taking time removing lens cap so I'm personally not using caps and always looking for smallest filter profile possible.
B+W and some other modern brands are making filter frames from durable brass alloy, which allowing slimmer profile and smaller size of filters while keep them strong enough. Optical quality of these filters is also very high and in most cases do not interfere with image quality rendering.
Typically filter frame is adding +5-6mm to a lens length, and there is a filter thread allowing to stack another filter on top. Over all these years of shooting my personal needs didn't include attaching second filter, so at some point I decided that I don't actually need front filter thread.
Removing front filter thread
At that point decision was made - to cut front filter thread away on one of my B+W filter that had significantly damaged and hard to repair thread.
At first I disassembled filter frame and took the glass out. Alternatively you may just cover glass surfaces with masking tape. Then I was using large sheet of sanding paper and just manually grinded front filter thread until it almost reached front naming plate surface. Finally I polished and smoothened cut edges and filter outer side and inserted glass back.
It resulted in about 2mm thick profile exposed once mounted on lens and has following look on Voigtlander 50mm F1.5 Nokton S.C lens.
B+W filter with shaved front thread looks quite good and nicely fits retro design of many RF lenses. It remains perfectly functional as a filter, however with slimmer profile it is harder to attach/detach filter to lens, involving rubber gloves or rubber strap. From the other side I'm attaching filter to the lens and never have a reason to remove it.
Here is comparison of B+W 52mm filter in original and front thread cut form.
Some filter remain thicker even after cutting off front thread due to initially more thick glass used like in this B+W 43mm IR/UV cut filter with red tint below.
Existing ultra-slim filters
It's not a new idea of having so compact filter - you may find some number of old options on eBay that are made without front thread right on factory with main purpose of having minimal size.
It took some time to find good filter option for ultra-compact Voigtlander 40mm F2.8 Heliar Vintage Line lens. It has quite rare 34mm filter size. I decided to purchase old 34mm Canon screw in filter, though there was a challenge to attaching it. Filter profile is so slim that glass is positioned inside too close to the front lens it can not be completely attached because filter is starting to press on front glass.
The solution for that was to add custom shim made of copper wire to attach filter without completely screwing it in.
As you can see on the image below, the Voigtlander 40mm F2.8 Heliar lens shows bright copper wire line under the filter edge.
So far I modified only three B+W filters for lens which I'm most often shooting with. Some lens having built in hood like Voigtlander 15mm F4.5 where filter size doesn't matter (unless you cut off the hood, but that's another story).
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