I’ve been meaning to do this for a while now, but watch the above video, it should clear up any questions anyone has on how to use filters with lenses that “can’t” take filters. But that I mean wide lenses w/o proper threads for filters on the front. The 3 biggest offenders are the sigma 12-24mm, the nikon 14-24mm and the panasonic 7-14mm. I’ve owned all 3 lenses at one point or another (never at the same time) and I’ve used filters with all three. You will need to be able to modify parts to make this work, but it does work.
For the sigma you use a 95mm adapter ring with spare cowl for the lens. You can get the cowl from Sigma for ~$30 and the adapter ring wherever you get your filters. Once you have the parts, you need to make the cowl so it slides onto the lens. To do this you have to remove the metal lip by either grinding/milling it off, or cutting the front portion off the lens. When you do this it’s likely you’ll destroy one of the 2 felt rings inside the cowl but they’re not needed for this. MAKE SURE you remove all the metal filings before putting this back on your lens! You then press fit the cowl into a 95mm cokin ring. If you’re unsure what that means, get out a hammer, a piece of wood, and make it work….
For the Nikon, it’s a 105mm adapter ring (available where ever you get your filters) and a spare lenscap (available where ever you got your lens). You cut the center out of the cap this time, either from the inside through the end, or you can cut the front ~5mm off completely. You’ll be gluing this to the 105mm ring, so think ahead as to how you’re going to make that work. I left a lip on the cap so it would glue inside the ring making it easier to line everything up. This method means more careful filing though. You also have to remove some of the material inside the cap as the hood on the 14-24mm actually gets thicker as you move in from the ends. Take your time and it works though.
For the olympus 7-14mm it’s a bit easier because everything is smaller. It uses the 77mm adapter ring which you might already own… With that ring you can use a livestrong band and make it work, or you can use the lenscap trick again. The oly can also work with Z filters (4×6) which gives you a lot more options. I only used the 7-14mm for a few weeks though so I never dialed it in honestly, but it DOES work.
Make sure you read the notes under the images below: