This is a filter holder for some Nikon lenses. It let's you attach a welding glass to your lens to act as a neutral density filter, in order to get longer shutter speeds. (see this Flickr group for examples: http://www.flickr.com/groups/weldingmaskglassfilter/) Welding glass is used in all kinds of metal welding techniques, to protect your eyes from the light. The glass is very cheap and can make an inexpensive neutral density filter for photography (means you can use very long shutter speeds during daylight to e.g. make water very silky or do amazing stuff with the clouds). For this we need a rectangular shape of glass as used for electrical welding. The glass has to be 110mm wide to fit the holder. I guess there are different sizes but hopefully they are a bit standardized. I bought my glass at a local store for 3€. You can also buy ND filters in photography stores, but they can get very expensive, 100€ and more. You will get much better quality for your money, but the aim here was to get it done cheap. Note: One of the pictures is an example photo, taken with the filter.Now, how do we attach this welding glass to the camera? Many people are using rubber bands and while I am a big fan of improvised photo gear, I also felt that this was not a good solution. Why? Because I want to frame my picture and set focus without the filter. Then I'll mount the filter and the viewfinder of my camera gets pitch black – good for taking the picture, bad for framing and focusing.Thats how you do it – It reads long, but it is dead simple: 0) Use ABS if possible. I printed two on a Makerbot Replicator and ABS turned out ok. I did not test PLA, but I guess ABS is better because it is more flexible. (I typically print this one with these settings: Infill 35%, ABS at 226°C extruder and 110°C heated plate. 1) Print the mount raftless. Make sure that the first layer will be very flat on the bed. Otherwise the mount will probably sit too firm on the lens and you'll have to sand it a bit. 2) Print the filter holding plate raftless* 3) You might need to carve out the filter holding plate a bit with a knife to make the filter fit. If the glass sits too lose, glue a piece of clothing in there. 4) Snap both pieces together (see https://www.youtube.com/watch?v=eiquqivFiRk). They are designed to press fit. The backside is a bit rounded so, thats the side that has to do in first. Make sure the small pockets of the mount are exactly Top/Bottom. If unsure, connect the mount to your lens and see how the holder plate has to go on there. If the mount sits to firmly at the lens, use sandpaper and sand off a bit from the part that goes to the camera (make the mount thinner). 5) Done. Slide your glass into the holder. Point your camera to something, focus, snap the Filter holder to your lens and give it a go.This works probably for all lenses, that use the Nikon HB-32 mount for lens shades – yes, it snaps into the lens shade bajonett, it is not screwed into the filter thread. It should work for the following lenses: Nikon 18-105 (I tested mine with this one) Nikon 18-135 (Not tested. But a friend owns one of these, so I'll ask him to try it) Nikon 18-70 (Not tested yet)== OPTIONAL =========================