ND filters cut with a CNC machine to fit under the existing P3 Camera lens cover..I use some of the best GEL material available, Kodak Wratten and Tiffen GEL material that are more resistant to fingerprints and can be easily wiped clean without scratching. The cost for a set of 2 - ND90 3 Stop filters is $5 shipped to anywhere in the US... I will also ship International and will research the rate to your destination so you do not over pay for postage. Just start a conversation with me on the forum by right clicking on my name and in the popup click on Start a conversation. Safe Handling Instruction for the filters are as follows: As with any camera equipment we want to try and keep it clean and dust free as possible.. My suggestions and how I handle my filters is to use a set of non-powdered latex gloves, I carry a pair in my camera bag and also in my P3 case. I also carry a lens cloth with me which can be had for very low cost if not free from your local camera store. Prior to each flight and as part of my pre-flight check : 1. Gauge my lighting conditions I will be flying in and choose how many filters I will be needing to keep my frame rates in check. 2. Gently remove my Glass lens cap and glass lens cover. 3. Use my lens cloth to clean the glass lens cover prior to inserting the ND Filters also in this process and before wiping the glass lens cover I give it a quick blow of air in case there is any particles that may scratch the lens cover when I wipe it with my lens cloth. 4. Pull out the required number of filters and again give them a little blow of air and I usually hold them up to the light and look through them to be sure they are clean if not use your lens cloth and give them a light wipe, the Wratten and Tiffen GEL can be wiped clean of fingerprints and any other debris. 5. Place the lens with filters installed back on the Camera housing and lightly screw back on until snug , Please be careful to not over tighten. 6. I always give the front of the glass lens cover a quick look and wipe if necessary to be sure it is clean. 7. Go FLY and Enjoy.