Flatport length issues in Photography Gear and Technique Posted October 23, 2020 Hi I am struggeling a bit with the length of my flatportcombination with the 105VR2. I have the impression that there is too much space in front of the lens for the optimum use of wet diopters. I have a Nauticam D750 housing and I now use a compact base, 20mm extension and the 30 compact port. The effective internal length from base to glass is 90mm. Since the 105 sticks 80mm out in front of the housing, there is a full 1cm room between lens and port glass. Couple of questions: 1. Is this too much (for the use of wet diopters)? 2. There is a dedicated port for the 105. The macro port 87. What is the exact internal length of this port? Is this 87mm?