180 Sturdee Street Cove

I went back to Sturdee Street Cove in Esquimalt, BC yesterday but this time I swam to the right rather than to the left which I did last week.

Sturdee Street Cove and Foster Street Cove

This first video starts with a view of the entry/exit point to show what the beach looks like when the Esquimalt Harbour tide height is 1.5 metres. It then switches to a view of the beach in the cove at the end of Foster Street because it was on the way to where I turned around at Denniston Park. With its convenient set of stairs, the Foster Street shore access would be a good one for snorkelling but I use Sturdee Street because parking near the former is restricted to local residents.

Trifocal Dive Mask Experiment

The main objective of this snorkelling session was sightseeing but I also wanted to continue work on finding the optimal solution for me being able to see clearly underwater. In a previous blog post, I described my use of stick-on lenses to turn a dive mask into a set of bifocals that let me get get a sharp view of my camera screen. This time I took the idea to the next level and created a trifocal configuration by adding weaker lenses above the other ones.

I took a pair of Skyway +2.0 diopter soft plastic lenses and sliced off the bottom third of each before attaching them just above the +3.0 pair. As the video shows, they are also slightly farther apart. The lower lenses have a 55 mm centre-to-centre spacing because they are intended for looking at subjects about 50 cm in front of my face. The upper ones have a 65 mm separation because I wanted to optimize them for subjects at an approximate distance of 1 m. I calculated the required parallax-accomodating distances based on the refractive index of water and an imprecise estimate of the distance between my corneas and the faceplate of the mask. That gave a different result from at-home trial-and-error so the 55 mm and 65 mm separations were a compromise between the theoretical and experimental results.

Optically, both pairs of lenses did work as expected when I tried them in the ocean but the new ones were just not that useful. Most of the time I preferred to simply look over the top of them. There was only one occasion I actually appreciated their presence. Not surprisingly, that was when taking a critical look at something about an arm’s-length in front of me. That made me feel good about having chosen full-size +2.0 diopter replacement lenses when I bought the mask I use most often.

Mechanically, the experiment was less of a success. The beginning and middle parts of the video show the new lenses exactly where I placed them but the last part shows that, by the end of the session, one of the lenses had shifted out of position. By the time I got home it had become completely detached and, despite me being moderately careful, I had lost it completely by the time I had all of my equipment set to dry. Though disappointing, this was not much of a surprise because I was not able to squeeze out all of the air under the lenses when installing them on the faceplate so it would have been easy for water to seep in between. More surprising is how well the original, +3.0 pair have stayed where I put them.

I used my nostalgic Aqualung Atlantis mask because its oval faceplate allowed the lenses to be positioned that close together while also that far down. That is not possible in most dive masks, especially for the 55 mm spacing, because they make room for a nose compartment. My next experiment will be to ignore geometry and centre the +3.0 lenses as far apart as my pupils are.

Underwater Snorkelling Sights

The third video includes some of the underwater highlights. Despite there having been very little wind, the water was still inconveniently rough at the spots with the best invertebrates so maintaining a constant distance, and hence sharp focus, was usually difficult for close-up imaging.

I used a wrist-mounted Light and Motion Sola 1200 to illuminate many of the scenes but for one brief period the clouds thinned enough for me to get acceptable results with natural light. I was most intrigued by the nudibranch at about 0:50, possibly a Red-gilled Nanaimo dorid, and some of the anemones turned out quite well but my favourite might be the parts where I was just swimming past the multi-coloured kelp.

By Brian

Owner and administrator of this website Resident of North Saanich on Vancouver Island in British Columbia, Canada

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