I made this flat lens because I don't want to buy another case and the sony flat door. It is expensive if you don't dive really deep. And since I the spk-as2 case had good waterproofing for its rated depth, let's slap a flat lens on top of it.
The flat lens is:
37mm uv filter
Things you need:
37mm uv filter
37-52mm step ring
52mm uv filter
white teflon tape (for tubing)
waterproof super glue
acetone - for cleaning the super glue
a metal file, screw driver, plier
Instead of 37-52mm + 52mm uv filter, you can try just another 37mm uv filter. Just glue the glass on the outer side, SEE LAST STEP for example.
The uv filters can just be generic, to make the cost cheap. You can maybe use a multicoated 52mm uv filter to reduce glare. But I don't know if it can survive dipping in sea water.
Because of the step ring having an edge inside and not a cone shape, this is only good for 120 degree setting, and will vignette on corners.
Step 1: Remove the Glass of the 37mm Uv Filter
Step 2: Put the 37mm Uv Ring From the Last Step to the Door
Attach all 37mm uv ring, 37-52mm step ring and 52mm uv filter (not too tight), then put it on the case door. Using a mobile phone, through PlayMemories app, check if there is vignette in 120 degree setting. If it does, we need to file the rear of 37mm ring,s o we can push back the glass and the step ring closer to the lens.
If you file too much, the 52mm uv filter glass will be too close and hit the door's glass. We dont want that.
Step 3: Glue the 37mm Uv Ring to Case' Door
Put the 37mm uv ring on the door, and put super glue inside the ring, between the glass and NOT ON THE GLASS. You shouldn't put too much or else the glue will block the screw thread inside the ring. And that will prevent you from screwing the 37-52mm step ring firmly. Wait for the glue to fully dry. Some white mist may appear around the glue, you can clean that with acetone. Just put a small amount on a piece cloth and wipe. Use the acetone to correct poorly applied glue.
*If you filed the rear of 37mm uv ring, you may want to cover the filed part with some kind of paint or glue, as protection. It may rust over time, especially in sea water, even aluminum. Mine is covered with a sharpie black because I forgot to cover it with glue
Step 4: Seal the 52mm Uv Filter
If you used a multicoated uv lens, you need to use a different sealant than super glue. Because you'll damage the coat if you clean excess glue with acetone
Step 5: Attach the Whole Thing
Put teflon tape also on the 37-52mm ring.
Step 6: The Finished Product
Sample vid: Sony action cam diy flat lens test (120 deg only): http://youtu.be/uOF8cmQNbmc
Thanks to Sony Action Cam Philippines (https://www.facebook.com/groups/1497987923774865/) for the teflon tape and feminine napkin idea