Sweet. Today, the glass elements for the test rig (lenses and 90 degree prizm) arrived today, which I wasn't expecting because they were the last things to dispatch, according to AliExpress. No idea how they jumped the queue but I'll take it. Looking at tracking, I predict to have everything else this week, so I probably should get started on designing the test rig.

I wasn't expecting the lens to have a way deeper curve on one side than the other. Good thing I didn't assume they'd be even on both sides and tried a computational simulation.

For (checks notes) £2 worth of lens, the first one inspected looks really nice. I'm glad I haven't yet needed to attempt to 3D print something custom, because I doubt even a theoretically perfect #SecSavr Suspense [gd0105] would get this visual clarity.

[some time later]

Checked all the glass and it all looks divine.

The prism has a mirror-coated face but it doesn't extend all the way to the edges so this would only be usable for moving the beam around. 

The total internal reflections look cool though, and it indeed does the dove-prism reflection thing if looked at from the right angle. I feel like I'm not going to get a perfect edge-to-edge merge using plain prisms, but I do think I can get close. Even Samsung shipped out a phone with a crease line, so I've got to give my hobbyist run some slack.

Lastly, the F-40 lens (deep/shallow curved face)

Assuming the packaging is massless, the lenses weigh 140.9g. 92.6g is the 3 F-30's and 48.2g is the 2 F-40's. Average lens weight is 28.18g. Prism is 10.7g, so I'd assume a beamsplitter is 2x that at 21.4g and 10mm prisms are 1/8th at 1.3g. Thus, in glassware alone, I'm estimating a weight of 496.2g. That doesn't sound great. Google suggests that the average motorcycle helmet is 1.5kg, so perhaps I could still obtain a comfortable solution for prototypes.

Chromatic abberation of the lenses looks minimal, but the entire view is minimal so it might be more apparent in testing.