The left is using a 35mm beamsplitter and the right is an older concept of the current proposed solution. The good news is that the 300mm design means that it looks (and would likely feel) much smaller; I didn't even notice that the helmet got taller until I compared it with an older render. It also looks more modern than the previous concept, yet still not as sleek (and dare I say edgy) as the single combiner concept.

Speaking of the single combiner, I don't think I'm going to be using 2-way mirror for this. Let me explain why.

These are the 2 devices I shortlisted for a not-so-temporary temporary TyMist (similar to the i3 Amoled being my not-so-temporary temporary wearable whilst mining for #Tetent TimerSpy [gd0136]) but there were 2 things that just failed the solution: FOV and blackness. Notice how I didn't say resolution. The HUAWEI uses 1600^2px screens and the Royole is 1080p; it's not ideal but it is servicable. The issue is that the pixels are spread over a uselessly massive area, and even if it was reduced, there'd be complete darkness around the screen. I can't tolerate that for regular screens even when watching videos, much less doing any work.

This made me realise that I don't just need to see the outside world, but that there has to be a good amount of light coming in too.

I've printed some 40mm "cubes" that should give a geometric and visual indication of looking thought the beamsplitter. Due to the shallow angles between the faces I've printed on the actual beamsplitter cube, those faces would reflect light and not allow light to just pass through. 

It's... okay. 40mm is slightly too big, but the PPD calculator says that I won't be able to do a 30mm cube with a 25mm eye relief at 90PPD. I could do 97.5PPD though, barely. 35mm sounds like the nice middle ground. The "optical bezels" are also quite large (like 30% of the width of the see-though area), but because they're a medium-light grey instead of black, it's not so bad actually.

It also seems that the left+right faces of the cube (that have that diagonal line on it) are frosted to prevent such reflections.

Speaking about the price, it sure increases fast after 25mm^3. I coudn't specifically find a 5:5 35mm^3 but there are 40mm ones where the listings usually say that the cube can be customised and those ones are £50. Now that's a lot of £££, but I'm struggling to compute a solution using the much cheaper but quite thin beamsplitting panes since they seem harder to mount in the 300mm cylinder and I imagine it visualy looks worse from both the first and third person perspective.

The 300mm helmet visibly looks nicer to move in, but the real bargaining chip it has is that I can buy a 300mm acrylic tube section but I can't get a 350mm one.