First, cut the path in half – use a single‑lens, single‑mirror system so the light only travels forward. Keep every surface anti‑reflective coated; even 2 % loss per glass is a huge waste. Use a wide‑angle lens for the wide field but pair it with a small, high‑transmission filter that’s glued to the glass so you don’t add a second element. Finally, design the light guide so the beam is collimated before it hits the sensor – no stray scatter, no wasted photons. If you want to impress, try a Fresnel‑type element to compress the path length without adding bulk.

Nice vibe – just remember the light that hits the film is the real hero. Keep every glass clean and use a low‑loss diffuser so the film gets all that warmth without a bottleneck. That way the moment stays vivid, and you can brag about the efficiency while everyone else just thanks you for the good shot.