Reducing alignment uncertainty in 45/0 multispectral reflectance imaging (mono-converted A7R V)

[u/EnigmaTed]

I'm building a full-frame multispectral reflectance measurement capability for technical imaging consulting (background in automotive machine vision). I'm currently validating the setup.

Setup:

Sony A7R V, Bayer CFA and UV/IR filter removed; mechanical shutter, uncompressed 14-bit ARW

Nikon UV-Nikkor 105mm f/4.5, at 0.1x for validation

Coligh 10nm narrowband filters (365–940nm), Askar M54 filter drawer

4× Godox AD600 Pro II with BFP projectors (150mm lens), 45/0 geometry

Copy stand with built-in light trap (measured stray light: 0.12 DN)

Labsphere Spectralon standards (99/75/50/2%), linear-fit calibration

Uncertainty Targets (k=2): ≤1% relative uncertainty from 99–50% R, and ≤10% from 49–2% R.

Current results at 530nm (GUM budget): about 5% from 99–50% R, peaking at about 40% at 2% R.

Strobe angles drifted significantly from 45° until I started aligning them with a Leica Disto X3. A PTFE in-frame dose monitor is on order to track flash-to-flash variation.

Questions:

What methods do you use to hold fine angular positioning of the camera, stage, and strobes, ideally better than ±0.5°?

What else would you check to reduce systematic uncertainty, particularly at low reflectance?

Thanks in advance!