To be honest, if I were in charge of this, I would change things a bit. I would accord it some more priority because I think the results might guide decisions and that means it is important.
I would build an enclosure for it to reduce ambient light. The enclosure could be a cardboard box, but preferably something like a collapsible plywood thing. It is open on one side for easy access. It is painted flat white inside. It is big enough to contain the rig.
This approach is sound in its taking over full control of the 'shooting environment' and eliminating any possibility of the shot being contaminated by variables. While professional photographers can control the variables, expecting a bunch of 'snapshooter' level scientists to do so is more than what we can expect.
The approach which I had espoused earlier also 'takes over control' by making ambient light contribute what is effectively 99.5% of the exposure, but I will admit that it is not as 'fully in control' as what Archibald suggests to be considered.
I agree, that would be ideal, but unfortunately we have to move really fast to keep up with drilling. Sometimes we drill more than 200+ feet a day with one person taking photos every 5 feet, in addition to writing descriptions and keeping detailed notes. We have a lot of other gear to carry as well and usually only one geologist per site, so whatever I can do to simplify, at this point, is my goal. The photos are mainly to track changes in the type of sediment and distribution, so I don't think it will need to be as high-quality as other geologists' photos may need to be. Hopefully knowing this information will assist us with other jobs (we are a consulting firm) that allow a more controlled environment!