Brilliant! Thanks so much! I’m still not sure whether I’ll go the entire mile to reproduce something similar since I did some further tests with my Ulanzi and I’m wondering if I’m already close to there with that.
Using a toy spectroscoop:
I analyzed the light coming out of the Ulanzi to find out which LEDs are used. The spectrum was a bit hard to photograph with my phone, which also has some distinct r, g, and b sensor. I was able to make a crummy video of the light cycling through some demo setting that roughly shows what I was looking for, but apparently I cannot upload that so I made some screenshots:
The video is very crummy and the actual R, G, and B lines are better defined when just looking. The Ulanzi uses LEDs with blue at 455 nm, green at 525 nm, and red at 625 nm (assuming that the scale of the toy spectroscoop is located accurately…). I would have preferred the red to be somewhat longer wavelength so as to lie further beyond orange (which enables better negating the mask), but alas. It’s convenient and cheap.
My current setup can be seen here:
As shown there, I also tried a proper Solux bulb, and a “white light” Rollei led array, but now abandoned both in favor of the Ulanzi RBG light with an additional diffuser (borrowed from the Rollei light).
This gives, when placed close to the negative, a quite homogeneous light intensity, apart from being about 8% less bright in the corners, which I find acceptable considering that many lenses have a stop or so falloff in the corners anyway, which is a factor two, and usually still not too disturbing. 8% is not very visible in actual photos.
Nevertheless your sphere is inspiring, and I am now playing with the thought of adding that. Perhaps some stainless steel half balls such as these:
https://www.amazon.com/dp/B096VGSCT9/ref=syn_sd_onsite_desktop_0?ie=UTF8&psc=1&pd_rd_plhdr=t
Can be polished internally to obtain a spherical reflecting surface. Just brainstorming along…it’s a never-ending optimization it seems, but for now I’m a happy camper. Perhaps when I find some time, I’ll go the extra mile and reproduce your highly inspiring setup!