A lens for photography is supposed to simply let the light through to the film/sensor behind it. We only want to make sure that the right part of the image is in focus and we want to control the amount of light that goes through (via the aperture).
However, this is not true at all. How else would it be possible that lens X supposedly renders colors more beautiful than lens Y? How could it be that a certain lens produces beautifully warm images under all circumstances whereas others simply don’t?
Well, while the former is a very complex topic that I unfortunately am not able to explain myself, the latter usually is simply caused by a color cast in the glass itself. This is especially prominent with lenses containing radioactive elements (Read more on that topic in my articles about radioactive lenses and the actual measurements of my radioactive specimen.).
Here’s what the typical color cast of radioactive lenses looks like:
How did I measure the color cast / light transmission of my lenses?
I sat the camera on a tripod and put the grey card (cheap chinese one) on the wall, then I used a continuous light source (45W putting out 5’500 K) to guarantee unchanging conditions for all contenders.
The Yongnuo was used to set the white balance for all the lenses because it is said to have very good/even light transmission and color rendering. (Source)
I took the first shot and set exposure mode to manual with the shutter at 1/15 s at iso 100 (best color quality on the sensor) and f/2.8 to have the same aperture on all lenses.
The only thing I did in Lightroom was setting the camera profile to Neutral and of course set the white balance identical for all the lenses. No sharpening, no contrast or clarity, no adjustments to brightness, exposure, shadows, etc.
After correcting the white balance in Lightroom. (Temp 5’450K and Tint +25 was suggested by the WB selector) the picture from the Yongnuo looked like this:
Keep in mind that the lamp was standing really close (45cm) and at about 45° angled to camera right of the grey card. (That’s the reason for the brightness gradient you see in the pictures)
The camera was at a distance of about 50cm too and the images were cropped to show only the center part of the frame.
The Color-Ultron, unfortunately, has not better light transmission than all the others (despite the picture being the brightest) but the aperture wasn’t closed down to f/2.8 when I made my test (the adapter wasn’t working properly in the beginning). However, correctly set to f/2.8 the Color-Ultron is only about 0.1 EV darker than the Yongnuo.
Additionally, it gets the exact same color temp and tint as the Yongnuo! That’s pretty amazing, if you ask me.
The Nikkor comes in at a mere 100 K warmer than the Yongnuo (and +2 on the green side). It’s also only 1/6 EV darker than the Yongnuo.
The Tessar also gets close at 200 K warmer (+7 on the green side). It’s a whopping 0.5 EV darker, however. I took the crop from the image center where vignetting shouldn’t be an issue but I cannot be 100% sure about that. Seems like f/2.8 isn’t f/2.8 here.
The Helios comes in 250 K warmer with +9 on the green side. It’s 1/3 EV darker than the Yongnuo.
The radioactive bunch:
Here we really see a color cast that’s visible with your bare eyes.
The Takumar comes in at 650 K warmer and has +12 on the green side. It’s 1/4 EV darker than the Yongnuo.
The Pancolar adds 1’300 K more warmth and +47 on the green side. It’s 2/3 EV darker than the Yongnuo. This lens will need a lot of curing!
The Fujinon adds 1’350 K more warmth and +24 on the green side. (that’s why it looks more “golden” than the Pancolar) It’s 3/4 EV darker than the Yongnuo.
Even though I love the warmth that the Fuji adds to pictures, I don’t want to lose 3/4 EV of light (that’s f/1.8 vs f/1.4) just for that “effect”.