Lens: Super Takumar 105mm f2.4 – medium format lens for Pentax 67 6×7 camera with rear optical element made of radioactive thorium glass
2 bulbs 6W UVB 10.0 were used for the procedure (Purchased on Ebay from China).
( UVA UVB Reptile Light Bulb Small Pet Heating Bulb for Turtle Lizard Snake )
The bulb is at a distance of approximately 5cm from the optical front/rear element. No overheating problem did appear.
!!!Keep your eyes safe from light bulbs – at a sufficient distance and for a very short time!!!
Measuring device for comparison before and after de-yellowing procedure:
Enlarger Magnifax adapted for scanning + camera Sony A7R III + Negative Supply Light Source PRO
Camera and enlarger lens (Componon-S 5.6/100) settings were same for all (before/after) measuring and distances between the lightsource, Takumar lens and the camera had also the same values:
Exposure time: 1/10 s
Aperture: f8
ISO sensitivity: 100
White Ballance: 4700 K
Distance A: 38 (units read on the scale of the Magnifax enlarger)
Distance B: 13
The biggest difference/de-yellowing effect was made in the first 12 hours. However, I left the light on for another 8 hours. In the pictures below you can see the difference after 20 hours of lighting with 2 bulbs.
I left the light on for another 9 hours.
Rough values of light transmission increase before/after 29 hours:
RED: +0.25
GREEN: +0.45
BLUE: +0.95
There may have been some variation in the measurements and the differences (20/29/40 hours) may be inaccurately, but most likely there are differences in the end.
40 hours
We can read from histograms some small increase of lens light transmission again (29 hours / 40 hours). Also blue channel comes closer to red and green but red and green are starting to move apart.
Super Takumar 105mm f2.4 vs. Nikon 16mm f2.8 AF-D Fisheye color cast comparison
Draw your own conclusion and maybe you’ll prefer a permanent yellow filter for a black and white photo.
However, I prefer a lens that will affect colour rendition as little as possible, more light will pass through it and I can put the yellow filter on at any time – I want to have that choice.
*Click on pictures to enlrage and open in new panel.
Also you can check my analog pictures on https://www.analogova.fotoradost.cz/
Recent Comments