Post by belgiumreporter on Nov 14, 2016 8:52:38 GMT -5
i've recently stumbled upon an article that states the JANSJÖ work lamp from Ikea (Item number 101.287.34) is able to remove the yellow thorium cast in lenses with such elements.
As i happen to have such a lamp and a badly yellowed takumar 50/1.4 i tought why not give it a go, as the sun here in Belgium isn't very cooparative in producing the neccesary UV radiation.
However,after two days of beaming the light through the lens the cast was allmost gone,another four days cured the lens somewhat further but there still is a slight yellow cast that won't go away. So in my experience the claimed 24hour cure didn't work.
The strange thing in this procedure is the ikea led lamp produces next to nothing in the UV range, nevertheless to some extend, it seems to work. Question now is why? Is there another (longer?) frequency of light that is able to cure the thorium cast? One awnser suggests the ikea led is of cheap Chinese origin and the UV radiation isn't as low as it should be.
People do seem to get inconsistant results with this technique, wich could point to difrent leds being used througout the production of the ikea lamps.
Before the takumar showing a serious yellow brownish cast that "eats up" one stop of light transmission!
after one week of ikea cure: the cast is allmost gone, i can't find no diffrence in the amount of light transmitted between the cured and a non contaminated lens.
The non contaminated and the cured next to one another, note there's still some color cast in the cured example.
The non contaminated dates from before the contaminated one( serial numbers 1481936 / 1964324), so age dosn't seem to be the prime problem in the yellowing of thorium lenses.
As i happen to have such a lamp and a badly yellowed takumar 50/1.4 i tought why not give it a go, as the sun here in Belgium isn't very cooparative in producing the neccesary UV radiation.
However,after two days of beaming the light through the lens the cast was allmost gone,another four days cured the lens somewhat further but there still is a slight yellow cast that won't go away. So in my experience the claimed 24hour cure didn't work.
The strange thing in this procedure is the ikea led lamp produces next to nothing in the UV range, nevertheless to some extend, it seems to work. Question now is why? Is there another (longer?) frequency of light that is able to cure the thorium cast? One awnser suggests the ikea led is of cheap Chinese origin and the UV radiation isn't as low as it should be.
People do seem to get inconsistant results with this technique, wich could point to difrent leds being used througout the production of the ikea lamps.
Before the takumar showing a serious yellow brownish cast that "eats up" one stop of light transmission!
after one week of ikea cure: the cast is allmost gone, i can't find no diffrence in the amount of light transmitted between the cured and a non contaminated lens.
The non contaminated and the cured next to one another, note there's still some color cast in the cured example.
The non contaminated dates from before the contaminated one( serial numbers 1481936 / 1964324), so age dosn't seem to be the prime problem in the yellowing of thorium lenses.