[hjoseph7]

How long does it take to remove the yellow tint from a lens ? I have a Takumar 50mm f1.8 (7 elements) which has been sitting on the window shelf in my room for the past 4 days. The lens gets strong rays of sun at around 3:00-6:00PM, but so far I don't see any progress..

[jlstrawman]

I have been at it for close to a week using a LED light on my SMC Pentax 50/1.4. I can see progress, but expect
another week in my case. I think it is quite variable. Use the search thread for this forum, as there are other
threads covering this ground.

[timw4mail]

How long does it take to remove the yellow tint from a lens ? I have a Takumar 50mm f1.8 (7 elements) which has been sitting on the window shelf in my room for the past 4 days. The lens gets strong rays of sun at around 3:00-6:00PM, but so far I don't see any progress..

I would imagine it depends on how yellow the lens is, and the strength of the UV light used on the lens.

[AstroDave]

You will do better if you can put it outside.

Glass is generally a pretty good UV filter, and you are counting on the UV to "fix" your lens (I think).

[stevebrot]

I have had very good results using the JANSJÖ compact LED desk lamp from IKEA. The neck of the lamp is flexible and allows placement of the light right up against the lens rear element.* Put aluminum foil over the other end to reflect the light back out. I was able to clear my badly-yellowed ST 55/1.8 and Auto Rikenon 55/1.4 lenses in only a few days without the risk of grease migration due to excess heat from the sun.

http://www.ikea.com/us/en/catalog/products/20169658/


Steve

* The yellowing is usually in the rear element or an element towards the rear of the lens.

[hjoseph7]

I have had very good results using the JANSJÖ compact LED desk lamp from IKEA. The neck of the lamp is flexible and allows placement of the light right up against the lens rear element.* Put aluminum foil over the other end to reflect the light back out. I was able to clear my badly-yellowed ST 55/1.8 and Auto Rikenon 55/1.4 lenses in only a few days without the risk of grease migration due to excess heat from the sun.

JANSJÖ LED work lamp - black - IKEA


Steve

* The yellowing is usually in the rear element or an element towards the rear of the lens.

Thanks stevebrot, that IKEA lamp looks like a plan. Do you use this regularly because when I first purchased this lens 3 years ago it had no yellow tint, or the tint was not as pronounced as it is today ?

[stevebrot]

Thanks stevebrot, that IKEA lamp looks like a plan. Do you use this regularly because when I first purchased this lens 3 years ago it had no yellow tint, or the tint was not as pronounced as it is today ?

I used it once and have not had to use it again except as a desk lamp. Yellowing (actually more of a dingy brown) due to radioactive rare earth elements in the glass mix is something that happens over decades.* Once cleared, it should last a long time. Yellowing of the balsam optical cement also happens over decades, but is not reversible using the light treatment. Yellow reflection off the lens coating is supposed to be that way.**


Steve

* The radiation disrupts the orbital distribution of valence electrons (move to higher energy state) in the glass itself to create so-called color centers. The color may be removed by heat annealing or by energy injection using intense light (need not be UV), both of which perturb the bonds between the atoms and allow the color center electrons to seek a lower energy level.

** Every so often, a user will report that they cannot clear the yellow appearance of the lens front element and it turns out they mean the reflection from the coating

[hjoseph7]

"JANSJÖ compact LED desk lamp from IKEA" - It's strange how this lamp does not mention anything about UV rays yet it seems to work ?

[stevebrot]

"JANSJÖ compact LED desk lamp from IKEA" - It's strange how this lamp does not mention anything about UV rays yet it seems to work ?

The light does not have to be UV.


Steve