Welcome to our community

Be a part of something great, join today!

Log in
  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Question about Cooke Speed Panchro coatings for you!

B

BRANDON JAMESON

Well-known member
Joined
Dec 2, 2008
Messages
1,724
Reaction score
0
Points
36
Location
San Diego, CA
Hello fellow REDusers.

I have a Question about Cooke Speed Panchro coatings.

We have taken about a year to collect all the Cooke Speed Panchros (except the 100mm deep field) and now find that some are VERY warm and the others are not!

Is there a way to remove the yellow cast?

Is this a glass or coating issue?

May I please ask for the contact of an expert to do what needs to be done?

Thanks in advance.

Go, RED!!!!
 
All I can say is you're not the only one.

We have a set of our own as well, I think it's the 75mm that's the warmest of them all (has a yellow tone to it). And actually, that the lens our clients tend to use the most!
 
no way to correct it. some lenses are worse than others. As you expose to lens elements to light they will go yellow. - image wise some have a greenish yellow cast, others more pure yellow... etc

this is part of the reason why you shouldnt just rehouse these old lenses with out having them matched - not for rental anyways.

- I already own one set -rehoused, which matches lens for lens.

for my next set I had to buy more than 3 three sets so I could build one that matches for the rehousing. and the way the prices are now, its quite expensive building a matching set:)
 
Thank you both for your responses. Our 75mm is the worst too.

Can these yellow lenses be balanced to match the others in color correct?
 
My lens tech is telling me that those lenses were designed for black and white photography...
This should be the reason for this warm coating.
 
sam renollet said:
My lens tech is telling me that those lenses were designed for black and white photography...
This should be the reason for this warm coating.
Click to expand...

That makes PERFECT sense, Thanks, Sam!

Dang, not sure what to do now to make this set work...!!!

Any thoughts?
 
The 75mm are radioactive, which is why they are always going so yellow, made some 50 years ago. I don't think anyone at the time thought they would still be used 50 years later. I of the B&L lenses is very radioactive as are some Nikon lenses from the same era.

Historically one would test all the lenses at a rental house & make up your own set, you could match sharpness at shooting stop & colour . Trying to match wide open was not useful unless you intended to shoot wide open, which was rare at the time.
 
Stephen Williams said:
The 75mm are radioactive, which is why they are always going so yellow, made some 50 years ago. I don't think anyone at the time thought they would still be used 50 years later. I of the B&L lenses is very radioactive as are some Nikon lenses from the same era.

Historically one would test all the lenses at a rental house & make up your own set, you could match sharpness at shooting stop & colour . Trying to match wide open was not useful unless you intended to shoot wide open, which was rare at the time.
Click to expand...

Hmmm.. I know that for a lot of the radioactive lenses that have yellowed, people put the lens in the sun for a few weeks to take away the golden cast...might that work for these, or is that an old wive's tale?
 
BRANDON JAMESON said:
Hmmm.. I know that for a lot of the radioactive lenses that have yellowed, people put the lens in the sun for a few weeks to take away the golden cast...might that work for these, or is that an old wive's tale?
Click to expand...

It can help but really it's hardly an issue with digital colour correction..................
 
What about dialing in a custom white balance specific to that lens, or putting on some color correction filters.
 
There are reports you can reduce the tint through UV annealing.
 
thank you, Florian!

today I bought a UV sunlamp on Ebay and plan to shine it directly at the lens for a week or two.

seems like it may be a cool test on a theory and I will post the results (if any) here.

please stay tuned!
 
The topic of thorium glass going yellow came up on dvinfo a few years back. There was published info linked to at the time and it seemed valid. A Hong Kong based member commented that it had been a practice where he was to routinely "sun" the lenses to deal with yellowing and also help reduce fungus. Artificial UV light is more controllable. The natural sun moves. As glass absorbs UV you don't do much good parking the lens in the window. You may find it helpful to swap the direction the lens faces the UV source front to back so that the thorium glass element receives UV in both directions. I tried natural sunlight on an old Nikon 35mm f1.4 lens I bought off eBay. Out of the package it looked magnificent. It appeared a little grubby so I gave the barrel a wipe over with some cleaning spirit and that's when the black parcel marker ink came off and uncovered the bare metal patches beneath. That said, it still was a nice lens except for the yellow colour cast. Five cumulative days seemed to improve it a bit. Using sunlight outdoors whilst keeping a lookout for likely rainfall is a bit of mission. Another source of a yellow cast may be deteriorating balsamic bond between glass elements. I am not so sure that the deterioration of balsam may not be accelerated by UV exposure. - Take care that the lens body does not become hot. There's sunlamps and sunlamps, not all being equal. If the lens body becomes hot and your environment is cold, wrap the body in a towel after switching off the light to allow it to cool slowly. This will reduce the risk of thermal shock cracking any glass. Optical glass does not like extreme thermal changes. - Matthew Duclos may be the best mentor here on this topic. Hopefully he will comment.
 
Last edited:
Robert,

Thank you for your generosity of wisdom and providing some facts that are rather encouraging!
 
Here's a bit more info -

http://www.pentax-manuals.com/repairs/yellow.htm

Additional to my comments is that if a lens is left in sunlight, the barrel being black and which absorbs heat, should be wrapped in silver foil to reflect the sunlight and minimise the heating.

Apparently, high temperatures, as well as possibly imparting a mechanical load on the glass through differential expansion, may cause the lubricants inside to liquefy and migrate onto the glass or iris blades.

There is a comedic link to a guy who proposes an alternative method for eliminating the thorium glass problem from the lens. He mashed one with a big hammer. - It probably was not such a good move because other published information suggests that the alpha radiation from thorium is relatively contained within the glass with propagation possible only from the surface of the glass.

Now that the comedian has mashed his thorium glass into powder sized fragments, he has an efficient alpha-particle propagation source in his yard. I hope his kids if he has any don't play there and eat dirt.

The discolouration of the thorium glass is apparently created by microscopic paths being burned through the substance by the emitted alpha particles. My wild guess is that UV may bleach chemical by-products created by the alpha particles as their short journey vandalises the glass. Please do more research on this topic.

I have an old Series 2 Cooke Speed Panchro 75mm, which to the subsequent horror of lens techs I repaired myself. It and a 50mm were severely fungus-damaged and had been abandoned as pointless to repair. That was of course before a few thousand REDs were turned loose on the world and suddenly anything sharper than a coke-bottle base was in the running on eBay.

Having been making 35mm groundglass adaptors and making my own optical glass disks from blanks, I had adequate materials for polishing. By the time the fungus was gone, most of the coatings in the 50mm and all of the coatings in the 75mm had gone.

This 75mm does not have a noticeable colour cast, so my thoughts fall more in the direction of the coatings causing the warm colour change. I could be way wrong on this.

Please do not take to the lens coatings yourself. There is all manner of folklore published on forums including this about how you can polish glass. I was just plain dumb-luck fortunate.

There are so many ways to scratch and gouge the surfaces into irrepairability it is not funny. I would not have taken to the lenses myself had I known their true potential worth. I think it is more sensible for as many imperfect lenses as possible should not be messed with so that more blends of a greater imperfect population can occur to create more restored examples. P+S apparently cannot get enough of them to restore and re-barrel. There is said to be a cache of Cooke One's and Two's out here in Australia somewhere, one of those legends like the Spitfires buried in boxes in a cave in Queensland or the more recent Spitfires said to be buried in Burma.

Instead of going do-it-yourself, please enquire with the likes of Matthew Duclos and other optical engineers who contribute here from time to time.

Here is a comparison clip I shot with the SI2K which is an approx Super16mm sized sensor. The looks in my computer had somehow been messed up and I had to grade back from the brown and green colour all the images yielded.

The same colour adjustment values were applied to all the lenses including the Cookes. Don't pay too much attention to the grade. There was a nice mauve colour to the sky but I am partially colour-blind, so what means something that makes sense to me may be whacky to others.

Those old lenses held up quite well for sharpness compared to the CP Ultra lenses which are purposed for the smaller image format. As 25 points of sharpening were added to all shots, the vision is not representative of the native sharpness of the glass.

The best sharpness number for the 50mm has been 72 at f5.6 f8 in adequate light. The CPs range up to 118 at f2 - f4.

The Cookes do flare more, the 75mm the worst due to more of the coating being gone.

http://www.youtube.com/watch?v=9Sf9xXE5QrU
 
Last edited:
If they where mine and not for rental use i would not worry. You could easily shoot some charts and pick match them to create a lut for each lens that would even them out perfectly. But if you do not want the hassle of applying luts to all your shots then I would get a stack of filters and see if I could get them to match by applying filter glass. Then when you know whats needed you can have a front glass element for each lens made without too much cost involved. My dad used to be a optician before he retired and back then he could get me all kinds of filters and also fit them for lenses.

An optican can get pretty much all from ND's to kelvin filters. So back then I had everything from rayban wayfarer filters to hicon orange cast shooting range filters to play with, and they also got the workshop to fit them a front glass.
 
You must log in or register to reply here.
Back
Top