Cook lens coating

[kissssss]

Hi everyone,

I have a chance to buy a Cook lens series IIA which was my dream portrait lens for a long time. But I don't know much about their specific.

The seller told me that the lens has haze and blemish internal. I think haze only happens on the lenses which are coated, and Cook series IIA seems not being coated. Am I wrong somethings?

I would listen to your recommendations.

Regards

[mhayashi]

IIA Portric was made from c.1909 to 1930 according to the Cooke compendium.
https://cookeoptics.com/compendium/

The IIA Portric wouldn’t be coated considering the production period.
Ask the seller what he means by haze, as it would be cleaned easily if it’s simply the thin layer of dust.
So you may ask him to disassemble and clean the whole lens elements.

[Mark Sawyer]

Some older Cooke lenses were restored and coated by Burke and James after WWII. But I doubt that's the source of the haze. More likely, someone lubricated the internal workings and the lubricant off-gassed, leaving a residue. That would wipe off easily. Or it could be a fungus infection, which may have etched the glass. That is a bigger problem.

Those are beautiful lenses. Good luck with it.

[paulbarden]

The seller told me that the lens has haze and blemish internal. I think haze only happens on the lenses which are coated, and Cook series IIA seems not being coated.

Nope. Coatings have nothing to do with haze showing up on internal surfaces. Most often its the volatile components of lubricants depositing on the inner glass surfaces that causes haze. Sometimes mistaken for haze is a clouding up of the cement used to glue cemented pairs together. This often happens when a lens is stored in a cool damp location for years.
Internal haze on surfaces is (usually) easily removed. Cloudy balsam is not easily fixed.

[Mark Sawyer]

...Sometimes mistaken for haze is a clouding up of the cement used to glue cemented pairs together. This often happens when a lens is stored in a cool damp location for years.
Internal haze on surfaces is (usually) easily removed. Cloudy balsam is not easily fixed.

Fortunately for the prospective buyer, the Cooke Triplet has three single elements and no cemented surfaces.

[paulbarden]

Fortunately for the prospective buyer, the Cooke Triplet has three single elements and no cemented surfaces.

Oops, I should have realized that. Apologies.

[kissssss]

I just look on the photos that the seller sent to me. Here the haze that he's mentioned:



Are they serious problems?

[mhayashi]

That looks like the residual on the internal surface of the outermost element.
It should be cleaned upon disassembly.
The picture looks the front and rear most elements.
So request him to clean first as they can be unscrewed easily before you decide to buy the lens.
If he refuses, then don’t buy. Something must be wrong in my opinion.

[kissssss]

I appreciate you guys' experiences and recommendations. I have contacted the seller. Hopefully everything gets better

[Hugo Zhang]

That looks like the residual on the internal surface of the outermost element.
It should be cleaned upon disassembly.
The picture looks the front and rear most elements.
So request him to clean first as tey can be unscrewed easily before you decide to buy the lens.
If he refuses, then don’t buy. Something must be wrong in my opinion.

Sometimes it is very hard to open the front element even with a lens wrench. I could not open my IIA lens to clean it. Maybe you can give me some tips?