Lens Polishing and Re-coating
This procedure is usually too expensive for generic type lenses or entire lens systems, and is really intended only as a repair. There are also certain apochromatic glass and ED glass that may be too risky for this procedure because of their sensitivity to heat. We have had success with this glass, but the risk of breakage increases from about 1% to about 50%.
There have been some misleading reports that there is no way to remove scratches from a lens element without ruining the performance of the lens system and it certainly is true if performed by inexperienced technicians. As with any service it is possible to ruin any mechanical or optical device if you have no expertise in the service required. We only remove coating and never enough glass material to change the formula and therefore compromise the optical integrity. If a scratch is deep enough to feel with your fingernail, then it is probably too deep to repair. Another way to tell if the glass is damaged beyond repair is with a 5 to 10 power loupe, look at the scratch and see if there is fracturing under the surface. If there is fracturing under the scratched surface, we would need to remove enough glass material to get to the bottom of the fracture, and that would risk the possibility of changing the radius curve and render that lens useless.
Some lenses like the early Zeiss Planars have cemented doublets for their front elements. A cemented doublet should never be put into a coating chamber due to the problems it can cause and therefore must be de-cemented before the coating deposition as the 287º F temperature will cause cement failure, leading to breakage or contamination of the entire coating run.
Lens Cement Separation Repair
Lens cement separation repair is also labor intensive, mostly in separating of the two or three glass elements. This is done with heat, but very slowly as to reduce any risk of thermal fracturing. Then these elements are recemented with optical grade copolymer cement, optically centered, and cured. We use various tools to center the elements for optimum performance.
Some elements and or doublets are machined into their mounts meaning that instead of a threaded retaining ring being screwed down on the element, there is a thin wall of metal left above the glass edge and the mount with glass is returned to the lathe, and the thin wall is burnished over the glass. This style is more expensive to remove and in rare cases must be cut from its mount.
Fungus and Haze Removal
Fungus can be a real problem in high humidity environments and from condensation as well, and even though we have several ways to remove the damage, some are not economical. What you see is not the fungus but what the fungus has left behind. It usually looks like a cotton seed or spider web and may even take on some very unusual patterns. The appearance can be due to corrosion, staining, or even a destructive etching. The fungus arrives in your lens with moisture in the form of condensation or humidity, and as it lives in this environment, it secretes hydroflouric acid. This starts the corrosive action that can form on the surface. It attacks the coating or the glass and may etch it beyond repair. The hydrofluoric acid can seep thru the pores of the coating and make contact with the heavy metal content of the glass material. We need to perform a test to know if it will clean up without extensive polishing and recoating.
Haze is a different problem and with certain lens elements it can be cleaned out without a lot of expense but again when high heavy metal content (rare earth) elements have moisture making contact by seeping through the coating pores, then the corrosion starts and outgases through the pores creating tiny white dots by the hundreds that to the naked eye appear as haze!
Most of these optical repair operations are not without risk of breakage because heat is involved. There is no way to know what flaws may be lurking in any particular piece of glass. In the vacuum chamber, the environment is heated to 287ºF to insure good bond between the glass and the coating. The glass is also heated during the setup for polishing to adhere the bare glass element to the spindle. In manufacturing there are always extra elements made because of the possibility of breakage during grinding, lapping, or polishing and also vacuum deposition coating. The glass is also heated in the decementing process for cement separation repair procedure. Although we take every possible care in the handling of these elements, there is on occasion breakage with no visible reason, and therefore the risk is the customers. We cannot replace many of these elements and even though we will not charge you for any of the service to this point, we also will not pay for any replacement or compensate the customer for their loss! If you are not willing to take these risks please do not send your lenses in for this type of service!