Sodium Chloride does not exist as a vapour at room temperatures therefore if the salt is physically constrained within a fabric bag, it can't corrode nearby metal.
Lenses are usually coated with metal halides eg MgF2 which will not react with or corrode in the presence of salt. The reference quoted refers to salt spray on sailboats and near the ocean and then cleaning off the abrasive dried residue - a completely different transport and damage mechanism
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Desiccants
While I doubt that salt will cause corrosion, I don't think it is a particularly effective desiccant. If you must use a desiccant, why not just use silica gel? The reason it is used so widely is because it is a very efficient desiccant. You can buy it sealed in sachets, or just keep it when it's supplied with all sorts of electronic equipment and other products. Some types are able to be regenerated in an oven. Silica Gel itsel clear bead form is not toxic. It is chemically identical to beach sand but structurally very different which gives it its hygroscopic properties. Note: Sand won't work!
If you want to regenerate it in a food oven - regular or microwave, be careful to use the clear beads and not to use the indicating types. The type that is blue and turns pink when saturated is Cobalt(II) Chloride which is both toxic and carcinogenic and has been banned in many countries. The type that changes from Orange to Violet is Methyl Violet which is also toxic and carcinogenic albeit less than Cobalt(II) Chloride.
A cup sized volume of silica gel in my labs in Canberra needs to be regenerated about once a month when desiccating a container similar in volume to a 4" refractor that get opened once a day. My labs have a humidity that varies from 50%-80%.
Desiccant free method
The easiest and simplest solution for refractors or Catadioptric systems is probably to forget silica gel and leave the eyepiece holder open so dry warm daytime air can circulate.
This may not work in the far north where humidity is high for extended periods but should be ok anywhere south of the tropic of Capricorn.
If you are concerned about insects crawling in cover it with a piece of mosquito netting and a rubber band.
If you want to drive water out after an especially dewy observing session, put on a halogen work light and gently heat the tubes for an hour or two after observing with the eyepiece end open or covered with mesh. Add a timer switch so you can go to bed. This method can work on tube left mounted on an observatory mounted instrument or tubes placed on a shelf in the garage. Depending on the size of the tube(s) and distance to them use a 150W or 500W halogen light. You only need to heat the tubes so they are luke warm to the touch - 10-20C above ambient for an hour or two.
Bringing a cold tube back into a warm and humid house especially in winter is the worst thing you can do. Houses are much more humid than outdoors and so the cold metal condenses much more water inside the tube. A garage or tool shed shelf with a halogen heater is the best way to keep the tubes dry.
These same types of lamps can be used to heat and regenerate desiccant rather than putting them in the oven with the Sunday roast.
Joe
