The USM,will the lubricating oil evaporate?

[lake_0571]

Some of the inner glass of my frequently used lenses as 35L,70-200/2.8Lis seems to have oil fogs,hence the

question.Will high tempriture aggravate?Thanks for your advice.

[sarah_fox]

I would think the temperature would have to get awfully high.

 

It's probably of little help, but I once left a 135 Takumar in a hot car in West Texas in full sun. The temperature got high enough to melt a couple of plastic items near the lens. The lens came out fine, with no fogging of the elements. Another photonet member recently baked his 30D camera and lens at 115-120F in an electric oven for 3 or 4 hr to dry it out. I don't remember the type of lens he had, but I vaguely remember it was a nice one -- probably with USM. His optics came out clear, and the camera was restored to functionality.

 

As with any evaporation/condensation issue, the lubricant would have to be hotter than the lens elements for it to condense on them.

[mark u]

Lubricating oils and greases have very high boiling point ranges and flash points (vapour concentration sufficient to be flammable): after all they are designed to work in some really hot environments - think of a jet engine for example. They are made from fractions of petroleum that are the last to boil off (usually under quite strong vacuum to avoid cracking of the molecules). You will not have reached such temperatures unless you were photographing industrial furnaces at close range - in which case the lens glass probably became hot enough to distort and flow. Fogging is almost certainly water based condensation, although you may need to take care that you aren't providing ideal conditions for fungal growth. Have Canon do a CLA before you get really expensive problems. Make sure you have your lenses in ziplock bags and leave them there to acclimatise if you are moving between indoors and outdoors at very different temperatures to avoid dew/condensation.

[jcolwell]

What are "oil fogs" ?

[alan_myers]

Hi,

 

I doubt it's related to the lubricating grease at all.

 

Most lens lubricants are now synthetic, which is even more resistant to thinning and "gassing off" (or thickening under cold conditions).

 

In all likelihood, what you are seeing is just what Mark wrote... Fogging related to water, moisture or high humidity, and evaporation/condensation .

 

I'd say it's time to have that lens cleaned!

[lake_0571]

Thanks for all your advices again.