Eyepieces fogging up.

[Jim Smith]

About two seconds after I raise my Canon 10x30 IS binoculars to my eyes, the eyepiece lenses fog over, blurring the view. This does not happen with my Olympus DPS I 8x40s. They stay clear. I view without glasses.

Does anybody have any ideas as to why this might be? Different lens coatings?

Thanks in advance, Jim

Edited September 24, 2019 by Jim Smith

[Ruud]

Two things play a role: dew point and collection kernels.

Dew point: For every surface at a temperature below boiling point, there is a maximum humidity beyond which condensation will try to form on it. Maybe the eye lenses of the Canon are cooler than those of the Olympus. Do you carry the Olympus closer to your chest? Also, if the Olympus allows more ventilation between the eye lenses and your eyes, humidity has less chance of building up. Do the Canon eye caps trap the air when held close to the eye?

Collection kernels: Condensation has to start somewhere. If there is more dust on the lenses of the Canon or if their coating is less smooth, condensation will form more readily on them.

If you keep your binocular close to your chest (and on colder nights under your coat) they have a better chance of being warm enough to prevent condensation.

[Jim Smith]

Thanks for the thoughts Ruud. I think the difference in fogging may be mostly due to the ventilation factor. I've just checked and the eyecups on the Olympus binoculars are significantly wider than the Canon ones. I can see more daylight when using them. I would think more ouside air can circulate over the lenses as you suspected.

It's interesting that this makes such a big difference in usability. I prefer the Canons in many ways, but if I can't see through them...