Fogged lens

[hobbymandoc]

This weekend while shooting ducks with my 400 mm fixed lens, I noticed the lens would repeatedly fog over. Finally called it quits and left - until the afternoon and shot more. Problem was a high humidity, foggy location in the morning. Had been sitting for over an hour (before sunrise - to get in place) so it is not a matter of acute temperature change to the outdoors.

What is a good remedy? It would fog over after cleaning with a lens cloth.

[CP140]

My guess (it was a still day with virtually no wind?) is....

Sitting there before sunrise, your camera/lens reached ambient temperature. Once sunrise occurred, the ambient temp and/or humidity started to rise which meant your camera was now colder than the dew point of the surrounding air. As the sun hits the ground, it warms the ground a little bit and all the moisture at ground level now gets pulled into that thin layer of slightly warmer air where it lies in wait for the first cold object (car window or camera/lens) to attach itself to or until it mixes with slightly colder air above the earth's surface and forms fog.

Cold (camera/lens) relative to the surrounding air allowed for moisture to condense. Similar to what would happen if you were outside in a (relatively) cold environment and brought the camera indoors.

One possible option in this situation might be to keep the camera above ambient temperature... inside a fleece bag with one of those little hunter's warming packs to keep it warm and happy.... pull it out, shoot, put it back...

If on a tripod, drape an insulating blanket/cloth over it and tuck the warming pack in with the camera/lens

I will of course defer to others who have experienced it firsthand as I am rarely ever up that early...

Regards

[pnodrog]

It is a problem I have encountered often. Get out of a car with nice cooling air conditioning on to take a photo and bang you can hardly see a thing through the lens. While traveling in India I sat with my hand clamped over the lens hood to try and keep the front element warm with limited success. A hot house or butterfly house often causes the same problem.

You need to keep your camera and lens temperature slightly above ambient. Keep a small non leaking thermos flask or warming pad in a compartment of your camera bag. Do not store your camera gear in the car overnight. Try and start the day with your camera and lenses warm even if you need to hug them under your jacket. I will follow this thread with interest.

[rawill]

Try this, some dishwash on a softcloth and wipe the lens. A light brush off afterwards.

It is a common trick in motor racing to stop visors fogging up.
You can also by some aftermarket liquids to do this. Go to an auto shop and talk about Rainex or similar.

[pnodrog]

I would be very wary of putting any detergent etc on the coating of the front element of the lens. If you try it try it on a protective UV filter that will be cheaper to replace. However one of the problems is as you zoom to telephoto your lens will suck the cold air in and you can end up with fogging on an internal element which will take forever to go away. Best to have the whole lens warm. When driving to location in a nice warm car make sure you have the camera bag open. The foam protective padding insulates the camera very effectively if the bag is closed and the camera/lens will remain cold.

[rawill]

Fair point - I would hate to damage a protective coating!~!

[CP140]

I too would be reluctant to put chemicals/soap on the lens and the zooming/focusing pulling cold air into the internal workings of the lens isn't something I had even thought of (thanks for that BTW).

Detergents, despite what the manufacturers might want you to believe, are not gentle... ask any nurse who has to wash her hands many times a shift.

Best(?) options... if going into the cold, keep it warm... if going into the warm, keep it tightly wrapped and loaded with desiccant...

[MilT0s]

Dishwash can not damage a lens coating, actually it is the best way to clean it.

I wouldn't recomment it as a solution however as it could just go everywhere including the edges, threads, into the interior of the barrel and stay there for ever. A tiny amount on filter sounds like a good idea if your are extremely carefull.

[MilT0s]

I was curious if any anti-fog products for camera lens exists so I found this:

Nikon 8073 Fog Eliminator


Not sure if is a Nikon original product or if it actually works, I suggest you read the amazon comments and never use it straight on the lens front element but rather on a (cheap?) filter. Those products usually leave a tiny oil-like film but I have no idea what's the case for this one.

[Manfred M]

I personally would never use a dishwashing liquid anywhere near my lens. The reason being is that they all contain a chemical, sodium laureth sulphate (SLS), which has both desirable properties; SLS is a wetting agent, which means it reduces the surface tension in water which prevents the formation of drops, i.e. the desired effect here. As well, it is a detergent, which will break down the lubricants used in your camera, should it get in as well. It also will leave a film, unless it is thoroughly rinsed off.

As Mitos has already stated. if it gets into the filter mounting threads of your lens, it will be difficult to remove safely.

Condensation will form whenever the temperature of an object is below the dew point where you are shooting. Relative humidity, atmospheric pressue and the ambient temperature all determine exactly when this will occur.

I've tried a commercial lens cloth containing a wetting agent, but as Mitos has mentioned, it will leave a thin deposit. I found that the best way to remove it was with either a commercial lens cleaner or a home-made mixture that is 1/3 water, 1/3 isopropyl alcohol and 1/3 household ammonia.

Having a lens that is warmer than the ambient temperature is probably the best way to do this, but frankly is a pain to achieve when out in the field.

[MilT0s]

As well, it is a detergent, which will break down the lubricants used in your camera, should it get in as well.

That's a very good point Manfred.

BTW it's Miltos, not Mitos, or if you like Miltiades that is my full name

[rawill]

Well it seems most/all opinions put the "Rainex" type idea down the drain!

[Manfred M]

Sorry about that Miltos - The old eyes are not as good as they used to be and I had to put my nose almost to the screen to see the il in your name proprerly.

[jcuknz]

Another solution ... don't get up and about before the crack of dawn

[hobbymandoc]

Thank you all for your great advice and my wife and some of my friends would likely agree that I shouldn't be up before the crack of dawn. The explanations of keeping the lens a bit warmer is likely the best advice and could be achieved with a commercial hand warmer and camo cloth. As a diver, we find dish washing soaps work for reducing fog in our mask but I too think there are inherent risk with using it on an expensive lens. Perhaps the Nikon cloth is a good option too but I have no personal knowledge about those other than what their advertisement says. Will make attempts to put your advice to work this weekend, but weather may be kinder this time out. Thanks to each of you for enlightening me on the subject.

[Inkanyezi]

I think that better understanding is needed here.

Fogging depends on two factors, one of them is decreasing temperature. We cannot solve that problem by warming the lens, its temperature will inevitably decrease more, the more we heat it. Maybe it works as long as the lens really is hot, but sooner or later, it will become fogged if we don't check the other factor as well.

The other factor is humidity. It might seem as we could counter it by heating the lens or its environment, but we cannot.

The reason that heat won't help is that hot air can contain more water than cold air, and when we keep our lens hot, we also keep its humidity dissolved in the air - inside the lens. For a 400 mm lens, that is a considerable amount of water, because it contains a lot of air. When the lens, containing humid air, cools down - inevitably when we take it out from the heated condition - some of its parts will become cooler, and when the temperature of its front glass decreases, the stored water in the air inside the lens will condense on the inside of the front element.

So the solution actually is contrary. We need to keep the air inside the lens dry. It can be accomplished in several ways, but preferably, there shall not be a large temperature difference from the outside, and, importantly, a lower temperature is preferred.

The simplest way to get the water out is to use desiccant. A bag of desiccant inside the lens itself, as for example a cylindrical one that is removed when the lens is taken out, or a tube-shaped desiccant container, that can stay in the lens barrel when it is used. If you sew a tubular desiccant container of black velvet, which can be put into the lens barrel, and you store the lens in a bag that does not communicate water to any great extent, you can keep its inside dry, and no condensation will form on the inside of it.

Condensation, water inside the lens, is a reason for fungus growth, so storing the lens in a dry condition will give it longer life and sharper images with less flare.

Desiccant may be dried in an oven when it has collected water, and it can be reused over and over.

[pnodrog]

Fog occurs when the relative humidity is close to 100%. At this stage the moisture in the air will condense on any surface that is colder than the air. The rate of exchange between environmental air and the internal air in the lens will be dependant on lens design, focussing method and amount of zooming done. For a zoom lens the original internal air may be as low as 25% of the new air volume after the first full zoom. The humidity of the air that existed within the lens before it started to be used will eventually become irrelevant. To prevent condensation the lens needs to be no less and preferably above the ambient air temperature.

If you fully extend the zoom and manually adjust the focus to the closest distance before you enter a foggy environment you will at least prevent a sudden intake of high humidity air.

In ultra cold environments where both the humidity and temperatures are low the water content of any humid air within the lens will probably start condensing first on the inside of the lens's metal barrel and later on the front element of the lens. Under these conditions unless you started in room with low humidity warm air extending the zoom and focus before you were brave enough to go outside would be of no benefit.

The correct storage of lenses is certainly well worth doing.

[Colin Southern]

I would be very wary of putting any detergent etc on the coating of the front element of the lens.

In my experience, dishwashing liquid is actually quite corrosive -- I'd hate to find that it had corroded a filter thread or the likes.

If anything, just do it to a protective UV filter that's attached.

[pnodrog]

It may seem that Urban (post #16) and myself are offering conflicting advice. We are not. My approach is a simple and practical approach that works in relatively mild climates.

If you have a lens in a room at 20degC at 20%RH you can operate that lens down to about -4degC before any condensation will occur due to the moisture held by its internal air or become more of a problem than the air from the foggy conditions you encounter.

The following is a link to tables that may help you workout how you need to operate in your conditions. http://www.tis-gdv.de/tis_e/misc/klima.htm

[Manfred M]

In my experience, dishwashing liquid is actually quite corrosive -- I'd hate to find that it had corroded a filter thread or the likes.

If anything, just do it to a protective UV filter that's attached.

In that case Colin. I hope you are very careful when you wash your hair, as the active ingredient (sodium laureth sulphate) in dishwashing liquid is the same as in shampoo and for that matter as in liquid soap. Most of the rest of the chemicals make it look and smell nice.