Dealing With Dew-Introducing The Digital After Dark® LensMuff™

What’s the most frustrating you have to deal with as a night photographer? If you’re like me, dew forming on your lens or telescope is near the top of the list. You spend a lot of tedious time making sure your composition is good, focus dead on, exposure settings right, intervalometer programmed correctly—on and on—only to discover that your lens is covered in dew when your time lapse or star trail is finished.

It’s enough to make you want to take up daytime photography!

Fortunately, there are solutions, although admittedly they add yet another step to the making-sure-everything-is-set-up-properly list. For some of you, this may not be an issue in the first place. If your night photography consists mostly of short exposures during twilight or shortly afterward, you probably don’t have a problem with dew. But if you shoot star trails, night time lapses, or leave your camera set up on a tripod for several minutes at a time after dark, you’ve no doubt encountered dew on your lenses if you photograph in an area that is prone to it.

LensMuff for dew prevention

The LensMuff uses hand warmer packs to prevent dew from forming on your lenses.

Before I tell you about the LensMuff™, I want to go into in a little detail about dew and the other solutions for keeping it off your lens. If you’re an old hand at dealing with dew and just want to learn about the new product, scroll on down towards the bottom.

First, let’s talk about the science behind dew formation. As you probably know, dew is water droplets that form when moisture from the air or ground condenses onto objects that have cooled to the dew point temperature. The dew point temperature is based on the relative humidity. In high RH conditions, the dew point is close to the current temperature and in low RH, the dew point is much lower than the air temperature.

This is helpful information because it provides a general idea of when dew is more likely to form. In southern states with high humidity, dew can form easily with only a minor drop in air temperature. In the desert, it generally must get much colder at night than the daytime temps for dew to form. (This happens often, by the way, so don’t think you’re going to escape dew just because you’re in the desert.)

The best way to judge the potential for dew is simply to know the dew point temperature. Meteorologists use a complex formula to determine this temperature, but you can find it out simply by checking the local weather forecast. Also, a number of Apps will calculate the dew point for you.

Knowing the dew point temperature is extremely helpful, but I can tell you from frustrating experience that you shouldn’t rely on it totally. There are simply too many variables in play, especially when you shoot in the mountains where a small change in elevation can bring you into different weather. If you carry a portable weather station around with you, you might be able to determine reliably when dew is going to form, but for the rest of us, the best approach is just to assume that it’s going to form every night and take the proper steps to combat it.

 Here are a few generalizations that might be helpful:

•   Dew forms more easily when the air is calm. Wind circulates the (usually) dryer air from higher above with the moister air near ground level, as well as circulating any warm air pockets. This helps to keep the temperature at ground (or tripod) level from reaching the dew point.

•    While a calm clear night is ripe for dew formation, dew can still form on a cloudy windy night when the relative humidity is very high.

•    If the dew point is below the freezing point, moisture condenses in the form of ice instead of water droplets. On many occasions, I’ve returned to my camera after a star-trail sequence and discovered a thin layer of ice covering the lens.

•    If you photograph in very dry environments, such as the desert, you can reasonably expect that dew won’t begin to form until well into the night. Conversely, if you shoot in very humid climates, you can expect dew to start soon after sunset.

•    It is MUCH easier to prevent dew from forming in the first place than it is to remove it after it starts. Wiping dew off the lens is not a solution. Once it starts, you’ll never keep it off by wiping with a cloth or blowing it off with a bulb blower.

 That last one is a biggie. If you think you’ll just start shooting and wait until you start seeing dew before you do anything about it, you can pretty much forget about shooting for most of the rest of the night. Once your telescope or camera lens cools to the dew point, it’s hard to warm it up again. As I mentioned above, the best approach is to assume dew is going to form and take steps from the outset to prevent it.

Star trail exposure without dew

One exposure from a star-trail series. This one is from early in the session before dew started to form.


Dew On Camera Lens

An exposure from the same star-trail session as above. This one shows the effects from dew on the lens.

There are five basic methods to combat dew:

1. Hoods
2. Fans
3. Heat guns
4. Heat strips
5. Hand warmers


The same hood that you use for blocking stray light from entering the lens is also helpful for preventing dew because it slows down cooling on the front lens element. For regular camera lenses, you should use the longest hood that will not interfere with the field of view. For a telescope, you might not need a hood that long. Twelve inches is probably plenty long enough.

You can buy specially designed hoods for cameras lenses that won’t cause vignetting. Hoods for telescopes are available, too, but you can easily make your own using cardboard or closed-cell foam (like the material used for a backpacking sleep pads). The latter works a little better because it also helps to insulate the air inside the hood. Regardless of the material you use, it’s a good idea to paint the inside using matte black paint to help prevent stray light from bouncing around.

I consider a hood to be the first line of defense against dew, but it isn’t effective as the sole method. With some wide-angle lenses, like the Nikon 14-24mm, a hood is worthless since it can’t be long enough to shield the glass properly without interfering with the field of view. Plus, the 14-24 has a big bulbous front lens element that attracts dew like Angelina Jolie attracts the paparazzi.


The idea behind a fan, like the ones used to cool computers, is to keep a constant current of air blowing across the lens to prevent dew from forming. This might actually work in low humidity situations, but the disadvantages far outweigh any advantage in my book. First, you have to have a source of power, but an even bigger problem is that you have to have a way of supporting the fan. You can’t attach it to the shooting tripod because of vibrations, so you have to set up a second tripod or something else to mount the fan to. Not something I care to deal with, especially considering that a fan might not work when there’s a lot of moisture in the air.

Heat Guns

Specialty heat guns are available to warm the optics above the dew point. They are helpful for removing dew that is already on the lens or to prevent dew for short periods, but they are not very practical. For one thing, they require a source of power (usually 12 volts), but more important is that they require regular use throughout the night. It doesn’t take long for the optics to cool back down and dew to start forming all over again. If you’re shooting a long time lapse or star-trail sequence, you’re probably going to have to use the heat gun a few times during the session, so you have to be extremely careful to keep it out of the field of view while you’re exposing.

I don’t recommend the heat gun approach for these reasons, but some people swear by them. If you want to try one, I recommend a gun made especially for the purpose. A typical hair dryer gets much too hot and can cause problems with image distortion from heat currents and even focus problems due to the optics warming up too much.

Heat Strips

You can buy special heat strips made especially for telescopes and camera lenses. This was my main weapon against dew for many years. They operate on 12-volt power and supply a constant supply of low heat to the optics. The big advantage of this method is that you can hook up the strips when you first start imaging and they will keep the optics above the dew point all night long. And they work. Usually.

The big disadvantage is that they require a constant source of 12-volt power. If you’re shooting close to your vehicle, you can run a cord to the 12-volt socket in your dash, but I don’t recommend it for all-night sessions. Car batteries are designed to deliver very powerful and quick bursts of power. If you submit them to a long slow draw, you are liable to find yourself stranded in the morning.

A better option is a true deep-cycle battery, which is designed for multiple cycles of deep discharge and recharge. Deep cycle batteries are used in golf carts and for RV auxiliary power. They are widely available and relatively inexpensive. Before you can use it, you’ll need to wire plugs onto it, set up some sort of carrying strap or container, and purchase a good charger separately. (Don’t skimp on the charger!)

A more practical solution is to buy a battery made specifically for powering portable 12-volt equipment. I use a 28 amp-hour unit from Xantrex called the Powererpack 600HD. Its design allows it to take quite a bit of abuse. It has a built-in AC inverter, comes with its own charger, and is completely sealed and maintenance free. It’s a vital piece of gear when I need 12-volt power, but it weighs about the same as the anchor on a small battleship. Not something you want to lug far from the car.

A much lighter and smaller 12-volt option is to rig up a power pack using eight D-cell alkaline batteries. Radio Shack sells plastic holders for four batteries. Wire two together in series along with a 12-volt female plug and you have a very portable 12-volt power pack. It won’t last nearly as long as the unit described above, but the one I made powers a medium-size dew heater for about twelve hours, which is not bad. The obvious disadvantage is that you have to change the batteries once they run out. If you go this route, you definitely want to use rechargeables. Also, make sure you wire the two holders in series (doubles the voltage of the two holders) and not parallel (doubles the capacity, but keeps the voltage at 6-volts). Google “series versus parallel” for instructions.

Battery Powered Dew Heater Strip

Setup showing the Dew-Not heater strip applied to camera lens and plugged into the Orion Dew Zapper Pro controller box. The controller is plugged into a 12-volt battery.

You’ll need a heater strip AND a controller. Most of the companies that sell strips also have their own controller, but you can buy strips from one company and the controller from another. Just make sure that the controller you get has a fuse to prevent overloading. The controller I use is Orion Dew Zapper Pro.

Perhaps the best controller you can get is the DewBuster. It uses a thermostat to control the heat strip automatically and keep the optics slightly above air temperature. The DewBuster website provides a wealth of information about controlling dew, including detailed instructions for making your own heat strips.

The strip I use is made by Dew-Not, a relative newcomer to the market. Kendrick was (I think) the first company to sell dew strips and I used their products for many years, although with quite a bit of frustration. I kept having to replace the strips because the wires pulled loose. One night, a strip shorted out and burned up the controller. I was a few feet away and started smelling smoke, but by the time I figured out where it was coming from, the guts of controller box had melted. The next day, I decided to shop around for a different strip and controller. I should emphasize that the Kendrick strips and controller I was using were very early models. I think they have totally redesigned their products and I’m sure they are much better quality than the ones I had. However, I am also sure that their products are much more expensive than those from Dew-Not.

My Dew-Not strip is model number DN004, which is 13 inches long and costs less than $30. In the world of dew heater strips, this is a steal. You might not need a strip this long. The DN004 is the right length for my Nikon 14-24mm, which has a huge front element. I could use a shorter strip for other lenses and save a little power in the process, but I didn’t want to buy and carry more than one strip and so I got the one that would fit all my lenses. I still have a few old Kendrick strips for those times when I set up two cameras at the same time. I’m hoping that the fuse in the new Dew Zapper Pro controller will actually work if one of those old strips decides to go rogue on me again.

As far as I know, all of the commercially available heat strips use the same RCA-type connectors and they will fit any brand of controller, but you should check to make sure before you buy.

Dew heater strips work very well, but about the only time I use them nowadays is when I shoot around the house. I rarely carry the Powerpack battery with me in the truck anymore. Instead of the heat strips, I started using hand warmer packs.

Hand Warmers

Sometimes low tech is the best solution, and for me, this is definitely one of those times. Those little chemical hand warmer packets produce enough heat to stop dew from forming for several hours, and often all night long. Hand warmers have many advantages over the other methods, the biggest for me being convenience. I can stuff a few hand warmers in my pack and be ready for the dew when I’m miles from the car. They are also quick to apply and generally less expensive than heat strips.

The only real disadvantage is that you have to throw away the packets after each usage and start again with new ones. But at only about $1.50 per pair, you can fight a lot of dew before you reach the price of one dew heater and controller box, not to mention a 12-volt battery if you don’t already have one.

Hand Warmer Packs

Most any chemical hand warmer pack will help keep dew from forming on your lens. This is the type I use.

The first time I used hand warmers I attached them around the lens using a rubber band. The second time I used gaffer tape. Neither method being the poster boy for convenience, I made a holder for the packets using a piece fleece fabric and Velcro. I simply laid the packets onto the fabric and wrapped it up like a burrito, securing it on the lens with the Velcro. It worked fine, but it didn’t win any MacGyver awards and it took a little too long to set up.

After about the second time of wrapping warmers in fleece, I started thinking of a better solution using the following criteria:


• It had to attached and remove in seconds.
• It must be perfectly secure on the lens.
• It had to last a long time.
• The material and design must maximize the heat, limiting its dissipation into the air.
• It must be made of weather-resistant material since it would be exposed to the elements night after night.
• It must not scratch or harm the lens in any manner.
• It had to accommodate one, two, or three hand warmers at a time.
• If I were to sell them, it had to be reasonably priced.
• It had to look good. (Yeah, I know. But sometimes my lenses can be a little vain.)

Introducing the LensMuff™

Meeting every one of these criteria was going to be a tall order. Designing the LensMuff™ was easy, but I was concerned that I wouldn’t be able to find a company that could produce them at a good price. Fortunately, I lucked up. I found a local company that offers vocational training for people with disabilities. As a non-profit, they only needed to charge enough to cover their expenses, so they were able to manufacture them at a reasonable price. And, wonderfully, I get the added benefit of knowing that I’m helping the cause for my neighbors with disabilities.

LensMuff Camera Lens Dew Prevention

LensMuff attached to the Nikon 14-24mm lens.

For general night and time-lapse photography, the LensMuff™ it is the perfect solution. It sells for only $24.95 and it will last a lifetime. (If it doesn’t, I’ll replace it.) It’s easily packable, being the size of an empty billfold. The outer cover is made of tough, weather-resistant pack cloth with a long, 1-inch-wide strip of Velcro to secure it to the lens.

You can use up to three warmers at a time with the LensMuff™. For smaller lenses, such as the 16mm fisheye that I sometimes use, one warmer might be enough. For most lenses, you’ll want to use two warmers at a time. For lenses that have large front elements, like the Nikon 14-24mm, I use three warmers.

You’ll need to buy your own hand warmers to use in the LensMuff™. If you live in a region that has cold winters, you can find them in any outdoor store or Walmart. They run about $1.50 per pair, but you can save a lot by buying them by the case. There are several different types, but most any of them will work fine. I use Grabber Large 10+ Hour Hand Warmers and buy them by the case of 40. In summer and by the case, you can find them for $1 per pair or less.

In addition to warming your lenses, the LensMuff™ is great for keeping your camera batteries warm, or any other small object that you need to heat. You can wrap it around your ankles or wrists to help keep your feet and hands warm, and even around your neck if you don’t mind looking like you just had neck surgery.

LensMuff Camera Lens Dew Prevention

Outside and inside view of the LensMuff. Hand warmer packs are inserted into pockets on the inside.

For astrophotographers who photograph or view the night sky through telescopes, the LensMuff™ will work for you as well, but you’ll probably need to use two or more of them to cover your lens or mirror since the LensMuff™ measures only 12 inches long. One will probably be all you need for the finder scope and it’s more than enough for the eyepiece. In all honesty, though, if you’re shooting through a telescope, you’ll probably be better off using heater strips whenever you have easy access to 12-volt power.

Oh, one more little tidbit of advice that applies regardless of which method you use to fight dew. Don’t shine a flashlight into the lens to check for dew while the exposure is going on. Go ahead and laugh, but I promise you, it’s going to happen sooner or later if you don’t pay close attention to what you’re doing. And, unfortunately, I know of no way to determine if there is any dew on the lens without shining a light on it, so you just have to make sure you set up everything properly and then hope for the best until the exposure is finished.

Now, choose your weapon and do away with the dew!

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