Jump to content


- - - - -

Bustin' Dew for Good with The Dew BUSTER

What do you do about dew? Do you worry about dew?

You do if you live in a location where high humidity makes nature's little, damp gift a prime enemy of the working observer. Since I live on the Gulf of Mexico coast, dew is an omnipresent fact of my observing life. Many a promising Summer observing session has been ruined over the years by fogged, dripping, dew-SLIMEY optics! But with the release of the Dew Buster Controller I've gone nuclear in my war against midnight optics baths!

What's a Dew Buster? How does it bust dew?

Let's not get ahead of the story. Let me turn back the clock to those stone-age days of amateur astronomy, the early 70s. There was this new scope being advertised in Sky and Telescope. One that had hit amateur astronomy like a thunderbolt, the Schmidt Cassegrain in the form of the original Orange Tube C8. The new, mass-produced Celestron was the telescope that a lot of us had been waiting for. It combined elegant, useful features into a package that virtually made it a portable observatory. Oh! how happy I was when I got my new Celestron out into the field for the first time on a clear July evening.

I was happy for a while, anyway.

After a few hours I noticed that stars weren't as sharp as they had been. And the brighter ones were developing foggy little haloes. Was something wrong with my new baby? Yep. A look at the corrector showed it to be a dripping mess. Thus ended my first observing run with the Orange Tube. It was a nice demonstration of what happens when you point a big lens at the heat-sucking sky in a humid environment: dew "falls" (or "forms," really ). Since it appeared that I was back in the Southeastern United States to stay, I knew I had to do something to make my Summer (and Fall, Spring and sometimes Winter) evenings less miserable dew-wise. But what?

First Blood.

Step one was one of those thingies like I saw on the ends of my buddies' Unitron refractors: dewshields. A dew shield is a simple thing that works on a simple principle. It's nothing more than an extension of the tube in front of the corrector (or objective). It works by shielding the lens from the normal, full 180 degree view of warmth-sucking space that it would otherwise be looking at. For people in some parts of the country, a dewshield is all that's needed. For areas with low humidity and light dew, you can probably get away with just a shield. Even if you live in a dew-heavy area, a dewshield is a good investment since it serves as a light shield and tends to keep inquisitive fingers off your corrector plate.

Things heat up.

For observing locations where dew is heavy and dewshields alone eventually fail to keep optics dry (usually just at the moment when you're finally about to track down the Horsehead in your C8), there's just one way to prevent dew: keep the corrector (or objective, or eyepiece, or whatever) warmer than the ambient temperature. It doesn't have to be much warmer-just warmer. Various devices came along to do just that. First were the blow dryers. I mean it! Just a blow dryer you swiped from Sis or girlfriend (or your own, maybe--these were the 70s, the days of Big Hair for everybody). This really worked. So long as you did it right. You couldn't pump 1500 watts onto the scope-do that and you'd find that it took quite some time for your optics to reacclimatize. You had to use gentle heat, and you had to have a source of AC or a big battery/inverter combo. A better choice for astronomy was the little 12volt blow dryers, which were sold as window defrosters in truck stops or, quickly, as "dew zappers" by enterprising scope merchants. But this was not the ideal solution, either. Sure, a zapper would get rid of the dew, but in damp conditions it becomes real old, real soon to have to keep zapping the corrector every couple of minutes.


We amateurs are not known to let a problem go unsolved forever when it comes to our beloved equipment-maybe a decade or two, but no more! Late astronomy entrepreneur Roger Tuthill turned things up a notch by introducting his "No-Dew Heated Dew-Caps." These things worked, more or less, but were a little clunky. And expensive--at about a hundred bucks a pop (C8 size) in big 1980s dollars. But a better idea was already coming off amateur kitchen tables. Eventually, somebody cracked the code as regards dew. Make yourself a heating element to go around the corrector plate. Make it from a string of resistors Work things out so that just a leetle heat is applied, just enough to keep the corrector dry. Glue 'em around the end of the tube. Or maybe tape 'em in place.

No doubt there were a couple of these "dew heaters" made commercially before Jim Kendrick came along, but he was the man who really brought the idea to fruition. Canadian artist Kendrick was a new scope owner who couldn't believe that these silly, SILLY amateur astronomers hadn't come up with a better way to keep dew off a C8.

If nobody else would, Jim would. By the early 90s he was selling the "Kendrick Dew Remover System." And what a system it was! He produced heating elements that looked good and worked well, with the active elements being built into nice cloth strips that were fastened around your corrector/objective or other optics with Velcro. From the beginning, he made heaters for everything from a .965" eyepiece to a C14. And, most importantly, you didn't just plug these into a 12volt battery as you had the kitchen table masterpieces or the earliest commercial dew heaters, you plugged them into a controller. This allowed you to vary the power to the heaters, keeping your optics dry and your battery alive for a whole observing run! And man did the Kendrick System work! I still remember my first use of the Kendricks on my C8. At a horribly dewy star party, I, the only person with this new-fangled "System," had the only undewed scope left on the field by midnight.

Nothin' is perfect.

So the Kendrick System is all you need? Can't be improved upon? That's what I thought 'til last Fall. I was at our local star party, the Deep South Regional Star Gaze, one humid PM when Louisiana amateur Ron Keating trotted over holding what I at first thought was a Kendrick controller. Nope, said Ron, this was a Dew Buster. A "replacement" or "alternative" controller for use with the Kendrick heating elements. Ron told me he really had something, he thought, and with the help of some associates, was planning on putting the controller (and maybe some of his own heating strips) into production. "Why?" said Skeptical Old Rod. "You can't improve on the Kendrick System, can you?" Ron said the thought he could, and had, and proceeded to tell me the how and why.

Goliath Kendrick has a weak spot?

When people first see the knob on the Kendrick controller, they just naturally assume it varies the temperature of the heating elements. It must be a thermostat, right? Wrong. As is clearly stated in the Kendrick literature, the system doesn't know anything about the temperature. The farther you advance the control, the longer power is applied to the heating elements. On "low," they get power 40% of the time. Crank it up to "full" and current flows constantly. This works OK, but it is not the perfect situation. Most people, seeing dew beginning to form on the tube of the scope, have a tendency to crank up the Kendrick all the way until the heater elements feel warm to the touch. This is bad for several reasons. First, the heaters don't have to be hot to work, they just have to keep the lens above ambient. Turning them up may introduce seeing-destroying air currents or may even cause the corrector to deform slightly. And you will suck down the battery in a hurry.

Out Kendricking the Kendrick.

The Dew Buster out-does the Kendrick by doing what you first assumed the Kendrick would; the dew buster senses the temperature and maintains it at a constant figure. It's just like the thermostat on your central heater at home. Once you've got an idea of how damp the evening will be, you set the controller to the required temperature above ambient air temperature (the dial's scale indicates degrees above ambient--see figure 1) and forget it. The Buster will maintain that temperature all night long. And your scope will remain dew free. And you'll use no more power from your poor battery than need be. And you won't get the corrector (or objective if you're a refractor type) too hot. And, best of all, once you've got the Buster set you won't have to WORRY about it or the dew any more!

How well did it work at Pine Lake?

I had a chance to use Ron's prototype the last evening of the star party, and was impressed. It kept my optics dry at any rate. But I was more focused on observing than on a dew controller, and was tired from several late-nighters. I did mention to Ron that if he'd send me a production model once he got going, I'd let the folks know what I thought of it. He replied in the affirmative and that was that and there matters stood for a couple of months. One March afternoon, however, a little package appeared at my front door. "Ahhhh…astrogoodies from somebody," I said in my best Homer-Simpson-meets-the-donuts voice. Ripping the box open revealed a full-up Dew Buster.

It's not an overstatement to say I was quite impressed. I've seen a lot of garage-type astro products over the years, some of them really good, but almost all having that "homebrew" look. Not the Dew Buster. It looked every bit as "professional" as the Kendrick to me. Since it had been some months since I'd seen the prototype, though, I was surprised that, when you got beyond the good looks it shares with the K, how different this controller is.

For Starters, in place of the Kendrick's 4 output plugs, this sucker has 8. And that's a good thing if you have heaters for everything and lots of piggyback stuff riding on your OTA like I do. Sure, you can use splitters for the Kendrick outputs, but that's a clumsy solution. I further noted that 6 of the elements were labeled "AUX," while 2 were labeled "AUTO." What was up with that?

A glance at the (simple, but clear) instruction manual reveals that the 6 AUX jacks are not temperature controlled. These are intended for your "accessory" heaters: eyepieces, finder objectives, Telrads, whatever. The heaters used for these items are relatively small and of low wattage. They don't draw a lot of battery power, so merely cycling them off and on like the Kendrick controller does its heaters does not adversely affect battery life. Also, getting a finder objective or eyepiece a little hotter than necessary is really not a huge problem. These outputs supply current to the heaters 40% if the time, just like the Kendrick Controller at its lowest setting. But they have an added, very nice feature. When the Dew Buster is first turned on, it supplies "boost power" to the AUX jacks. This initial 100% power application means that the accessory heaters warm up quickly. If they started out at 40% it would take a heck of a long time to get them warm enough, making the formation of dew a possibility.

But the stars of the show are the 2 AUTO jacks. These AUTO receptacles work in conjunction with a temperature probe that plugs into a mini-jack on the top right surface of the Buster. The probe incorporates 2 sensors; one is placed under your corrector heater strip (see figure 2). The other senses ambient air temperature. When everything is set up and working, the AUTO output keeps your corrector at a selectable temperature of from 0 to 25 degrees above ambient (depending on the setting of the temperature controller knob) by pulsing power to the heater at from 0 to 100% of the time as NEEDED.

What else is different about the Dew Buster? In place of the Kendrick's single red power light, this baby has three LEDs, two reds and a yellow. The left-most indicator, "AUX" indicates power is applied to the AUX heaters, as you'd guess. The right-most LED blinks as current flows to the temperature-controlled AUTO jacks as required. The yellow LED is the system's low-battery indicator, and is just the outward indicator for a rather sophisticated low-power management system. At 11.5 volts, the yellow LED glows dimly, indicating your battery has just about had it. When voltage drops to about 11.2V, the LED glows brightly and power to the heaters is immediately shut down. Since many lead acid batteries will be ruined if you drain them too far, this feature may save you from buying another lawn-tractor battery, something that's happened to me more than once.

The Dew Buster comes with a nice, long (about 10') power cord terminated in a heavy duty cigarette-lighter-type male plug. Ron says that the plug is rated for 10 amps, more than most C14s covered with heaters will need, but that the Buster itself is rated for a whopping 20 amps internally, and can be special-ordered with an even heavier-duty power cord.

But how would this fancy-shmancy thing work in the real world? I set out to find out. The first opportunity I had to try the Buster was at the March Members-Only-Star-Party that I run for my club, the Mobile Astronomical Society, at our Pine Lake facility. Yep, I said "lake." Combine an unseasonably warm March night, a body of water only 100 meters away, and very high humidity, and I figured the Buster would be put to the ultimate test.

The first order of business was getting the system set-up on my Celestron Ultima C8. I was a little leery of routing yet another wire on the scope-the temperature probe-but this device is connected to the controller with comparatively light-gauge cable, and didn't make my scope look any more like an octopus than it already does. All the heating elements went on as normal, with everything but the corrector heater plugging into the AUX jacks. Since the night was sure to be WET, I'd brought out the complete arsenal, with heaters for finder objective, finder eyepiece, Telrad and main eyepiece. Installing the C8's corrector heater was slightly different on this night, since I knew the temperature sensor would be involved. A glance at the instructions showed that the "telescope sensor" was to be placed underneath the corrector heater strip and held in place with a small clip. The dew shield would then be placed over the heater and sensor. The ambient air sensor, which extends out from the telescope sensor, would extend forward of the scope sensor and must not touch the scope. Since I use a hard-plastic dew shield, I had to modify these instructions slightly, but everything worked just as advertised (figure 3).

And that's the bottom line. How did everything work? Incredibly well. My scope optics were free of dew all evening long. I started out at 10 degrees above ambient, didn't touch the control all night long, and basically just forgot about the nice Buster. I'd occasionally glance at the controller just to be reassured by the friendly pulsing "AUTO" LED that everything was well. I was running the system off a small 7 amp-hour battery pack that I like to use with the C8, since it's nice and light. A couple of times I've come close to draining it with the Kendrick after a full night of observing. Not with the Dew Buster. At the end of the evening, my wimpy little battery pack still had plenty of get-up-and-go!

By chance, a buddy was set-up next to me with a NexStar 5 equipped with the Kendrick System. I noticed that he kept fiddling with his controller off and on as the dew got heavier and heavier and heavier.

"What's wrong?" says I.

"Just trying to keep this darned heavy dew off…but I don't want to get the corrector too hot," says he. "You don't seem to be having any trouble with dew tonight."

"Nope," says I. "I've got a SECRET WEAPON."

Should you get a Dew Buster? That depends. If you live where the dew ain't bad, you can probably get by with the Kendrick controller at 75 dollars (plus the cost for heaters, naturally). It's a fine, well-made piece of equipment. Mine's been providing excellent service for 7 years now. And the Dew Buster controller does cost more, at about $150.00. The Buster is not a "replacement" for the excellent Kendrick; it's the next step up, a premium alternative.

But the Dew Buster works better. It's not just the cool lights, or the temperature sensors, or the extra jacks. All that is just icing. It does a better job of keeping your optics dry under demanding conditions. And if you, like me, live in a virtual swamp, you owe it to yourself to stop losing observing time because of dewed optics, stop losing hair trying to get your dew heaters running right, and losing money buying yet another K-mart tractor battery. At less than the cost of a mid-grade eyepiece, how can you go wrong with the Dew Buster? Well, you can't. Go get one, boys and girls.

How do you get one? Just go here and all your questions will be answered: http://www.gbronline.com/ronkeating/dewbuster.html

Note: The skies have not been good this Spring, so I've only had a chance to try the Buster with my C8. I now have a NexStar 11 (C11) here, and will annotate this review with a report on its use with a larger aperture scope just as soon as possible.

  • G4Jon, n2068dd, The Electrician and 1 other like this


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics