At one point or another, every astrophotographer will experience the dreaded lens dew while taking photographs of the night sky. They’ll be minding their own business trying to capture meteors, beautiful Aurora Borealis displays or just a simple time lapse when a layer of moisture appears on the lens glass and turns every captured image into a blobby mess.
This moisture is dew, a normal atmospheric occurrence that we will have all no doubt seen on early morning grass or the inside of poorly insulated house windows. In the following video we can see a short time lapse of the night sky taken over the course of about 40 minutes. Almost straight away a layer of moisture begins to appear on the lens. By the end the frame is so fogged only the brightest stars are visible with everything else blurred.
The trick to solving this common problem is by simply understanding what is happening.
If the temperature of the glass on your lens drops below the ambient temperature of the surroundings, moisture will form. Ergo, to prevent this you need to keep your lens warm.
This may seem like a strange suggestion, however if you’re shooting in your back yard it’s likely you’ll have a hairdryer close to hand. You’ll be able to take your camera back inside intermittently and give it a quick blast to up its temperature.
- Car Heater
If you’re out on location and didn’t hike or get the bus you’ll have a built in lens heater in your car. Just as with the hairdryer, bring your lens back in to the warm before the dew starts to form.
- Shoot indoors
As we pointed out in a previous post, if you’re in the right location and your window faces a clear non light polluted view then the problem is less likely to occur as buildings tend to be heated.
- DIY projects
If you’re handy with craft making or stitching why not try and make your own solution? Wrap a sheath around your lens with hand warmers inside, or build a large glass enclosure that will act as the camera’s own personal atmosphere.
- Dew shields
These are typically designed for telescopes and work by using a lining of felt in the inside of a tube to absorb moisture in the air. The Astrozap range are for telescopes with much wider dimensions than lenses however the principle in which they work is the same so it could work as an answer to another DIY project.
- Dedicated lens heaters
None of the large camera brands have a dedicated lens heating solution, however there are a multitude of independent suppliers that can help prevent that pesky dew. The Lens Muff™ is designed to hold hand warmers which could prove problematic and expensive over time. The Kendrick Camera Cozy is an altogether more complete approach that keeps the lens at a constant temperature using batteries which you can recharge at the end of a session.
If you have any solutions of your own or discover a product that you feel should be mentioned here, please drop us a line in the comments so we can update this post.
Good luck & clear skies!