Hi
I’m interested to know how you protect your cameras, eyepieces and scopes from getting moisture on them or getting inside them.
Primarily i’m concerned about this happening when the equipment is brought back into a warm house, but what is the risk of moisture getting inside equipment when outside?
Does having equipment outside when temperature is at dew point carry a high risk?
Thanks
Mark
A dew strap (or two depending on size) is all thats needed to keep dew from forming on the objective, inside and out. This is my only real area of concern as the dew droplets can leave residue on the objective.
The camera itself, as long as it’s on, should never accumulate dew. Rare occasions it can form on the window itself. Small amounts of dew may accumulate on the rest of the OTA, but it’s generally pretty light, but it’s certainly not going to damage anything. A mini PC will generate enough heat to keep itself dew free.
My equipment stays outside 24/7 in the moist, damp environment that is North Carolina. The only place where you can tell on any of my equipment is the alt/az knobs on my EQ6’s, they rust easily. You should not be getting any dew when you bring your gear inside because any air conditioning will lower the dewpoint/relative humidity. Years of my gear living outside in the humidity, spiders and bugs are a bigger concern than dew.
Brian Puhl · Apr 29, 2026, 11:16 AM
A dew strap (or two depending on size) is all thats needed to keep dew from forming on the objective, inside and out. This is my only real area of concern as the dew droplets can leave residue on the objective.
The camera itself, as long as it’s on, should never accumulate dew. Rare occasions it can form on the window itself. Small amounts of dew may accumulate on the rest of the OTA, but it’s generally pretty light, but it’s certainly not going to damage anything. A mini PC will generate enough heat to keep itself dew free.
My equipment stays outside 24/7 in the moist, damp environment that is North Carolina. The only place where you can tell on any of my equipment is the alt/az knobs on my EQ6’s, they rust easily. You should not be getting any dew when you bring your gear inside because any air conditioning will lower the dewpoint/relative humidity. Years of my gear living outside in the humidity, spiders and bugs are a bigger concern than dew.
Thanks Brian.
I live in the UK and most houses don’t have air conditioning (although some recent summers, I wish I did!). But, it's reasonably warm, so I tend to just lay out everything on the bed for an hour or so, to let any moisture that forms when coming in from the cold, disappear.
Bringing cold optics into a warm environment can cause condensation, though I don’t know what the delta T needs to be. When I was bringing my scope in after imaging (before I built an observatory), I would put it into a trash bag first and seal it as well as I could. I also brought it into an unheated basement, but still the delta T could be as much as 60 deg F and I never had a condensation issue.
Cheers,
Scott
If you find dew on the equipment then you know it has reached the dew point overnight and so it was this morning, with the laptop lids fully dripping (in two cases out of 3 as one is set not to ever turn off the display) as well as most of the exposed areas of the scopes ( but not the lenses!). For refractors in general a dew-strap is almost always a necessity and so I do have half a score of them for both guide-scopes and lenses. For reflectors with open tubes (read newts) a mixtures of forced rear cell ventilation and insulating dew-shield/cladding do the trick of keeping dew from forming on either the secondary or the primary. Cameras are always internally generating heat but dew (or frost!) can occur on the camera windows and/or the sensors if the said cameras are poorly sealed (read: ASI and Altair cameras) and the general environmental condition favors high water content in the air (read: warmer wet weather) and the key here is not to cool down the camera too much. So far over the many many years I have kept my kits outside in all kind of weather 24/7 (and nearly 365/365) spiders have proved to be more of an annoyance than dew. And few spots of rain at times, too…
Bottom line: don’t fret over it. I once had ice forming inside a DSLR and on the sensor too and nothing came out of it.
andrea tasselli · Apr 29, 2026, 12:52 PM
If you find dew on the equipment then you know it has reached the dew point overnight and so it was this morning, with the laptop lids fully dripping (in two cases out of 3 as one is set not to ever turn off the display) as well as most of the exposed areas of the scopes ( but not the lenses!). For refractors in general a dew-strap is almost always a necessity and so I do have half a score of them for both guide-scopes and lenses. For reflectors with open tubes (read newts) a mixtures of forced rear cell ventilation and insulating dew-shield/cladding do the trick of keeping dew from forming on either the secondary or the primary. Cameras are always internally generating heat but dew (or frost!) can occur on the camera windows and/or the sensors if the said cameras are poorly sealed (read: ASI and Altair cameras) and the general environmental condition favors high water content in the air (read: warmer wet weather) and the key here is not to cool down the camera too much. So far over the many many years I have kept my kits outside in all kind of weather 24/7 (and nearly 365/365) spiders have proved to be more of an annoyance than dew. And few spots of rain at times, too…
Bottom line: don’t fret over it. I once had ice forming inside a DSLR and on the sensor too and nothing came out of it.
Thanks Andrea
Your comment about cooled cameras made me raise an eyebrow: hopefully this won't be an issue with the Asi533 mc pro i’m planning to get.
I tend to bring my kit in and out (mainly because I don't trust people not to nick it overnight 😏). So spiders don’t get enough time. I’m more worried about my cat squeezing itself down the 10” newt.
I live in a dry enough climate that dew is a much rarer occurrence than most. But I leave my equipment out when it is damp and let the morning sun dry it off. Then bundle it up. Right now, it is setting out warming with the sun.
I avoid covering my equipment anytime there is dew apparent. Covering it in that state is just asking for it to go deeper into your equipment. You are bagging it with moisture that will penetrate deeper than if is left in the open.
About 2-3 years ago (Maybe more?) I added a positive ventilation system to my equipment, which lives setup and gets covered when not in use. A piece of vacuum hose (Shop Vac) with a computer cooling fan mounted in the end. It runs on 12VDC and draws the air from the highest reaches of my cover on the telescope allowing the natural convection to dry the equipment while the small fan draws the air from the high point and dispels it out.
Having the positive airflow assures my equipment dries and stays dry even on rainy days.
Currently, my outside condition is 75% RH while my indoors is 38%. I used to bring in my Telescope and just let it dry inside the house. Which worked fine, because it is always drier inside. But my telescope outgrew my ability to dismount it every morning. So I’ve adapted.