Filter fogs but camera lens doesn't
Nov 18, 2020 21:29:23 #
Tonight is clear and I am doing some night sky photography. Its 37 degrees, so have taken the camera and filter outside for 20 minutes to allow temperature equilibration to avoid fogging. Set up the camera, took a half hour sequence of shots, no problem with fogging. Added a screw-on light pollution filter and within 10 minutes, the filter, not the camera lens, is badly fogged up on the surface facing the lens. What do you think the solution might be? The filter is the Hoya Starscape filter. It does a great job of reducing light pollution.
Nov 18, 2020 21:50:27 #
dleebrick wrote:
Tonight is clear and I am doing some night sky pho... (show quote)
Did the filter come from a pocket like your pants or shirt?
Nov 18, 2020 22:26:37 #
PixelStan77 wrote:
Did the filter come from a pocket like your pants or shirt?
That was my thought, also.
Nov 18, 2020 23:08:46 #
PixelStan77 wrote:
Did the filter come from a pocket like your pants or shirt?
Both camera and filter were left outside for 30 minutes to equilibrate with the outside conditions.
Nov 18, 2020 23:32:34 #
Grasping at straws maybe, but was the filter in a sealed case? If so there may have been just enough trapped moisture that condensed from the heat of the electronics in the camera and/or lens once it was screwed on. My best guess (underscore guess) for the minute.
Mark
Mark
Nov 19, 2020 05:59:30 #
dleebrick wrote:
Tonight is clear and I am doing some night sky pho... (show quote)
This could be due to a number of factors, possibly you exhaled on it as you were attaching it. Most likely the temperature dropped to the point where dew formed, the coatings on astro filters are often metallic like, as such they would have a higher rate of thermal conductivity compared to the lens. So they will cool faster.
Amazon has a number of small inexpensive battery operated dew heaters which work well and will prevent this from happening.
Best,
Nov 19, 2020 06:53:47 #
billnikon
Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont
dleebrick wrote:
Tonight is clear and I am doing some night sky pho... (show quote)
Don't keep Starscape filter in your pocket or holder device, make sure the filter is also open to the elements and let it stay outside for 20 minutes, again, do not store in filter holder or pocket.
Nov 19, 2020 07:04:50 #
Leitz
Loc: Solms
dleebrick wrote:
Tonight is clear and I am doing some night sky pho... (show quote)
Obviously the filter and lens were not the same temperature.
Nov 19, 2020 07:23:45 #
dleebrick wrote:
Tonight is clear and I am doing some night sky pho... (show quote)
Did you attach the filter to the camera before you took it outside? If that is the case, then the moisture was condensing on the filter because of the humidity and temp. Differences. Just like the moisture on a glass of ice and water on a warm day.
Nov 19, 2020 08:11:19 #
That is a big problem in astrophotography, although lenses are not common on Refractor scopes (see
https://optcorp.com/blogs/astronomy/the-basic-telescope-types?gclid=CjwKCAiAzNj9BRBDEiwAPsL0d1NRrom9r7RZmWkEcA_m2qqNlCjFNquNrhIR8CsyGJ2K1-Yd5EZMVBoCvtUQAvD_BwE ) for scopes types. Even my 16" mirror diameter (2.5" thick glass) would fog up way Down inside the 88 inch long 21" diameter tube.
The temp equilibrium is not the prime factor; the humidity is. Eventually with enough humidity on a damp night both will fog up, but the light weight (low thermal mass) filter will go first.
We always have scopes set up and all hardware outside by dusk, but later in the evening sometimes the dew starts to get worse. At a star party with many observers/scopes it is common to hear a hair blow dryer start up and run for a few seconds to a minute. Your situation may just have been a combination of time of night (dew usually starts later as it gets cooler), and the very low thermal mass of the filter (it cools rapidly) compared to the heavy camera/scope. On some nights the hairdryers are used a lot, on other nights hardly ever.
Verryl
https://optcorp.com/blogs/astronomy/the-basic-telescope-types?gclid=CjwKCAiAzNj9BRBDEiwAPsL0d1NRrom9r7RZmWkEcA_m2qqNlCjFNquNrhIR8CsyGJ2K1-Yd5EZMVBoCvtUQAvD_BwE ) for scopes types. Even my 16" mirror diameter (2.5" thick glass) would fog up way Down inside the 88 inch long 21" diameter tube.
The temp equilibrium is not the prime factor; the humidity is. Eventually with enough humidity on a damp night both will fog up, but the light weight (low thermal mass) filter will go first.
We always have scopes set up and all hardware outside by dusk, but later in the evening sometimes the dew starts to get worse. At a star party with many observers/scopes it is common to hear a hair blow dryer start up and run for a few seconds to a minute. Your situation may just have been a combination of time of night (dew usually starts later as it gets cooler), and the very low thermal mass of the filter (it cools rapidly) compared to the heavy camera/scope. On some nights the hairdryers are used a lot, on other nights hardly ever.
Verryl
Nov 19, 2020 09:15:47 #
Verryl wrote:
That is a big problem in astrophotography, althoug... (show quote)
Would the average disposable handwarmer, laid out on a flat surface, provide enough heat to dissipate the humidity on a lens filter?
Nov 19, 2020 10:48:43 #
Verryl wrote:
That is a big problem in astrophotography, althoug... (show quote)
That's the best explanation I've seen so far.
Nov 19, 2020 11:58:27 #
dleebrick wrote:
That's the best explanation I've seen so far.
I'm puzzled by your question and some of the responses. Was the camera and filter colder than 37 degrees when you took them outside? Did your glasses fog when you went outside? Just based on the science fog forms (condenses) on surfaces colder than the dew point of moisture in the air. It doesn't form on surfaces warmer than the air temperature. If that were the case coffee mugs would sweat rather then iced tea glasses. I'd bet you wouldn't have seen any fog on the camera lens or filter if you'd started shooting immediately when you went outside. If the humidity increased after you were out there a while and the temperature of your gear was now colder than the dew point you'd get fog. Fog/dew forms on the coldest relative surfaces. In this case your filter may have been colder than your camera which you had in your hands and there are electronics inside. I'm also going to guess your glasses and your camera glass would have fogged up when you went back inside
Nov 19, 2020 13:38:19 #
one_eyed_pete wrote:
I'm puzzled by your question and some of the respo... (show quote)
The filter and camera were at room temperature (70 degrees) when they were taken outside. They were both allowed to sit outside for 30 minutes before shooting began. A 25 minute sequence was shot with the camera before attaching the filter, and no fogging was observed on those images. The filter had nearly an hour at outside temperature before it was attached to the camera. Within about 10 minutes with the filter attached, the inside surface of the filter began fogging, destroying the camera image quality.
You are correct, both the camera and my glasses fogged up when I went back inside.
Nov 19, 2020 18:15:15 #
LOL, I didn't think you experience that much 37 degree weather in SC. I'm in upstate NY and freezing my arse off right now. Bringing a camera back inside when it's freezin cold is always a concern up here. I try to ensure the caps are all secure and let them sit for 1/2 to 1 hour to warm to room temp.
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