LensFogLens fog forecast
See whether your lens will fog when you carry it out of the AC or back in from the cold, from the dew point where you are. If it will, the advice is how long to leave the zipped bag in the new air before you open it.
Wiping it doesn’t help.
A camera that’s been in a 70°F hotel room is five degrees colder than the 75°F dew point of a Savannah evening, so the glass fogs as soon as you step outside. A cold drink sweats on a summer afternoon for the same reason: air leaves its water on anything colder than its dew point. Each verdict in LensFog is based on those two figures, how cold your gear is and the dew point of the air you’re carrying it into.
For gear that’s been in air conditioning. Pick where it sat: an AC room (70°F), an AC car (64°F) or a temperature you set yourself. The dew point outside is from Apple Weather’s hourly forecast for where you are.
For cold gear carried back inside. Pick a quiet room or a crowded one; a packed reception with a dance floor and a kitchen puts a lot of water in the air, so its dew point is higher. Gear that comes in below freezing frosts over first, and the frost melts into fog.
Whichever trip is more likely to fog goes on top, with the verdict set big and the gap under it: “Gear 8°F below the dew point.” A close call is gear from a touch below the dew point to about 4°F above it. The band reaches that high because forecast dew points run a degree or two low near water, over lawns and at dusk.
Zipped in a bag, gear warms about half as fast and the water lands on the bag instead of the glass. So on a fog verdict the advice is a time: “Set the zipped bag outside 50 minutes before you head out.” Coming in, it’s how long to keep the bag zipped once you’re inside. The time follows the slowest lens in your bag, so it’s shorter without a telephoto.
Search for the venue and pick a day and time up to nine days out to see that hour’s forecast. Times are on the venue’s clock, and the head start becomes a clock time: “Set the zipped bag outside by 4:35 PM.”
Each trip gets a ribbon for the hours ahead, with a line like “Fog risk from 9 PM.” Underneath are the air temperature, humidity and dew point right now, from Apple Weather.
Small and medium widgets for the Home Screen, and three for the Lock Screen. The medium one adds the advice line and the next change in the hours ahead.
Search for the venue and pick the hour you’ll carry your gear out, up to nine days ahead. For a 5 PM ceremony at Magnolia Plantation, with the cameras in an air-conditioned bridal suite all afternoon, the zipped bag goes outside by 4:25. Times are on the venue’s clock, so it works the same for a wedding two time zones away.
Email me if something isn’t working, or if a verdict didn’t match what your lens did.
It helps to include the place, the time, and the verdict on screen. A screenshot works too.
It’s as good as the forecast and the gear temperature. If your gear has been somewhere colder or warmer than the AC presets, set its temperature yourself. A temperature you set lasts until midnight, or until the shoot if you set it for a planned one.
Under a fog verdict there’s a line for that, like “Already fogged? 4–23 minutes to clear.” The range runs from the fastest lens in your bag to the slowest. Wiping only clears it for a moment; the fog keeps coming back until the glass warms up.
No. With it, you get the dew point where you are. Without it, you can still search for a place and check it there.
Yes. Units follow your iPhone, or you can pick °F or °C in Settings. There’s a light and a dark theme there too, and a How It Works page that goes through the physics with a worked example.
Yes. That’s the Coming in trip: gear that’s been out in the cold, carried into a heated room.
No. There’s no account, no ads and no tracking, and nothing is sent to me. Your location goes to Apple Weather and Apple Maps to get the forecast and the name of the town.
