Sunday, October 1, 2006
Handling Condensation From Temperature Changes
Condensation And The Camera • Save, And Save Again • Scanning Formats • Are LCDs Worth Their Color? • Sensor Cleaning • Just Blowin' In The Wind
A) Condensation isn't a problem for the newer high-end cameras and lenses, such as the Canon EOS-1D MKIIn, the Canon EOS-1Ds MKII and the Nikon D2x, D2Hs and D200. These pro cameras have sealing gaskets on all external controls and the lens mount. Some lenses also are sealed at the points where moisture might enter; check your manufacturer's list of lenses for more information.
For most other cameras and lenses, moisture will cause damage as it seeps into the mechanisms; in fact, a common problem in the tropics is the growth of fungus on the surface of lens elements! To avoid these hazards, seal the body and lenses, along with a desiccant canister, into plastic bags as soon as you enter the air-conditioned space. When you take the gear outside again, let it warm up while sealed inside the bag. Condensation will form on the outside of the bag, rather than on the equipment, and the desiccant will take care of any moisture that might be inside the bag.
Note that desiccants do, after a time, reach their maximum absorption capability, so periodically warm them up to dry them out again. Look under "silica gel" on the web to find numerous sources of desiccant products.
Keep in mind that the same dynamics can take place in the opposite conditions. In cold weather, we take our cameras into a heated enclosure and then later return to the cold outside, only to have our equipment fog up and condensation form on the warm camera parts. Then the moisture can freeze inside the camera, causing any number of problems.
I've struggled with these conditions while photographing in the winter in Yellowstone National Park and around Churchill, Canada, where polar bears are active. As in the tropics, use the sealed bag, and wait for the temperature of the gear to equalize with the air temperature before you begin to use it.
Save, And Save Again
Q) In OP, you said that every time you open and resave a JPEG image, photo quality is lost. I did an experiment in Photoshop and opened and resaved a file 10 times. The file size didn't decrease (although it varied slightly each time). Doesn't the fact that the file didn't get smaller mean that the JPEG didn't lose image quality?
Via the Internet
A) Every time you save the image, the program recalculates and restructures the pixels. The file didn't get noticeably smaller because you didn't change the compression rate from one save to another. But the slight variances in file size mean that the file was changed slightly each time you saved your test image.
If you always save at a low compression level, you would probably need to open and resave many more than 10 times before you'd see a change in image quality due to the cumulative effect of the slight restructuring of the pixels that occurs in each save. If you're saving at a high compression level, however, the degradation of the image will reveal itself more quickly in the form of artifacts and banding that cannot be corrected.
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