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Old Sep 7, 2004, 9:20 AM   #1
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On the Website http://myfototest.narod.ru/ is an description for using an RAW mode with the G400/G500. Some hacks in an "test mode" of the cams, but it's in russian language, i don't understand. Could someone translate the procedure ?

Does anyone know an similar hack to extend maximum exposure from 15s to 60s or so for very dark environments (i do astronomy images for a long time)?

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Old Sep 7, 2004, 11:41 AM   #2
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There is a reason that the manufacturer limited exposure length to 15 seconds in these models.

With any of the smaller sensored cameras, you have a lot of hot pixels at anything much over 1 second exposure. It is not uncommon for cameras using smaller CCD's to have hundreds of hot pixels at an exposure of less than 10 seconds for the models that allow you to disable noise reduction.

Basically, the noise reduction systems take two photos. One simulates a lens cap on exposure with the shutter closed, then another is of your subject.

Since both images use the same camera settings, then the two images usually display the hot pixels in the same locations. Then, the camera uses the "black frame" exposure to determine the locations of the hot pixels in the actual exposure. It then replaces the hot pixels with values interpolated from neighboring pixels so that they are no longer visible in the final image.

This technique is known as "black frame subtraction".

The pixels that were replaced is information that is lost from image taken by the camera. The longer the exposure time, the less likely the camera will be able to find and replace all of the hot pixels. This is why exposure times are limited.

This is also why cooled CCD's are needed for astronomy purposes (to reduce the hot pixels that will occur).

I would strongly caution you against using the test modes on these models. I accidently performed an autofocus calibration a while back that virtually ruined my camera. I've just recently got it working almost as good as new (after numerous calibration attempts).

This mode is very dangerous, and can easily ruin your camera.

I would avoid trying to make a camera do something that it was not designed to do.

For astronomy purposes, you're better off taking several shorter exposures, then "stacking them" using software.

There are techniques to do this via photoshop; or here is a package designed to stack multiple images:


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Old Sep 15, 2004, 11:30 AM   #3
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Against my better judgement, I put what you wanted to know in this thread:


BTW, exposures of longer than 15 seconds arenot supported (even from the Developer Menus).
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