有提到要用某個軟體
似乎是多圖接力的(如15秒*4＝60秒)
『理論上可以無限制曝光時間』
盡力了，還是看不懂
有大大瞭解的話請解釋，謝謝!
轉貼部份：
...However this doesn't mean that such a thing is impossible
with your camera, it'll just take a little extra work on your part. The results
beating any other camera's on earth, making it worth the extra effort.
What you do is use any of the CHDK intervalometer scripts with some
pre-planning.
Go into CHDK's RAW menu options and turn Noise Reduction to OFF. This disables
the dark-frame noise-reduction routine that happens on all shutter speeds longer
than 1 second. Instead of having an 18 second gap between exposures (the time
needed by the camera to do a dark-frame subtraction on a 15-second exposure),
you'll now only have a little over a 1 second delay between shots. Keep in mind
too that this affects JPG files as well as RAW, whether you are saving RAW files
or not.
Set your intervalometer script to shoot in continuous burst mode for as long as
you need for your whole exposure. If using an S-series camera then I recommend
the OMNI-Intervalometer script as that has the option to use the camera's own
burst mode. For others who are not using that script with an S-series camera
then you'll have to use one of the other intervalometer scripts in non-stop mode
using a very short delay between shots, or write your own script with the
appropriate commands to use its burst mode.
During the shooting session, every few minutes or so, you'll have to record 1
dark-frame by capping or covering the lens so you can later do dark-frame
subtraction manually using something like this freeware "BlackFrame NR" utility
from http://www.mediachance.com/digicam/blackframe.htm Covering up the lens
every now and then is known in astro-photography circles as the "hat-trick
technique" because a hat really was used to cover up the larger size of the
telescope's optics. Being able to hold the hat apart from touching and
disturbing the telescope and camera while still blocking out all light for a
dark-frame exposure.
The number and interval of dark-frames that you'll have to record will depend on
the length of your photo session, the ambient air-temperature (warmer weather
means a warmer sensor means more thermal-noise in sensor; longer sessions means
warmer sensor too), and the quality of the sensor that was used to build your
camera. Sensor quality varies from camera to camera, even the same models built
on the same day on the same production line. You might have lucked-out and
obtained a very quiet one. You will probably be able to get by in most
situations by recording 1 dark-frame every 5 to 15 minutes worth of 15-second
exposures. Recently I did just fine with only 1 dark-frame taken at the end of
20 minutes worth of 15-second exposures. I compared the use of earlier
dark-frames with using just the last one and there was no difference.
Later you can combine all these 15-second exposure images into one long exposure
image using a freeware utility called Registax from
http://www.astronomie.be/registax/ There are others but this is one of the
better ones.
Using this method you are able to get noise-free images at any ISO for any
exposure length that you desire. Yes, I typed that correctly, at any ISO. Noise
averages out and disappears when using frame-stacking methods with enough
photos. That's also why this technique is so popular in astronomers' circles for
decades. Getting exposures of this length is impossible to do with any other
high-resolution digital cameras using just its own capabilities, unless tethered
to a bulky and battery-time-limited laptop to control it. Today this method is
still being done with web-cams and video cams but at greatly reduced
resolutions. They're the only other devices that had the capabilities needed,
that which CHDK now adds to a high-resolution still-frame camera.
Pretty cool, eh?
(Side info: the reason the "Noise Reduction" option ended up in the RAW menu is
that originally there was a problem with the camera's dark-frame routine in the
cameras causing a shut-down when saving RAW in continuous high-speed modes. Both
these problems were fixed so you can use dark-frame subtraction and RAW in
high-speed mode too. In earlier builds of CHDK we had to turn off Noise
Reduction if we wanted to use RAW in burst modes. As a result of these
experiments and old bugs in CHDK we got this fantastic Noise Reduction toggle.
When turned to ON it then applies a dark-frame routine at ALL shutter-speeds.
This removes all hot-pixels from all photos, no need to send your camera in to
have any hot, warm, and stuck pixels re-mapped. Setting it to Auto is just
leaving it at the camera's own defaults. Rightfully this "Noise Reduction"
option should be in the Misc. menu because it affects all JPGs too whether you
are saving RAW or not. Anyway, that's how it got where it presently sits in
CHDK's menus. Many people wonder why it was filed there since it's not just for
RAW anymore. Then too, because of this, they don't realize its other great
uses.)
p.s試玩CHDK中，所以才查查看，但內文提到的方法應該一般DC也行
也有CHDK的朋友喜歡星象攝影(都學生，沒預算
)所以他有興趣的部份是B快門(chdk：64秒)而我也想充實一下，謝謝各位囉
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4/28
哇...都沒人回耶
看來我要自己想辦法了
