Gain - ISO setting. ISO is like the old ASA settings of film. The higher the ISO number, the higher the sensitivity which produces more grain (noise). By default, the gain will be set to level 4, ISO 1600. Personally, we like level 3 - ISO 800 providing faint details while keeping the noise down. It’s a personal preference. Some like level 2 - ISO 400 while other prefers level 4 - ISO 1600. Experiment with different settings to your liking. The lower the level – ISO the less sensitive the CMOS and more exposure time will be required. The more exposure time; the hotter the chip becomes creating more noise. You have to find that happy medium of high sensitivity and low pixel noise. If you can keep the chip cool by applying dry ice to the camera, you can use higher ISO settings, but I would not recommend this practice especially in humid areas. Condensation is likely to enter the internal works of the camera causing possible damage. Newer CCD cameras are now coming on the market with Thermal Electric Coolers called TECs.
Offset: Leave the setting alone. It is automatically set by Canon EOS series DSLR cameras and should have been grayed-out.
Step #6: Taking a series of images. Well it looks like we’re ready to image. First thing you need to do is tell the computer what the name of the object is and where will the RAW images be stored. Go just below the Abort button and give your images a name. If you are taking photo of the Trifid, get rid of “Series 1” and type in “TrifidRaw.” (Note: It is a good practice to change the name of your images at every step in the process just in case you want to go back and reprocess) Just below that, click the “Directory” button and select the folder that you named previously, “Trifid.” If you forgot to make a folder, click the “Make New Folder” button and under “My Computer” name it, “Trifid”
Let’s say that you have determined the exposure time to be 60 seconds; you have decided to use gain at level 3 - ISO 800. Offset is set by the Canon DSLR camera and should have been grayed out. Set your number of exposures. We personally like 30 exposures for ease processing, but there’s nothing wrong with trying 10, 20 30 60 or as many as you like. It is better to take 60 exposures at 30 seconds than to take 30 exposures at 60 seconds. Both are 1800 seconds (30 minutes) of data but 60 exposures at 30 seconds will have less chip noise. The important thing is to get as much data as possible. You cannot get enough data. Set your number of exposures. If you want to keep your CMOS chip cool, allow it take a break and select 60 second between exposures. This will also allow you to take a short break if you’re manually guiding. For those who autoguide, this is the time to start your autoguiding program such as PHD. Select a star and insure that the telescope is going stay on the selected star during the time of capture. If you are ready and the autoguider is working well, click “Capture Series.”
Step#7: Taking darks. Some people don’t take any darks, flat or bias frames and have excellent images, but if your camera has been imaging all night, it is possible that the chip may have gotten some hot pixels. You may want to take some dark images to get rid of those nasty little hot pixels during processing. Place a lens cap on the imaging telescope. Change the number of exposures to 10 or 20. Change the name of the images to “TrifidDarks” and now click “Capture Series.” The directory will stay the same until you change it. It’s important to take your darks at the same exposure time and
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