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Well, after 3 hours and 20 mins. I would think Andromeda would move right out of the frame if the camera never moved. But I could be wrong. Just a wild guess really. So if it was unguided does that mean the camera was moved by hand (panned) during frames or something?
Well, after 3 hours and 20 mins. I would think Andromeda would move right out of the frame if the camera never moved. But I could be wrong. Just a wild guess really. So if it was unguided does that mean the camera was moved by hand (panned) during frames or something?
Derek
Yes, you're right. At 200mm, the galaxy would surely be out of scope in a few minutes or less. He mentions the camera was piggy-backed on his scope. But then he says it was unguided, so I don't know. Auto-tracking is what I would expect.
First the hardware: the camera was piggybacked on top of a telescope OTA (optical tube assembly), which was sitting on top of an equatorial mount, which was sitting on top of its tripod. In astrophotography, tracking and guiding have two distinctly different meanings. The mount tracks the motion of the stars across the sky -- all motorized mounts do this. How well a mount tracks over how long a period of time depends on the quality of the mount + the quality of the setup by the user (e.g. balancing all the equipment accurately) + the quality of the alignment by the user (e.g. polar alignment). So that's unguided tracking. Depending on the aforementioned factors, you can get good unguided tracking from anywhere between 30 seconds to 5 minutes.
However, even with the best gear and alignment there will be some errors in tracking over long periods of time. So guiding comes in to correct for those errors. Guiding is simply an additional error correction that makes sure the stars in the field of view don't move even slightly. There are two types of guiding: manual and auto. In manual guiding, you use an illuminated reticle to target a star in the FOV -- if the stars starts drifting out of target, you adjust the mount to keep it in target. With auto-guiding (pretty much the default for most astro-imaging), this same function is done by a computer software. An autoguider camera is attached to a secondary scope which then makes sure the stars are steady by sending commands to the mount to move as needed.
With manual guiding, obviously you have to be looking through the viewfinder the whole time (laborious for a 3.5-hour session). With autoguiding, you set it up and the computer does everything (hampered only if the target stars is obscured by clouds, trees, etc.). I went down the autoguiding route. However, for this Andromeda shot, since I was shooting only 60-sec subs, I didn't have to worry about setting up the autoguider. I knew that my unguided tracking was good enough for at least 60 seconds.
So for my imaging, I set everything up, take a few test shots to make sure my tracking, guiding, framing, and focus are okay, set the software up to take however many shots I want, and then go to bed. This is sometimes risky because the focus point moves with large changes in ambient temperature.
For this Andromeda shot, I took 200 light frames. I'd taken about 60 dark frames matching the same ambient temperature of the light frames on a different night, so I calibrated with those. I also had 60 flat and 60 offset frames taken at other times that I calibrated with. All calibration and stacking was done in DeepSkyStacker, which does everything for you.
Speaking of stacking, I may as well add this one to the thread. You can actually see all the meteors if you look carefully. The long lines extending towards the lower right are airplanes.
Wow, kdog, that photo is amazing and beautiful! Thanks for sharing it!
Wow, I'm just amazed by the stars and Milky Way in those first shots!! Living here in San Francisco (aka Fog City), we rarely even see the sky - let alone any stars in it. Great shots!!
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Thanks for sharing it!
Living here in San Francisco (aka Fog City), we rarely even see the sky - let alone any stars in it. Great shots!!
