Thursday, August 13, 2015

#8 - Thursday, August 13, 2015 - First stacked image

I moved the telescope from the asphalt to the grass – we originally moved it to the asphalt to reduce dew, but the grass helped reduce vibration during long exposures. I even waited until I sat down to hit the shutter. Thank goodness for the remote shutter! It’s the only way to take long exposures.

I tried the Lagoon Nebula again, and after trying different exposure times and ISOs, I decided on 30-second exposures and ISO-3200, and took 10 of them to try a post-processing technique called stacking using a software called DeepSkyStacker. Of the 10, only 8 were jitter-free, so this made for a 4-minute total exposure time. The resulting photo didn’t turn out much better than the individual ones, although I didn’t mess with the color or luminance settings. [About a week later, I did; below is the result. Much improved!] Also, my camera automatically subtracts a dark frame from photos with exposures longer than 6 seconds, so I didn’t use any dark frames in the software.
My log entry seems to disagree with the files I have; I count 12 images.
Nikon D3100 on my C8, 12x30s, ISO-3200

The sky rotation is evident in the stacked pictures – you can see the turning in the edges of the photo (before I cropped it). The DeepSkyStacker software is very good at aligning the points of light. Since the light pollution is too bright around here to do longer than 30-second exposures, an equatorial wedge isn’t necessary just yet. At some point though, when I live somewhere darker, I’ll shell out the money for one. [I later corrected this little problem with a light pollution reduction filter.]

Next, I tried the Eagle Nebula. While I can see the stars, I can’t see any gas, or maybe it is just barely visible in the image. Perhaps stacking several images for a 10 or 20 minute total exposure time will reveal it (thought later). Images I see online contain a lot of red, though, which may not show up well on my camera, since I don’t want to have the IR filter removed.

Next, I tried Messier 101, a spiral galaxy in the northern sky. You can just make it out in the image – you can see the core, and just barely see the arms. This one may also be a good candidate for stacking.

Next, I tried M17, the Swan/Omega/Checkmark Nebula. It showed up well on the camera screen, but turned out to be darker when I looked at it on a larger screen. Will need to try this one again as well. Also a good candidate for stacking.
Single frame on M17, using my Nikon D3100 on the C8.
30s, ISO-3200.

I figured out that if I sync the scope to a nearby star, it is more accurate at finding the object – M17 was nearly in the center of the view on goto.

I tried the Eagle Nebula again, a couple 20-seconds and a 1-minute, but no go.

I tried the ET Cluster, NGC 457, and it is a very nice cluster of stars. Will need to try again to try and get a shot without jitter.

Helix Nebula – used Deneb Algedi to sync. Couldn’t find it, or was very dim.

Wild Duck Cluster – synced to Altair. Couple bright stars, lots of noise though. Not much to see in the shots.

Not many meteors tonight. It was supposed to be the peak of the Perseids!

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