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There is a long time I don’t have such a great night. From dawn to dusk no clouds, no wind, perfect. And now that I learn to use properly the autoguider, i can do very long frames.

So I setup to get some shots at Whirlpool Galaxy (M51). It is a very beautiful merger galaxy where the bigger is feeding on the smaller one. I manage to have some very good aiming and tracking. And everything seems great. To take 20 frames of 10 minutes it is almost 3 and a half hours.

After my first picture I was amazed. I could clearly see the galaxy without any editing. Just the raw one frame was there a beautiful galaxy shape. But I notice that after a while, I couldn’t see it as good anymore. I thought it could be some passing clouds? But there was none. Maybe it get some good and bad frames? But the quality was just degrading with time.

Since my target was to pass at Zenith and I would need to do a meridian flip. And after that was not possible to find the galaxy again. And it was late so I decided to stop the process. I had taken 14 from the 20 shots, it was good enough for a day.

But, I am aware that my corrector plate is always getting dew. And I could do the math. Dew + time = each shot has less light passing through. So in the end, my 14 shots are useless. Because of the annoying Dew. I made a GIF to show what happen. Each frame of the GIF is one of my frames, raw data, not processed. It starts as a nice galaxy, and finishes as a small dot.


Whirlpool Galaxy (M51)
Celestron AVX 8″ SCT
Filter: Astronomik CLS-CCD
Focal Length: 1278 mm
Aperture: f/6.3
ISO: 1000
Shutter: 600s
Frames: 14
Total exposure: 140 (wasted) min
Aquisition: Maxim DL
Taken Apr 14, 2015 around 23:32 CEST

Luckily I already have a Dew shied (which delays but don’t avoid it to happen), and in the way there is a dew heater band, to be able to end this horrible nightmare.

Note that the sky looks blueish, it is because of light pollution of the sky, which lit it up very bight for long exposure pictures, in combination with a light pollution filter I always use, to avoid that the picture is just a completely orange and no galaxy or stars can be seen.

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