Seeing influence on telescope Deep Sky Performance

Hi gang, there has been a while since my last post, but the weather has not been that good, an the few nights that were clear had a very bright moon…

Anyhow I wanted to demonstrate the fact that good seeing can be CRUCIAL to proper deep sky imaging. To illustrate, please have a look at thes 2 pictures of M63:


and this one:


These two pictures were taken 3 nights apart, with the same setup and more important, with the same collimation. The only difference is that the less resolved M63 is the result of 2 hrs total exposure while the more resolved one is only 45 min total exposure. I had programmed the PC to take 15 x 10 min exposures, but unfortunately, I was not watching it and the PC performed an automatic update and rebooted while I was not watching (I was in bed actually!). The real difference between the two shots is seeing. For some reason I find M63  to be more sensitive to seeing than other objects, but I did not really expect seeing would make such a big difference… As I am getting more used to my setup, I can now tell how good the seeing is going to be, not by looking at the FWHM but, by simply checking by how many pixels in both axes the guide star is moving around while guiding. on the first picture, the guide star was barely moving by 1.2 pixels RMS, while on the second, it was moving by about 3 pixels. Turbulence impact can be easily seen by looking at a small double star to the left of the galaxie (near the bright star on the left). on the best picture, the couple is fully resolved, while on the other, it is not. I remember reading somewhere that turbulence has no impact on deepsky astrophotography. Well, this proves that it has, at least while imaging with such long focal length. This also shows that, while collimation is not as critical for deepsky as it is for planetary astronomy, it has to be good enough to have a resolution higher than that of seeing.

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