NGC 7635, also called the Bubble Nebula, Sharpless 162, or Caldwell 11, is a HII region emission nebula in the constellation Cassiopeia. It lies close to the direction of the open cluster Messier 52. The "bubble" is created by the stellar wind from a massive hot, 8.7 magnitude young central star. The nebula is near a giant molecular cloud which contains the expansion of the bubble nebula while itself being excited by the hot central star, causing it to glow. It was discovered in 1787 by William Herschel- The star BD+60°2522 is thought to have a mass of about 44 M☉ (from Wikipedia).

When I saw the HST image of NGC7635 I did litterally fall in love with this wonderful nebula. The challenge is that the bubble is only few arcmin in size, thus with my smaller scopes I realized that there was no way to achieve a high resolution image. Since a couple of month I received my new 180mm refractor, which I call the beast. With a weight near 23kg, being mobile becomes a real challenge. For instance setting up the system takes me now more than 2 hrs (incl. calibration of the 10 Micron mount) and the slightest modeling error of the 10 Micron ends up with blurred images. So, I had to work hard to get it running properly.

By selecting NGC7635 as first light narrow band object, I wanted to assess if the scope can deliver highly resolved images. Shortly the anwser is yes and I am really impressed be the performances. To my slight disappointment I have the impression that 1285mm focal length is not sufficient to achieve the maximal resolution from earth. I guess that 2500mm may be the minimum. Of note I used to some extent BlurExterminator to increase sharpness (stars and nebula), but as a matter of fact I observed that on faint details of the nebula this leads to artefacts, whereas on the regions with strong signal it may lead to overcontrasted details. So, in the Ha channel I generated 6 layers of different light intensity and blended them in PS so to reveal faint regions while avoiding to blow up the bright ones. On these layers I applied BXT to 3 out of 6. This ended up from my perspective to an optimized level of light and details by minimizing the risk of artifacts. By comparing the HST image with this version I essentially confirmed that the details of this image are real.
Finally I tried to reveal color nuances from the HSO layers by playing with the contrasts of each individual layer and with the "selective color" function.
I hope you like this version. Don't hesitate to comment it.

CS and happy new year

Nicola