Two observations in my log for this nebula:
The first back in 2007, under Dutch skies using an 8" SCT @ 78x / 38':
26mm Plössl: A diffuse, grey area surrounding two mag. 11 stars at a PA of 045°.
26mm Plössl, #908B Broadband Nebular: Using this filter the nebula is clearly much brighter and its is clearly a grey patch surrounding the mag. 11 stars. Especially towards the east the background is slightly patchy, too.
10 years later, in the French Ardennes in my 14" @ 168x / 29':
17mm Nagler T4: A faint, SW-NE elongated glow with two mag. 10 stars NE of the middle, aligned SW to NE. To the SW of these stars the nebula is slightly larger NW to SE. Quite a nice nebula.
17mm Nagler T4, Lumicon UHC: Using this filter it is clear that the larger part of the nebula to the SW of the mag. 10 stars is also a brighter part of the nebula, slightly tapering towards the NE. The nebula is brightest to the SW and the SSW of the two mag. 10 stars. With AV, to the ENE of the NE mag. 10 star, an interruption in the nebula is visible, a dark part with a slightly north-south elongated part to the east thereof.
17mm Nagler T4, Lumicon OIII: Comparable to the UHC filter but not as strong an effect.
Rated it 6/10 on both occasions.
ngc7538-1.jpg ngc7538-2.jpg
Click here to download the guide.