The Dolphin Head Nebula is a beautiful nebula, located in the southern sky if you are in the USA/Northern Hemisphere.  From my location it only rises to around a -24 dg declination (36dg Altitude) at its highest point in the sky.  The bright star Udra, that marks the dolphin's blow hole, is visible to the naked eye in dark skies.

I used a narrow band binary band filter for OSC (Optolong Extreme).  The Dolphin Head nebula light is almost exclusively in the Oiii range (blue- blue/green).  I limited my exposures to 120 sec due to poor seeing and to mitigate the flare/halo for Udra.  The nebula itself is not very bright, so it appears as a faint blue outline in a single 120 second exposure.  This image is a 3 hour, approximately 40 minute integration.  It reveals the structure of the nebula but only hints at the other cloud structure that surrounds it.  It would, I believe, reveal much more detail with more data (image frames), so I will be attempting further imaging, weather permitting.

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Update:
I added just over 4.5 hrs of additional integration time to the original set, this time with 180sec exposures.

Within PixInsight, I used dynamic alignment to register/align the two different exposure time masters after first cropping, and DBE.  I used Pixel Math to create a single master image.  Then I denoised, ran the autocolor script, and applied EZ Stretch script.  I used Star Exterminator to create a Stars and Starless image, and used curve to increase the color saturation in the Stars image.

I separated the Starless version into the RGB channels.  Blue was very noisy, so set it aside.  Not much signal in the Read channel, but the G and B channels were very bright, the G lacked the noise present in the B channel.  I create a new B channel with a .4 + .6 merge of the R & G with Pixel math and used the LRGBChannel combination tool to recombine, use the G channel also for the L channel.  I then used Curves to tweak the final image.

This increase the total integration time to over 8 hrs, over double the original integration time and I believe that is evident in comparing the two different versions.
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A combination of monochrome LRGB (for the surrounding stars) and nb Oiii frames would seem to be a productive imaging plan for this target with a monochrome imaging setup.

300 second (5 minute) exposure would have revealed more structure per image and an improved SNR, but the seeing last night just would not support that, plus the halo of Udra would have been even more overwhelming.  (The halo is not 'real'; it is due to sensor bloom and internal filter reflections - usually in the blue band).  I made two false starts on imaging and had to stop to tweak PHD2 settings to manage the seeing issues/achieve decent guiding performance.

From WikiPedia:

Sh2-308, also designated as Sharpless 308, RCW 11, or LBN 1052, is an H II region located near the center of the constellationCanis Major, composed of ionised hydrogen.  It is about 8 degrees south of Sirius, the brightest star in the night sky. The nebula is bubble-like and surrounds a Wolf–Rayet star named EZ Canis Majoris. This star is in the brief, pre-supernova phase of its stellar evolution. The nebula is about 4,530 light-years (1,389 parsecs) away from Earth, but some sources indicate that both the star and the nebula are up to 5,870 ly (1,800 pc) away.  Yet others indicate the nebula is as close as 1,875 ly (575 pc) from Earth.Sh2-308 surrounds the Wolf–Rayet star EZ Canis Majoris, also designated EZ CMa or WR 6. Its apparent magnitude varies from 6.71 to 6.95. Its spectral type indicates that the star is very hot and luminous. The spectrum shows that it is devoid of hydrogen at the surface. Canis Majoris is expected eventually to explode in a supernova, therefore subsuming the nebula.

The nebula was formed about 70,000 years ago by the star EZ Canis Majoris throwing off its outer hydrogen layers, revealing inner layers of heavier elements.  Fast stellar winds, blowing at 1,700 km/s (3.8 million mph) from this star, create the bubble-shaped nebula as they sweep up slower moving material from an earlier phase of the star's evolution. The hydrogen composing the nebula is ionised by intense ultraviolet radiation.  The nebula is approximately 60 light-years across at its widest point. 

The most favorable period for observing the nebula in the night sky is between the months of December and April. Its southern declination makes it easier to observe from the Southern Hemisphere, though it is easily visible from most of the Northern Hemisphere as well. It appears as a faint cloud in photographs taken with high-power amateur instruments, with the help of special filters.