For an excellent description of narrowband imaging, its advantages and disadvantages, and the wide variety of color palettes used, see http://starizona.com/acb/ccd/advimnarrow.aspx.  Narrowband images are inherently false color, since the filters do not pass the kind of broad spectrum light used in normal vision.  They pass one spectral line, for example, the hydrogen alpha line.  Creating a color picture from a set of narrowband exposures involves some choices.  One of the common choices, called the Hubble palette, assigns Red to SII, Green to H-alpha, and Blue to OIII.  This is in wavelength order but generally produces images that look nothing like normal color images or photographs.  An object we are used to seeing as very red will be bright green using this palette.  Another common choice is the CFHT palette (for Canada-France-Hawaii Telescope).  In this case, Red is assigned to H-alpha, Green to OIII, and Blue to SII.  The colors are not in wavelength order but the results are generally much closer to the familiar appearance.  A third palette, called HOO, uses Red for H-alpha and assigns both Green and Blue to OIII.  It gives pleasing results for many objects, especially planetary nebula.  My exposure times will always be listed in CFHT order (H-alpha, OIII, SII) but I will indicate which palette was used for the image and will show some images in more than one palette.
 

  
   Sharpless 2-254, 5, 6, and 7

   10-inch Newtonian, ST2000XM, 70:85:70

   This is a narrowband image, my first in a long time.  It is shown in the CFHT palette.  For an explanation of the various palette choices, see the Narrowband page.

The largest (and faintest) nebula is Sh 2-254, on the right.  Moving left, the larger nebula in the center is Sh 2-255 and the little tuft below it is 2-256.  On the left, the brightest nebula is Sh 2-257.  This one also has an IC designation, 2162.  The group is dominated by H-alpha emission, but there is some significant SII emission and a tiny amount of OIII as well.  The right-hand buttons below will take you to monochrome H-alpha images.  Each of the nebulae has a fairly bright star near the center which provides the energy that stimulates the emission.

   IC 443 (Jellyfish)

   10-inch Newtonian, ST2000XM, 110:50:70

   This is a narrowband image of a very faint object.  Its common name (to the extent it has one) is the Jellyfish but I might have named it the Brain.  It did not quite fit into my field but not much is cut off.  The color palette is a custom one as I did not like the results using any of the traditional palettes.  Red is a blend of SII and H-alpha, green a blend of H-alpha and OIII, and blue is all OIII.  IC 443 is a supernova remnant interacting with surrounding molecular clouds.

I've only included half size images because the full sized ones are very grainy.  The H-alpha monochrome image is, for me, more attractive than the color image.

   IC 405 (Flaming Star Nebula)

   Astro-Tech AT66ED, ST2000XM, NB 120:140 minutes, 73' x 84'

   This narrowband image from Fort McKavett, TX, is shown in the HOO palette, where H-alpha is mapped to red and OIII is used for both the green and blue channels.  The H-alpha and OIII were shot on different nights.  I was concentrating on matching the N-S positioning and did not do a good job with the E-W position, so the images overlapped only in the area shown.

The brightest star is the variable AE Aurigae.  The brightest area of nebulosity surrounding the star is historically known as the Flaming Star Nebula, but the nebulosity extends throughout the field, and beyond.

I'm again including a monochrome H-alpha image.  The OIII image is rather boring, with little to see except a few tufts very near AE Aurigae, and some diffuse background glow.

   IC 410 and NGC 1893

   10-inch Newtonian, ST2000XM, NB 136:72:80

   IC 410 is also cataloged as Sh2-236 and LBN 807.  The loose star cluster just left of center is NGC 1893.  A wide-field LRGB image of the same objects can be found on the Diffuse Nebula page.

The image to the left is displayed in the Hubble palette.  Usually I like the CFHT palette better but in this case the Hubble seems to show more, especially the Tadpole nebulae in the upper left corner of the image.  I've also included a example of the HOO palette, which produces a more natural color.  However, I like the monochrome H-alpha image best of all.  The buttons below will take you to 75% scaled images in each of the palettes.
 

   M42 and M43 (NGC 1976 & 1982)

   Astro-Tech AT66ED, ST2000XM, NB 80:80:40 minutes, 76' x 102'

   This is a wide-field, narrowband image of the great Orion Nebula shot from my backyard in The Woodlands, TX.  Regular LRGB images of this object, both wide-field and close-up, can be found on the Diffuse Nebula page.  M43 is the small flame shaped tuft above and left of center, and the large nebula occupying the rest of the center of the field is M42.

The image here is shown in the CFHT palette, but the buttons will take you to  Hubble, CFHT, and HOO palette images.  Definitions of the palettes are given above.  The HOO image looks most "realistic" -- more like an LRGB image -- but realism is not our primary objective in narrowband imaging.  Because the HOO palette only uses two filters, it contains less information.  If you carefully compare the images, you will see that certain areas show a lot less structure in the HOO image compared to the Hubble and CFHT images

   LBN 667

   Astro-Tech AT66ED, ST2000XM, 110:120:20 Narrowband, 69' x 96'

   This is my first full narrowband image, made through Hydrogen-alpha, Oxygen-III, and Sulfur-II filters.  The Sulfur-II exposure should have been longer but would have made little difference -- there is almost no S-II emission from the nebula.  The tiny detached tuft of nebulosity near the left (E) edge is IC 1871.  All of the remaining nebulosity in the field is LBN 667, and it extends about 20% further to the right.  The bright but sparse open cluster near the right edge is IC 1848.  The lobe occupying most of the left half of the image includes the open cluster Cr 34, but for me it does not appear any more concentrated than the general background.

The palette used was the CFHT, as described above.  This image was acquired from my backyard in The Woodlands, TX.  It was reprocessed by Al Kelly, which greatly reduced the noise.