HA

HA or Hydrogen Alpha is a feindishly hard way to take photographs of the stars. The filter cuts out just about everything apart from the HA wavelength light that is being pumped out by the emission nebulas - a vivid shade of red.  This means that it is more or less impossible to see through your view finder and only really bright objects will show up on a camera live view screen - something that makes focusing a wee bit problematical.  It is difficult enough already to focus on a pin point of light against a black back ground.  You then erect additional hurdles by fitting the HA filter and things are about twenty times harder.  Fortunately techniques such as pre-focussing on a really bright object like Jupiter, or spending the time in the dark and cold to locate and mark infinity for HA (which is different to infinity without) pay dividends.

Then there's processing.  Your images arrive back from the dark site, a rather shocking shade of red, but Photoshop soon sorts that out, with the final touch being to convert the image into striking Black and White images like the one of Barnard's loop above.

California Nebula

Heart & Soul Nebulas

The very feint Cone Nebula and the Rosette Nebula