DSLR and narrow band imaging

Hi,

It's emission  nebulae where Ha gives you detail in the sense that we usually have in mind when discussing narrowband pics.

Galaxies are the very definition of a broadband target since they contain stars of all spectral types plus all the other deep space objects. They are also thousands of times farther than nebulae, and almost all of them (including M81) are really, really faint.

Granted, some of them will have really prominent Ha regions (M101 and M33 spring to mind) but they will show up as bright red or purple splodges hanging from the spiral arms, kind of like the lights on a Christmas tree. You would not really be able to resolve the detail in Ha like people do with a nearby emission nebula, unless you had a scientific grade telescope/observatory combo. The only

The detail on galaxies comes primarily from dust lanes.

Now, narrowband in general is a bad idea with an one-shot-colour camera and it does not matter much if it is modified or not. Because you are collecting very little light to begin with and only one out of every four pixels in your sensor (the red pixel) is sensitive to it. It is not impossible and can even be rewarding with a bright source such as the Lagoon, but for a galaxy you need so much exposure to register anything above your offset, that thermal noise and other factors associated with ultra long exposure (random breezes etc) become significant enough to render the whole exercise futile.

Cheers,
D.