A happy chance has lead me to acquiring an Astrodon SII narrowband astrophotography filter for a very low price.

Tri colour narrowband astrophotography is one of the most difficult aspects of our hobby. However, it does appear to be the direct in which I am rapidly moving.

Simply taking RGB astrophotography images of deep space objects is getting a little tiring. Unless you are really good at it, like the Parker / Carboni team the results are a little mundane. If you are really good at it the results are extremely impressive. But, like Greg, a nice dark site does help a lot!

Narrowband astrophotography is very different. We construct the colour image using images captured with narrowband astrophotography filters. These filters allow is to image a very slim band of light centred on the emission from certain elements in our nebula targets. Normally we use H-alpha, OIII and SII.

The secret to a good narrowband astrophotograph is exposure time. Just like Greg with his massive 24 hour+ integrations, a really good narrowband astrophotograph has a massive amount of exposure. Doing 10-15 sub exposures of 20minutes sub exposure time on EACH channel is not unusual. If the target is particularly faint in one or more channels, then massive extra exposure time must be included. Some narrowband astropohotograhers include several days of exposure in a finished image.

A few weeks ago I purchased a OIII narrowband astrophotography filter from Baader so that I could use bicolour techniques to add some interest to my images.

In a stroke of remarkable good fortune, an astronomical acquaintance in the uk offered me an Astrodon SII filter which he'd had for a while, but no real plans to make any use of it. He offered it to me for a price I could not refuse.

SII is sulpher two. This is the emission of sulpher atoms at a wavelength of 673nm. It is deep into the red - even deeper than hydrogren alpha. It is right on the edge of human seeing.

Of course, with all my Heart of the Heart Nebula data from last year, you can guess my first tricolour image... Yesterday I visited Greg in the New forest for a cup of tea, and we were both looking forward to a fine clear night. We were calling it "the last day of summer". So last night I was able to capture 15x1200s of SII data on the Heart of the Heart nebula. Last week I got 11x1200s of OIII data. Now for the processing marathon!