July 2011: Narrowband against full-Moon light

More of narrowband. This time, I tested the H-alpha filter on a delicate object in a full-Moon night. Of course, the light of the Moon washed out almost any signal from the R, G and B filters (the R one did capture some). But, as expected, the H-alpha subs were perfect, with no trace of light from the Moon. I even increased exposure time to 700 seconds in the subs. 

The target was the North America Nebula (NGC7000). Well, a small fraction of it, because it’s a quite wide object. In this case, I targeted the “central america” portion of it.

I’ll have to come to it again without Moon!

(H-Alpha + R)GB, with 700-second and binned 2X2 for H-alpha, and 300-second and binned 3X3 for RGB: 5 subs for H-Alpha, and 3 subs for R, G and B. Imaged with the QSI583WSG, guided with the DSI (and re-processed from the previous version after six months, trying to apply my improvements in processing!!!)

Go to this object description and this image technical detail.

July 2011: The challenge of processing narrowband with broadband

Well, nobody said that this was going to be easy! Using narrowband filters (here I’m using an H-alpha one) gives you a lot of flexibility in astrophotography. Specially, with nebulae, in which strong H-alpha emissions exist, this type of filters can get really deep inside details, and they also filter out undesired light (as, for example, polution light).

But, achieving a good balance while processing narrowband images together with “normal”, broadband RGB frames, has proven to be a real challenge for me. A lot of things have to be taken into account. To begin with, the size of the stars in the pictures are smaller in the narrowband images. Also, using H-alpha as a Luminance layer brings in new problems, as a lack of colour in the final image. And, if we try to weight it down, we lose the incredible detail it contains!

I’m NOT happy with my processing of the Crescent Nebula. But I’m not sure if I’ll be able to improve it in the short term. For this image, I’ve finally blended the R and H-alpha channels, but before that I’ve processed the narrowband component alone to allow for maximum detail and, at the same time, reduce noise in the background. Deconvolution, with the help of masks, has worked some “miracles” with the fine details and tendrils of the Crescent. The global colour balance has been achieved working with the R, B and G components histograms.

(H-Alpha + R)GB, with 600-second, binned 2X2 frames: 5 subs for H-Alpha, and 3 subs for R, G and B. Imaged with the QSI583WSG, guided with the DSI.

Go to this object description and this image technical detail.