My first crack at Ha imaging

[allan gould]

Nice one Alex. Have just got my Ha and O111 2" filters and so will be doing some synthetic colour shots as soon as this cr@ppy weather disappears from Brisbane.

[Hagar (Doug)]

Originally Posted by JohnH

Tj,

I am very glad you brought that subject up.

Is there a way to optimise the Gain/Offset settings for a particular CCD - the linked article addresses offset by taking bias shots and looking for the singnal "floor" if I am reading it correctly but the English is not crash hot. There is no mention of GAIN settings at all. In the case of the 145m I have set the gain to 400 (there are 1024 levels available). I did this based on the two attached graphs which show me S/N ratio increases with gain to at least that level.

I would love to confirm my interpretation, what is the best setting to use? I guess I will be trading some dynamic range for sensitivity if I go too far? What is a good rule of thumb 3/4 of max? Half?

Should I set it perhaps based on the sky glow level - eg set an exposure length I can track well to routinely like 240s and then adjust the gain to get the sky glow histogram showing nicely and then set the relevant offset?

Any advice welcome.

Gain and offset are probably the most dificult settings to come to terms with. The link I have attached here is a link to the user guide supplied by Craig Stark of Stark labs for his capture program, Nebulosity2. In my opinion the best and easiest to use capture program on the market today. Craig himself is an avid user of the QHY8 camera and has included a very comprehensive description of the use of gain and offset for the QHY8 and other cameras. look at page 20 onwards of this user guide.
http://www.stark-labs.com/downloads_...osity2Docs.pdf

This should give some idea of the use of these settings and ideal settings.

[gregbradley]

Originally Posted by Hagar

A combined image of M8. 24 X 5 min exposures stacked and calibrated in IP3. Not sure about this Ha stuff but it looks like I have quite a way to go with it. CS3 stuffed me up in curves with the grey scale image. All upside down quite unusual to me. The image w
as shot tonight under the full moon so the result is interesting.

Hi,

You convert the image to RGB before you process and all the Photoshop levels and curves will work as usual instead of "upside down".

Mode/rgb

Also was this binned 2 x 2? It should be more detailed for 2 hours of exposure.

With a one shot colour only one in 4 of the pixels is really getting much signal with Ha (the red one in the matrix of 4). So binning 2 x 2 is more efficient and more sensitive and with virtually no loss of signal.

Greg.

[Kevnool (Kev)]

Great image there Doug.....cheers Kev.