Thanks all
I centred on ra 08h 29 mins, dec -44, 46, frame orientated long axis north-south. In this image east is up. Im glad I fitted in most of it, its hard to be sure till after processing is done, as the nebulosity is so faint it barely shows up on each sub.
Yes the Ha filter is 2 inch. Its actually one of Baader's prototypes, and is un mounted, but thats okay, it sits snugly in the back of the 300mm lens, along with a clear IR filter to make sure no unwanted IR light sneaks past. Baader actually gave me the filter as thanks for their using some of my earlier DSLR images shot with their UHC-S filter
Bert has the right idia for narrowband imaging, by cooling the camera. The dark current noise is more noticable with narrowband imaging, particularily with 7 Nm. The background is so dark that a good deal of what background there is, is thermal noise. Though proper dark subtraction gets rid of most, it cannot get rid of every bit.
Overall the modded camera accounts well for itself considering only about 1/3 of the pixels are used (the red ones) Theres no usable signal with the green and blue, thats why I only use the red channel and delete the other two. Id give my right arm to Canon if they made a DSLR without the bayer filter (a monochrome sensor).
The 300mm lens comes in handy, helping offset the reduced signal with its very fast f ratio of 2.8.
Baader also happen to make their HA filter with a slightly offset passband, that favours fast instruments with a wide light cone, and so is perfectly suited for the 300mm lens
I should mention that on setting up I first find a bright star and take some short test images, to get the star centred, then I align a finderscope on it, then use that to see what the lens is pointed at, as the filter is completely dark to the eye, only the moon and Sirius are bright enough to see in the camera viewfinder. I get proper focus by taking 10 second test images, then adjusting focus till stars are as small as possible. I have camera connected to laptop so I can examine the images at full size on the laptop rather then the cameras tiny screen, then I locate a guidestar with the Q guider cam on the Orion 80mm short tube guidescope, magnify it 400% with the Q guider software, put an artificial reticle over it, sit back and manually guide it and wait for the neighbours cat to jump on my lap and keep me company for the imaging session
