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Originally Posted by tornado33
Lovely image there. I take it you were using the SBIG Adaptive Optics system, they are a great idia, especially on lesser quality mounts, I believe they can easily account for a few mins of periodic error with pin sharp images.
What focal ratio was that image shot at? Its amazing that it requires 1 hour sub exposures to get through the H alpha filter.?
Heres a 2x 20 minute shot I took with an unmodified Canon 300D , 10 inch F5,6 newtonian and a 7 nm Ha filter of Eta carina
http://www.users.on.net/~josiah/baader/eta%20carina%207%20Nm%20H%20alpha%2 0small.jpg
Now if I can just get a hold of a narrowband SII and OIII filter.... 
Scott |
Hi Scott,
No I didn't use a AO-7 for this image. I do own one tho. I would use it if it worked with my AP x.67 FR. They will account for mounts with large amounts of PE. +/-120 with ease.
Readout noise is a pain in the rear end.
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The darker the site the longer it takes to overcome. Basically you want the background of your image to exceed your readout noise.
All the faint good stuff shares almost the same space in the histogram as the noise:
Example Only
20 min HA exposure
Readout Noise - 500 ADU (Analog to Digital Units) - 12bit CCD have 4096
Shot Noise - 250 ADU
Faint Part of Nebula - 400 to 600 ADU (50% of faint part of the nebula is readout noise)
45 min HA exposure
Readout Noise - 500 ADU
Shot Noise - 500 ADU
Faint Part of Nebula - 500 to 800 ADU (much better outcome)
Hope this helps.
That’s a really nice image. What mount are u using?
Yes, these filters are very expensive. Someone really should start a library.
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Cheers,
Brad