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I finally have a full clear night coming up and I would like to image some broadband targets. I am currently thinking of doing the Dark Shark Nebula. What are other targets I should consider? I have read that it is not beneficial to take exposures above 30 seconds while imaging broadband at F/2 but I'm not clear on the reasons. Is this a myth, what else should I be looking out for in a bortle 7 area? I will have 12 hours of clear skies so the number of exposures will be a consideration. The camera I will be using is an Altair 26C, are there any settings that would optimise the session? |
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| I take 300sec exposures at f2 with an Edge8 and Hyperstar without issues on dimmer objects, like the Shark. I also take 50-60 60sec exposures and use those for the stars in the final image. You don't have to, but you end up with slightly sharper stars if you want to take those extra steps. |
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I would image M78 and Barnard's loop in Orion, which has both broadband and narrowband elements. I have imaged this pair with a Hyperstar rig from a Bortle 8-9 zone last year: https://www.astrobin.com/k95l7a/C/ I was pleased with the result, but I think it could be done (and indeed has been done) much better. Also, I think you can extend your exposures to about 60 seconds. More than that and you will risk blowing out your stars at f/2. Finally, I would also suggest IC 447, Dreyer's nebula, in Monoceres. I'm working on this now with a slower setup and I'm craving f/2! Hope this helps and clear skies! Matt |
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| You should use some light pollution filter. |
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| Thanks for the tips, I have also thought about doing M81 and M82 to try and get some IFN but my field of view may be too large to capture the galaxies in detail. |
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Arpad R: Even if you are not worried about the complicated gradients, there is another fundamental issue you will be facing at Bortle7. It is background sky noise. Once you have totally gathered, say, X e- of the sky, you get SQRT(X) of noise added to your data. There is no way to fix this but driving somewhere under the darker skies or using narrowband filters. |
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You mention above that you were not clear on the reasons for selecting a certain exposure time. There is this excellent talk of Dr. Robin Glover about sub-exposure time, depending on your sky brightness and the read noise of your CMOS camera (link below). It is worth viewing the entire video and will help separate some of the myth from theory. I've used his approach for calculating sub-exposure time and the results can be surprisingly short sub-exposure times for my Hyperstar rig and ASI2600MC-Pro. I take the results as minimums and add time for light pollution or narrowband filters. Good luck! Darrell https://www.youtube.com/watch?v=3RH93UvP358&t |
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| Similar to Darrell, I use up to 300sec for NB (Bortle 8) and up to 30 seconds for broadband for my stars. For galaxies, I never go over 60 secs as stars get blown-out. For dark zones, the sky's the limits! |
