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Poll: What approach to use in long-exposure images [Multiple selection possible]
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What approach to use in long-exposure images [Multiple selection possible]
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Old 26-08-2014, 02:37 PM
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Meru (Michael)
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Question Advice for my first mega-exposure image

Hi everyone,

I finally got around to getting my pier installed and plan to do my first mega-data image this week (>16 hours) Widefield of NGC6188 + NGC6164. I need advice about the following two topics (Image Capturing + Hardware):

  1. Get mega data in Ha and use it as L, with OIII & S2 binned 2x2 for colour only. This is my normal routine and find it works very well.
  2. Go for a true Hubble Palette image i.e. Use SHO as RGB directly. Never done this before.
I am leaning towards 1) as it will give me oodles of Luminance data in that channel that will be rich with data, rather than spending 6 hours on each channel.

  1. Use 80ED with Flattener. This gives a very well-corrected image but only @ f/7.5 d)
  2. Use 120ED with my 0.67x reducer @ f/5. Edge performance isnt very good (though tolerable) but gives me a full stop extra of light.
I am leaning towards 2) as an extra full stop of light (i.e. double the amount) over 16 hours. I've shot an image with the 0.67x reducer (see here) and dont think I will have too many issues processing the coma out in Startools.


Thanks for reading, and what would you recommend? I have a poll to make it easier

Last edited by Meru; 26-08-2014 at 03:12 PM.
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Old 26-08-2014, 02:50 PM
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Depends a lot on your target What are you aiming for?
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Old 26-08-2014, 02:53 PM
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Sorry probably should have mentioned that! Widefield of NGC6188 + NGC6164 (Elephant's Trunk Nebula)

[Original post updated]
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Old 26-08-2014, 03:04 PM
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I've never heard that called the Elephant's Trunk before? That name is usually reserved for IC1396.

Since you're unlikely to be getting any significant benefit from hardware binning on a QHY9 I'd go for unbinned data in all three filters and decide what to do once you've collected a couple of hours in each. You can still software bin OIII and SII if you want.

You won't see the OIII halo around NGC6164 very well if you use Ha for Lum, but even if you don't it is pretty faint...

Cheers,
Rick.
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Old 26-08-2014, 03:13 PM
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Sorry, 3.30itis finally kicking in


Hmmm that's a good point, I can always bin in software. So maybe spend the first night getting a few subs of each and then see what the data looks like? And when you say not much benefit are you referring to the shallow well depth and not much gain in quality of data when binning on the 8300? Or something else?

And yes I was thinking about that, I might see if I can get some O3 on the weekend if all goes well
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Old 26-08-2014, 03:34 PM
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Quote:
Originally Posted by Meru View Post
Hmmm that's a good point, I can always bin in software. So maybe spend the first night getting a few subs of each and then see what the data looks like? And when you say not much benefit are you referring to the shallow well depth and not much gain in quality of data when binning on the 8300? Or something else?
The only benefit of hardware binning is reduced read noise. In a perfect world you'd get the same read noise for a 2x2 superpixel as you get for a single pixel read. The KAF-8300 sensor doesn't do as well as some others. There's probably some benefit but it's only small and if you're doing decent length subs so that read noise isn't overwhelming then it will be even smaller. Better to do unbinned and have the extra flexibility.

Cheers,
Rick.
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Old 26-08-2014, 04:39 PM
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hi,

There is the other issue with horizontal blooming on the kaf8300.

qhy recommend software binning for horizontal and hardware for vertical (in a forum).
no idea how this'll be done but the horizontal blooming when binned 2x2 is a pain. I now bin 1x1 for all. it can quite easily be fixed in Maxim as it doesn't affect target data, just saturated stars.

As for the 2 options, I'd go with the larger aperture.


Cheers
Alistair
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Old 27-08-2014, 12:34 PM
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Ah ok, thanks for the advice Rick & Alistair. Yes I think going unbinned will be the way forward for the flexibility.

Last night I tried the 120ED + reducer combo and with 20min subs got an unbelievable amount data in Ha. However I was faced with some issues with my new pier setup, field rotation + dew killed the imaging session. Hopefully I can sort this out tonight and give it another shot
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