NGC 6791 - Open Star Cluster in Lyra
NGC 6791 is an enigma. The stars are twice as old as our Sun but have an Iron-to-Hydrogen abundance ratio (metallicity) that is more than twice that of the Sun. This flies in the face of the rule of thumb that "older means metal-poor". NGC 6791 is one of the most studied star clusters.
(see following post for technical details and comments)
Brian
NGC 6791
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Please upload large images to photo sharing sites (flickr, etc) rather than trying to upload them as forum attachments.
Please share the equipment used and if possible camera settings to help others.
Please upload large images to photo sharing sites (flickr, etc) rather than trying to upload them as forum attachments.
Please share the equipment used and if possible camera settings to help others.
NGC 6791
- Attachments
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- NGC_6791_LRGB_258m_G100_BL20_Bin75.jpg (167.75 KiB) Viewed 2847 times
Re: NGC 6791
Technical Details:
William Optics 71mm f/5.9
Altair 290M camera (uncooled)
Optolong LRGB filters
Unitron Model 142 GEM
Passive tracking with PEC
No active guiding
Gain 100 (FWD: 15ke-, 3.66 e-/ADU)
Offset: 20 ADU
Captured over 3 nights:
L: 45 x 60s
R: 80 x 50s
G: 80 x 50s
B: 80 x 60s
Total integration time: 4.3 hours
PIPP 2.5.9
Deep Sky Stacker 3.3.2
StarTools 1.3.5.289
Comments:
Low gain was required to capture wide dynamic range from brightest stars (8th magnitude) to faintest stars (16th magnitude) without saturation.
Luminance stack was acquired two weeks earlier with a gibbous Moon. Unfortunately I did not take Flats. No dust motes but noticeable vignetting.
First version had total integration time of 3.2 hours. I was unhappy with noise level so I captured more RGB in this second version. Only a very slight improvement in SNR, less than I expected. Since then I've come to learn that 50 darks, instead of 30, yields significantly lower noise.
I think it is time for a cooled camera.
Brian
William Optics 71mm f/5.9
Altair 290M camera (uncooled)
Optolong LRGB filters
Unitron Model 142 GEM
Passive tracking with PEC
No active guiding
Gain 100 (FWD: 15ke-, 3.66 e-/ADU)
Offset: 20 ADU
Captured over 3 nights:
L: 45 x 60s
R: 80 x 50s
G: 80 x 50s
B: 80 x 60s
Total integration time: 4.3 hours
PIPP 2.5.9
Deep Sky Stacker 3.3.2
StarTools 1.3.5.289
Comments:
Low gain was required to capture wide dynamic range from brightest stars (8th magnitude) to faintest stars (16th magnitude) without saturation.
Luminance stack was acquired two weeks earlier with a gibbous Moon. Unfortunately I did not take Flats. No dust motes but noticeable vignetting.
First version had total integration time of 3.2 hours. I was unhappy with noise level so I captured more RGB in this second version. Only a very slight improvement in SNR, less than I expected. Since then I've come to learn that 50 darks, instead of 30, yields significantly lower noise.
I think it is time for a cooled camera.
Brian
Re: NGC 6791
Brian
A good image backed up with technical details - should help others when trying to imaging this type of object.
Dave
A good image backed up with technical details - should help others when trying to imaging this type of object.
Dave
Re: NGC 6791
I dug down into the StarTools documentation to discover how to create Synthetic Luminance from the RGB data. Using this technique cuts down my at-the-telescope time by 25% since I no longer need to capture with my Luminance filter. I've read that variations of this technique can be used to add Ha to the image of an emission nebula, and for processing SHO data. Much more to learn.
Brian
Here is my NGC 6791 using Synthetic Luminance:
Brian
Here is my NGC 6791 using Synthetic Luminance:
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- NGC_6791_SynLRGB_138m_G100_BL20_Bin75_20180618_BMorgan.jpg (190.16 KiB) Viewed 2775 times
Re: NGC 6791
Brian, nice image! Since you have captured a Luminance channel, would love to see your comparison of Luminance vs synthetic L on the RGB data.
Cheers
Minos
Cheers
Minos
Re: NGC 6791
Minos,
Yeah, that's the tricky part. If you scroll all the way to the top of this topic you will see an image that used actual Luminance, not Synthetic. The problem with it is that it was taken a few weeks earlier with my Orion luminance filter, not my Optolong luminance filter. Processing in StarTools was quite challenging with a heavy blue cast on the initial stretch -- that is a clear indicator to me that something ain't right. (Ah, now I remember, the Gibbous Moon was bright and I did not take Flats.)
What I'd like to do is this: on the next moonless night I'd like to capture the target with my Optolong luminance filter. That way I can be assured that LRGB is balanced from the same manufacturer.
I've attached my latest Synthetic LRGB of NGC 6791. I learned from the StarTools docs that I was denoising the final image too soon.The colors are a little less dramatic but I think it agrees nicely with the image of NGC 6791 taken by Dark Horse Observatory with his 10-inch Takahashi Baker-Ritchey-Chretien !
http://darkhorseobservatory.org/images/ ... 1_full.jpg
http://www.takahashi-europe.com/en/BRC-250.php
Brian
Yeah, that's the tricky part. If you scroll all the way to the top of this topic you will see an image that used actual Luminance, not Synthetic. The problem with it is that it was taken a few weeks earlier with my Orion luminance filter, not my Optolong luminance filter. Processing in StarTools was quite challenging with a heavy blue cast on the initial stretch -- that is a clear indicator to me that something ain't right. (Ah, now I remember, the Gibbous Moon was bright and I did not take Flats.)
What I'd like to do is this: on the next moonless night I'd like to capture the target with my Optolong luminance filter. That way I can be assured that LRGB is balanced from the same manufacturer.
I've attached my latest Synthetic LRGB of NGC 6791. I learned from the StarTools docs that I was denoising the final image too soon.The colors are a little less dramatic but I think it agrees nicely with the image of NGC 6791 taken by Dark Horse Observatory with his 10-inch Takahashi Baker-Ritchey-Chretien !
http://darkhorseobservatory.org/images/ ... 1_full.jpg
http://www.takahashi-europe.com/en/BRC-250.php
Brian
- Attachments
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- NGC_6791_SynLRGB_138m_G100_BL20_Bin75_20180618_BMorgan.jpg (161.94 KiB) Viewed 2745 times