central bright area...vignetting?

Discussion of using SharpCap for Deep Sky Imaging
psy1280
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Joined: Wed Oct 24, 2018 4:52 pm

Re: central bright area...vignetting?

Post by psy1280 »

Once again, much thanks Brian,

I sent you the flat files. I'll look forward to your analysis. The flats were take at 120 gain (same as last outing), 1/2 second exposure (this is probably different from what I took outside, not sure the exposure is critical). I sent along a screen shot of the flat histogram. Also, I have a IDAS LP filter attached to the HyperStar.

Question. I hadn't thought of this until our discussion. If, in fact, I keep the same camera orientation, the same focus, the same gain, and the same temperature (don't think this is critical), when I go out next time I won't have to make a new flat (if all of the above remain constant)? Wow, that would be great. And if so, are there any disadvantages to pr-taking flats?

Can't wait to see what you come up with,
Joe
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oopfan
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Re: central bright area...vignetting?

Post by oopfan »

Joe,

I received a Gmail from you an hour ago having 51 attachments. When I tried to download them, Google says that I don't have access to your Gdrive. I sent you a request for access, but nothing has changed.

On August 11, you successfully sent me Bias and Dark files over Gdrive. You contained all the files in a folder named "2021-08-11". I've taken a screenshot of it here:
Joe Gdrive share.jpg
Joe Gdrive share.jpg (30.45 KiB) Viewed 553 times
Whatever you did worked then. Can you repeat what you did? I'd be happy if you could add the 51 files to the existing folder "2021-08-11".

Brian
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oopfan
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Re: central bright area...vignetting?

Post by oopfan »

Hi Joe,

Your Flats look excellent! Here is a screenshot of the histogram:
MF-IG_120.0-E_2.0s-ZWO_ASI294MC_Pro-4144x2822-St-histo.jpg
MF-IG_120.0-E_2.0s-ZWO_ASI294MC_Pro-4144x2822-St-histo.jpg (5.34 KiB) Viewed 518 times
and here is the Master Flat:
MF-IG_120.0-E_2.0s-ZWO_ASI294MC_Pro-4144x2822-St.jpg
MF-IG_120.0-E_2.0s-ZWO_ASI294MC_Pro-4144x2822-St.jpg (226.19 KiB) Viewed 518 times
All of your calibration files are perfect. Next step is to capture Lights on the next clear night.

Here are the guidelines I want you to follow.
1. Turn on the cooler.
2. Perform Polar Alignment.
3. Point the scope at the DSO of your choice, and then prepare for imaging:
4. Set Color Space to RAW16.
5. Set Gain to 120.
6. Set Exposure to 30 seconds.
7. Set Output Format to FITS.
8. Use the Capture Frames tool like you did for the calibration frames. DO NOT LiveStack. There is plenty of opportunities to LiveStack after we confirm that the "old school method" produces a beautiful astrophotograph for you.
9. When complete, upload the Light frames to Google Drive. I will process them

Your equipment appears to be in top working order, so I expect that you will have a beautiful image to show off. Almost always the culprit is human error. My opinion is that your lack of success with LiveStack has to do with human error. We need to track it down with the help of everyone here on the forum. But that comes later once we confirm that "old school" works.

DO NOT LiveStack (for now).

Brian
psy1280
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Re: central bright area...vignetting?

Post by psy1280 »

Brian,
You've been most generous with your time and effort to help me. I can only hope when I achieve some modicum of success in this hobby, I too will, as they say, 'pay it forward.
'
One quick question. Can I use the flat I sent you when I image since the exposure, temperature, gain and camera orientation haven't changed?

Yours,
Joe
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oopfan
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Re: central bright area...vignetting?

Post by oopfan »

Joe,

Absolutely! All you need to do is concentrate on capturing Lights. We have all of the calibration files we need, just as long as you stick with 30-second exposures and gain 120.

This so-called "old school" method is what all astrophotographers practiced before LiveStack was introduced to the world. I still use "old school" because I'm old :-)

You will practice "old school" just long enough to prove that there isn't something wrong with your equipment. Once we prove that your equipment isn't at fault, then we transition over to LiveStack. My hunch is that you have been using it improperly. In the meantime, one step at a time.

Brian
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oopfan
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Re: central bright area...vignetting?

Post by oopfan »

Hi Joe,

You did a great job capturing the North American Nebula and Pelican Nebula. You suffered through a long stretch of bad weather, so I can understand why you jumped at the chance to image the other night. However, the 90% Moon was only 60 degrees away. Then, combine that with the ungodly light pollution of New York City, and you've got your work cut out removing that LP.

I have three shots to show. The first shows the result of stacking (using Astro Pixel Processor) of 164 30-second Light frames using calibration frames that you captured earlier in the week. The second and third shots are the same but scaled differently to fit your browser. Those two shots incorporate: light pollution removal and star color calibration using APP, followed by de-noising and stretching using Affinity Photo.

Joe, your camera is oriented in Portrait Mode. You may want to consider rotating it 90 degrees to achieve Landscape Mode. It will fit better on computer monitors. Just remember that you need to re-capture Flats if you change orientation.

A last note: you may see a "cool" spot near the center of the last two images. That is not a vignetting problem. It is an artifact of light pollution removal. Notice that there are other cool spots at the lower left corner and on the right margin. I could have eventually removed them given enough time with the tool. I used APP. I am not familiar with SharpCap's ability to remove light pollution, but this is a pretty extreme case. I think that you will need to do further LP removal in some other software. Like I mentioned, I use Astro Pixel Processor, but that is fairly expensive. Affinity Photo is a remarkable value but I'd have research if it can remove LP.

Here are your photos: first shows the extent of LP coming out of stacking, and the second and third show LP removal:

Brian
Joe NA Neb.jpg
Joe NA Neb.jpg (103.3 KiB) Viewed 476 times
North_American_Nebula-fy-90degCW-1.0x-LZ3-NS-SC-St-AFF-resize-more.jpg
North_American_Nebula-fy-90degCW-1.0x-LZ3-NS-SC-St-AFF-resize-more.jpg (341.23 KiB) Viewed 476 times
North_American_Nebula-fy-90degCW-1.0x-LZ3-NS-SC-St-AFF-resize.jpg
North_American_Nebula-fy-90degCW-1.0x-LZ3-NS-SC-St-AFF-resize.jpg (677.34 KiB) Viewed 476 times
ChrisR Oz
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Re: central bright area...vignetting?

Post by ChrisR Oz »

Hi Brian,

If I can comment a little late on this …

The Dark you show has a characteristic diagonal flare. I have found using the 294MC Pro that it has a light leak at the back in the ventilated chamber. So you must cover the rear as well, or use a darkened room.

Cheers, Chris.
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oopfan
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Re: central bright area...vignetting?

Post by oopfan »

Hi Chris,

The Dark on Page 1 is from my Altair 290M. The strong diagonal flair is amp glow to the best of my knowledge. I don't think it is a light leak. At times I've used that camera for lunar at dusk when there was still a lot of ambient light...no problems.

I did show a Dark on page 2 (or is it 3?) for Joe's ASI294MC. He does have amp glow, but it doesn't look suspicious. I'll take your word for it.

I walked Joe through the process of taking 30-second Darks with his camera removed and in his home office. He concentrated on ensuring that light did not sneak through to the sensor from the front, but we didn't think of covering the back end. Joe said he captured with the lights turned off and the door closed.

Chris, what do you think of the possibility that stray light is sneaking in as he is imaging with a Hyperstar configuration? He's got Bortle 7/8 skies.

Thanks,
Brian
ChrisR Oz
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Re: central bright area...vignetting?

Post by ChrisR Oz »

Hi Brian,

The amp glow from the 294MC is a radiating pattern in the top right (and a weaker one on the left). It does not really show a more diagonal streak, as the Dark that you referred to. However, I was plagued by a diagonal streak that I eventually found to be a light leak from the rear (trying to do Darks in the daylight with a covered scope). Hence my comment …

That’s a good question. But I think the amount of stray light you’d get with any ‘bright sky’ is orders of magnitude weaker that this stray light during the day. Just a hunch really …

Cheers, Chris.
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