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fredvanner

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Apr 17, 2019
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I see now from some very nice images online what your talking about.
It's worth noting that most of these "very nice images" are false colour narrowband images. While you won't match a 4m survey telescope, you can get good results with your equipment (and a bit of patience).
 

Muskoka

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Here's a first attempt following a few different flows, going back and forth, trying different things.

Pelican Nebula Resize.jpg
 

fredvanner

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Most of the colour in the Pelican is H-alpha, so the "natural" colour is red (-ish). If you follow the sequence I described and do PCC early in your processing, the initial colour balance will have this red colour. There is absolutely no reason why you should not choose the colour that you have in your image - but it does raise the question of whether it is intentional or accidental.
 
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Muskoka

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Hi Fred, the natural color "in reality" may be red, but that's not how they look after pre-processing. I took some images a while ago of the Sadr Region, and it also came off very tan / brown, not red at all. Nothing has ever looked "red" coming from my current setup. This is how it looks as a unlinked auto stretch. I just left the color in it's natural state from pre-processing, as best I could. I can alter it to look red, I guess, but if it's supposed to be red, why doesn't it process as red, instead of tan / brown? Could the "cheaper" uv/ir cut filter I'm using cause this?


original color.jpg
 
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Muskoka

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Could be a personal thing as well. Here's two examples I found online. I much prefer the dominant tan / brown / redish image than I do the red one?IC5070_Pelican_Nebula_Steve_Richards2048.jpgPelican-Nebula.jpg
 
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fredvanner

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If you look at the example I linked in post #38 above, you will see that colour calibration with PCC gives the natural H-alpha colour; since PCC uses the stars as photometric references, this is about as close to "correct" colour as you will get. Unlinked STF is particularly unsuccessful with this image, since so much of the image is not neutral background (it is effectively trying to make the image neutral grey - and most of the colour in the nebula is "neutralised").
Could the "cheaper" uv/ir cut filter I'm using cause this?
This filter should have no significant effect on this image.
 
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Muskoka

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Here's after PCC and a stretch, more redish? I don't mind that look, and could continue processing that. Here's the stats as well, which are a lot more balanced now.
red.jpg
STATS.jpg
 
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pfile

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are you using the unmodified T3i for these images? if so that's the 'problem' - the IR cut filter cuts something like 80% of the Ha light from all targets and this nebula is predominantly Ha (like most, really...) so the signal is just weak. but the color in your most recent post looks right to me.

rob
 
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fredvanner

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Perhaps I should emphasise that, in my example (link in post #38) I did nothing to try and make the image red, I just ran PCC, and PCC calibrated the colour (I did no processing that is not listed in #38). Note that unlinked STF is not colour calibration - it simply equalises the histograms of the R, G, B channels; in a typical image where most of the histogram is background, the result is to neutralise the background, but this is a very crude estimate of colour calibration.
 

Muskoka

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are you using the unmodified T3i for these images? if so that's the 'problem' - the IR cut filter cuts something like 80% of the Ha light from all targets and this nebula is predominantly Ha (like most, really...) so the signal is just weak. but the color in your most recent post looks right to me.

rob
No, this was all taken with the 533mc Pro as Fred has stated, gain 100, offset 30, -5c, 10.9 hours of integration.
 

pfile

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i assume as an astro camera then this has no IR cut filter (or at least one that avoids the Ha line at 656nm?)

10.9 hours of integration is a lot if you are really at bortle 3. something seems off.

rob
 

fredvanner

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I don't see anything particularly "off" in this image (this version is my "basic processing" workflow from post #38); there is nothing unexpected about the colour, once it is properly calibrated. The long integration time shows up in the very low background noise (not visible in this jpg). The level of detail is now probably limited by the 61mm aperture.
I'm more puzzled by the relatively high minimum values in the statistics in post #47 above; that seems to be an artefact of the post-processing of that image; my image below has retained the zero minimum from the initial "fixed stretch" STF.

1624046977809.jpeg
 

pfile

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by "off" i mean that there should be a lot more signal available there in the pelican. the colors are right but the signal seems weak to me for so much integration, especially from a dark site. it just feels more like 10h from a bortle 8/9 than a bortle 3.

rob
 

Muskoka

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I shouldn't have to post this, I know where I live, and I know it's Bortle 3, but here goes anyways.

Assuming the site I got this from is accurate enough? Here's the stats for my 6 acres of heaven. My nearest neighbors are both 300+ft away, through dense bush. I live off grid, in the middle of the bush, so there's little to no ambient light. When there's no moon, you can quite easily walk into something without seeing it, which I've done. My site is most definitely Bortle 3, as I stated.:)

If the images do not appear that way, I don't know the reason why. But the Bortle class of where I live, is not the reason.

light polution.jpg

And here's the 329 120 second images that total 10.9 hours of data.

images.jpg

And a screenshot of a single 120 second sub as it appears in AsifitsViewer.

single sub.jpg
 
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pfile

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hey - i'm not attacking you. you've just misunderstood. when you get more experience in the hobby you'll understand that in order to get an equivalent SNR out of a target from bortle 8 as from bortle 3, you'll need to spend many, many more hours on the target. i don't remember what the ratios are like anymore, but for me, here in bortle 8, i have to put 10 hours on a target (per channel!) to get what you might expect from maybe 1-2 hours in bortle 3. and somehow that's what the image looks like to me. i didn't mean to imply that you are lying about where you live or what you did...

for bortle 3, after 10 hours, i'd expect a lot more signal. that's all. this might mean that your gain/offset is not right. or maybe the subexposures are too short for the particular gain/offset. or it may indicate something wrong with the camera. or maybe that camera just has a low QE... or it may indicate that nothing's wrong at all, and i have misanalyzed the situation. all i can say is i have 12+ years experience with astrophotography and have seen a lot... a lot... of images of the pelican nebula, and taken a lot of them myself from bortle 8 and bortle 3.

rob
 

Muskoka

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Jun 8, 2021
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hey - i'm not attacking you. you've just misunderstood. when you get more experience in the hobby you'll understand that in order to get an equivalent SNR out of a target from bortle 8 as from bortle 3, you'll need to spend many, many more hours on the target. i don't remember what the ratios are like anymore, but for me, here in bortle 8, i have to put 10 hours on a target (per channel!) to get what you might expect from maybe 1-2 hours in bortle 3. and somehow that's what the image looks like to me. i didn't mean to imply that you are lying about where you live or what you did...

for bortle 3, after 10 hours, i'd expect a lot more signal. that's all. this might mean that your gain/offset is not right. or maybe the subexposures are too short for the particular gain/offset. or it may indicate something wrong with the camera. or maybe that camera just has a low QE... or it may indicate that nothing's wrong at all, and i have misanalyzed the situation. all i can say is i have 12+ years experience with astrophotography and have seen a lot... a lot... of images of the pelican nebula, and taken a lot of them myself from bortle 8 and bortle 3.

rob
I don't think I misunderstood anything, too old, and wise, for that. I'll just leave it at that.

So, what do you think is the reason for your questioning of the 10.9 hours in a Bortle 3? What are you seeing, or not seeing, that makes you think there's a lack of data, or the data is weak?

With all your experience, can you give me some suggestions on how I can improve things? Is more integration time needed? Would exposures longer than 120 seconds help? Would a different filter help, or removal of the uv/ir cut filter I'm currently using? Is it perhaps the way the integration was done in Pixinsight? Could it be the fact that there was a bit of moon on a couple nights?

There's very little noise in the master integration, the camera has done it's job, so why is the signal low, in your estimation?
 
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