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Old 08-07-2019, 02:37 PM
Gavin1234
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Too many stars?

Hi,

I’m working on this image of m20. There’s still a bit to fix up like where I’ve pushed the blue too much. But I feel like the stars are overpowering it. I’m not sure why they look so prominent.

Any thoughts on this?
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Old 08-07-2019, 02:48 PM
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Well Gavin it is pretty wide field image an IMHO that is about right for the Star field.

Leon
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Old 08-07-2019, 03:15 PM
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Hi Gav, I agree with Leon, with a field that wide there will be plenty of stars.
A bit of colour correction & you have a lovely Triffid there. You could always tighten your stars slightly if you think they're too overpowering.
Alternatively you could crop the image a bit to make M20 more prominent or perhaps even squeeze the Lagoon in to share the space(no pun intended). Just my two bobs worth.
Cheers,
Antonio
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Old 08-07-2019, 05:23 PM
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I think the stars should be a little smaller - could be due to poor conditions, not sharp enough focus, a processing issue such as over stretching?
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Old 08-07-2019, 05:32 PM
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Agree with others. Looks about right to me. It's a pretty busy part of the intergalactic superhighway
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Old 08-07-2019, 08:56 PM
raymo
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Not only are the stars too big, they have had the colour processed out of them so they are all bright white, making them more prominent.[not that there are many strongly coloured stars in this field].
Shorter subs will produce fewer stars without affecting the nebula much, it being very bright. I found with a DSLR at ISO 1600 45secs
worked well.

Last edited by raymo; 08-07-2019 at 09:02 PM. Reason: more text
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Old 08-07-2019, 09:50 PM
RyanJones
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Nice work Gavin. I always reduce and tighten my stars in post processing and now I’m using a dual narrow band filter the stars are reduced even more. That being said, my fields of view are nowhere near this large. I think you get to a point where, as you have, you start to get enough stars to show the Milky Way. At this point I think it gives the object a different perspective and actually becomes another feature of the image. Just my 2 cents
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Old 08-07-2019, 10:56 PM
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Gavin, which scope/camera did you use?

Apart from the already mentioned atmospheric conditions, focus and processing issues, if you used a refractor another possibility is the inadequate colour correction for UV.

Most of APO refractors (unless you sell you kidney and your car to get one) will have some "star bloating" in blue/UV. This includes triplets but to a smaller degree. If your camera is sensitive down to 380nm then this may be a reason for the size of the stars.
(Reflectors are not affected by this)
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Old 09-07-2019, 04:41 AM
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It looks good to me. I think the key is keep capturing and building data and as time goes on you may get to reprocess and develop more techniques to adjust your images to suit your preference. Well done I say.
Alex
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Old 09-07-2019, 09:49 PM
Cimitar (Evan)
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Hi Gavin,

You've got a great image coming together there
Similar question to what Luka asked - which scope/camera did you use?

If you used your Canon 600D, what ISO? When I used my Canon on ISO 1600 I often found the stars were more overwhelming as opposed to using say ISO 800. When that happens, one way to fix is take 2 exposures - one for the DSO (ISO 1600) and one for the stars (ISO 400 or 800). Then you can merge the exposures using the layers. This will prevent the stars from getting washed out & losing their colour.

Where possible it's always best to try and get the cleanest image you can in the field (e.g. optimal focus, good weather, optimum exposure times etc), however, sometimes it's just not possible.

Processing can address some of these concerns which is good news!
Out of curiosity, I downloaded your image and had a play with the stars to see if anything could be done. I'm happy to share my result, however, only with your permission.

Cheers, Evan
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Old 11-07-2019, 07:32 PM
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Thanks guys, this one was taken using the Asi071mc and an esprit 100.
I
Its one of my first attempts using the auto focuser the frames were taken over two nights and looking back at the individual subs it looks like one of the two nights the focus wasn’t great. I might try again after discarding those frames.

Evan I would love to see what you’ve done with it if you don’t mind.

Last edited by Gavin1234; 11-07-2019 at 07:45 PM.
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Old 13-07-2019, 07:53 AM
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Started again, a bit more work in this version so far. Also went back the original subs and threw most of them out. Will need more data now.

Just learnt star mask and morphological transform in PI.
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Old 13-07-2019, 10:39 AM
casstony
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Quote:
Originally Posted by Gavin1234 View Post
Just learnt star mask and morphological transform in PI.
You're two up on me, I've barely scratched the surface in PI. The pic already looks better.

You could try Photometric Colour Calibration to see if it brings colour back to the stars - you have to enter a few figures but it's self explanatory - tell it you're at M20, the focal length and pixel size..... not much else needs to be adjusted from memory.
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Old 13-07-2019, 11:38 AM
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Is the lack of star colour due to saturation? Hover over the stars in one of the original sampled subs and check. If many of them are saturated it might be hard to get colour? I've just started on the Trifid and had to drop the exposure time compared to some other targets I've been doing.

Star masks, now you're on the slippery slope to ... Range masks, range-star masks ... A few interesting variations on star masks that I've tried. The second is a doozy!
https://www.cloudynights.com/topic/6...good-starmask/
https://pixinsight.com/forum/index.php?topic=11879.0
And there's also starnet which has now be made into a pixinsight process. But at present it can only be used on non-linear stretched images

Edit: Gavin I just looked at an autostretched version of the M20 I've started on (only have 2.5hours so far). The bigger stars on mine are very white/blue, only the smaller ones have much colour. You might have a look at the Trifid war over on the other forum - the big stars on many of them also look white/blue

Last edited by ChrisV; 13-07-2019 at 11:49 AM.
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Old 13-07-2019, 07:59 PM
Gavin1234
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Yeah based on some other threads and advice I’ve gotten I think I might be taking too long exposures with the gain also too high. Will try out photometric colour calibration tomorrow. I had problems with colour calibration yesterday, couldn’t create previews for some reason.
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Old 14-07-2019, 02:36 PM
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There's PLENTY of stars in that region! Leave 'em be

This is my massively cropped image of Trifid (old data - redone 'cause I was tired of not imaging)...LOTS of stars still

https://www.astrobin.com/413519/B/
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Old 14-07-2019, 07:01 PM
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Wow you’ve really nailed that emission nebula Lewis
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Old 14-07-2019, 07:36 PM
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Quote:
Originally Posted by Gavin1234 View Post

Evan I would love to see what you’ve done with it if you don’t mind.
Hi Gavin,

Just saw your 2nd iteration. Looks great! The reduction in the stars really brings out the nebula

I'm attaching a copy of my processing result, with a little artistic flair added to the bright star in the corner. Copy of your original also attached.

Cheers
Evan
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