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JSeaman

M51, Struggling

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I just don't seem to get the results I'm after at the moment. I've had all sorts of issues with the mount and I'm only getting Tot ~1.5" in PHD2 which isn't helping

The image is with between 4 - 9 hours on each of three filters but I'm not quote getting the detail I was hoping for

 

05.jpg

Edited by JSeaman

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What do the individual subs look like when stretched?  Share a few of them. 

Are you being ruthless enough throwing out the bad ones?

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This looks massively black clipped. You have a jet black and uniform background sky and little faint data. This is where you need to be careful:

Healthy:

spacer.png

Black clipped:

spacer.png

You must always have some flat line to the left of the rising histogram peak or you'll be discarding precious data. It is tempting to black clip in order to get rid of gradients but resist this temptation.

Olly

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The black point is just a matter of taste, I prefer it dark (even in your example). I just mask off anything faint if I want to protect it

I'm struggling with blobs for stars which I've seen a few people mention on the atik 314l so may just be a feature of the camera?

I was hoping for more definition on the spiral arms than I managed, a sub from each filter attached chosen at random, I have no issue throwing subs away if it helps

 

 

M51-1_010-1.fit M51O3_010.fit M51_SII_010.fit

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46 minutes ago, JSeaman said:

The black point is just a matter of taste, I prefer it dark (even in your example). I just mask off anything faint if I want to protect it

I'm struggling with blobs for stars which I've seen a few people mention on the atik 314l so may just be a feature of the camera?

I was hoping for more definition on the spiral arms than I managed, a sub from each filter attached chosen at random, I have no issue throwing subs away if it helps

 

 

M51-1_010-1.fit 2.76 MB · 0 downloads M51O3_010.fit 2.76 MB · 0 downloads M51_SII_010.fit 2.76 MB · 0 downloads

Firstly - are you imaging M51 in narrowband?

Secondly - you should go through each sub manually, look at it, and deselect or delete any bad ones - giving us three subs 'chosen at random' is pretty much pointless if I'm being honest with you.

 

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I'll try and read that as though you're trying to help

If you look at the title you'll see there is one ha one o3 and one S2

By at random I mean from the set that made the cut

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1 hour ago, JSeaman said:

I'll try and read that as though you're trying to help

If you look at the title you'll see there is one ha one o3 and one S2

By at random I mean from the set that made the cut

Your file titles say ‘1’ and O3 and Sii.  I had to decide if it was really NB or a typo or a labelling issue.  I don’t think I’ve come across anyone imaging M51 in narrowband only.  Seems possible but very unusual.

I had a look at the files and unsurprisingly there isn’t much data in the two of the channels.  How long were the subs?  How many of each?  What scope?

My phone doesn’t give me your signature so a guiding of 1.5 could be ok depending on the scope  

 

 

 

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Why are you imaging a galaxy in narrow band? Is there anything in particular you are trying to achieve with this? Maybe you are not seeing the detail you want as you are comparing this image to LRGB images?

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Scope is an ED80, 600 second (10 minute exposures), between 4 and 9 hours on each filter

Reasons for narrowband are that is all the filters I have, light polluted area, all shot under a full moon

You may be right though about LRGB, not something I have done before

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I would swap to a new target if I were you. A galaxy is not a narrow band target.

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Agree with the others, galaxies are LRGB targets, perhaps with H-alpha to pick up the HII regions, and not really doable under full moon.

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You have several issues going on here, besides previously mentioned items (NB on galaxies and clipping the black point). I think the first step would be to figure out what’s going on with the stars. I would start with getting the guiding down, if your stars aren’t right, neither will the target. 

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Looking at the image as some have said there are a number of issues: -

1. One of the finest members with regards to processing @ollypenrice commented that it is too black, personally I would heed his advice as you won’t get finer.

2. The ED80 is capable of excellent results and to me the focus is out, have you used a bahtinov mask?

3. I live in a light polluted area and I choose my targets around the moon, and would choose NB targets when the moon is a pain and LRGB targets when it isn’t.

The stars aren’t going anywhere so just enjoy it when the seeing/moon/time is right.

Like you I used to rush to capture images in windy moonlit nights, now I take my images when everything is right rather than rush and waste time.

HTH

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1. Yes I have a lot of time for people like Olly but if something is subjective then that's down to personal opinion

2. Yes and this was focused with a bahtinov mask

3. The moon wasn't the issue as this was nb, there was no rushing only frustration!

The whole galaxy/narrowband was the problem, I didn't realise this was a no go area

Thanks for your feedback though

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4 minutes ago, JSeaman said:

3. The moon wasn't the issue as this was nb, there was no rushing only frustration!

 

The moon is a big issue for Oiii.

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31 minutes ago, tooth_dr said:

The moon is a big issue for Oiii.

Yep Adam, fully agree, I tend to shoot Ha when the moon is at its largest followed by SII and then hopefully the OIII when the moon is out of the way.

Its all about planning.

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On 15/02/2020 at 09:04, JSeaman said:

 

I just don't seem to get the results I'm after at the moment.

 

With the greatest respect your opening sentence was as above.

When I first started I was guilty of too black background and I missed so much of the detail, I knocked it back and my images started to come alive.

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I have 3 nm Astrodons, even so I wouldn't try [OIII] with any more than a sliver of a moon, and that well out of the way. Even [SII] is "iffy". I have managed reasonable results with [NII] but that's not a widely used filter.

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3 hours ago, Jkulin said:

With the greatest respect your opening sentence was as above.

When I first started I was guilty of too black background and I missed so much of the detail, I knocked it back and my images started to come alive.

Think most of us have been guilty of that one...I certainly have..

Seems to me there's some drift showing in the stars, the channels don't seem to line up so maybe cut back on the exposure time, or hone the PA abit better...why not try the drift tool in phd2,  takes abit longer but certainly gets those rms figures down..

Much that it's your choice to use narrowband it's not a total moon blocker, even in the narrowest of bandwidths.. I'd only even think of HA 

Edited by newbie alert
Added info

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The O3 was without moon, the Ha and SII were with

The results I'm chasing are the clarity of detail, nothing to do with the black point, that's the very last thing I tweak

There is indeed drift and I have been working on PA - see other thread for the drift alignment I did the next time I went out!

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35 minutes ago, JSeaman said:

The results I'm chasing are the clarity of detail, nothing to do with the black point, that's the very last thing I tweak

Black point should in my opinion be one of the first things yo do so that you can determine how good the data you have without masking it, you will then be able to see how far you can stretch the detail, making it dark hides all that.

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43 minutes ago, JSeaman said:

The O3 was without moon, the Ha and SII were with

The results I'm chasing are the clarity of detail, nothing to do with the black point, that's the very last thing I tweak

There is indeed drift and I have been working on PA - see other thread for the drift alignment I did the next time I went out!

 

As long as you are happy to gather lots of exposure, then there is no reason that you cannot shoot a galaxy in narrowband.  You will get different results, but that shouldn't make them any the less interesting.

I think that there are two problems with the above image.  The first is focus.  It looks a bit off to me.  Do you have any software that can measure the FWHM, or HFD?  I find this very useful.

 

The second issue is that the stars look a bit elongated.  A good PA will help of course, but I feel that people spend too much time getting the error down to 6".  If you have a flexure problem, then accurate PA won't fix it.  You could experiment with using shorter Ha subs, and then using the Ha stack as a Luminance on the colour image.  Another approach would be to remove the stars altogether (Starnet+ for example) and then replace them with stars made from shorter subs.

 

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Well we have differing views about black point, I know it's widely popular to avoid dark backgrounds but I like it so that bit stays

Don4l - thanks that's useful to know, I am just starting out in nb so finding my feet.

The focus was set with a Bahtinov and I can indeed measure FWHM, although I've never used the numbers, what does that give over the mask?

PA is something I worked on last time and I considered flexure too and have tied the guide scope down harder

I might well play with the Ha short stack you mentioned and see how I get on - thanks for your thoughts

 

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That's much more like what I was after using Ha as a luinance mask, thank you again!

6+8 2.jpg

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