Jump to content

sgl_imaging_challenge_2021_annual.thumb.jpg.3fc34f695a81b16210333189a3162ac7.jpg

M51 a waste of time


Recommended Posts

This is effectively a 7 hour long mistake.

The reason I say that is that I had the theory wrong in my head about S/N ratio so on this I persisted on 5 minute subs and ended up with 84 of them... Sure it built up bit by bit - see other thread - but then it started to tread water stuck in S/N limbo.

Following discussions here and elsewhere (south of France for example...:)) I realize that this could have been better if I'd gone for 10 minutes or even a tad longer - light pollution being the biggest enemy in terms of data collection - processing aside:glasses1:.

So the plan is to return to this target with the same equipment but longer subs. 15 minutes would be great if the smog allows me but 10 for sure.

I kick myself for being stupid and might honour kill my scope.

6904574934_7f1fb4cb0a_b.jpg

Link to post
Share on other sites
  • Replies 49
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Posted Images

That is a very nice image, but given the number of subs I am surprised that the background appears a bit noisy. 84 subs should suppress noise well. How many darks did you take?

Link to post
Share on other sites

Cheers starnut, I'm a novice too, just learned a few acronymes!

Ags, I am not sure why this is noisier. It is from a smoggy city centre, but this one came out unusually bland. I think longer subs would increse the 'gap' between the target and the stars vs the background making life easier for processing. At least that's what my hopes are for next run at this. I cannot remember the sky quality. Normally I can just about make out Polaris and perhaps one or two in the plough visually...

Darks - 0. 20 Bias frames that could worst case be up side down! (AA flips my Neb shots vertically for some reason...)

Link to post
Share on other sites

Your skies sound like mine. I would be very pleased to get an image like this, but of course there is always room for improvement as you say...

Link to post
Share on other sites

Learning is one of the kicks of this whole business I think:).

I am very pleased that I can get anything under the circumstances, I thought that Galaxies were out of bounds, along with nebulosity of any wave lenght - leaving errm.. stars. Not too sure Ha/OSC/LP is a good gig tho...:)

I may eat my words on this little fella, but I think it can be done better. Fingers crossed for the spring:).

Link to post
Share on other sites

To be honest who are we trying to please when we take a photo as it seems to me it is all down to people that can manipulate a photo with the help of expensive equipment and photoshop, surely your photo is pleasing to the eye so what more do you want, or are you lot too blumming fussy.

The other day someone said it had fluff bunny’s, I could not see them and I'm still looking for the flats :), maybe there not built yet, or have I got a lot to learn......

Link to post
Share on other sites

Dont be so hard on yourself I think this has tons of detail in there and certainly nothing there that processing could not pull out and correct. Getting the data to work with is the biggest battle some times and you have tons to work with there for sure. I would be happy with that for sure.

Link to post
Share on other sites

Apart from a slight purple tint to some areas of the galaxy, there's nothing at all wrong with the image and you should be very happy to capture so much from the centre of Lyon, or any other big city.

I too have a distinct limit to what can be picked up out of the skyglow, and although it's frustrating, have to accept this.

You will inevitably get background noise coming out in processing if you are trying to stretch something that is only just above that background sky, no matter how many subs.

Go for longer subs, but they may not, on thier own, stretch the faint target regions more than they will stretch the background skyglow.

Are you using a LPS filter?

Cheers

Rob

Link to post
Share on other sites

Thanks guys for all input, my point is that with better fundamental understanding this one could be a notch better - at least that's what I hope, and I don't like it when my head is to blame... 3 clearish nights in a row without a Moon are not all that common here.

Anyways all good fun to learn and hopefully progress.

Starnut, all images are pleasing to look at, they all carry a quality but it's easier to enjoy someone else's image, just like it's nicer to have food cooked for you. For most objects being imaged over and over again, a certain standard is being set as to how the target - say a galaxy - should look. There's a certain colour range, and for each scope there is a certain level of detail you'd expect so when you miss that ball park it is reason enough to try again, sometimes with processing and sometimes with brand new data.

After some time working with images you get more and more sensitive to 'errors', and you spot most of them straight away - be that dust bunnies or other funny things. For me the last colour tweak is the hardest, it's like you go colour blind after staring at a screen too long. That hint of too much blue for instance disappears to your eyes, and won't notice until the next day, or not at all until you post on here and others give you a nudge in the right direction.

Who do we please? Very good question. It's a bit like fishing by a river for hours on end. You feel happy to finally catch something but still like to share your catch with friends over dinner. That's pretty much it. And if they are fellow fishing enthusiasts you'll most certainly ask for advice on how to catch bigger next time, we are that fuzzy!

Olly your eyes are like screen calibration tools! The very last thing I did was do dim the blue a tad... Got me!

Rob I was actually pleased to see some purple hints as the whole thing is leaning towards an eerie green to my eye... I don't use any filters. I can't really argue a strong case for why not. I believe though that I'm up against more than vapour and reflected street light. There's always at least a 1000' thick brown lid of car and factory exhaust hovering over the city due constant temperature inversion. Even London air in comparison is fresh to breathe. I believe this layer is my biggest 'enemy' in the capturing, and not sure that a filter would help. But I'm all ears on SGL.

Thanks again all for looking and commenting!

Link to post
Share on other sites

Hi Jesper.

In your situation anything that you can do to increase the difference between your background skyglow and your target is going to be good....you will still need lots of data but have a better chance of stretching it out wothout hitting noise too quickly.

I would give something like the Hutech IDAS filter a try.

Cheers

Rob

Link to post
Share on other sites

OK, I'll look into that. The Hutech is expensive but prehaps worth it. Would that stack over the IR cut I use on the M25C or does the Hutech take care of IR on its own?

Thanks for the advice.

Edited by Jessun
Link to post
Share on other sites
Would that stack over the IR cut I use on the M25C or does the Hutech take care of IR on its own?

TBH...I don't know!

I'd be interested to know myself as I have a Hutech that I am going to try :)

Rob

Link to post
Share on other sites

I can't contribute to the 'Imaging Techno Talk' I'm afraid but agree with others on there being plenty of detail available to pull out.

I just happened to look at the original image through a pair of 3D glasses,as one does :), and it seemed a good candidate for a little tinkering.........minor brightening and saturation etc.then movement of red & green channels.........

You will probably hate the result but it's a little different and fun to do.

P.S. Red lens over right eye.

post-13495-133877759803_thumb.jpg

Link to post
Share on other sites

Cloudwatcher I've seen some of your work, in particular there was another M51 that you edited and I was very impressed. I think I have some 3D DVD around here somewhere with glasses! I'll dig them out for sure!

Link to post
Share on other sites

Jessun,

if this image was taken a the center of Lyon, then you have got nothing to kick yourself about. I do not really think 15 min subs will improve anything as sky background will drawn M51. Have you tried using a PL filter on the camera? That image is nice, you just need to correct color balance (way too much red) and not push the colors too much. As for noise, I don't really see it but try to do some darks, it really helps with keeping noise down. You can do them on a cloudy night, so as to keep them out of the critical path. Then, you can really stretch your image to the very bottom without having noise coming up (just background sky) to reveal more details.

Rgds

Serge

Link to post
Share on other sites

Thanks for the advice Serge. Loads of good points, and I should really go back to my data and re-work it again. And then take a whole new set of longer subs - since I've sort of committed to that argument in this thread...

OK, more blue, less purple, less red...

I actually don't think darks will help an awful lot. The noise is skyborne I think. My BIAS might be up-side-down though...

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.