M82

[Rodd]

Here is another redo--but one that I think is worth it.....hey, if I had more clear sky I wouldn't regal you with my old obsessions!--such is AP.  Anyway.  Based on posted images of M82I alsways thought my M82 was way over saturated, though I did not really know how to fix it.  There is a halo like grayness that surrounds the disc that is terrible difficult to remove.  Idid not whooly succeed.  But I think the image is improved.  This is an aggressive crop of a TOA 130 and ASI 1600 image--about23 hours of exposure --pretty much evenly distributed except Ha which has 9 h0 (all 300 sec subs).  I am pleases with the level of detail attainable with a 5" scope.  That surprised me a bit seeing as the target is fairly small--this is a big crop.  It is still probably oversaturated....but if I reduce the color further--it starts looking gray and wan....maybe that is how it it should look....what do you think...I don't see very many super saturated M82s...the resaon for my efforts in this matter.

new

 

 

old

 

[geoflewis]

Hi Rodd, both versions are excellent, but I agree with you that the less saturated new version is an improvement.

[tooth_dr]

Very pleasing images Rodd. 

[Rodd]

11 minutes ago, geoflewis said:

Hi Rodd, both versions are excellent, but I agree with you that the less saturated new version is an improvement.

Thanks Geof--here is a bit more desaturation--the rabbitt hole beckons1

 

 

[Rodd]

11 minutes ago, tooth_dr said:

Very pleasing images Rodd. 

Thanks Doc

[MikeCM]

Impressive shot. Certainly more detailed than my rendition

[Rodd]

1 minute ago, MikeCM said:

Impressive shot. Certainly more detailed than my rendition

Thnk Mike

[MarsG76]

Those images are superb.... I dare say this is the best amateur photo I have seen of the M82.... only better one was a hubble image.... well done.

 

[Rodd]

6 hours ago, MarsG76 said:

Those images are superb.... I dare say this is the best amateur photo I have seen of the M82.... only better one was a hubble image.... well done.

 

Thanks Mars.  Quite the compliment. 🙏

[Xiga]

Lovely images Rodd. M82 is a personal fav of mine, and i'd be over the moon with any of these. I'm quite prone to a bit of saturation myself, but I do like the new version in the OP the best. The original was just ever so slightly over-saturated in my eyes.

That TOA really does crop well. I've found that 80mm is simply not enough to do heavy crops, so there must be a tipping point somewhere in between, probably somewhere around the 100mm mark, where things improve.  I'm sure @vlaiv could explain the technicalities to me as to why!

If I may offer a slight bit of feedback - I would try backing off the sharpening just a tad. I think it could give it a more natural look. Also, the big star just under the galaxy has some green in the halo. Actually, how come the stars have some colour fringing? Was the focus off between some of the filters? Images like this are where PS works at it's best. When you have a centralised ROI in a sparse star field, it's pretty easy to blend the galaxy with a lesser-stretched version just for the stars themselves. I'm not sure how you'd go about that in P.I though!

[vlaiv]

@Xiga I would love to try to help - but I've got no idea what you mean when you say that certain sensor "crops better".

Can you explain what you mean by that?

[andrew s]

13 minutes ago, vlaiv said:

@Xiga I would love to try to help - but I've got no idea what you mean when you say that certain sensor "crops better".

Can you explain what you mean by that?

I suspect he means image scale large enough to allow a pleasing "enlarged" image once cropped.

Regards Andrew 

[Xiga]

12 minutes ago, vlaiv said:

@Xiga I would love to try to help - but I've got no idea what you mean when you say that certain sensor "crops better".

Can you explain what you mean by that?

Sorry Vlaiv, my fault for not being clear. I don't mean the sensor, what I meant was, does it take a certain amount of aperture in order to be able to do tight crops? I know that with my 80ED, tight crops don't work well. I think it's mostly just down to the FL, but maybe it's a combination of both FL and aperture? i.e 'Aperture at Resolution'.

[smr]

Fantastic. I love images of this Galaxy. It's beautiful, fantastic image.

[Rodd]

2 hours ago, Xiga said:

Lovely images Rodd. M82 is a personal fav of mine, and i'd be over the moon with any of these. I'm quite prone to a bit of saturation myself, but I do like the new version in the OP the best. The original was just ever so slightly over-saturated in my eyes.

That TOA really does crop well. I've found that 80mm is simply not enough to do heavy crops, so there must be a tipping point somewhere in between, probably somewhere around the 100mm mark, where things improve.  I'm sure @vlaiv could explain the technicalities to me as to why!

If I may offer a slight bit of feedback - I would try backing off the sharpening just a tad. I think it could give it a more natural look. Also, the big star just under the galaxy has some green in the halo. Actually, how come the stars have some colour fringing? Was the focus off between some of the filters? Images like this are where PS works at it's best. When you have a centralised ROI in a sparse star field, it's pretty easy to blend the galaxy with a lesser-stretched version just for the stars themselves. I'm not sure how you'd go about that in P.I though!

Thanks Ciarán.  You think these stars are bad...you should see my usual ones!  Stars are my weakness (one of many).  Using a different image with a lesser stretch for the stars is something i do frequently--I just forgot to do it in this case!.  Back to the drawing board.

With respect to cropping--your 80mm could crop well if you use small pixels and a reducer.  I have found that the FSQ 106 with the ,6x reducer and the small pixels of the ASI 1600 are eminently crop-able.  For me cropping is tied to FOV and resolution--a wide field shot with high resolution will be more crop-able than a smaller FOV with high resolution.  Data quality helps too (meaning sky quality assuming folks know how to collect data, which is understood)......this seems to be teh case for me anyway

Rodd

[Rodd]

51 minutes ago, smr said:

Fantastic. I love images of this Galaxy. It's beautiful, fantastic image.

Thanks SMR

[vlaiv]

1 hour ago, Xiga said:

Sorry Vlaiv, my fault for not being clear. I don't mean the sensor, what I meant was, does it take a certain amount of aperture in order to be able to do tight crops? I know that with my 80ED, tight crops don't work well. I think it's mostly just down to the FL, but maybe it's a combination of both FL and aperture? i.e 'Aperture at Resolution'.

Ah, ok, I think I get it. Follow two simple rules and you will be able to crop any sensor "perfectly".

Rule 1 - don't crop smaller than presentation size.

If you are going to view image here on SGL or anywhere else where you can get the sense of the size of the image displayed (not actual size of images - but display size of the image) - don't crop smaller than that.

Many viewing utilities by default have "fit to screen" or "fit to viewing area" enabled for images - if your image is larger than viewing area - it will be sampled down to pixel count of viewing area - and that is ok, you don't loose anything by sampling down for display, but you don't want the opposite - small image being sampled up to fit viewing area. When sampling up - "missing pixels" need to be made up by sampling up algorithm and detail can't be made up and things look blurry when you up sample them because of this - avoid your images being upsampled if you can.

In most circumstances you want your crops not end up below common computer screen sizes - like 1280 or 1600 (or even 1920 nowadays) in width unless you are sure it won't be up sampled for viewing.

Rule 2 - make sure you have a proper sampling rate for conditions.

This one is tricky because you don't know proper sampling rate until you finish sampling. Luckily you can get to proper sampling rate with algorithms. Proper sampling rate is about FWHM/1.6 in arc seconds. Let's say you have your stack and you measure FWHM of it to be on average 3.5". What is proper sampling rate for this? It is ~2.2"/px (3.5 / 1.6 = 2.1875). This is your target resolution. Imagine that you sampled at 1"/px, what then? Well first bin your data x2 to get to 2"/px and then down sample it to 2.2"/px (or leave it at 2"/px - if you are fairly close to proper sampling rate you are fine). In any case - use regular binning, fractional binning or down sampling to get to proper sampling rate.

If you are already sampling coarser than proper sampling rate - you are fine - no need to do anything special (and certainly don't up sample). Someone will say - you can do drizzle, but I don't think drizzle works in amateur setups and in fact I would like to do experiment with who ever is willing - I'll provide under sampled data - or we can use any existing data that can be made under sampled by binning - and then compare two approaches - drizzle and upsampled stacking. I state that upsampled stacking will provide same level of resolution but will have much better SNR than drizzle - but this is digressing.

There you go - two simple rules.

 

[Xiga]

5 hours ago, Rodd said:

Thanks Ciarán.  You think these stars are bad...you should see my usual ones!  Stars are my weakness (one of many).  Using a different image with a lesser stretch for the stars is something i do frequently--I just forgot to do it in this case!.  Back to the drawing board.

With respect to cropping--your 80mm could crop well if you use small pixels and a reducer.  I have found that the FSQ 106 with the ,6x reducer and the small pixels of the ASI 1600 are eminently crop-able.  For me cropping is tied to FOV and resolution--a wide field shot with high resolution will be more crop-able than a smaller FOV with high resolution.  Data quality helps too (meaning sky quality assuming folks know how to collect data, which is understood)......this seems to be teh case for me anyway

Rodd

Rodd, when you say that stars are your weakness, are you sure it's not the 1600 that's more to blame rather than you? From looking at images done with this sensor, I personally don't think it does well with stars, the well depth just isn't deep enough. So you may well be bashing your head against a wall for no reason. You could always try shooting a small-ish number of longer subs at zero gain, with the intention of blending them in for just the brighter stars only, but i'm not sure how well that would work in practice, and it's also introducing yet more complexity to one's workflow!

I see you also have a CCD with an 8300 sensor. If it were me, i'd put the 8300 on there and never move it! How come you don't use it, is it a personal preference thing (CMOS vs CCD) or is there a technical reason?

[Xiga]

4 hours ago, vlaiv said:

Ah, ok, I think I get it. Follow two simple rules and you will be able to crop any sensor "perfectly".

Rule 1 - don't crop smaller than presentation size.

If you are going to view image here on SGL or anywhere else where you can get the sense of the size of the image displayed (not actual size of images - but display size of the image) - don't crop smaller than that.

Many viewing utilities by default have "fit to screen" or "fit to viewing area" enabled for images - if your image is larger than viewing area - it will be sampled down to pixel count of viewing area - and that is ok, you don't loose anything by sampling down for display, but you don't want the opposite - small image being sampled up to fit viewing area. When sampling up - "missing pixels" need to be made up by sampling up algorithm and detail can't be made up and things look blurry when you up sample them because of this - avoid your images being upsampled if you can.

In most circumstances you want your crops not end up below common computer screen sizes - like 1280 or 1600 (or even 1920 nowadays) in width unless you are sure it won't be up sampled for viewing.

Rule 2 - make sure you have a proper sampling rate for conditions.

This one is tricky because you don't know proper sampling rate until you finish sampling. Luckily you can get to proper sampling rate with algorithms. Proper sampling rate is about FWHM/1.6 in arc seconds. Let's say you have your stack and you measure FWHM of it to be on average 3.5". What is proper sampling rate for this? It is ~2.2"/px (3.5 / 1.6 = 2.1875). This is your target resolution. Imagine that you sampled at 1"/px, what then? Well first bin your data x2 to get to 2"/px and then down sample it to 2.2"/px (or leave it at 2"/px - if you are fairly close to proper sampling rate you are fine). In any case - use regular binning, fractional binning or down sampling to get to proper sampling rate.

If you are already sampling coarser than proper sampling rate - you are fine - no need to do anything special (and certainly don't up sample). Someone will say - you can do drizzle, but I don't think drizzle works in amateur setups and in fact I would like to do experiment with who ever is willing - I'll provide under sampled data - or we can use any existing data that can be made under sampled by binning - and then compare two approaches - drizzle and upsampled stacking. I state that upsampled stacking will provide same level of resolution but will have much better SNR than drizzle - but this is digressing.

There you go - two simple rules.

 

Thanks Vlaiv. Very informative as always 👍

I've never even bothered checking the FWHM in my stacks! Hopefully at 1.5" i'm not too far off where I should be, although i'm probably over-sampled. I should really go back and analyse some stacks and see what my skies are actually like. Then I should have a better idea of how much to bin in software. Thanks!

[Ags]

That's a really great capture of M82.

[Rodd]

3 hours ago, Ags said:

That's a really great capture of M82.

Thanks Ags.  I think Ciarán is right--a tad less sharpening will be my next goal with this....almost there!

[ollypenrice]

A very fine image. I find the background sky a bit 'colour busy' with some mottled green showing on my monitor. This should be an easy fix if you decide you agree.

The stars could be cosmetically fixed in Ps using the radial blur feature within a circular selection but this is in no way scientific.

I do prefer the less saturated images and agree that, once again, a refractor with small pixels can take on the big stuff.

Olly

[Rodd]

32 minutes ago, ollypenrice said:

A very fine image. I find the background sky a bit 'colour busy' with some mottled green showing on my monitor. This should be an easy fix if you decide you agree.

The stars could be cosmetically fixed in Ps using the radial blur feature within a circular selection but this is in no way scientific.

I do prefer the less saturated images and agree that, once again, a refractor with small pixels can take on the big stuff.

Olly

Thanks Olly--I think I have addressed the background in a subsequent version that I did just for that reason.  Let me know if I was successful.  As far as the stars go--yes they are not great.  the fact that this is a crop does not help.  Perhaps the best fix will be to use a second version with a reduced stretch for teh stars--I don't know why i did not think of that.  probably because there are not that many stars and they are not the focus of the image.  As always--thank you for the input.

 

[Rodd]

14 hours ago, Xiga said:

Rodd, when you say that stars are your weakness, are you sure it's not the 1600 that's more to blame rather than you? From looking at images done with this sensor, I personally don't think it does well with stars, the well depth just isn't deep enough. So you may well be bashing your head against a wall for no reason. You could always try shooting a small-ish number of longer subs at zero gain, with the intention of blending them in for just the brighter stars only, but i'm not sure how well that would work in practice, and it's also introducing yet more complexity to one's workflow!

I see you also have a CCD with an 8300 sensor. If it were me, i'd put the 8300 on there and never move it! How come you don't use it, is it a personal preference thing (CMOS vs CCD) or is there a technical reason?

The 8300 jams--the filter wheel will get stuck and it wont rotate.  Sometimes it will break through but it requires me to shut it off and turn it on repeatedly.  Sometimes it wont break through and I will have to take the camera off and unstick it manually.  That of course ruins my flats and my framing.  But--the ASI 1600 does not register correctly often enough so that I must shoot flats before every filter change or at end of night anyway--so I guess its no better.  But the real reason I got the ASI 1600 is for use with the FSQ 106 and the .6x reducer.  The small pixels of the asi 1600 coupled with the F3 (318mm) setup, makes for widefield higher than  normal resolution images.   The stt-8300 will not work with the .6x reducer because it has a self guiding filter wheel that takes up too much back focus.  I am using the asi1600 with the TOA 130 as an experiment to see how it works on galaxies.    The ASI 1600has the same or better well depth as the STT-8300 I think.   My stars were bad with that camera too.  the ASI 1600 does really stink at stars of 4th or greater magnitude.    My sky is bad, so to get my images where I want them, I have to stretch aggressively, which ruins the stars.  But--the stars in this image, for me, do not ruin the image.  I don't think they are so bad.  Considering this is a fairly aggressive crop--these stars would look very good at normal scale.  No, they are not perfect, but for me they are better than usual.

BTW--I sent the STT-8300 to SBIG and to OPT (my vendor) and they could not find anything wrong with it--on multiple occasions.  They say they had it on the bench operating for over 24 hours--but I don't know if I believe them.   I was shafted with that camera.   Now the ASI 1600 doesn't initialize properly.  I guess I have bad luck with cameras.

Edited March 10, 2020 by Rodd

[Xiga]

Oh dear Rodd you certainly haven't had the best of luck with your cameras that's for sure. It's a shame the 8300 keeps jamming on you, otherwise you could just keep the 1600 on the Tak and keep the 8300 on the TOA.

Oh, and I hope it didn't sound like I was implying that the stars were ruining the image (they definitely dont'!) so apologies if I was giving that impression.

What Gain do you use on the 1600 for broadband imaging? At Unity Gain the 1600 only has a FWC of about 4k, whereas the 8300 (from memory, which isn't saying much! lol) I think is about 25k. I've heard that the sweet spot for the 1600 is around Gain 76 for broadband imaging. This doubles the FWC to around 8k, preserves star colours better, and the noise profile is still meant to be ok too (unlike at Gain 0 which I've heard is much worse for FPN).