M13 RGB

[Rodd]

C11Edge native F10, unguided, 20 sec exposures, ASI 1600 Bin 2x2

Red-325; green-317; Blue-203

My goal was to resolve the core and provide a color palette using the Hubble images as a guide.  The colors are to saturated for normal image appreciation, I think...sometimes.  I am torn, I just can't decide.  A very interesting way to image.  The short subs retained color as the FWC was not blown.  I may have been able to get away with 40 sec subs, but i wanted to maximize FWHM.  unfortunately seeing was very poor for most of the shoot.  The first night I was able to achieve FWHM values of 1.5 arcsec/pix.  I was elated.  But over all it was a struggle to achieve <3.  I think the Red and Green stacks ended up being 2.45 and 2,75 respectively.  Not sure about blue.  The biggest challenge was teh need to correct for drift every 30 minutes or so.  Time to install the OAG I guess.

[scotty38]

Love it, I've been messing with M13 when I'm given the chance and have not got anywhere near resolving the core yet!

[peter shah]

Wow love the scale.....great shot

[Rodd]

35 minutes ago, scotty38 said:

Love it, I've been messing with M13 when I'm given the chance and have not got anywhere near resolving the core yet!

Thanks--Its hard because its so bright.  Short exposures help allot.

[Rodd]

14 minutes ago, peter shah said:

Wow love the scale.....great shot

Thanks Peter.  

[Rodd]

Here is a more relaxed version--not sure which I like better.  

 

[scotty38]

45 minutes ago, Rodd said:

Thanks--Its hard because its so bright.  Short exposures help allot.

Agreed, and I accept I have a totally different setup to you (GT81, 0.8x and OSC - ZWO294) but my last attempt was 240x30s exposures and it's still blown out. I keep meaning to go and have another try with the data though....

[Rodd]

10 minutes ago, scotty38 said:

Agreed, and I accept I have a totally different setup to you (GT81, 0.8x and OSC - ZWO294) but my last attempt was 240x30s exposures and it's still blown out. I keep meaning to go and have another try with the data though....

Keep in mind I am imaging at F10--which is MUCH slower.  There is also processing involved.  My core was pretty blown at first.  I had to process fairly aggressively to bring the stars out.  They most important consideration to me-the over riding factor, is whether the image looks realistic.  Does it look like it would look through an eye[piece.  I am not sure I have succeeded there.  Obviously with a globular concession must be made regarding the extreme brightness.  in an eyepiece the core is blown--or at least not resolvable due to the glare.  In the end, I don't know, maybe I am going around in circles.

Edited May 17, 2021 by Rodd

[vlaiv]

Very nice image.

It can serve to study resolution achieved. I've imaged M13 on few occasions with different gear. This gives us nice chance to do comparison. In particular I want to focus on 3 prominent stars that are close together.

This is screen shot from your image. Stars are almost touching. There is also fourth star as well - blue one, in that group that almost seems to be touching one of three main.

Here is same triplet of stars in one of my images. This was with 8" scope. Guiding was poor and most of my stars are a bit elliptical because of that.

This one is done with 80mm scope. This image has been enlarged to 300% of original (original at 2"/px).

 

[vlaiv]

I managed to track one really resolved image at similar pixel scale:

Same star triplet that actually shows bunch of smaller stars around it.

[Rodd]

19 minutes ago, vlaiv said:

t can serve to study resolution achieved. I

A lot has to do with the level of stretch.  I reduced my stretch considerably after viewing this and the stars grew much smaller, hence farther apart.   But that did not look right.  Also--one has to look at the stars around those 3.  In mine--there are many more brightish stars.  hard to tell from screen shot, but if you stretched yours so more stars were bright--the 3 stars would get larger and closer together.  I just noticed the enlargement factor of the 80 mm scope.   That makes it hard to equate with a visual comparison.  

Take my image out of the mix....I have very mixed feeling about it anyway.  maybe 20 sec unguided is no way to image.  The details I was getting in M99 were great though.  Maybe it was the seeing.  I don't know.  But if you compare your 8 inch to your 80mm, the stars from 8" are much farther apart than the 80 mm.  Therefore, I think that is a respectable offering was made with an 11" scope, the stars would be farther apart (smaller) still.  So as aperture goes up, star sizes go down.  All else being equal.  

Time to use the OAG I guess.  But that will steal a night (at least)

Just saw you second post--that's more like it

 

Edited May 17, 2021 by Rodd

[lenscap]

1 hour ago, Rodd said:

Here is a more relaxed version--not sure which I like better.  

 

 

 

". . . . oh my God! . . . . it's full of stars. "     David Bowman,   "2001: A Space Odyssey",   Arthur C. Clarke

[vlaiv]

2 minutes ago, Rodd said:

A lot has to do with the level of stretch.  I reduced my stretch considerably after viewing this and the stars grew much smaller, hence farther apart.   But that did not look right.  Also--one has to look at the stars around those 3.  In mine--there are many more brightish stars.  hard to tell from screen shot, but if you stretched yours so more stars were bright--the 3 stars would get larger and closer together.  I just noticed the enlargement factor of the 80 mm scope.   That makes it hard to equate with a visual comparison.  

Take my image out of the mix....I have very mixed feeling about it anyway.  maybe 20 sec unguided is no way to image.  The details I was getting in M99 were great though.  Maybe it was the seeing.  I don't know.  But if you compare your 8 inch to your 80mm, the stars from 8" are much farther apart than the 80 mm.  Therefore, I think that is a respectable offering was made with an 11" scope, the stars would be farther apart (smaller) still.  So as aperture goes up, star sizes go down.  All else being equal.  

Time to use the OAG I guess.  But that will steal a night (at least)

 

Aperture size certainly makes a difference - but I think we are hitting limit - both with 8" image and with your 11" image.

That is not due to aperture size - but rather due to seeing. There is also fact that as you stretch more - you get more bloat in stars, however - one should be able to detect certain splits - that is what resolution is about.

Look at that last image I posted - star sizes are not considerably smaller compared to our images - yet there are clean splits in some cases.

There is small star in this group:

Here there is no question about it.

My 8" version seems to show it, but we can't be certain due to level of stretch:

In your image - it also seems to be there, but there is no split - it looks like joined to larger star - as if larger star is a bit deformed:

What I'm trying to say is that actual resolution is not supporting pixel scale - similarly to that 80mm image that was enlarged to 300%.

Maybe we image at 0.67"/px in my 8" case or 0.56"/px with your 11" - but detail is not there.

 

[Rodd]

15 minutes ago, vlaiv said:

Maybe we image at 0.67"/px in my 8" case or 0.56"/px with your 11" - but detail is not there

It may also have to do with focus.  But you are right about resolution on this day.  However, when I shot m99 unbinned the details were fantastic (0.28 arcsec/pix).  Seeing was likely much better.  But this brings me to a point I made earlier about not losing anything if shooting oversampled and you said it reduces SNR, which is true.  But for bright objects like stars (globular clusters, or bright galaxies), it doesn't make much difference.  But it  allows you to take advantage of better seeing as my m99 revealed.  Image attached for reference.  maybe I am wrong.  

I think the 2 greatest things that effect resolving those stars are seeing and focus.  Since my exposures were only 20 seconds unguided, guiding was not a factor.  Maybe collimation is off.  M99 would not seem to indicate this.  BTW, did you screen shot from my original image or the second one.  the second one has a less aggressive stretch.

Edited May 17, 2021 by Rodd

[vlaiv]

3 minutes ago, Rodd said:

However, when I shot m99 unbinned the details were fantastic (0.28 arcsec/pix). 

I understand that you think you have detail in that image that is supported by 0.28"/px - but it is far from it.

Here is what can be recorded at that resolution (I eyeballed resolution, but I think it is pretty good match):

Those things that are featureless blobs in your image are in fact rather interesting clusters, At this resolution you should be able to start to resolve those clusters in individual stars.

Look what happens if I reduce that M99 image of yours to 25% of its original size and compare it with same comparison image:

Now they look pretty much the same in terms of detail that they show. Fact is - this image might be sampled at 0.28"/px - but in reality contains detail for only ~1.12"/px - which is still great. Not many people can image at 1.12"/px resolution.

8 minutes ago, Rodd said:

BTW, did you screen shot from my original image or the second one.  the second one has a less aggressive stretch.

I used first one. With second one and a bit less aggressive stretch - that one star is easier to spot, but still not quite resolved (in terms of split between the stars).

[Rodd]

6 minutes ago, vlaiv said:

I used first one. With second one and a bit less aggressive stretch - that one star is easier to spot, but still not quite resolved (in terms of split between the stars).

Seeing was bad, what can i say.  I suppose I could collect hundreds of subs more per channel and then only use subs with FWHM < 2.0.  Then integrate and see if it makes a difference.  But that could take a long time as seeing is rarely decent.  Also--I am not sure I want to spend all my time on M13.

But you have shown me that I should definitely bin and not think twice.  A guy on Astrobin (Gary Imm) shoots with a C11Edge and a small pixel camera and was not binning for a while--now he bins but the binned scale is still small (.4 I think).  His skies are much better (Bortle 4) and seeing must be better.  Still--He seems to defy the laws of physics and achieves much better resolution than he should be able to.  Unless it just seems that way--very much like my m99.  

Here is a question for you.  Other than narrowband (which is a big factor, but ignore it for a moment)-is there a compelling reason for me to install the OAG and guide as opposed to continuing broad band targets with 20 sec unguided subs?  If I guide my exposure size would increase, making the stars grow.  Is the 20 sec unguided method really viable, or was I deceived like I was about the resolution of my m99?

[Rodd]

26 minutes ago, vlaiv said:

but in reality contains detail for only ~1.12"/px

Are you suggesting I bin 4x4?  Any reason not too, other than it seems crazy.

[vlaiv]

3 minutes ago, Rodd said:

Here is a question for you.  Other than narrowband (which is a big factor, but ignore it for a moment)-is there a compelling reason for me to install the OAG and guide as opposed to continuing broad band targets with 20 sec unguided subs?  If I guide my exposure size would increase, making the stars grow.  Is the 20 sec unguided method really viable, or was I deceived like I was about the resolution of my m99?

I think that 20s unguided is viable - you've shown that it works. Question is - does it work better than guided?

Not sure if I can answer that one - but I do think that guided longer subs will go deeper and get you better SNR as result for your overall imaging time. One benefit of going deeper is that you can sharpen more without bringing out noise as much.

Maybe that will yield better results - not sure. I think it is the way I would approach things - guide, get better SNR and then sharpen image (within limits and until it makes sense - don't over sharpen).

Another important thing to do is - well,

accept resolution limit imposed on us by seeing. I know that this is hard and we like to think that we can do close ups - and most people try, but as you have seen - although we can get in real close - that does not mean we get the detail.

15 minutes ago, Rodd said:

A guy on Astrobin (Gary Imm) shoots with a C11Edge and a small pixel camera and was not binning for a while--now he bins but the binned scale is still small (.4 I think).  His skies are much better (Bortle 4) and seeing must be better.  Still--He seems to defy the laws of physics and achieves much better resolution than he should be able to.

Just checked some of his images with C11Edge - and it does not look like that to me. They seem over sampled as one would expect at those resolutions.

[vlaiv]

4 minutes ago, Rodd said:

Are you suggesting I bin 4x4?  Any reason not too, other than it seems crazy.

Not sure why it would seem crazy? There is only limited amount of detail in the image - if you want to match detail in the image with sampling rate - then you should go for bin factor that is suitable.

If you achieve on average 2" FWHM - appropriate sampling would be 1.25"/px. If in turn your native resolution is 0.28"/px, then 1.25 / 0.28 = x4.46. You should bin at least x4 to get to 1.12" sampling rate.

Of course - you don't have to - it is a choice, and again, it depends on whether you think you have the detail or not. I don't think that detail is there - but you can also take your image and compare it to some really high resolution ones - like HST images. Match them at different pixel scales and see what sort of detail you have in your image and what sort of detail there is in HST image. HST image will depend only on resolution selected - it has enough detail, but your image might not have detail at high resolutions and might look blurry. Try to match them to see what is the actual resolution of your image - one where you have detail to match.

[Rodd]

5 minutes ago, vlaiv said:

One benefit of going deeper is that you can sharpen more without bringing out noise as much.

I thought that total exposure time was the important thing.  If you compare a 3 hour stack of 18 10 minute exposures with a stack of 540 20 sec subs--would there be a difference.  With the CMOS cameras I think the 540 stack will be cleaner (I have noticed that my stacks of hundreds of subs are cleaner--and gain 300 helps).

[Rodd]

5 minutes ago, vlaiv said:

Not sure why it would seem crazy?

Well--take my M99 stack and software bin x4 and tell me if detail is lost.  i bet it will be

[Rodd]

1 hour ago, lenscap said:

h my God! . . . . it's full of stars. "     David Bowman,   "2001: A Space Odyssey",   Arthur C. Clarke

Ha Ha...that's great.

[vlaiv]

1 minute ago, Rodd said:

I thought that total exposure time was the important thing.  If you compare a 3 hour stack of 18 10 minute exposures with a stack of 540 20 sec subs--would there be a difference.  With the CMOS cameras I think the 540 stack will be cleaner (I have noticed that my stacks of hundreds of subs are cleaner--and gain 300 helps).

For same total imaging time - less longer subs wins over more shorter subs. This is because of read noise.

If read noise is 0 - the those two are equal - then it does not matter how long are your subs - as long as you accumulate same total imaging time. As read noise is not zero - it makes a difference. It makes less difference to CMOS cameras, because CMOS cameras have lower read noise.

Whenever read noise is low enough - difference is small enough - you almost can't tell the difference between few longer subs over many shorter subs (again - same total duration).

Higher gain - means even lower read noise (by a bit).

This is particularly important if you use high resolution / long focal length - as read noise stays the same - but it grows in relationship to other noise sources.

100 x 5 vs 5 x 100 will have more difference at 0.5"/px than it will at 1"/px for same aperture.

[vlaiv]

5 minutes ago, Rodd said:

Well--take my M99 stack and software bin x4 and tell me if detail is lost.  i bet it will be

What is the difference between these two images except for noise grain?

[Rodd]

10 minutes ago, vlaiv said:

What is the difference between these two images except for noise grain?

The bright star is larger in binned one.  And the resolution is not as high.  Looking at the edges between light and dark regions you can see they are less sharp in the binned.   But this just might mean 4x4 was too much.  3x3 maybe would be perfect.  Flashing between them I can actually see quite a bit of difference.

 

But this aside--if you use the software binning on board the ASI 1600, you actually get 10 bit readout.  Some say it is better to collect 1x1 and software bin after on the computer.  Would you agree?  They also say its ok to software bin after noise reduction and some processing.  I thought binning should be done in linear state.  

Edited May 17, 2021 by Rodd