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NGC 1333 lum.....done?


Rodd

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40 minutes ago, ollypenrice said:

It can, yes, but it isn't in its comfort zone at full size. Mind you, there are processing decisions to be made which depend on the intended presentation size. If you're not going for a full size presentation you can do more extreme star reduction, for instance.

Olly

the way I see it is if my image can not stand up to full resolution viewing, it is either unfinished, or a failure (some data is just not able to get there). I am usually in a rush to post and sometimes forget to check.  In those cases, I discover that the image fails under full resolution viewing, and I scramble to try and tweak it into tolerance so I can edit the post before it is seen.  There is no better feeling than to hit the full resolution button and discover that your image holds up well.  

Rodd

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On a separate note, while marveling the noise control that I pulled off (although Rodd is not quite happy with it :D )

I've managed to spot couple of background galaxies - did not expect to see them in the image, but here they are (is there official pixel peeper title around here? :D ) :

image.png.53d0c9bb1d1e6e0dc8303942a649587c.png

image.png.476e39a9ea9f2d6eae9677205cad4596.png

And two more "candidate" galaxies (not sure if they are indeed galaxies - with these it is bit harder to tell):

image.png.6e053365658a75f605e68992bf0d47a1.png

image.png.e9ce91e1aee637c121f78fcd34f66b1a.png

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8 hours ago, wimvb said:

full res, but stars are getting fat in this version. Impo, this one is a bit overcooked.

Lum_305_cc_blend.thumb.jpg.3d4fb595bf8fff9a26d1efd7caf749a0.jpg

I know of no way to avoid this happening to the larger stars but correcting it is easy. You can 'reverse process' them. This has to be done star by star unless the background level around the stars is very similar, as it might be in this image.

Make copy bottom layer.

Bottom layer: Pick a star, open Curves and pin the curve at the level of the surrounding background. Put a fixing point below it and then gently pull down the curve just above the upper fixing point. You can restore the top of the curve if you wish to leave the core unchanged.

Top Layer: use a feathered eraser to take off the top layer over all the stars which lie in the same level of background brightness.

Repeat for stars lying in different background levels.

I only do this for brighter stars and aim to keep their relative brightness unchanged.

Olly

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22 minutes ago, ollypenrice said:

I know of no way to avoid this happening to the larger stars but correcting it is easy. You can 'reverse process' them. This has to be done star by star unless the background level around the stars is very similar, as it might be in this image.

I used RBA's method from Lessons from the Masters, to separate the detail (small scale) from the background (large scale). Then I increased contrast in the background, and recombined it with the small scale image. What I didn't do properly, was remove the last bit of star halos from the large scale image.

If I have time later on, I will revisit this step.

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1 hour ago, wimvb said:

I used RBA's method from Lessons from the Masters, to separate the detail (small scale) from the background (large scale). Then I increased contrast in the background, and recombined it with the small scale image. What I didn't do properly, was remove the last bit of star halos from the large scale image.

If I have time later on, I will revisit this step.

Can you share a link to the book you refer to Lessons from the Masters please.

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22 minutes ago, wornish said:

Can you share a link to the book you refer to Lessons from the Masters please.

https://www.springer.com/la/book/9781461478331

I was lucky and got a review copy from Astronomy Now. I use some of the techniques routinely and there is a good chapter on the F ratio myth as well. :icon_mrgreen:? It's more Photoshop orientated than PI but both are discussed.

Olly

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2 hours ago, ollypenrice said:

there is a good chapter on the F ratio myth as well. :icon_mrgreen:?

You started it!  Just a quick inquiry...in the end, after having observed many images taken at F3 with the FSQ 106, and considering the total exposure times, would you venture to say that I have been "gotten" by the myth, and that the only benefit realized by the .6x reducer is a larger FOV?  Its worth it just for that, the resolution combined with the FOV make for dynamic images, but exposure times?  

Rodd

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1 hour ago, Rodd said:

You started it!  Just a quick inquiry...in the end, after having observed many images taken at F3 with the FSQ 106, and considering the total exposure times, would you venture to say that I have been "gotten" by the myth, and that the only benefit realized by the .6x reducer is a larger FOV?  Its worth it just for that, the resolution combined with the FOV make for dynamic images, but exposure times?  

Rodd

If you want the extra FOV I've always been clear about my position: you will get a satisfactory S/N faster with the reducer than without it, in accordance with the familiar F ratio/exposure time rule. Here's the relevant bit of graphics I posted right at the start of this debate:

reducers%20used%20properly-L.jpg

My contention (and that of the book) is that there is no point in cropping the image on the right to match that on the left but there is every point in using the reducer to catch the wider target (and catch it more quickly) if that's what you want.

Olly

 

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40 minutes ago, ollypenrice said:

(and catch it more quickly) if that's what you want.

So here is my thought.....If the target is captured more quickly with the reducer (the entire FOV), then if you crop it, the crop was captured more quickly (every part of the FOV is captured more quickly).  The crop won't have the resolution as the unreduced image of the same size, of course.  BUT, if you use a camera with smaller pixels, you can recapture that resolution and beat the myth. (or at least equalize it).

My second thought is....I am not seeing the "catch it more quickly" on the entire FOV.  the theory says I should, but if I had to advise someone I would say, the FSQ at f3 is not that fast.  It will still take you many hours per channel.

Rodd

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1 hour ago, Rodd said:

So here is my thought.....If the target is captured more quickly with the reducer (the entire FOV), then if you crop it, the crop was captured more quickly (every part of the FOV is captured more quickly).  The crop won't have the resolution as the unreduced image of the same size, of course.  BUT, if you use a camera with smaller pixels, you can recapture that resolution and beat the myth. (or at least equalize it).

My second thought is....I am not seeing the "catch it more quickly" on the entire FOV.  the theory says I should, but if I had to advise someone I would say, the FSQ at f3 is not that fast.  It will still take you many hours per channel.

Rodd

Hmmm; to your first point  I say that using smaller pixels has the same effect on both reduced and unreduced systems. Of itself it slows them both down and improves the resolution of both. The effect of the reducer remains what it was before. Unless, of course, the improved resolution cannot be recorded because of the seeing or guiding. So no, we must compare like with like. My point in the illustration I posted is valid for systems using the same camera, the same aperture and a reducer or not a reducer.

To your second point I can only say that you are trying (successfully) to take top quality astrophotos. It takes time. It takes everybody time. There are processing specialists who squeeze remarkable colour and depth out relatively short data. This is admirable but not, personally, to my taste because it shows. Just as I'm prepared to focus with my very reliable fingers (which never tell my brain 'Device Not Recognized' - or not yet!) I'm prepared to follow my excellent friend and guest, Maurice Toet, and devote to an image 'As long as it takes.'  The quick gratification, stunningly deep, stunningly high quality 2 hour astrophoto does not exist outside the virtual reality of the Hyperstar website.

I think you are chasing a moving target. You are setting yourself higher standards as you improve your kit. Very good! Keep at it...

Olly

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9 minutes ago, ollypenrice said:

I say that using smaller pixels has the same effect on both reduced and unreduced systems. Of itself it slows them both down

Ahh...herein may lie the issue.  Never thought of this.  Any benefit of shooting at F3 may be countered by using small pixels.  And I tend to agree...if its worth imaging, its worth imaging as good as possible.

Rodd

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18 minutes ago, Rodd said:

Ahh...herein may lie the issue.  Never thought of this.  Any benefit of shooting at F3 may be countered by using small pixels.  And I tend to agree...if its worth imaging, its worth imaging as good as possible.

Rodd

Small pixels are issue that is easily corrected - you don't need anything special - just bin them, either in hardware if CCD or in software.

Simple as that. Take for example ASI1600 that you used for this image. If issue is with it's 3.8um pixels, how about 7.6um pixels? That is certainly respectable pixel size, topped only by CCD sensors with 9um or 12um pixels.

When you use software bin x2 you will end up with 7.6um pixels at 3.4e read noise. Still better than CCD cameras with larger pixels - most of them have 5e or more read noise.

There is additional benefit of doing software bin - you can achieve same thing as larger pixels without introducing pixel size blur into the equation. Instead of using regular 2x2 bin - split each of your subs in 4 parts (just sort pixels into different parts instead of adding them). Effect will be that of x4 more exposure (you will get 4 times as much subs), and hence x2 SNR increase per stack without pixel size blur associated with larger pixels.

Speed of telescope / camera system is best expressed as Aperture at Resolution, rather than F/number. That way you get comparable "speeds".

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20 minutes ago, Rodd said:

Then I lose the resolution I have come to love.   I would rather have resolution than speed in this case.

Rodd

You can actually have more speed at the same resolution. There are couple of ways to do it.

One is at expense of FOV - just take larger scope with greater focal length and "increase" pixel size - either by using camera with larger pixels, or simply binning ASI 1600. You are currently working at around 320mm focal length. Doubling that to 640mm and binning x2 pixels will get you same exact resolution, but like I said at expense of field of view - although you are doubling pixel size, you are not doubling chip size.

Other way to do it is of course to keep the FOV - that simply means going larger aperture with matching focal length and larger pixels but also larger sensor - one that will be able to provide same FOV.

If FOV is important then going with larger scope will not be beneficial - you will need to do mosaics and you will spend more time - for each panel.

There is no free lunch here - not many scope / camera combinations will provide all three - FOV, resolution and aperture, and it will not come cheap, so you need to balance it by giving up on something (for these sort of resolutions / focal lengths it is usually aperture).

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2 minutes ago, vlaiv said:

You can actually have more speed at the same resolution. There are couple of ways to do it.

One is at expense of FOV - just take larger scope with greater focal length and "increase" pixel size - either by using camera with larger pixels, or simply binning ASI 1600. You are currently working at around 320mm focal length. Doubling that to 640mm and binning x2 pixels will get you same exact resolution, but like I said at expense of field of view - although you are doubling pixel size, you are not doubling chip size.

Other way to do it is of course to keep the FOV - that simply means going larger aperture with matching focal length and larger pixels but also larger sensor - one that will be able to provide same FOV.

If FOV is important then going with larger scope will not be beneficial - you will need to do mosaics and you will spend more time - for each panel.

There is no free lunch here - not many scope / camera combinations will provide all three - FOV, resolution and aperture, and it will not come cheap, so you need to balance it by giving up on something (for these sort of resolutions / focal lengths it is usually aperture).

I know how to do it by changing gear....The challenge is to do it with THIS gear

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15 minutes ago, vlaiv said:

 

There is additional benefit of doing software bin - you can achieve same thing as larger pixels without introducing pixel size blur into the equation. Instead of using regular 2x2 bin - split each of your subs in 4 parts (just sort pixels into different parts instead of adding them). Effect will be that of x4 more exposure (you will get 4 times as much subs), and hence x2 SNR increase per stack without pixel size blur associated with larger pixels.

 

Speed of telescope / camera system is best expressed as Aperture at Resolution, rather than F/number. That way you get comparable "speeds".

How can we split the files into 4?  Can this be done with software that we already have, or can obtain easily?

 

I think that "Aperture at Resolution" is where this thread has been heading.  It sounds like it has the potential to save us all a lot of confusion.  Is there a way to express it in numbers?  If there isn't then we should invent one.

My pixels are 9u, and my resolution at F5 on an FSQ106 is 3.5".  If I used an extender to go to F10, then I would have a resolution of 1.75".  However, on my F10 Tal200 with the same camera, my resolution is 0.92".  It sounds like the Tal is depositing roughly 3 times as much light per unit of area for any given F number.  Have I got this right?

 

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1 minute ago, don4l said:

think that "Aperture at Resolution" is where this thread has been heading. 

Where I have been going is Big FOV, High resolution, and fast focal ratio.  This setup is what I came up with

Rodd

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2 minutes ago, Rodd said:

Where I have been going is Big FOV, High resolution, and fast focal ratio.  This setup is what I came up with

Rodd

I don't explain myself very well.  I just meant that the answer would eventually involve aperture.

 

I think that you have been very successful with your objectives.  There are not many people out there getting such high resolution images with that FOV.   I commented as much on one of the first of your images that I saw.

 

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4 minutes ago, don4l said:

I don't explain myself very well.  I just meant that the answer would eventually involve aperture.

 

I think that you have been very successful with your objectives.  There are not many people out there getting such high resolution images with that FOV.   I commented as much on one of the first of your images that I saw.

 

Thanks Don.  I think it is in our nature to never be satisfied.  I am please with the FOV and resolution--but speed, well, not so much.  I think you are right that aperture would increase speed if the FL remained the same.  But as aperture goes up, the FOV usually goes down--hence Vlad's suggestion of a bigger sensor.  But even with a big sensor, its hard to get this FOV with aperture over 6"--and hard to get F3 as well.  Only the Rifast scopes offer this (other than Hyperstar as Olly pointed out).  But I think they are F3.5.  Its a tough game. 

Rodd

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37 minutes ago, don4l said:

How can we split the files into 4?  Can this be done with software that we already have, or can obtain easily?

 

I think that "Aperture at Resolution" is where this thread has been heading.  It sounds like it has the potential to save us all a lot of confusion.  Is there a way to express it in numbers?  If there isn't then we should invent one.

My pixels are 9u, and my resolution at F5 on an FSQ106 is 3.5".  If I used an extender to go to F10, then I would have a resolution of 1.75".  However, on my F10 Tal200 with the same camera, my resolution is 0.92".  It sounds like the Tal is depositing roughly 3 times as much light per unit of area for any given F number.  Have I got this right?

 

Not sure if it is implemented in any software as such, but its really simple thing to do - very much same process as simple debayering, but instead of splitting into colors we split image into 4 parts. Out of each group of 4 adjacent pixels (2x2), each part will end up with 1 pixel, maintaining order (so top left goes to first part, top right to second, bottom left - third, bottom right - fourth, and so on). This way, each part will contain grid of pixels, sampling resolution will be halved (like with binning), there will be x4 samples to stack - giving boost of x2 for SNR (same as binning), but difference to software x2 bin will be that we keep original pixel size instead of increasing them (hence no increase in "pixel size" blur).

I've written a plugin for ImageJ that does this, and I believe it would be fairly straight forward implementation for PI in it's scripting engine (have not worked with PI, so can't tell for sure, but from what I've gathered it has very good scripting support).

As for comparing scopes and light deposition - what are are you talking about? Sky area or imaging plane area? There is difference between the two.

If talking about sky area, then relation is simple - larger scope will deposit more photons per unit sky area (arc second squared) by ratio of two aperture surfaces - in your case, Tal200 will gather roughly x3.6 more light from 1 arc second squared.

When we talk about imaging plane area (or pixels, because those lie in imaging plane and have surface), then it depends on how much sky area is mapped to imaging plane area.

In this particular case - FSQ106 with extender to make it F/10 and Tal200 that is F/10, if using the same camera and hence same pixel size, both will deposit same amount of photons in given time from given target. This is root of F/ratio myth (or not myth, in this particular case it almost works as advertised - when you fix pixel size). This happens because F/ratio contains as part of its definition focal length. And focal length is crucial factor for converting sky area to imaging plane area. Thus two cancel out.

As an example: We said that Tal200 collects x3.6 more light from one arc second squared than FSQ106. But with Tal200 that light is spread to ~1.18 pixels (pixel surface being just under one arc second squared - or precisely 0.92x0.92") and with FSQ106 and extender - this light is spread over ~0.33 pixels (single pixel having 1.75"x1.75" surface). Now let's look at ratio of these two: 1.18 / 0.33 = ~ 3.58 or like we said about x3.6.

F/ratio myth is myth because it states that F/5 scope is "faster" than F/10 scope (always, period). And it is if you keep your pixel size the same, but you can use different camera with different pixel size, and there is the problem with F/ratio myth. F/10 scope can be faster than F/5 scope if matched with proper pixel size. This is where aperture at resolution comes in as handy - it shows that scope with greater aperture for given resolution will always be faster (not just in particular case). This definition also hides some complexity away, because it is very hard to match resolution precisely - it is derived from both focal length and pixel size, and each of those are not arbitrary in size - there is finite number of pixel sizes and focal lengths out there.

 

 

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