Dan13

24 minutes ago, Ouroboros said:

You might miss the lower noise of your camera, assuming it’s cooled. 

Yes i would for sure, it would only be a travel rig i think for the occasional dark sky site visit. i have seen people use there cooled cmos with dslr lens so may look into that also 

6 minutes ago, Ouroboros said:

@Dan13 Excellent. I wish my first attempt at M31 had been that good. My second too come to think about it.   It is difficult to process, which is kinda counter intuitive given its size and brightness as compared with other targets. I think you’ve got the colour balance just right, to my eye and on my screen anyway. It looks natural, whatever natural is. I often feel less is more when it comes to colour saturation.  It’s also very encouraging to see a one shot colour camera giving such a nice result. 

The other aspect that helps is that your equipment scales the object well. Am I right in assuming that you used a focal reducer to fit it onto that size chip? 

@Ouroboros Hi, thnak you.

Yes it was def a fiddle to process this just how i wanted it, I do like to stay on the side of "natural colouring" if i can when processing. I think im building up a good eye now for what i think is enough and to much.

MY OSC is fantastic, coupled with the L-po or Enhanced its really keeping the urge for a mono purchase at bay  

Yes that right i used a 0.8x flattener which gave me a FL of 444 mm, this is my limit as this isnt cropped at all. I cant fit the heart nebula in i dont think which is a shame as that was going to be next, going to pick up a cheap dslr again i think for some wider field shots with my 300mm lens at some point .

13 minutes ago, Adam1234 said:

Lovely image 

Thank you Adam  

3 minutes ago, MarkAR said:

Excellent image, processing looks really good.

Thank you Mark, much appreciated 

1 hour ago, merlin100 said:

I was trying to find this in the early hours of this morning, without any success.

To image or observe @merlin100 ? I'm quite fortunate, didnt realise before but at this time of year it rises right in front of me in the back garden! Couldnt image it all night! 

8 hours ago, tooth_dr said:

What a great image!  M31 is a difficult one to process, but yours is really nice, particularly the stars.

It certainly is, def one of the harder ones I've had to process lately. Mnay thanks for the kind coment 

2 hours ago, maw lod qan said:

Very nice image!

I get a thrill every time I sit and look long enough to just make out the wispy outer spirals. To think how far away it is and that I'm seeing it.

Youve collected some really old photons there!

Agreed! Its magical, its often a pinch yourself moment in this hobby. Many thanks for the kind words 

2 hours ago, callisto said:

Excellent 

 

Mark

Thank you Mark very much appreciated, clear skies 

First time at this amazing target! Actually found this one of my hardest yet to process.

3.5 hours intergration, stacked and processed in P.i

Altair 80ED-R

Altair 50 mm guide scope

Asi294mc pro

Asi 120 mm-s

HEQ5 pro

Optolong L-Pro

Clear skies all

Great image well done, congrats on joining the magical hobby

lovely image, love the way the crescent is just out there all alone  great job

My first crack at a "Quassi hubble palette" look on an earlier posted Cygnus wall, A fair few blemishes but will probably go back to this in the winter months and reprocess.

was fun and frustrating process for my first time doing these colours.

All equipment posted in my previous post.

41 minutes ago, vlaiv said:

Ok, this is going to need a bit of explaining again, but this will by the easiest bit by far so bear with me.

Here we are dealing with "digital" phenomena. Both image is digital as being collection of numbers or pixels and display device is digital - again having certain number of display dots or pixels. Both have certain resolution  - here term resolution is used to denote number of dots / pixel count or "megapixels".

Easiest way to display image on the screen is to assign each pixel of the image (a number value) to corresponding pixel of display device (light intensity corresponding to that number value for each display dot).

This is so called 100% zoom level or 1:1. First of these two gives "scaling factor" (we will talk about that in a more detail shortly) while other just says the same with ratio of two numbers 1 divide with 1 gives 1 and that is a whole value or 100%.

Problem with this approach is that not everyone has same resolution display nor images all come in same "standard" resolution. Images vary by size (pixel count) and so do display devices. We now have 4K computer screens while old mobile phones have resolutions like 800x600. That is quite discrepancy between them.

For that reason we scale image - we don't change it - it remains the same, but we rather change mapping between it and the display screen. Most notably there is "fit to screen" scale mode. It will fit whole image - however large to pixels that are available on screen. Let's say you have 1920 x 1080 computer monitor and you have 5000x4000 image.

Image will be displayed at 26.74% of its original size in order to fit this screen. Or in another words it will be displayed at 1080 : 4000 ratio (it will use 1080 pixels available to the screen to display 4000 pixels of image).

This means that image is scaled down for display - again image is not changed - it is only displayed differently.

Numbers in PI in window title like 2:1 or 1:5 - show current display zoom in the same way. First one 2:1 - means that image is zoomed in x2 since 2 screen pixels are used to display single image pixel. 1:5 means that image is displayed at 20% of original size since one screen pixel is used to display 5 image pixels (it won't display 5 pixels at the same time - software and computer chooses which one of 5 pixels will be shown but to our eye it looks as it should).

Now we understand display scaling - 1:1 and fit to screen "modes" of displaying the image.

Two of these are very important - 1:1 and Fit to screen.

Fit to screen shows whole image at once regardless if image is larger or smaller than screen - it will zoom in/out just right amount to be able to display all of it. It is very useful for viewing image as a hole to see composition in the image and to see relation of target to FOV and such.

1:1 is also very important as it shows image to the "best level of detail" that current display device can show. If you look at your screen with single pixel turned on - you should be able to see it. Computer monitors are made so that you are seeing finest detail in the image when sitting at normal distance away from it.

We should make our images the same - we should optimally sample the image and when we display such image in 1:1 mode - it should look good and sharp. You can always recognize if image is over sampled when looking at it at 1:1 zoom level. Are stars small and tight / pinpoint like or are they "balls of light"?

Now the final words related to this. Software does not see pixels as little squares or dots of light. Software considers pixels to be values with coordinates. In some sense, software always see image as 1:1 or 100% scale.

When you zoom in or zoom out image when looking at it in PI - you are not changing the image itself. That will have no impact on how Starnet++ sees it for example.

If you rescale your image in software then you are actually changing it and rescaled image will appear differently to Starnet++. Rescaling changes pixel count of the image, while zooming in and out does not do anything.

Drizzle integration rescales your image - makes it have more pixels (x2 or x3 - depending on your settings) and this is why it looks larger - because it is larger, however detail in the image does not change (it is supposed to change - that is why algorithm has been developed in the first place - but even if it does change and resolution is restored - that happens under very specific circumstances - like original image is under sampled and you dithered and all of that). It is the same as if you took your image and upscaled it by factor of x2.

Stars now have more pixels across and when we view that image in 1:1 or 100% (As software sees it) - stars look bigger than in original image. Starnet++ has probably been trained on properly sampled images with tight stars and that is why it has problems when stars have many pixels across - it just can't tell star from a nebula feature that has many pixels across (it expects stars to have just few pixels across).

Hope all of this makes sense and helps?

 

Thank you Vlaiv, it does make sense and you have been more then helpful so greatly appreciated. have a good week and clear skies  

6 minutes ago, vlaiv said:

I just realized that there is probably more down to earth way to explain things. For example first part relates how different things that blur image add up.

Here is intuitive way to understand it (and to try it out) - take any image and do gaussian blur with sigma 1.4 for example. Do another round of gaussian blur with sigma 0.8. Resulting image will be the same as if you did just one round of gaussian blur with sigma of not 2.2 (1.4 + 0.8) but rather of ~1.6 which is sqrt(1.4^2 + 0.8^2). So blurs add in quadrature and three main blur types are seeing blur, guiding blur and aperture blur.

In any case, it is a bit complicated stuff, so main point is - you can't really use lower sampling rate than about 1.7"/px when using 80mm of aperture and in most cases you should go for 2"/px - that is if you don't want to over sample.

I honestly don't know. I understand drizzle algorithm. I have my doubts if it works at all and how good it works in general case - but that needs further investigation. I have improvement on original algorithm that should work better if original algorithm works in the first place (yes, I know, it's funny to improve on something that you don't think works in the first place).

However, I don't understand how drizzle is implemented in pixinsight - so I can't comment on that one. I think that DSS implementation is straight forward, but interestingly enough - original algorithm calls for 2 parameters not one so I don't know how ticking x2 translates to two parameters.

Original algorithm asks for - resulting sampling rate and pixel reduction factor. x2 is directly related to resulting sampling rate. It will enlarge image x2 hence it increases sampling rate by factor of x2. However, you don't need to reduce original pixels by factor of x2 - you can reduce it more or less as per original algorithm and I have no idea what selecting x2 (or x3 in DSS) does with this parameter.

I think my 11am brain has taken in waaaay to much info already today   but i really appreciate the info and will def to continue to read over this.

one last thing, you pointed out that one image i posted was double the zoom the other was, why are my final stacked images not 1:1 they tend to be 1:5 or more, i dont understand what this is doing or telling me, seems the lower the ratio the better starnet works...

7 minutes ago, vlaiv said:

They look the same - this means no improvement from drizzle, but they are not the same with respect to starnet++

Left image is zoomed in x2 while right one is zoomed in x4. As far as Starnet++ is concerned - stars are twice as large in left image than in right image.

EXCELLENT! you have def pointed out something ive not taken into consideration, so i just ran star net on both, and the "more zoomed" image def keeps more stars then the lesser so thats great news and im guessing i can figure that out from here...

question. i use pixinsight to pre process and i add the drizzle files into the image intergration stage, im guessing DSS does this for you if the box (x2 drizzle) is ticked?

8 minutes ago, vlaiv said:

Ok, I'll be brief and to the point since this is rather technical, but here it goes:

- we can approximate resulting star FWHM from aperture size and corresponding Airy disk, seeing error and guiding error. You need to convert everything to "sigma" of corresponding Gaussian approximation. Guiding error is already given as that. Seeing is converted by dividing with ~2.35482 (that is two times square root of two times log of two - a conversion factor between the two FWHM and sigma for Gaussian) and Airy disk is converted to sigma by conversion factor of 0.42 / 2.44 - this is for Airy disk diameter. You take these three and calculate resulting sigma as square root of sum squares.

Multiply with 2.35482 to convert back to FWHM

- As for sampling rate, it is about Nyquist sampling theorem and star PSF gaussian approximation of certain sigma/FWHM. We can get that with following approximation: Fourier Transform of Gaussian is a Gaussian. We take a frequency of Fourier Transform that has value less than arbitrary threshold - for example 10% and we see what is sampling rate that corresponds to this frequency (twice max frequency).

If we do the math, it turns out that FWHM/1.6 is a good approximation as frequencies beyond that are attenuated more than 90% and hence can be neglected.

thank you, this may take me a couple of reads but appreciate the info

@vlaiv both stacked quickly in DSS using same settings except the one on the left is drizzle x2 and the right no drizzle. i think there identical so may rule this out....

2 minutes ago, Ken82 said:

Looks good to me Dan, I take it your using a colour cam ?

could be a little bit of spherical aberration Giving you a slight halo but nothing to worry about. 

Thanks Ken, i guess now im getting a lot more comfortable with my set up and astro as a whole im starting to see things that i didnt used to know were there if that makes sense. yes mate im using the asi 294 mc pro cooled cam OSC

1 minute ago, vlaiv said:

Excellent! I also have Heq5 that I tuned and belt modded myself and indeed it runs at about 0.5" RMS when sky plays along (had it once at 0.38" RMS!!).

there cracking mounts for the price when tuned for sure! i love mine.

2 minutes ago, vlaiv said:

n no universe will any amateur with scope less than 8" benefit from sampling rate of less than 1"/px, but they say 0.67"/px is fine.

For 2-4 FWHM seeing and 80mm scope, even with excellent guiding of 0.5" RMS, star FWHM that you can expect will be 2.71" to 4.4". With those star FWHM, sampling rate should be (FWHM/1.6) in range of 1.7"/px to 2.75"/px and not 0.67"/px-2"/px

You are at lower bound of that so there is a chance that you are slightly oversampled rather than undersampled. General rule is that for 80mm scope you want to be at around 2"/px.

If you wish, we can go into a bit more detail on sampling resolution and FWHM and all of that so I can explain reasoning behind what I've just written but it is a bit technical,

def would like some more advise on this if possible that would be very helpful, i think i may have said under instead of over sorry, plus you would need to add my reducer into that equation which is 0.8x bringing  the F/L to 444

when i ran psf script in pixinsight i cant remember exactly what my FWHM was but it seemed a little high which made me feel my stars were slightly fat, im just running a new stack now without drizzle

9 minutes ago, vlaiv said:

0.48" to 0.64" (in arc seconds) is exceptional thing and requires belt modded and tuned HEQ5 mount.

apologies i should have stated, yes in Arc seconds. i have belt modded my mount and also tuned with new bearings etc a couple weeks ago.

10 minutes ago, vlaiv said:

ny reason to use drizzle? Drizzle is algorithm developed for cases where you have undersampling and you want to try to recover missing resolution. In 99% of cases with amateur setups, one won't be having undersamping and I don't think that anyone is going to do research grade data reduction that requires restoration of missing resolution.

On the other hand, when done properly, drizzle algorithm reduces your SNR, and why would you like to do that when the name of the game is get the best SNR you can.

Reason why your stars look fatter than they should is because you drizzled - you increased pixel scale without effective resolution gain (you were not under sampled to begin with).

I believe i am slightly under sampled depending on the seeing in a given evening, asi 294mc pro and the 80ED-R on astro tools suggests this? ive usually used drizzle due to dithering and killing some walking noise. maybe ill tryu run the stack again without drizzle and see the outcome

12 minutes ago, vlaiv said:

Starnet++ is neural network platform and as such - it is not 100% effective. It only "knows" how to deal with data that has been "taught" to deal with. If your image is too much different that data set that has been used to teach starnet - it will fail. People having newtonian scopes have issues because starnet++ does not know how to deal with diffraction spikes, for example.

One of reasons why Starnet++ might be failing is drizzle. Try to do regular integration without drizzle and see if that improves things with starnet++

thats a fair comment and observation, i genuinely believed it was due to how potent the stars were and it just cant ris then, again ill try a stack with same data without drizzle. and yes its 2x drizzle ive been using 

9 minutes ago, rl said:

Cooling the camera allows longer exposures because the dark counts drop by half for every 7-10C cooling. But the maximum capacity of the pixels remains unchanged.....if a pixel saturates out at 20,000 captured photons at 20C it will still saturate at 20,000 photons even at -20C. Once a pixel is full that's it....you're only option is to allow in less light. 

Makes sense! im going to try 3 mins or less, M31 is my next target so want to keep lower EP time as i dont want to blow the core anyway. yes that star is particularly blue and big i must admit! ill check some of my last targets and see if im getting the same thing.

11 minutes ago, vlaiv said:

It happens on much more expensive scopes, so nothing to worry about.

I guess in a way thats

11 minutes ago, vlaiv said:

Like said - you might have a bit of issues with focusing or maybe seeing was particularly poor on that night. Maybe your guiding was not spot on, what ever the reason - stars are not quite pin point

guiding that evening was between 0.48 and 0.65 for my HEQ5 pro id consider that good so im ruling that out, the focus issue is a pain as with the mask ive never really had too much issue, maybe i do need an auto focusser after all  

any reason why not use drizzle? ive always seen good results with this?

any idea why starnet wont remove all stars? seems to be only with the big bright blue ones such as the example ive shown?

17 minutes ago, rl said:

I guess this is the  reason people invented triplets...the colour correction is better, especially for photography.

I'd try halving the sub time just to see if it's some sort of saturation issue on the camera. A luminance filter that cuts off sharply in the violet might help.

Yea im going to go to maybe 180 secs and see whats thats like for my next image, shame because it handles 240 really nicely bar this issue. I have often read that less exposure on the cooled cams is better which always stumped me because there cooled you would think longer?!

29 minutes ago, rl said:

That's a nice shot seen in context.

Assuming the Bahtinov mask is matched to the scope then the focussing should be spot-on..in which case then yes, you're seeing residual CA, which is a little bit strange because it's not the fastest 80mm doublet out there. The slower ones usually have CA better controlled.  Is yours the original Starwave 80ED? I note they now advertise a Starwave 80ED-R which claims "better colour correction in the blue regions of the spectrum" which probably tells you something.

https://www.altairastro.com/starwave-80ed-r-ed-doublet-refractor-telescope-466-p.asp

 

Thank you, yes the Mask is mayched for the scope, they were baught together from Altair.

Its not the original its the new one the 80ED-R that you posted a link too. You think that blue hue is to do with that then? 

Its more the size of the of the stars, I do think there a little bloated .

For more info this is the final stacked image with just DBE carried out and an STF nothing else. star in question is top left