Rodd

On 26/12/2023 at 10:29, vlaiv said:

I guess that you don't cycle filters, but rather take some time to do the Ha, then OIII and in the end SII, not necessarily in that order?

Was this a single night?

In any case, depending where target is in the sky - slight PA error + guiding can lead to different levels of field rotation.

You can have PA error in altitude and/or azimuth - meaning your mount needs to be turned "left/right" to reach true NCP or it needs to be tilted "up/down", or some combination of these. Left/right error differs from Up/Down error in sense that it causes DEC drift in different part of the sky.

One is near meridian and other is when the mount is pointing east or west.

Depending where you are on "a circle", and depending how big your DEC error in that moment - guiding will cause more or less field rotation (field rotation is created when there is DEC drift and guide system compensates. In fact - I think that it would be there even without guiding, guiding just helps to stay on target).

In any case - if you shoot Ha in one part of the sky and SII in other - this can cause one set of subs to have very small field rotation and other to have somewhat bigger.

Regarding filter cycling. I don’t think there would be much difference in my case because I collect allot of data. At least 2 nights per channel. So for each channel my target progresses from about 30 degrees to an hour (sometimes 2) past the meridian.  So each channel has data from the various declinations—just at different times. I check PA nightly, but often I make no adjustments

49 minutes ago, tomato said:

Glad you sorted out the grid problem. I can't understand why a suitable dark would not remove the amp glow. I use ASI 178 cameras which have horrendous amp glow at 120s exposures but this calibrates out completely with an equivalent dark. The cameras have been retrofitted with an external Peltier cooler so I have to be a bit careful to ensure the darks are taken at  the same sensor temperature as the lights, but this should be straightforward with the internally cooled camera.

Have you tried other software to calibrate your lights? I have had issues in the past where the darks have been rejected due to some difference in the subframe parameters, but no warning has been displayed, the software just doesn't use the darks in the calibration.

I have nog tried other TV software. I thought it might be due to old darks, but new ones are no different. I guess I could try maxim DL.  Good idea. 

1 hour ago, vlaiv said:

I guess that process of registration caused SII subs to have grid pattern. You no longer have raws?

You can "cure" grid pattern by not trying to stretch so much. It is really just noise and if you can see it - you are hitting the noise floor. Pattern forms out of noise because some pixels get more averaged out than others and this improves their SNR. These pixels lie on rectangular grid - and after denoising - grid is shown as darker and lighter zones.

I fouynd an alternatlyt registered SII stack that I used Windsor sigma clipping to register.  Itr was smaller in dimensions, but teh same scale.  I guess I must have registered to a cropped master.  Dont remember.  Seems to have worked.  Thanks!

C11 .7x ASI 1600 about 13 hours SHO

23 minutes ago, vlaiv said:

I guess that process of registration caused SII subs to have grid pattern. You no longer have raws?

You can "cure" grid pattern by not trying to stretch so much. It is really just noise and if you can see it - you are hitting the noise floor. Pattern forms out of noise because some pixels get more averaged out than others and this improves their SNR. These pixels lie on rectangular grid - and after denoising - grid is shown as darker and lighter zones.

I found an alternate stack registered with Windsor sigma clipping that doesn’t have the grid. But the FOV is smaller. I think I must have cropped out the right hand area and registered to a cropped stack as the ha, SII snd oiii combine well. 
 

thd other issue I have is my amp glow does not calibrate out. Others don’t have this issue. It is only apparent in 300 sec subs (NB). I took new darks recently to see if the darks were the problem, but the same glow is visible. The amp glow is supposed to calibrate out. The best answer is to get a 2600, but I can’t 

51 minutes ago, vlaiv said:

No, it is due to field rotation because of slightly off polar alignment.

It can also be that your subs are all aligned but there is small rotation between channels so one of the channels needed to be aligned to others.

Try restacking - but use different reference frame.

Out of luck. I checked and only have the registered SII subs and they all have the grid pattern.  

1 hour ago, AKB said:

Is it on the flats?

No. Only on SII subs

I’ll have to see if I still have the original subs. I usually delete subs once I register and keep the registered subs. I guess I can reregister the registered subs

but I only saw this this time. All other channels were collected over the same time and my PA was the same. I typically register all subs to the same sub. 

17 minutes ago, vlaiv said:

What software are you using for stacking and what interpolation algorithms does it offer?

Above is artifact related to a small angle rotation when aligning subs and using certain forms of interpolation.

I use PI.  I have not seen this before or since. I use either Windsor sigma clipping or linear fit stacking. These are the 2 out of about 10 the software indicates are best.  Does it mean there was rotation of the camera or tube or some other part of the system?

Does anyone have any idea what cuased the grid pattern visible in the lower right hand corner?  Its in the SII stack.  Very odd.  Only had this issue once.  The prominence of the lines makes nme think it is not one or two subs-but all of tghe SII subs.

Rodd

11 hours ago, Mr Spock said:

Very nice image 👍

But in your title, did you mean fiend or friend? They have opposite meanings! 

This a particularilly fiendish fellow, no?   Perhaps a bit on the cartoonish side (think Pink Floyd The Wall movie).

I started this while waiting for my target to rise.  It may seem ironic that there could be slim pickings for Ha targets at this time of year, but I have shot most of them and many others are not suitable for the FOV I am using.  I fret over traget selection, because completing an image  for me requires significant dedication due to the sky.  At .79 "/pix, seeing is critical, so even the darkest, cloudless nights can be a wash.  Seeing was good this night, the stack had a linear FWHM of about 2.0, with at least half the subs coming in below 2.0.  After the Moon set, luminance subs were coming in at 2.2".  There is only about 3.75 hours, so not complete by any means; but I posted at Bin 1 anyway as the level of noise is not too bad.  The bright star artifact reminds me that I simply must find a way to get my hands on a 2600 sensor.

TOA 130 with .99x flattener and ASI 1600.  Ha: 40 300 sec.

36 minutes ago, 900SL said:

I might make the leap to Pixinsight now I've got a mono camera. Thanks Oskari

Adding ha to the red channel is easy in PI using pixel math. You just have to know the method.  

1 hour ago, Padraic M said:

Absolutely Olly I agree, but you do still have some control over it, and processing at the linear stage is a relatively simple way to get started with HaRGB/LRGB/HaGB/(HaR)GB combinations etc. As you say, you are deciding how much you want to highlight the Ha content in your image at the expense of non-Ha red frequencies which is not a natural representation of the scene. You've given me food for thought on non-linear combination, work for another day!

@Rodd the Red stack contains all of the Ha light as well as other colours - the standard red filters on the market filter in a continuous range of wavelengths both shorter and longer than Ha at 656nm.

A narrowband Ha filter only allows through light at the Ha wavelength +/- half the bandwidth. It filters out all of the other red light that a standard red filter would have allowed through, but it doesn't include any light that is not transmitted by a standard red filter. So by selectively processing Ha and Red you are effectively emphasising that narrow band of Ha at 656nm by attenuating or even removing all of the other red wavelengths. All while (although not necessarily) leaving the green and blue colour levels untouched.

 

Yes but there is a big difference between an Ha stack and a red stack. If you remove all but Ha from a red stack, it does not equal an Ha stack. For one thing, in my sky my red exposures are 1-2 minutes and my Ha exposures are 10-20 minutes.  Many structures that are made from ha frequencies do not have enough signal in that frequency in a red stack.  A good example is Ha regions in galaxies-like m106. One adds ha to galaxies because the red channel doesn’t have enough ha signal to do them justice. One would have to collect way to much red to see the same structures, and they wouldn’t be the same, anyway. You’d have to remove non ha signal to see them.  Otherwise, narrow we band filters would be worthless

3 hours ago, ollypenrice said:

I don't want to present myself as a pundit but my view is that, if you combine it at the linear stage, you have relinquished almost all control over it.

Let's remember that there is no 'natural' value for the Ha contribution. There is no way to calibrate it 'scientifically' with the rest of the image because the calibrated Ha is, surely,  just what is already contained in the red channel.* The whole point of the addition of Ha is to distort its contribution to the image and allow us to reveal structures otherwise not visible, though certainly present in scene we are photographing. This is an artificial process and we are the the artists - or artificers - responsible.

Olly

*This does not apply to those daytime DSLRs whose filters do block most of the Ha.

Hmm. But if you compare a red stack with an Ha stack there are obvious differences. The red filter won’t pick up all Ha.  There is an overlap in frequencies, for sure, but they are not equal. Maybe I misinterpreted what you said?

Well, certainly not a glistening gem, but at least it is a pill I can swallow. I foreswore all aggression (unless cropping is considered aggressive).   Poor seeing, poor transparency, a full Moon, wind, and shaky guiding conspired to make this a thoroughly tortuous project (inclusive of processing.  I will not be revisiting this target to try and improve the image.  17 hours is enough.
 

TOA 130 with .99x flattener with ASI 1600. About 17 hours of Ha, SII, and OIII

1 hour ago, wimvb said:

Great image already. Do you have a sky darkness that allows you to catch the tail?

Part of it is faintly visible in the stacks. I am  hoping to capture lots of lum. 

I knew this one wouldn’t be finished, but  I have been up for 5 straight days, imaging this target from 2 am to 5:30 am each night.  It was torture. But I could not waste the clear sky.  It’s just RGB, about 10 hours. I’ll double the RGB and pile on the Lum over the next few months. No tail yet, which I am hoping to catch. I really want to portray this one bin 1, but it will take many nights of good seeing. The red channel was collected in decent seeing.  Blue and green not so much. I collected 10 sec subs to improve star color.

TOA 130 with .99x flattener and ASI 1600  120 sec and 10 sec subs

Bin 1 - it almost makes it   

18 minutes ago, Ibbo! said:

I tried this object a few years ago and for the same reasons as you state it did not see the light of day.

 

You have brought out more detail than I did.

It probably didnt help that I shot most of the Ha during a full Moon, and 1/2 SII during very poor conditions.  Still....

I'm not sure I have ever been this dissapointed in one of my images.  I just don't understand it.  This is the first narrowband image I have completed with the TOA and .99x flattener.  I had high hopes.  With 17.5 hours, you'd think there was 5.  Noise was off the charts, and there is what I believe to be incorrect red dust around the upper and right perimeter.  Conditions were very poor when I shot the SII, so maybe that's what it is.  I was hesitant to post due to the quality of the image, but I am done with it.  If 17.5 hours looks like this, 17.5 x 2 won't look much better.  So it is what it is.  The problem with adding data would be that all channels are weak; I would need to basically redo the shoot.  

TOA 130 and .99x flattener/reducer with ASI 1600..  137 300 sec Ha; 60 m300 sec OIII; 63 300 sec SII.  Bin2

Edit-decided to add another version.  The first is for lighter screens and the second is for darker screens

On 11/12/2023 at 04:44, maw lod qan said:

Beautiful !

You won't be sweeping all that dust under the carpet!

😊

Insight Observatory comes to the rescue again-clouds and storm,.  This is from the 12.5" RC, Namibia, about 20.2 hours, LRGB.

7 hours ago, WolfieGlos said:

Wow, incredible detail in those dust lanes! 

Thanks. The challenge was not to overdo them. 

7 hours ago, AstroGS said:

nice photo, the colours are really nice and the background very well controlled - very good  and thanks for sharing.

Thanks!

The dust lanes are bullies in this galaxy--They are like tentacles of s submerged nonster, rising and thretening as I beat them down like wack-a-moles.

Data from Insight Observatory remote 12"RC.  LRGB.-about 25 hours I think. As with most data sets I get from IO, it required substantial effort to tame.  Paerts of it are oversaturated, and other parts pale. The dust lanes control all.  It is very difficult to process this galaxy without darkenbing the dust lanes too much.

3 minutes ago, simmo39 said:

Nice!

Thank you!