WO Z73 first light results and advice needed

[Rustang]

So I had my first light with the WOZ73 Friday night. I also took the opportunity to push on to my first ever 20min long subs which Ive been recommended to do by a few people as I believe my particular camera (QHY-9) is better for it and that definitely seems so.

Ive attached a J peg and Tiff of a quickly processed 2hr 20 min stack with NO calibrations frames and the results are interesting and also concerning. I'm really pleased that it looks like 20 min long subs have really brought the noise down, there's a big difference which is great. What is very strange though is that the stack has no Vignetting which Ive had to put up with for so long and thought it was down to the 1:25th filters either not being big enough or close enough to the sensor.

So what's happened to cause no vignetting, the scope has changed obviously and now uses a dedicated WO flattener so could it have been the Altair x80 reducer I was using on the SW80 ED DS PRO? or was it the calibration frames going wrong?

The attached images without any calibration frames seem much better than any of my past images with this camera and filter combo in regards to vignetting so I have no idea what has been going on. Is it also possible for calibration frames to add noise if not correct!?

In regards to the image on the whole I'm really pleased, the stars are bright but i didn't do much to protect them in the quick process but they appear nice and round and not to bad in the corners so the flattener appears pretty good in regards to its distance from the sensor. I'm a little disappointed in regards to sharpness though, the B mask was spot on but its definitely soft so I need to see whats happened there.

20minSubteststretch.tif

Edited August 30, 2021 by Rustang

[vlaiv]

Different FF/FRs have different amount of vignetting and if you changed that component of optical train - then yes, level of vignetting will change.

[Rustang]

41 minutes ago, vlaiv said:

Different FF/FRs have different amount of vignetting and if you changed that component of optical train - then yes, level of vignetting will change.

I've just done a test with the last data from my original setup, stacked with no calibration frames and there's no vignetting either!? 🤔 

[vlaiv]

2 minutes ago, Rustang said:

I've just done a test with the last data from my original setup, stacked with no calibration frames and there's no vignetting either!? 🤔 

What do your flats look like?

[Rustang]

41 minutes ago, vlaiv said:

What do your flats look like?

1 hour ago, vlaiv said:

 

The original flats had vignetting 

[vlaiv]

15 minutes ago, Rustang said:

The original flats had vignetting 

That is interesting.

Did you change focus position between flats and lights maybe? Change in focus position can lead to vignetting - but it usually requires racking focuser further out.

What do you use for flat source?

 

[Rustang]

7 minutes ago, vlaiv said:

That is interesting.

Did you change focus position between flats and lights maybe? Change in focus position can lead to vignetting - but it usually requires racking focuser further out.

What do you use for flat source?

 

I use an LED drawing pad and paper. The focus between filters is the same so never moved it

[vlaiv]

18 minutes ago, Rustang said:

I use an LED drawing pad and paper. The focus between filters is the same so never moved it

Quite strange - I mean vignetting affects light that comes in thru the aperture of telescope - regardless if it comes from the stars or flat panel.

You should see it both in your flats (as you do) - but also in your uncalibrated lights.

[Rustang]

5 minutes ago, vlaiv said:

Quite strange - I mean vignetting affects light that comes in thru the aperture of telescope - regardless if it comes from the stars or flat panel.

You should see it both in your flats (as you do) - but also in your uncalibrated lights.

Its definitely strange. I think I have seen it on the lights but will have to go back and check but there's obviously no sign on this recent stack of just lights. Do you also confirm the above images are a little out of focus? When you zoom in it dies seem like the stars go a little blury quicker than normal but as I say the b mask was good and it's now a threaded connection from camera to scope. 

[vlaiv]

9 minutes ago, Rustang said:

Do you also confirm the above images are a little out of focus? When you zoom in it dies seem like the stars go a little blury quicker than normal but as I say the b mask was good and it's now a threaded connection from camera to scope. 

Yes, it does look like little bit out of the focus. You can see that on fainter stars - they are also like little discs rather than stars. Bright stars can appear disc like due to stretch - but faint ones should be pin point like - and they are not - they look like small circles.

[Rustang]

5 minutes ago, vlaiv said:

Yes, it does look like little bit out of the focus. You can see that on fainter stars - they are also like little discs rather than stars. Bright stars can appear disc like due to stretch - but faint ones should be pin point like - and they are not - they look like small circles.

Il will try and see what's going on then as I really took my time with the focus mask so can't think what's happened, maybe focus slip on the scope. Can there be anything else going on if the mask is good but the image is still out of focus? 

Edited August 30, 2021 by Rustang

[vlaiv]

Just now, Rustang said:

Il will try and see what's going on then as I really took my time with the focus mask so can't think what's happened, maybe focus slip on the scope. Can there be anything else going on if the mask is good but the image is still out of focus? 

Yes. Check individual subs to see if there is progression in defocus.

As telescope cools down - tube gets shorter because things shrink at lower temperature. If there was rapid temperature change during imaging session and you did not refocus (people usually just focus on the beginning of the session) - it can lead to loss of focus over time.

Another possibility is that scope was not properly cooled when you focused - if you focused at the beginning quickly after putting the scope on the mount and that it cooled before you started imaging.

Third option is simply - poor judgement of bahtinov mask pattern. I don't use B mask at all as I've found that I can't reliably tell if I have good focus with it or not. It is far easier to just check stars on computer screen and look at FWHM / HFR values.

[Rustang]

24 minutes ago, vlaiv said:

Yes. Check individual subs to see if there is progression in defocus.

As telescope cools down - tube gets shorter because things shrink at lower temperature. If there was rapid temperature change during imaging session and you did not refocus (people usually just focus on the beginning of the session) - it can lead to loss of focus over time.

Another possibility is that scope was not properly cooled when you focused - if you focused at the beginning quickly after putting the scope on the mount and that it cooled before you started imaging.

Third option is simply - poor judgement of bahtinov mask pattern. I don't use B mask at all as I've found that I can't reliably tell if I have good focus with it or not. It is far easier to just check stars on computer screen and look at FWHM / HFR values.

Thanks, what values should I be seeing!? Ive always done it the lazy way so guilty on that one but Ive not had an image that to me has seemed as out of focus as above before.

Edited August 30, 2021 by Rustang

[vlaiv]

5 minutes ago, Rustang said:

Thanks, what values should I be seeing!?

If you want to search for progressing defocus - just visually compare first and last sub of the evening.

First sub should have tight stars and last one should have stars as in above image. Difference should be obvious.

[Rustang]

6 minutes ago, vlaiv said:

If you want to search for progressing defocus - just visually compare first and last sub of the evening.

First sub should have tight stars and last one should have stars as in above image. Difference should be obvious.

Apologies, I meant what values to look out for when imaging, I use APT so is there away of checking values in that software?

Edited August 30, 2021 by Rustang

[vlaiv]

3 minutes ago, Rustang said:

Apologies, I meant what values to look out for when imaging, I use APT so is there away of checking values in that software?

I don't use APT, but here is APT help file section that describes focus aid tool:

https://astrophotography.app/usersguide/focusing_aid.htm#

It shows both FWHM and HFR values.

You should not look for particular values in either - they are both relative, and smallest value indicates best focus, but it will change from session to session as it depends on both seeing and guiding performance.

Idea behind using those is to use short frame & focus exposures (but make them at least 2-3 seconds long in order for seeing to average enough) and monitor values. Tweak focus until you get the lowest number. Numbers will change each time you make focus adjustment and you need to change focus until you get lowest values (that will include going "thru" actual focus position once or twice as you need to verify that numbers first fall and then start to rise once you go thru the actual focus position - pretty much like focusing visually - you rack focuser in/out until you are certain you have the sharpest view).

[Rustang]

Just now, vlaiv said:

I don't use APT, but here is APT help file section that describes focus aid tool:

https://astrophotography.app/usersguide/focusing_aid.htm#

It shows both FWHM and HFR values.

You should not look for particular values in either - they are both relative, and smallest value indicates best focus, but it will change from session to session as it depends on both seeing and guiding performance.

Idea behind using those is to use short frame & focus exposures (but make them at least 2-3 seconds long in order for seeing to average enough) and monitor values. Tweak focus until you get the lowest number. Numbers will change each time you make focus adjustment and you need to change focus until you get lowest values (that will include going "thru" actual focus position once or twice as you need to verify that numbers first fall and then start to rise once you go thru the actual focus position - pretty much like focusing visually - you rack focuser in/out until you are certain you have the sharpest view).

 I see, sounds like a lot of faff but I have just seen that where Ive gotten away with just using the focus mask before (probably could have still been improved) It now doesn't seem to be the case.  Ive just looked at the subs where I was achieving focus on the last session and its not great. The last sub with the mask was good,  the sub straight after with the mask removed, when zoomed in is not in focus, I missed this and so every Ha sub after is out, my bad but can the focus mask be that out when Ive never had it that bad before!?

[vlaiv]

4 minutes ago, Rustang said:

 I see, sounds like a lot of faff but I have just seen that where Ive gotten away with just using the focus mask before (probably could have still been improved) It now doesn't seem to be the case.  Ive just looked at the subs where I was achieving focus on the last session and its not great. The last sub with the mask was good,  the sub straight after with the mask removed, when zoomed in is not in focus, I missed this and so every Ha sub after is out, my bad but can the focus mask be that out when Ive never had it that bad before!?

I don think it is much worse than doing it with B mask, is it? I mean principle is the same - except you look at the numbers instead of spike pattern.

As for B mask precision, well, I'm not an expert, or to put it more precisely - I have almost 0 knowledge and experience with it   Used it couple of times, saw that I don't get good focus and decided not to use it anymore. Have two of them gathering dust (one for each imaging scope).

[Rustang]

8 minutes ago, vlaiv said:

I don think it is much worse than doing it with B mask, is it? I mean principle is the same - except you look at the numbers instead of spike pattern.

As for B mask precision, well, I'm not an expert, or to put it more precisely - I have almost 0 knowledge and experience with it   Used it couple of times, saw that I don't get good focus and decided not to use it anymore. Have two of them gathering dust (one for each imaging scope).

Yeah your probably right, my brain is just hesitant with change! The image below is where I thought I had achieved good focus, I think I'm right in saying that it should have been ok going off those spikes patterns but it's failed somewhere. One step forward, one step back! 😔

Edited August 30, 2021 by Rustang

[Rustang]

17 minutes ago, vlaiv said:

I don think it is much worse than doing it with B mask, is it? I mean principle is the same - except you look at the numbers instead of spike pattern.

As for B mask precision, well, I'm not an expert, or to put it more precisely - I have almost 0 knowledge and experience with it   Used it couple of times, saw that I don't get good focus and decided not to use it anymore. Have two of them gathering dust (one for each imaging scope).

I've just looked at a sub in APT with the focus aid, I know you said the values will change but low numbers are good, these seem low but are they low enough!?