QHY268M & QHY268C Users Thread (Please share your knowledge and tips)

[teoria_del_big_bang]

Cheers Ciarán, that's a real help to help me understand all this. 👍

I suspect then that the actual best exposure time, if you were to go to the nth degree, would change with target, seeing conditions, moon phase and LP but there will be a ballpark figure that suits most DSO targets for each filter (and hopefully the same ballpark figure for all RGB and all NB filters and L obviously much shorter).

Maybe some targets with massively bright stars, such as Alnitak, might then benefit to use the lower end of the figures you get and other targets with a much more even spread of dimmer stars can use the upper end, so some targets maybe 300 seconds for NB and others may be better at 400 seconds.

Also maybe I should be examining some of the first exposures in PI whilst the sequencing carries on just to check for mean ADU and also check the ADU of the brighter stars.

Steve

Edited January 20, 2022 by teoria_del_big_bang

[Stuart1971]

Math….🤯🤯🤯

so @teoria_del_big_bang are you going to work out some good sub lengths for us all…😂😂 as that may as well be written in Chinese for me….😂😂

[teoria_del_big_bang]

1 minute ago, Stuart1971 said:

Math….🤯🤯🤯

so @teoria_del_big_bang are you going to work out some good sub lengths for us all…😂😂 as that may as well be written in Chinese for me….😂😂

Ha Ha, if only I could I would gladly do so.
I used to be pretty good at maths but as I get older it gets harder with each passing year 🙂 
I guess if you trust the maths then no real need to fully understand it just put the figures in and see the result.
I need to look at the info and links @Xiga has in the last reply and then maybe try it in PI.
If I get a better understanding I will be back. 
Are my findings (or theirs) directly applicable to your colour camera, I suspect so regarding exposure length as basically same as me using the mono with RGB filters ?
I guess that if I need 30 exposures each R,G and B filters then to get the same total integration time you just have 90 exposures .
What will change things, to some extent, is the NB filter and will require longer exposures.

I guess ultimately you have to decide on a gain and mode then take some exposures and check the results for average ADU and also check the stars themselves to see how close to  maximum ADU they are and alter exposure length accordingly, I find PI really good for this.
As said it is a bit of a balance of enough exposure for the main target to swamp the read noise without over exposing the brighter stars. Some targets may allow this easily, others with very bright stars may be more tricky and require a compromise whereby the bright star(s) are pretty much saturated and you have to do some work in processing. One trick I have used in Orion is to take different exposure lengths, some of 180 seconds and some of 15 seconds then use the 15 second ones for the core and using blurred mask integrate that into the main image to replace the core. I know this is a bit of a special instance and that you would not want to do this on all images but could be done on a very bright star to overcome the issue (maybe ?)
What do you have to check ADU values ?

Another possibility is to use SharpCap Pro, its only £12 a year and that can also give you the ideal sub length by running a few tests on your camera.

From what I have seen lately if I were you I would try Mode 1 and 56 Gain (this seems to be what many with this camera use) and take the 180 seconds for RGB as a good start.
If using the LP filter then maybe a bit longer, say 240 seconds, take some images and then look at the results, or post some of the raw images and get some opinions, but that should be a good start to me, although my advice earlier about exposure time proved to be totally wrong so take my thoughts with a pinch of salt, I have found that when you think you know what you doing how completely wrong you can be 🙂 
But nobody said any of this was easy when I started.

Steve

Steve

[Phillyo]

If anyone is using NINA with Sharpcap Pro, you can use the optimal sub length calculator in NINA. I do that at the start of each session and go from there. During a moonless night shooting through a 5nm Antlia APT-L dual band filter it said my optimal exposure length was 225 seconds (I use a Samyang lens at f3.6 with an ASI533 so a little different to this camera but you get the idea) so I set my exposures to 240s (4min) as I already have a dark library for that and left it to go. NINA uses the Sharpcap analysis results from the sensor to calculate the optimal sub exposure length. Really good tool actually.

[scotty38]

11 minutes ago, Phillyo said:

If anyone is using NINA with Sharpcap Pro, you can use the optimal sub length calculator in NINA. I do that at the start of each session and go from there. During a moonless night shooting through a 5nm Antlia APT-L dual band filter it said my optimal exposure length was 225 seconds (I use a Samyang lens at f3.6 with an ASI533 so a little different to this camera but you get the idea) so I set my exposures to 240s (4min) as I already have a dark library for that and left it to go. NINA uses the Sharpcap analysis results from the sensor to calculate the optimal sub exposure length. Really good tool actually.

I must be doing something wrong here as for my 294 last night it gave me 127 minutes 🙂 🙂

[Phillyo]

1 minute ago, scotty38 said:

I must be doing something wrong here as for my 294 last night it gave me 127 minutes 🙂 🙂

Did you remember to take the lens/scope cap off the end?  

[scotty38]

8 minutes ago, Phillyo said:

Did you remember to take the lens/scope cap off the end?  

Haha yes, on for the Bias calc and then off.....

 

Anyway don't let me derail things, it's no doubt me, I will have another play with it tonight.

Edited January 20, 2022 by scotty38

[teoria_del_big_bang]

45 minutes ago, scotty38 said:

I must be doing something wrong here as for my 294 last night it gave me 127 minutes 🙂 🙂

hope your guiding is spot on 🙂 

Steve

 

Edited January 20, 2022 by teoria_del_big_bang

[scotty38]

21 minutes ago, teoria_del_big_bang said:

hope your guiding is spot on 🙂 

Steve

 

Seems ok but I did fail back to 5 minutes. Everything was great last night BUT I was trying to image the Jellyfish again and as it's quite dim I failed to notice my framing wasn't great so need to repeat again tonight.

Anyone want 100 poorly framed lights, just let me know 🙂 🙂

[Richard_]

1 minute ago, scotty38 said:

Seems ok but I did fail back to 5 minutes. Everything was great last night BUT I was trying to image the Jellyfish again and as it's quite dim I failed to notice my framing wasn't great so need to repeat again tonight.

Anyone want 100 poorly framed lights, just let me know 🙂 🙂

I'll trade you two evenings of my jellyfish subs with moon reflections from my l-extreme filter, deal? 😂 

[scotty38]

3 minutes ago, Richard_ said:

I'll trade you two evenings of my jellyfish subs with moon reflections from my l-extreme filter, deal? 😂 

Well that's interesting as mine are with the same filter and they seem to look ok in that regard. I did check where the nebula was and that the moon was far enough behind as it followed through the night.

 

Scrub that, the checking may have been for some M13 I did at the end of the night....

 

Edited January 20, 2022 by scotty38

[scotty38]

Here's mine from last night with just an Auto STF. Yep there is a significant gradient but how does it compare with yours?

[Stuart1971]

5 hours ago, teoria_del_big_bang said:

Ha Ha, if only I could I would gladly do so.
I used to be pretty good at maths but as I get older it gets harder with each passing year 🙂 
I guess if you trust the maths then no real need to fully understand it just put the figures in and see the result.
I need to look at the info and links @Xiga has in the last reply and then maybe try it in PI.
If I get a better understanding I will be back. 
Are my findings (or theirs) directly applicable to your colour camera, I suspect so regarding exposure length as basically same as me using the mono with RGB filters ?
I guess that if I need 30 exposures each R,G and B filters then to get the same total integration time you just have 90 exposures .
What will change things, to some extent, is the NB filter and will require longer exposures.

I guess ultimately you have to decide on a gain and mode then take some exposures and check the results for average ADU and also check the stars themselves to see how close to  maximum ADU they are and alter exposure length accordingly, I find PI really good for this.
As said it is a bit of a balance of enough exposure for the main target to swamp the read noise without over exposing the brighter stars. Some targets may allow this easily, others with very bright stars may be more tricky and require a compromise whereby the bright star(s) are pretty much saturated and you have to do some work in processing. One trick I have used in Orion is to take different exposure lengths, some of 180 seconds and some of 15 seconds then use the 15 second ones for the core and using blurred mask integrate that into the main image to replace the core. I know this is a bit of a special instance and that you would not want to do this on all images but could be done on a very bright star to overcome the issue (maybe ?)
What do you have to check ADU values ?

Another possibility is to use SharpCap Pro, its only £12 a year and that can also give you the ideal sub length by running a few tests on your camera.

From what I have seen lately if I were you I would try Mode 1 and 56 Gain (this seems to be what many with this camera use) and take the 180 seconds for RGB as a good start.
If using the LP filter then maybe a bit longer, say 240 seconds, take some images and then look at the results, or post some of the raw images and get some opinions, but that should be a good start to me, although my advice earlier about exposure time proved to be totally wrong so take my thoughts with a pinch of salt, I have found that when you think you know what you doing how completely wrong you can be 🙂 
But nobody said any of this was easy when I started.

Steve

Steve

Yes, will be out tonight before the moon appears, and will be using Mode 1 gain 56…and see how it goes…which me luck….😂😂

[Richard_]

25 minutes ago, scotty38 said:

Here's mine from last night with just an Auto STF. Yep there is a significant gradient but how does it compare with yours?

Sorry Scotty, I sent you a pm as I didn't want to go off topic (remember, I'm using an ASI533 camera). 

Here's my master lights of the four panels without any processing. Circled on the right of each panel is some condensation (which disappeared on second night when I heated the front of my camera with a dew strap). The arrows point to some very faint, blue halos.

Well, on the second night the halos moved over to the right side of the image. No dew was present like the first night. When I checked stellarium, it showed that the moon swapped sides with respect to the jellyfish and this would explain why the halos flipped sides in my images. On the second night I shot M42 Orion before jellyfish and saw no artifacts so I'm certain the blue halos are not dew. Perhaps the halos were caused by some internal reflections in my OTA/dew shield/filter etc.?

Images from first night 14th Jan 22

First night (14th Jan 22)

Second night (17th Jan 22)

[scotty38]

Agreed so my last derailing comment too but I replied with what i think....

[teoria_del_big_bang]

36 minutes ago, Stuart1971 said:

Yes, will be out tonight before the moon appears, and will be using Mode 1 gain 56…and see how it goes…which me luck….😂😂

I do wish you luck, I have mine out at moment under nice blue skies just waiting for the clouds to roll in, well that's what normally happens.

Steve

[scotty38]

same here....

[Stuart1971]

22 minutes ago, teoria_del_big_bang said:

I do wish you luck, I have mine out at moment under nice blue skies just waiting for the clouds to roll in, well that's what normally happens.

Steve

Yes it’s clearing nicely ATM, but the big old moon will be appearing around 11 ish for me, so should get a few hours of the Heart Nebula tonight…🤞🤞

[Stuart1971]

Well Mode 1 gain 56, does this look ok for 5min sub, with Idas P2 LP filter on, only a screenshot I’m afraid as typing this on my iPad…but does the death look ok for these setting, like what I should expect to see with a minimal stretch in NINA

there is not a black area at the top, that is just a shadow from iPad camera…

 

 

Edited January 20, 2022 by Stuart1971

[jjosefsen]

It is really hard to judge quality from that image.. 

But my first thought is that it looks OK actually, and Mode 1 Gain 56 sounds about right judging from the graphs shown earlier.

[jjosefsen]

Also.. If you have doubts about your own processing skills vs camera, it could be good to give the data to someone else and let them see what they can get out of it.

I did that when I started AP because I was so frustrated with my progress, and I was sure it was my equipment and not my skills.. That was a very humbling experience! :D

[Stuart1971]

51 minutes ago, jjosefsen said:

Also.. If you have doubts about your own processing skills vs camera, it could be good to give the data to someone else and let them see what they can get out of it.

I did that when I started AP because I was so frustrated with my progress, and I was sure it was my equipment and not my skills.. That was a very humbling experience!

You hit the nail on the head here….👍🏼

[teoria_del_big_bang]

Okay, so far so good, clouds have not yet appeared so doing some Ha and SII on Jellyfish, not bothering with OII as there is so little there and giving massive halos on the two bright stars.
So I have come down in exposure time big time from my usual 10 minutes to 4.
Looking at the statistics in EKOS I am getting a mean  of 475, so that is pretty much in line with what @Xiga suggested was correct for this gain and offset, but the maximum is 65534. When I look in Pixinsight the two bright stars are maximum ADU before any stretching, so I take it there is nothing I can do about the brightest of stars in the data itself and I will have to take care of that in the processing, because even a slightly shorter exposure time is not going to significantly reduce those two stars, if at all. I guess some stars you just cannot stop from being over blown when imaging dim targets and have to deal with them later.
 

Steve

[tomato]

On my QHY 268c with the dual band NBZ filter in place on an Esprit 150, I was using #1, High Gain mode, Gain 60, Offset 30, with 240 sec subs, temp set pt -20 deg C.

However, I have just shut everything down as a thick mist bank is rolling in from the North East.

[scotty38]

Those mists have impacted my Jellyfish.....