teoria_del_big_bang

I think for 3 hours, Bortle 6 and a near full moon that's about what I would expect.
With some calibration and work on the background it will probably pop out some more.

Steve

My scope is pretty heavy too so fitted a handle, which is essential for safe loading of scope onto mount in my case at least. and then swapped the short dovetail that scope came with for a much longer one and added that small red clamp, shown in close up in lower image.
So very much like @Saganite, the added advantage with this clamp is that  as I have changed the setup (heavier camera, new rotator, different guidescope) when I move the rig slightly to achieve perfect balance I just move the clamp and when I fit the scope onto mount it just slides down to the clamp and it it is in a balanced condition each time.

Steve

24 minutes ago, Xiga said:

Hi Steve

There will always be some stars that clip (it's unavoidable to some extent) so it's just about making sure the number that do isn't excessive. Those 2 stars are Very bright, so it's to be expected really. 

ps - don't give up on the Oiii either. A few years back i shot the Jellyfish in Ha and Oiii, using just a Nikon D5300, and found there to be plenty of Oiii, so you should have no difficulty with your mono CMOS. https://www.astrobin.com/384884/

I thought that was the case.

It was more the horrible halos that made me give up.
I will try another nights, whether it would be any better with less moon up or not I do not know ????

Your image on Astrobin is really nice, you have captured that OIII really well. I guess on mine there are some signs on the outer edges, maybe a bit longer exposure on OIII and more frames would add some nice detail so I must r=try at a later date (hopefully not too much later). I can deal with the halos in processing, a pain but would be worth it.

Steve

12 minutes ago, Stuart1971 said:

Ok, so stupid question…..is that the difference…..really…..?? 

Well yes I would say so because to get a colour image I have to take 3 of these images and combine so really the intergration time for one colour image is actually 12 minutes.
Okay this is NB but some checks I did earlier on using RGB looks like I need to be around 120 seconds for RGB images so for one frame of RGB would be 6 minutes.

Steve 

41 minutes ago, scotty38 said:

Those mists have impacted my Jellyfish.....

Pretty much the same here now, you could have kept them down there a bit longer 😞

Still taking images as it will flip in an hour and want to check it all works okay as I think it failed last time. But when I go out and look how cloudy it is I cant believe it is still guiding. I think all but a few of the early images will not be of any use but might as well achieve something before I lug all the gear back in.
You never know it may clear up again ?

Steve

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

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

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

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

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

13 minutes ago, scotty38 said:

And to add to the above @Xiga you say "At a Gain of 56 and an Offset of 25" yet those numbers don't appear to figure in the formula so are they irrelevant?

At gain 56 the readout noise is 1.6e- so indirectly it does appear, and that is multiplied by 10 because the aim is to swamp noise by a factor of 10, I just can't seem to see where the 0.45 and 400 come from., unless 0.4 is the system gain when in mode 1 at gain 56, which I think it is (approximately anyway)

Steve

On 18/01/2022 at 16:22, Xiga said:

I go by a simple formula to help me calculate my sub length. I look to swamp the Read Noise by a factor of 10. At a Gain of 56 and an Offset of 25, the formula is:

(10 X 1.6²)/(0.45+400) = 457

That is certainly a simpler formula than others I have seen on various forums and websites.

But it doesn't equal 457, is the 2nd parenthesis not required, because (10 X 1.6²)/0.45+400 = 457, but (10 X 1.6²)/(0.45+400) = 0.0639 

Also where do the figures 0.45 and 400  come from ?

Steve

If using for visual make sure it is designed for visual and not imaging.

Steve

8 minutes ago, Stuart1971 said:

My QHY driver in NINA says 0-60 for USB traffic, not 69

sorry my fat fingers it is 60 in EKOS too

15 minutes ago, Stuart1971 said:

Hmmm, I have 0-60 and I set it in 20, for USB traffic, but no memory setting…I thought there was 2gb memory buffer on these cameras….🤔🤔

As I say no idea why they were set to these values and whilst my EKOS agrees with you and the speed can be 0-60 the buffer memory can be set to between 512 and 4096 bytes, no idea what that really means as 4096 bytes is nothing in terms of memory, nobody really talks about anything less than Mb these days.

Steve

2 hours ago, Stuart1971 said:

Nice thread @teoria_del_big_bang I should find this very useful…

Now for a change, let’s talk USB traffic setting, never seen it mentioned, and I guess it’s not really an issue for DSO work, more for planetary video…so what setting do you guys use, it’s goes from 0-60 and mine came defaulted to 0 in NINA, but I changed to 20 and have left it there, does this have any impact with DSO work or any other positive or negative effect I should know about…??

Now this again is something I have not even given a thought to.

I have just powered up rig to look at what it is set to in EKOS and it was set to 56 and the buffer memory set to 512 bytes. Not sure how it ended up at these figures as it is not something I have set.
I assume the 56 is just a coincidence it is the same as my gain ???

Steve
 

50 minutes ago, Richard_ said:

I'll be following this thread with interest! I think this mono camera will suit my needs just fine, but will need to save the funds first for filter wheel and filters too as this is my first venture into mono. 

For readout mode #1, at Gain 56, offset 25 and luminance exposure of 300s, what sort of ADU value are you seeing on stars? Are stars not fully saturated due to high FWC at these camera settings? 

In short yes.
This is just down to my inexperience and the fact I have done very little LRGB stuff, usually NB.

In fact it is only just lately I have started looking at this and thinking I am doing something wrong.
If I am looking at this right then in LRGB at 300 seconds I am saturating pixels on all the brightest stars for sure and some not so bright, to be fair I have not done any Luminance but even my RGB have some saturation.

And in fact I think the very bright stars are saturated on my NB at 600 seconds, such as Alnitak (which I guess is easily done) but even some other very bright stars.

So this is indeed an area of my imaging I have misunderstood and need to put right.

Steve

42 minutes ago, Stuart1971 said:

Back to my question, why 56 and not 60, as the drop off starts at 56, but the lowest read noise seems to be at 60 on the graph…??

15 minutes ago, Xiga said:

From reading various posts online, I believe the firmware enables HCG at Gain 56. There is no gradual transition between LCG and HCG (unlike what the graph says), you are using either one or the other depending on if the gain is below or above the toggle point.

But in all honesty, whether you use 56 or 60 is such a minor point. 56 gets you a little more FWC, but it would be nigh on impossible to tell the difference between two images taken at Gain 56 and 60. So just pick one, set, and forget 🙂

As @Xiga says

Steve

40 minutes ago, Xiga said:

I too am using Mode 1, Gain 56 Offset 25. Seems to be the consensus that it's a good all-rounder and hard to go wrong with. 

Mode 3 looks interesting for those with fast scopes and large apertures, but be careful. Do not use a Gain of 0 with Mode 3. Up the Gain slightly to around 16 with that mode. See the posts by 2ghouls and my-spot in the link below:

https://www.cloudynights.com/topic/754530-qhy268m-read-out-modes-questions/

What sort of sub lengths and any sort of logic behind it or like me its just what seemed to work ?
I ask because there seems to be quite a consensus that more short subs are best way to go, not that they give you better data but that there is nothing to be gained over a certain sub length and that keeping the sub length low means less chance of lost data due to bad subs.

LRGB  should be easy to work out optimal sub length, NB maybe more difficult, obviously considerably longer than LRGB but also will depend on the actual bandwidth of the filters.

Steve

I think that is a great first image, far better than my first attempts.

And I never get tired of seeing this target 🙂 

Steve

Nice image.

I am not sure about the bad frames with double stars being wind.
Although your setup is pretty lightweight (I started with the WO73 and Canon 600D, I love the scope and still have it as I can't bear to part with it) a good sturdy mount and tripod does make life easier. But after saying that I would have thought wind would not necessarily give two distinct images of each bright star but be more blurry and give elongated stars. Also scope is pretty small and unless a gale wind is not particularly going to be a big issue (I would have thought - could be wrong).
It looks more like a jump in the tracking, or something moved suddenly.

Steve 

4 minutes ago, Xsubmariner said:

The main driver for me migrating to CMOs is the U.K. weather and general lack of quality skies for imaging. My CCD camera’s with 10-30 min frames produced too many incomplete data sets. In believe CMOs camera’s are just better suited to U.K. imaging.

If its like 2021 I think the only scope suited to UK imaging is a space telescope (is Hubble up for sale ?).

This has been an interesting thread, for myself who is pretty new I have no experience of CCD as both my cameras have been CMOS after a brief start with DSLR.

Steve

11 hours ago, Stuart1971 said:

Would you say gain 56 or 60, (in mode 1) as the start of the drop is 56, so would it not be best at 60 where it’s the lowest read noise….or don’t you think it matters….?

This is what it says on the QHY website which is why I think I went for Gain 56.

Multiple Readout Modes is a new function for newer QHY Cameras.  Different readout modes have different driver timing, etc., and result in different performance. The QHY268 currently has four readout modes, and more modes will be added in the future. These readout modes are currently supported in the QHY ASCOM Camera Driver, SharpCAP software and the N.I.N.A software.

Readout Mode #0 (Photographic Mode). In this mode there is a drop in the noise between Gain 25 and Gain 26.  We recommend setting the Gain to 26 to begin.  At this setting the full well is 27ke- and readout noise is 2.7e-.  For every long exposures you can lower the gain from this point to increase the full well capacity.

Readout Mode #1 (High Gain Mode).  Please note there is a HGC/LGC switch point at gain55 to gain56. Gain0-55 uses LGC and Gain55-100 uses HGC.

Also as it has sort of taken this tread off topic I have tried to start a new thread for QHY268 users to share information, whether it yields anything of interest I will have to see 🙂 

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

Steve

Multiple Readout Modes is a new function for newer QHY Cameras.  Different readout modes have different driver timing, etc., and result in different performance. The QHY268 currently has four readout modes, and more modes will be added in the future. These readout modes are currently supported in the QHY ASCOM Camera Driver, SharpCAP software and the N.I.N.A software.

Readout Mode #0 (Photographic Mode). In this mode there is a drop in the noise between Gain 25 and Gain 26.  We recommend setting the Gain to 26 to begin.  At this setting the full well is 27ke- and readout noise is 2.7e-.  For every long exposures you can lower the gain from this point to increase the full well capacity.

Readout Mode #1 (High Gain Mode).  Please note there is a HGC/LGC switch point at gain55 to gain56. Gain0-55 uses LGC and Gain55-100 uses HGC.

Readout Mode #2 (Extended Full Well Mode).

Now QHY268 adds #3 mode Extend Full Well 2CMSIT (yellow curve). The advantage of this mode is that it has the same full well value and system gain as the #2 mode Extend Fullwell, but the read noise is reduced by about 1.3 times.

This function needs to be used with 2020.6.26 or newer SDK. If your software cannot display this mode, please download the QHYAllInOne installation package to update the SDK in the software.

Mono V Colour

Whilst the QHY website states both the mono and colour versions have the same optical window.
I have seen may threads on various forums stating that the mono has a IR cut filter, but the colour does not and requires some sort of IR filter.
The QHY website says it is AR + AR coated, but this doesn't make sense so I am assuming it means IR +AR, anybody know any different ?