QHY268M has arrived

[smr]

1 hour ago, teoria_del_big_bang said:

If you are only getting the LRGB filters why not go for the colour version of this camera it has had some fantastic reviews, or are you hoping to go NB later on ?
The colour camera will keep another 800g or so weight off the focuser.

Steve 

Thanks for the replies Steve. If I went for Mono and LRGB it'd be a fairly considerable improvement in Signal to noise compared to the Colour Camera wouldn't it though, and yes if I went for Mono I'd have the ability to do proper narrowband imaging later on, after I've learnt how to do Mono imaging and focusing etc.

Re the stock focuser - I'll be upgrading to the ZWO EAF anyway as soon as they're back in stock so that would cover any issue with that wouldn't it? I'd definitely want to add automated focusing regardless of whether I go for OSC or Mono.

I'm am undecided though as to whether to go for the OSC or Mono but just trying to establish what I would need if I went for Mono.

[teoria_del_big_bang]

2 minutes ago, smr said:

Re the stock focuser - I'll be upgrading to the ZWO EAF

I was referring to the actual drawtube on the scope. I know on my Z73 I had to do some adjustments to stop any slop when using the ASI1600mm but could be I just had a bad un. After that it was fine, but this camera is a fair bit heavier than the 1600. The filter wheel is about the same weight as my SX which surprised me as it looks a lot bigger in diameter.  
Also the supplied spacers look quite beefy but as I haven't received mine yet don't know how much they weight, 

But it may be fine don't necessarily go on my worries (I always worry) but I would drop an email to Rupert and tell him what you are wanting to do and your scope and he will advise if it would be okay and maybe what adapters (if any) you would need for that scope.

Steve

[Spongey]

3 hours ago, Spongey said:

It is a good question and one I'm not sure of the answer to just yet.

I'll be building a flat library tonight and will also take some flat darks to compare with the bias frames. My understanding is that flat darks are preferable to bias frames with cameras that have unusual very short exposure effects (e.g. ASI1600). When dark current is negligible (which it is at -10c) and the camera is stable at very short exposures, bias and flat dark frames are essentially identical. From what I have seen and read, people with the QHY600 / ZWO6200 have been using bias frames over flat darks with no issues. I would hope that the IMX571 would be similar in this regard. 

In any case shooting off 50 bias frames doesn't take long!

So I've just stacked 30 dark flats at 0.68s each for my Lum filter and flat panel and the result is attached.

My conclusion: dark flats are not necessary with this camera and a master bias is sufficient to calibrate flats correctly.

My reasoning: The master bias I attached in my last post is essentially identical to this.

Master darkflat.xisf

Edited February 2, 2021 by Spongey

[tooth_dr]

7 minutes ago, Spongey said:

So I've just stacked 30 dark flats at 0.68s each for my Lum filter and flat panel and the result is attached.

My conclusion: dark flats are not necessary with this camera and a master bias is sufficient to calibrate flats correctly.

My reasoning: The master bias I attached in my last post is essentially identical to this.

Master darkflat.xisf 99.72 MB · 1 download

What exposure length is the bias?

[teoria_del_big_bang]

6 minutes ago, Spongey said:

My conclusion: dark flats are not necessary with this camera and a master bias is sufficient to calibrate flats correctly.

My reasoning: The master bias I attached in my last post is essentially identical to this.

TBH I would be not that sure what would indicate that Bias frames are unstable but yes I agree  they both look pretty much the same.
So you think going with the normal workflow in PI using the master super bias is the way to go ?

Steve

[Spongey]

2 minutes ago, tooth_dr said:

What exposure length is the bias?

Bias exposure length was set to 0 in NINA, FITS header reads it as 0.000001s

1 minute ago, teoria_del_big_bang said:

TBH I would be not that sure what would indicate that Bias frames are unstable but yes I agree  they both look pretty much the same.
So you think going with the normal workflow in PI using the master super bias is the way to go ?

Steve

Yes, calibrate flats with master bias (not superbias - there is conflicting info about this process), and calibrate lights with master dark and master flat.

Cheers

[tooth_dr]

Just now, Spongey said:

Bias exposure length was set to 0 in NINA, FITS header reads it as 0.000001s

Yes, calibrate flats with master bias (not superbias - there is conflicting info about this process), and calibrate lights with master dark and master flat.

Cheers

Thanks, going to do my calibration tonight.  I was aiming for -10deg, that should be ok?

[Spongey]

3 minutes ago, teoria_del_big_bang said:

TBH I would be not that sure what would indicate that Bias frames are unstable but yes I agree  they both look pretty much the same.

From what I have heard, some CMOS cameras can exhibit strange banding or blotchiness in very short exposures. I don't see any of that in my master bias or in the darkflat, and the statistics tool in pixinsight shows that they are almost identical.

[Spongey]

Just now, tooth_dr said:

Thanks, going to do my calibration tonight.  I was aiming for -10deg, that should be ok?

I'm also using -10 degrees. At this level of dark current going to -15 isn't necessary imo, and sticking with -10 means I can safely achieve that temperature all year round.

[Spongey]

Some more info incoming...

I ran the BasicCCDParameters script using some of my calibration frames for both Gain 0 Offset 10:

and Gain 56 Offset 10:

Looks like the specs match up quite well with the published graphs. I do note that the dark current seems quite high, but this is based on relatively short dark frames and it's been noted already that using short darks for this messes up the script. I'm taking some 99s and 999s darks at the moment so will re-run the script with these once they are done.

Edited February 2, 2021 by Spongey

[teoria_del_big_bang]

21 minutes ago, Spongey said:

From what I have heard, some CMOS cameras can exhibit strange banding or blotchiness in very short exposures. I don't see any of that in my master bias or in the darkflat, and the statistics tool in pixinsight shows that they are almost identical.

Yes, I did have banding with the 1600.
Thanks for the info, keep it coming. Hopefully when mine comes if the clouds clear I could hit the ground running 🙂 

Steve

[Spongey]

Updated BasicCCDParameters based on 99s and 999s darks:

Gain 0 offset 10

Gain 56 Offset 10

Dark current looks better on these, but still higher than expected / published. Not sure of the root cause, I don't think the script works well with such small values of dark current. In any case I'm not concerned.

[SyedT]

Did not realise a thread had already been created so I started another one elsewhere! I received mine yesterday, it's a beast. Had a short period of intermittent clear skies yesterday evening so had a go. Single frame of 300 seconds at the "Photographic DSO" setting (gain 102, offset 76) using 3 nm Chroma Ha 36 mm filter through a Takahashi FSQ85-EDX. TEC set at -10 degrees. No calibration frames applied. I was imaging towards a well-lit street and through intermittent clouds which explains the amount of glow (ADU was very high on SGPro as well which fits). File size 49.8 MB) present. I can see some light fall-off and star distortion towards the edges if I pixel peep (likely tilt), but I think I can live with it! 

All looks very promising so far, can't wait to test it out properly.

Edited February 2, 2021 by SyedT

[Spongey]

Incredible depth for a single 300s sub! I'm dying to get mine out under the stars, but it might be a while until we get a clear night here 

[Xsubmariner]

Nice first light SyedT, typically I have had blanket cloud for the past 2 weeks and it doesn’t look likely to clear for another week. May I enquire what version of SDK you are running with?

[SyedT]

12 hours ago, Spongey said:

Incredible depth for a single 300s sub! I'm dying to get mine out under the stars, but it might be a while until we get a clear night here 

Agreed, this is despite aiming towards a well lit street and clouds, so it should be even better when conditions are more favourable. I have no clear skies for the next week at least...

11 hours ago, Xsubmariner said:

Nice first light SyedT, typically I have had blanket cloud for the past 2 weeks and it doesn’t look likely to clear for another week. May I enquire what version of SDK you are running with?

Thanks, same here. That intermittent clear sky for me was an anomaly more than anything else! The SDK version is 20.6.26.0.

Edited February 3, 2021 by SyedT

[Spongey]

Managed to snatch a clear spot. First 300s sub with 268M and Antlia 3nm Ha Pro. Gain 56 Offset 10. Calibrated and stretched, that is all.

Having a host of other issues with my focuser etc. so used the bahtinov mask for this one.

Amazed with the depth from a single sub though... Taking some more subs now before the cloud comes in later tonight. Will stack tomorrow and see what I can get 

Cheers

[Xsubmariner]

Nice frame Spongey, great to see. The camera appears to be performing in line with the IMX455 sensor based units, just in a size better matched to a wider range of scopes. 

[Endolf]

I managed to get some dark skies last night and shot some test images. Seems I've got some tilt somewhere to take out.

I shot with the ZWO 7nm Ha filter, the Astronomik 6nm Ha filter and the Antlia 3nm Ha filter. There are 3 exposure times, 180s, 300s and a single 600s sub. There are 2 gain settings, 30 and 50 and 3 offset settings, 10, 30 and 50. The images have the time, the filter brand, the gain, and the offset (or 10 if not specified) in the file names. Sensor was chilled to -10 and the scope is a SharpStar 61 EDPH MKII. Most frames were focused before each exposure.

All images have been loaded in to PI and a soft stretch applied using the EZ processing suite. Hopefully they haven't lost much in the conversion to jpg. The 300s Antlia filters appear to have found the one period of cloud, which ruins the comparison, but I've included them anyway.

     

     

 

I suspect I'll end up at 300s, gain 50, offset 15 as a starting point for emission nebula for the Antlia filter.

Edited February 4, 2021 by Endolf

[Spongey]

Nina crashed just after I went to bed so only managed 13x 300s in the end  

A quick stack and stretch, no other processing applied.

Honestly I am both amazed and thrilled with this outcome! I can only imagine what 5+ hours would look like. I do have a halo on one of my stars at the bottom which isn't ideal. I might try flipping the filter.  

 

Edited February 4, 2021 by Spongey

[jiberjaber]

Is it me or does the ZWO offset 50 (i.e. second image in each row) appear to be the better of teh 3 filters? - it's hard to compare clicking through them on the screen - might need to download and blink through?

 

[teoria_del_big_bang]

All great information for me up front so keep em coming.

Is there a science to seeing what gain and offset works best, or is it a "suck it and see" technique ?

I think early on I tried a few gains and offsets but ended up at unity gain and offset 40 but didn't really see a lot of difference., when using my Ha fiter anyway
I often wondered if I should have picked my weakest filter for a certain target, usually SII to test the gains but never tried I think with my lack of clear nights I just stayed with the unity and offset 40.

 

Steve

[SyedT]

I found these to be good reads:

http://cosmic-colors.com/gear-reviews/qhy268c-review/

https://www.qhyccd.com/index.php?m=content&c=index&a=show&catid=23&id=263

[teoria_del_big_bang]

2 hours ago, SyedT said:

I found these to be good reads:

http://cosmic-colors.com/gear-reviews/qhy268c-review/

https://www.qhyccd.com/index.php?m=content&c=index&a=show&catid=23&id=263

Nice one, thanks 🙂 

Steve

[Endolf]

10 hours ago, jiberjaber said:

Is it me or does the ZWO offset 50 (i.e. second image in each row) appear to be the better of teh 3 filters? - it's hard to compare clicking through them on the screen - might need to download and blink through?

I think the conversion to jpg has done something to the background, they do look reasonable here, but when looking at the raw tiffs it was clear that the background was lighter and the overall contrast was not as good as either of the other Ha filters. The Antlia seemed to have the most contrast, I think I could go higher gain or longer exposures to get even more detail out of that filter.

9 hours ago, teoria_del_big_bang said:

All great information for me up front so keep em coming.

Is there a science to seeing what gain and offset works best, or is it a "suck it and see" technique ?

I admit my approach isn't very scientific, I'm more a suck it and see to some extent. I looked at the gain graphs for the camera, and thought about what a maximum exposure time might be, both in terms of what my gear will allow, but also what I'm willing to lose if a something happens to an image. I normally don't go above 300s, but have done 600s. I find the longer the exposure, the easier the image is to process, except for the stars of course. I live near a town, so no point going too long due to LP. I ended up looking at the mean ADU, 50 gives me a higher ADU whilst still not blowing out too many stars. For a target near a really bright set of stars, the gain or exposure time might get reduced, but then more images stacked. There are certainly more scientific approaches one can take than what I do, but I am liking my results which is what matters to me