ASI1600MM Narrowband Flat Strangeness

[Notty]

Not really sure where to put this, as I'm now not sure if it's a camera issue or something else.  I was getting strange narrowband flat patterns especially on OIII with my 1600MM and they wouldn't calibrate out.  I sent them to FLO who I purchased the camera from and asked for their opinion as I'd seen on another thread that someone else had a similar issue and ZWO had deemed it a camera issue.  To FLO's usual excellent service they got back to me straight away and told me they were replacing the camera (amazing service!).  So I've tried again, but I'm still getting a weird pattern on my OIII's.  I'm using Baader filters, and I'd be really interested to see anyone else fiats who may be using the similar combination?  These are stacks of 10 taken at 30000ADU using a Neumann flat panel and stretched to an inch of their lives.  I haven't taken any actual data yet to see if it calibrates out but given it's almost identical in nature to the one before I'm guessing it probably won't.  I've also posted the SII to compare which looks more like a normal flat although it does have strange bandings at top and bottom and I'd be really interested in opinions.  Maybe it's an interaction with the Baader filters, or just a single bad OIII filter?  I don't own any others to try unfortunately.  Thanks for any input, I'm beginning to suspect that my original camera maybe was not at fault at all?

OIII:

SII:

[groberts]

You might find my thread of interest:

https://stargazerslounge.com/topic/289940-flats-light-source/

The link towards the end from Odd Socks is worth reading.  

From my point-of-view the jury's still out but it's intriguing that I'm also using a ZWO 1600.  My suspicion is that it is to do with the camera's sensitivity and the optical train + internal reflections - using the 'weird' flats does take out the problem though.

Good luck, I'll be watching this thread too.  

 Graham

[alexbb]

I've seen something similar last evening also with the O3. I supposed there were some reflections. I tried to shoot them with a T-shirt pointing to the sky, but it seemed too bright. So I waited a while until I got the peak value on the histogram at about 3000 at 2s. That seemed to work well. I'm on the tablet now so I don't have the flat, but it looked pretty similar, but with much less noise. Do you use a high gain? Try to aim for a smaller ADU maybe.

[Notty]

1 hour ago, groberts said:

You might find my thread of interest:

Thanks Graham, yes very!

22 minutes ago, moise212 said:

Do you use a high gain?

I think I had it on about 500 but like I said I'd stretched these flats in software afterwards to see what was going on, as that was how the original problem revealed itself when I first encountered the problem.  The raw unstretched output doesn't show any gradient whatsoever

[alexbb]

I was wrong myself. The stacked flats look about the same as the brighter flats that I shot when the sky was brighter before sunset.

Here's my master flat, stretched. 51 subs.

Nevertheless, it seems to calibrate fine.

Regards,

Alex

[Notty]

5 hours ago, moise212 said:

I was wrong myself. The stacked flats look about the same as the brighter flats that I shot when the sky was brighter before sunset.

Was this your OIII? Looks sensible to me, with dark fringes and lighter towards the centre whereas mine is dark in the middle with a prominent "tide mark" shape.  I'd be happy with your one!

[alexbb]

6 hours ago, Notty said:

Was this your OIII? Looks sensible to me, with dark fringes and lighter towards the centre whereas mine is dark in the middle with a prominent "tide mark" shape.  I'd be happy with your one!

Yes, it was my O3. But I was wrong again, it doesn't calibrate fine. I took other flats with the tablet put in front the lens covered with a T-shirt, but no luck either. Now it overcompensates in the top left corner and undercompensates in the top right. I have to retake them some other way.

[Notty]

Oh well I guess it's just me then, but here's a better master here from 60 stacks and stretched, much more clearly showing the weirdness.   I'm posting it for reference so if anyone else has the same problem at least you know you're not alone.

 

[alexbb]

Mine's not far. I didn't retake the O3 flat, I combined 2 bad ones into one and I applied it to the frames. It didn't calibrate the subs perfect, but I managed to wipe them in StarTools.

Here are my Ha-10h, O3-6h, I'm working on S2 right now, the following one is only ~3hours. The final process will have 5h of S2. If you're interested, you can follow my thread which also describes the progress on IC1396, elephant trunk nebula. I live in a very light polluted area.

Regards,

Alex

[Notty]

Hi Alex, thanks for the steer to your post, this was the exact same target I tried when I first got my ASI1600mm, but unlike yours mine were a disaster. Its great to see your separate subs, and it looks like you found the same thing I did i.e not much info on just how these channels can look separately.  You have much more definition in yours; mine were just noise and strange gradients.   Your project is shaping up brilliantly though, but it brings me to tears thinking about how long it would take me to get the same amount of data as you've harvested so far.  With my job and the weather in the midlands UK I think more than 10hrs total data will probably be an elapsed time of a year or more!

[alexbb]

57 minutes ago, Notty said:

Hi Alex, thanks for the steer to your post, this was the exact same target I tried when I first got my ASI1600mm, but unlike yours mine were a disaster. Its great to see your separate subs, and it looks like you found the same thing I did i.e not much info on just how these channels can look separately.  You have much more definition in yours; mine were just noise and strange gradients.   Your project is shaping up brilliantly though, but it brings me to tears thinking about how long it would take me to get the same amount of data as you've harvested so far.  With my job and the weather in the midlands UK I think more than 10hrs total data will probably be an elapsed time of a year or more!

I'm sorry about the weather, today got cloudy here as well and it will remain like this for a while. About the job.. I haven't sleep properly for some weeks now. I've been going to work from <10 to ~18, at 20-22 I was going to sleep, at ~2 I was waking up and I was going back to bed at ~6 and sleeping until ~9. Then again. One week during this I've been traveling though. Not easy. However, if you live at house, you can expose much longer/night than my balcony allows me so you can gather light for a channel maybe in 2 nights instead of 4.

Good luck and clear skies! Waiting for your pics.

Alex