ASI1600 and 130PDS - about to give up, need help

[BrendanC]

Hi all,

So about two years ago I got more serious about my astrophotography and invested in an NEQ6 mount to go with my 130PDS and astro-modded EOS1000D. I had a hoot - really enjoyed it, got my workflow down with APT and StarTools, produced some images I was really proud of, all good.

However, I'm probably moving (back) to London in the next few months, and figured I should make the jump to mono, as that's probably the best way to make this work there. So, I got an ASI1600MM-Cool - and I just cannot get the results I should be getting, specifically with LRGB. Narrowband is OK, but I want to shoot broadband too.

There are two major problems:
* Weird, wacky gradients in my stacked/calibrated files which I have to fight in StarTools to overcome
* Bloated stars, on all channels

See NGC 4236 below. It's just not what I would expect, and it's as good as I can get it. I'm fairly confident I could have done better with the DSLR:

Details are:
3:35 hours (L 114x50s, R 16x150s, G 16x150s, B 16x150s)
Gain 75, offset 15, cooled to -20°C
Bortle 4, No Moon during shoot
25 flats and dark flats per channel, 50 darks per sub length
130PDS, NEQ6, ASI1600MM-Cool, ZWO EFW with 1.25" mounted ZWO LRGB & Baader HSO filters, Sky-Watcher auto focuser with HitecAstro DC Focus controller
APT, PHD2, APP, StarTools, Photoshop, NoiseXTerminator

Getting consistent answers on this when I consult the forums is like asking ten experts on anything what the problem is: you get ten different answers. They've encompassed:
* My flats are wrong - so I got a Lacerta light box and dimmer. Still there.
* My bias/offset is too high - so I just did an evening reduced from 50 to 15. Still there.
* I have a light leak in the focus tube - so I've got a snood with silver foil wrapped around the focus tube. Still there.
* My darks have light leaks - so I've redone them with said snood and foil in the fridge. Still there.
* There's an ambient light source somewhere - there's a faint, distant street lamp that never caused a problem before, moved the scope away from it behind a wall anyway. Still there.
* My focus is out - but I've checked APT's autofocus routine with a Bahtinov mask and it's spot on.
* I've got pixel leak - I mean, really, what can I do about this or test it?
* The filters are the wrong way around - nope
* My filters aren't any good - but they're the ZWO filters that should work with the camera
* StarTools isn't up to the job - don't know, tried the PixInsight trial, meh, still think there's something wrong somewhere that processing just won't fix

... among others. To date, nothing I've really produced is as good as I was getting with the DSLR. And the last shoot, last night, even my stars were all wrong which I think is probably collimation, which I think I might have fixed today, but I'm not sure I care any more.

So, right now, I really am, at last, on the verge of giving up. Four months down the road, I've reached a dead end. I cannot figure out what I'm doing wrong, and I just can't face another round of research, advice, trying to address X, Y and Z, build more libraries, spend a night or two gathering data, processing, waiting with baited breath and pounding heart, hoping against hope... and seeing the same crap come out.

It's actually starting to get me down, and this should be an enjoyable hobby. I simply cannot afford to throw more money at this, for example with new filters or software eg PixInsight.

So, my options are:
* Sell everything and end this madness
* Get my kit to work
* Sell just the camera and invest in an OCR, which is kind of what I wanted to do at first anyway but I'm not sure an OCR will hack it in London (although I could consider a dualband filter)

So, what would you do? If you have a VERY GOOD IDEA what could be going wrong, please feel free to offer advice, but PLEASE don't speculate because I've had enough of going through everything every time. 

If you'd like to take a look at my latest data - my fourth abortive attempt at NGC 4236 - then it's here, flats, darks, dark flats and subs, the whole thing (14GB): https://1drv.ms/u/s!AqovBuVZMwj3k7IhjlZENYMs2gXAvQ?e=0A26GS (the stars aren't right in these subs, but that's only as of last night, after messing around with collimation, which as I say I think I've fixed since)

At the end of the day, this really is just a hobby, and I have to keep this in perspective. I could even go back to a DSLR, but as I say, I'm tempted to go just one step back to a cooled colour astro cam and get, say, an ASI1533MC, which would match the scope and guiding system. Ideally I'd get my current kit to work, but it really, really is not having it. And if this continues to get me down, I'm prepared to jettison the whole thing and move on.

Cheers, 
Brendan

[Elp]

You shouldn't get discouraged, most of the work I've found is in post processing.

I haven't assessed your data yet, I'm just speaking from experience from when I process my LRGB data.

From the outset based on the image you've uploaded it looks like you're oversaturating the levels/contrast so you get that blotchy look you're getting around all your stars. This can be avoided by masking out your stars and separating them from the subject/background, some software automates this creating a star mask. With the stars removed you then have better control on the look of the subject which you adjust very subtly over many minute iterations. I generally do this manually with PS and I know LRGB I find is very difficult as you have to deal with gradients and getting LRGB stars to line up is also a challenge to the point I have to end up scaling manually each RGB image until the stars look aligned okayish.

Narrowband data is much easier to work with I find.

I have a 130pds also but haven't put it through its paces yet other than tests, I only do this once my refractor is setup which I generally have no trouble with, maybe that's an option to consider later down the line though you do state you didn't have trouble with a DSLR, so the scope shouldn't be the issue. I tend to get the opposite to what you're experiencing, I get weird patches and blotches with my DSLR but clean data with my 183mm.

[BrendanC]

I am discouraged though! Very!

Thanks for responding though.

Looking through my data again there seems to be the mother of all dust motes on the red filter, which I've noticed once before, but I don't understand why it hasn't been fixed by the flats.

Regarding alignment, when you say you find it difficult to align LRGB, surely you use stacking software?

Anyway, I'm just going to leave this now and see what the consensus is. I'm still very tempted to leave this all behind because it's a money pit, and I'm very uncomfortable shelling out hundreds of pounds on fixes.

[Elp]

2 minutes ago, BrendanC said:

Regarding alignment, when you say you find it difficult to align LRGB, surely you use stacking software?

I use stacking software (DSS) but only stack all L, R, G, B data separately from one another with their respective flats, dark flats, bias and darks (which can be shared by all of them). I then align each stacked L, R, G, B in PS so have four layers total to start off with, set each RGB layer as RGB respectively in their blending mode dialogue option and set the L to Luminence blend mode and stick it at the top of the layer stack. I then align each RGB one at a time to match the L channel scaling and rotating them until they fit. I know there's easier options but this way I learn how perhaps my focus could be adjusted between each filter or spread my sessions out over a few nights so the final stacks all align better (if you do one after another in the same night each channel stack ends up rotating slowly around unless if you use a rotator which I don't).

[StarryEyed]

Take a break from putting time into the  problem. Continue to think on it but no testing let the conversation do the work. Do some visual check out the moon with a cup of tea. 

You need to qualify the camera that it behaves. Did you ever check the linearity of the camera over different temperatures say 0 to - 20 steps of 5 and 180s caprures over an hour.  Sharpcap can automate this for you I think. 

Are your images similar to the DSLR with the camera at an ambient temperature. 

Edited June 3, 2022 by StarryEyed

[BrendanC]

Thanks, but I just cannot face another round of 'what if'. I need someone who has an ASI1600MM-Cool, preferably with something like a 130PDS, who knows what might be going on here.

@vlaiv, I understand you have this camera? If you have some spare bandwidth and time, would you be able to look at my data please?

[vlaiv]

3 minutes ago, BrendanC said:

@vlaiv, I understand you have this camera? If you have some spare bandwidth and time, would you be able to look at my data please?

Will do as soon as I find some time (need to urgently fix something on one of my projects).

[BrendanC]

Thank you. I'm working on the theory that my flats aren't working - I've heard tell that the ASI1600MM-Cool doesn't like flats of a short duration. Mine are taken with the light box at the dimmest setting, so without adding paper/t-shirts etc that's as long as they get. But I would very, very much appreciate your input.

[vlaiv]

2 minutes ago, BrendanC said:

Thank you. I'm working on the theory that my flats aren't working - I've heard tell that the ASI1600MM-Cool doesn't like flats of a short duration. Mine are taken with the light box at the dimmest setting, so without adding paper/t-shirts etc that's as long as they get. But I would very, very much appreciate your input.

I had no issues with short flats - in fact, I used few millisecond exposures for flats and it worked fine with my ASI1600MM-cool.

[Dan_Paris]

2 hours ago, BrendanC said:

Thank you. I'm working on the theory that my flats aren't working - I've heard tell that the ASI1600MM-Cool doesn't like flats of a short duration. Mine are taken with the light box at the dimmest setting, so without adding paper/t-shirts etc that's as long as they get. But I would very, very much appreciate your input.

I also shot flats with long exposure times (2 sec) with my ASI1600MM. To be able to get correct exposure, on top of putting the light box at the dimmest setting, I also lowered the gain, not to zero since it gave me some pattern noise, but to 1 or 2. Flats do not need to be shot at the same gain as lights frames (but of course dark-flats should).

 

 

 

[vlaiv]

@BrendanC

Would you mind "pruning" a bit above data (I'm on a metered connection and smaller download would be better) and placing it on another download location (it asks for account to be able to download and I don't want to register and account with Microsoft at this point).

As far as pruning - take all your calibration files (darks, flats, flat darks) for each channel and simply do average stack of those. Just make sure result is 32bit and there is no scaling to 0-1 range but rather ADUs are preserved.

 

[inFINNity Deck]

Hi Brendan,

the patterns around the brightest stars are the result of microlens diffraction, see https://www.cloudynights.com/topic/635937-microlens-diffraction-effect-explained/

There is not much you can do about that, apart from trying to reduce the amount of stretch and saturation around those stars.

The ZWO ASI1600MM Cool comes in a normal and pro version. The normal one does not like flats taken with exposure times below 1s (USB2) or 5s (USB2). Those produce a sloped ADU level when compared to longer exposures:

So these gradients can simply be solved by taking care that the flats-exposures are longer than 1s (USB3) or 5s (USB2).

HTH,

Nicolàs

Edited June 4, 2022 by inFINNity Deck

[inFINNity Deck]

Here is the same galaxy taken by myself using a ZWO ASI1600MM Pro Cool and SkyWatcher Esprit 150ED (it light lacks a lot of light):

https://www.dehilster.info/astronomy/deep-sky-objects/NGC4236_211029.jpg

Nicolàs

[BrendanC]

@vlaivI'm afraid I'm away from home this weekend and there's only so much I can do with my mobile phone. I'll see what I can do when I'm back.

@inFINNity Deck I've heard of the micro lensing effect but these are not especially bright stars. If this camera can't handle them then it's not a viable camera. 

[david_taurus83]

I wouldn't beat yourself up too bad. Its nothing you've done wrong and there's nothing wrong with the kit. I download all your files (eventually!), chucked it all into Pixinsights WBPP script and let it do everything including stacking. Then I done background extraction on each channel, combined RGB, colour balanced, stretched, added Lum and some levels and curves. This looks like a difficult target tbf, very faint and you've only got 1.5 hours in Lum and 40 mins each of RGB. I would keep adding data if its still possible. IMO this hobby is 25% image acquisition and 75% processing.

[ONIKKINEN]

The low integration time popped out to me too. I have taken 14 hours of varying quality subs (avg = bortle 5-6 maybe) of this galaxy and i dont think im even halfway there yet, granted different kit and camera so comparisons are not 1:1. Its a very low surface brightness galaxy and on top of that its quite blue, which is where most cameras have by far the weakest QE so its even more deceptively faint than the numbers suggest.

Edited June 3, 2022 by ONIKKINEN

[BrendanC]

Thanks all. I guess what's really bothering me is the weird gradients I'm getting with everything I shoot, plus bloated stars, not just this instance.  Integration time doesn't seem to make much difference. 

I really appreciate @david_taurus83 taking the time to do this, but still I can see mottling in the background and artefacts in the stars. On this basis I would still want to sell the camera. 

As I said, I'm away today and tomorrow but will give serious thought and feedback to all of your helpful suggestions, plus provide @vlaiv with what he needs. I'm still minded to move back to an OCR but let's see how things go here first. 

Thanks all again. 

[david_taurus83]

10 hours ago, BrendanC said:

Thanks all. I guess what's really bothering me is the weird gradients I'm getting with everything I shoot, plus bloated stars, not just this instance.  Integration time doesn't seem to make much difference. 

I really appreciate @david_taurus83 taking the time to do this, but still I can see mottling in the background and artefacts in the stars. On this basis I would still want to sell the camera. 

As I said, I'm away today and tomorrow but will give serious thought and feedback to all of your helpful suggestions, plus provide @vlaiv with what he needs. I'm still minded to move back to an OCR but let's see how things go here first. 

Thanks all again. 

The mottling is due to low signal (short integration) and me pushing up the saturation to bring some colour into the galaxy. A OSC camera won't fix this. You just need to collect more data. The stars look to me like the scope isn't collimated. There's nothing wrong with the camera. The diffraction pattern only really shows on very bright stars like Vega or Alnitak. I had a 1600MM. I sold it to go back to a DSLR. I now have a mono camera again and still have the 6D! I really think if you were to change anything it should be the scope for a refractor. Newts aren't an easy scope to master. You need to take special care to not allow any extra light from reaching the focuser tube. Not easy when it's so close to the front of the scope. This is why your probably struggling with flats. The only light that should be reaching the sensor should be what's reflected from the mirrors. A dew shield would help with keeping out stray light.

[BrendanC]

OK, so I'm back. Here's some food for thought...

Here's NGC 4236 using all my data, which is about 7 hours' worth. Slightly better maybe but still bad stars.

 

Here are some examples of what I've been up against - these are just taken into the StarTools Compose module, binned, wiped, and then given an AutoDev stretch to show what's going on in the data. Gradients a-plenty.

They were all taken in quite radically different sky conditions, different place in the garden, different methods of capturing flats and darks, different offsets and gains - but still, mad gradients and stars. I've been able to make something of them, but this is after judicious cropping and fighting the gradients, which I just feel I shouldn't be having to do with this camera. Regardless of how faint NGC 4236 is, one day I really will want to do a full star field, for example an open cluster, and I just won't be able to that at this rate.

So, state of play is:

• Bad stars - is this microlensing? Too much exposure? Too little? (btw I know the 'bitemarks' are the result of the focus tube impinging on the FOV which I'm also going to fix soon)
• Gradients - is this a light leak? Bad filters? Bad flats? Too little data? I don't quite see how more data will fix these gradients. 

@vlaiv Here are the averaged masters (plus stacks) that you asked for, all done at 32-bit in APP, 901MB in total, which hopefully you can download now (and anyone else who fancies a go): https://drive.google.com/drive/folders/1wt0HEs7_vwI--TeWzWcmMQO7MIKoXgQh?usp=sharing

You've already helped me establish that my library darks are ok, but that I might have a leak in my focuser tube. So, I've got the focuser tube wrapped in a snood, which also has tin foil lining it. However, I must admit I haven't since tested this using ImageJ as you recommended, which I probably should. I am sorely tempted to try, one night, actually wrapping the whole scope in foil, just to try and block out any extraneous light whatsoever, and see what difference it makes. I'm still very puzzled as to why this should be happening though, given that I was achieving 300s exposures with my DSLR, with perfectly flat wipes in StarTools. I should also mention that Ivo, the creator of StarTools, is very much of the opinion that my problem is with my flats, which is why I got the Lacerta box. However, given that you have short flats exposures then what do you make of this:

On 03/06/2022 at 14:28, inFINNity Deck said:

these gradients can simply be solved by taking care that the flats-exposures are longer than 1s (USB3) or 5s (USB2)

@inFINNity Deck - how do I determine whether I have one of the older models that has this problem? Is it possible that Vlaiv's model doesn't have this issue?

Other points:

On 04/06/2022 at 10:44, david_taurus83 said:

I now have a mono camera again

Which one? And, out of interest, why did you go back to a DSLR after the 1600? And then back to mono?

On 04/06/2022 at 10:44, david_taurus83 said:

I really think if you were to change anything it should be the scope for a refractor. Newts aren't an easy scope to master. You need to take special care to not allow any extra light from reaching the focuser tube. Not easy when it's so close to the front of the scope. This is why your probably struggling with flats.

Really don't want to change the scope too. I've invested 2+ years getting to know it, and it's a fab little performer. As I said above, I was achieving 300s exposures with the DSLR with none of these problems. The light box, when taking flats, is absolutely butted up against the OTA, with a retaining mask around it, there is no light leaking out from that at all.

On 04/06/2022 at 10:44, david_taurus83 said:

A dew shield would help with keeping out stray light.

Yes, and I do use one.

At the end of the day, my real worry is that, after all this, if I did then decide to go back to an OSC - not least because I also find the 4x time/storage/processing etc very fiddlesome with mono - and I continue to have these problems, I'll be totally at a loss. I find this all constantly gnawing at the back of my mind, like tooth ache, and it's not a good way to live currently. It's like those threads you read in the forums, and think 'Thank God that's not me' except, this time, it's me. 

The other big problem is that I'm doing this totally on my own, with nothing to compare anything with. I'm toying with the idea of contacting a local astro club to see if they could help. So, if anyone's reading this who lives in Oxfordshire or Bucks, and would like to help (and I'd be prepared to pay), then please feel free to message me.

Edited June 5, 2022 by BrendanC

[vlaiv]

17 minutes ago, BrendanC said:

So, state of play is:

• Bad stars - is this microlensing? Too much exposure? Too little? (btw I know the 'bitemarks' are the result of the focus tube impinging on the FOV which I'm also going to fix soon)
• Gradients - is this a light leak? Bad filters? Bad flats? Too little data? I don't quite see how more data will fix these gradients. 

@vlaiv Here are the averaged masters (plus stacks) that you asked for, all done at 32-bit in APP, 901MB in total, which hopefully you can download now (and anyone else who fancies a go): https://drive.google.com/drive/folders/1wt0HEs7_vwI--TeWzWcmMQO7MIKoXgQh?usp=sharing

You've already helped me establish that my library darks are ok, but that I might have a leak in my focuser tube. So, I've got the focuser tube wrapped in a snood, which also has tin foil lining it. However, I must admit I haven't since tested this using ImageJ as you recommended, which I probably should. I am sorely tempted to try, one night, actually wrapping the whole scope in foil, just to try and block out any extraneous light whatsoever, and see what difference it makes. I'm still very puzzled as to why this should be happening though, given that I was achieving 300s exposures with my DSLR, with perfectly flat wipes in StarTools. I should also mention that Ivo, the creator of StarTools, is very much of the opinion that my problem is with my flats, which is why I got the Lacerta box. However, given that you have short flats exposures then what do you make of this:

I did download masters and they seem fine (I still can't access individual subs on Microsoft one drive, but never mind that).

Here is luminance that you stacked:

It has all sorts of weird gradients - but this actually looks like high altitude clouds rather than something wrong with your imaging train.

I can download individual subs from One Drive (just checked) and will download some of luminance subs in order to see if I can spot any sign of high altitude clouds passing.

 

[tomato]

Hi Brendan,  my contribution doesn't really answer your questions but it is another processing take on your shared data, calibrated and stacked in APP, processed in APP, PI and AP.  Needless to say I noted the same gradients as Vlaiv, I agree it could be high cloud but I have seen something similar when I was suffering from moisture fogging on the sensor. I did note you were running the camera at -20 degrees C?

However, I have come much to the same conclusion as @david_taurus83, i.e. there is nothing inherently  wrong with your data, it is a faint target, and to get some colour I had to push the  saturation and then apply some hefty noise reduction, resulting in a blotchy background. It's something I see a lot with my images when I attempt a faint target with less than about 8 hrs of integration (Bortle 5/6 location), something I do much too often.

[BrendanC]

Thank you again @vlaiv

That would be par for the course given my luck so far! I've had a weird bug in APT in which a plan would crash if it ended after midnight, and then another where the camera wouldn't connect. Both took several hours to isolate, and were among the very first sessions I had with the camera. Neither of them were to do with anything I was doing wrong (I actually helped Ivo fix the second one, which was until then a showstopper for the v4 release).

I'm right now stacking the top 80% to see if that makes a difference (I wish APP were a bit faster). I'm also going to experiment with neutralising the background, which strictly speaking I shouldn't do when using StarTools but if it works, it works.

Edited June 5, 2022 by BrendanC

[BrendanC]

Thank you @tomato.

Maybe there was fogging too? I really don't know.

One thing I'm consistently seeing is that people are genuinely getting better results with PI than with StarTools. I simply cannot get the stars right in StarTools, and it's creating havoc with the gradients too. I'm currently trialing PI so perhaps I'll just spend more time on seeing how I get along with that. I understand that this is a faint target, and it's not so much what's going on with the DSO as what's been happening around it that's been bothering me.

Edited June 5, 2022 by BrendanC

[vlaiv]

Ok, so I took first 30 subs and examined them, and I think it's not high altitude clouds - it is some sort of external light - some reflection that changes as you track the sky.

It's not calibration issue - but it does show that it changes from sub to sub - and in fashion that has to do with tracking the sky - look at this animation of your subs (stretched):

[BrendanC]

Thanks again Vlaiv.

I'm completely stumped. I have absolutely no idea what could be causing this. I'll see if I can do a longer animation maybe using PIPP and try to understand this, but I'm afraid I'm back to square one. It's good to know the calibration's fine though.