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

[BrendanC]

So, I'll keep an eye out for dew/frost too. I'm going to habitually start using the dew shield from now on, as well as flocking it.

I will also be trying out the ASCOM drivers.

I'm also going to have a run with no filters at all (I have a spare empty slot) to see if that has any effect.

[vlaiv]

1 hour ago, ollypenrice said:

I still do suspect the camera but include in that the capture software. Brendan didn't have this with his DSLR. Can an increase in sensitivity fully explain the sudden appearance of this problem?

Should we be looking again at the filters? What if they behave differently under the different illumination produced by the sky and by the flats? Filters are quite batch-specific and could be faulty.

Sensitivity can be used to explain at least pat of why it is visible now.

Another thing to consider is filter wheel.

It was not there previously. How light tight is it? It is mechanical component after all that needs to move freely.

Don't think filters are to blame - I'm having hard time imagining what would cause them to have different response based on source of the light (they can't really tell where photon is coming from - they can only distinguish direction/location and wavelength - and that it shared between sky and flat panel).

[happy-kat]

And a run with no cooling and no filters to get a control point to compare

[ollypenrice]

2 minutes ago, vlaiv said:

Don't think filters are to blame - I'm having hard time imagining what would cause them to have different response based on source of the light (they can't really tell where photon is coming from - they can only distinguish direction/location and wavelength - and that it shared between sky and flat panel).

Direction may be a variable due to the proximity of the light source and the ray diagram cited from Oddsocks earlier on in the thread? Filters only work within a range of angles of incidence and if scattered light is falling outside that range artifacts would be expected.

Edited June 7, 2022 by ollypenrice
False click

[vlaiv]

@BrendanC

If you want to test above - if sky flats are different to flat panel flats and if there is issue with filters, procedure is rather simple:

- during daylight (or even better dawn / dusk) - point telescope to the sky (be careful not to point near the sun) and shoot some subs - just dozen or so. Be very careful not to saturate / over expose them as there is plenty of light (and why this is better done at dusk / dawn).

- shoot flats and other calibration frames right there, using flat panel. Again - you don't need much of each, this is just for test purposes, dozen or so of each is good.

- calibrate, stack, inspect.

Resulting frame should not have any sort of gradient on itself - it should be perfectly "flat" (meaning same average ADU all over the place and uniform gray image when stretched).

This test will rule out:

- issues with filters

- issues with telescope flocking and flats (if flat panel should be moved further out, or is it ok where it is sitting now)

[BrendanC]

Thanks, will do. 

[BrendanC]

@vlaiv OK, so I've taken the sky flats - and just realised, I don't know how to stack them! All my stacking programs want to find stars in the subs, obviously so that they can be aligned etc.

How do I stack essentially flat, blank subs?

Edited June 8, 2022 by BrendanC

[markse68]

How did you stack your other flats? You can stack flats in Siril- just don't register them. Do the PP with the dark flats first then stack but use the correct settings which I think are median stacking with multiplicative normalisation

Mark

[vlaiv]

28 minutes ago, BrendanC said:

How do I stack essentially flat, blank subs?

I guess that you can follow @markse68 's advice and stack in Siril without registration.

Calibrate with matching darks and use only regular average - no normalization is needed for this to work.

Alternatively - if you don't have bunch of files (and you should not - just a dozen from each is enough) - you can upload them somewhere and I'll stack those for you in ImageJ (which is another option to stack your subs without registration).

[BrendanC]

My understanding - probably wrong - is that Vlaiv was suggesting taking sky flats, then stacking them by calibrating them with my other flats, as if they were lights. But I don't know how this is possible. How do you calibrate flats with some other flats? 

[vlaiv]

2 minutes ago, BrendanC said:

My understanding - probably wrong - is that Vlaiv was suggesting taking sky flats, then stacking them by calibrating them with my other flats, as if they were lights. But I don't know how this is possible. How do you calibrate flats with some other flats? 

Yes, but I'm actually saying that you should really perform pixel math and see what you get.

You should stack "sky flat darks" and "sky flats" - using average, and similarly "panel flat darks" and "panel flats" - just using plain average stacking without alignment.

Siril should be able to do this, if not - ImageJ will certainly do it (and I can do it for you - or explain how to do it - which ever you prefer).

Then you should subtract respective darks from "lights" (or rather flats - we run a risk of confusion by terminology here ).

In the end - you should divide two resulting images. If you want "equation" - it looks like this:
 

(sky_flats_stack - sky_flat_darks_stack) / (panel_flats_stack - panel_flat_darks_stack)

Then take resulting image and see if it has any gradients - it should be rather "flat" (here flat meaning no gradients ).

[BrendanC]

OK, sorry, but I have absolutely no idea about pixel math or how to do any of these things you mention! I just put calibration files and subs into whatever stacking program I'm using and let it do its thing.

So, with that in mind, if you could take a look that would be great. This is the link, and it includes 10 sky flats, 10 'normal' flats, a master dark, and a master flat dark: https://drive.google.com/drive/folders/1wt0HEs7_vwI--TeWzWcmMQO7MIKoXgQh?usp=sharing

It comes to 312MB unfortunately, and I don't want to break your bandwidth, so if you'd prefer, say, just 5 each of the flats, let me know.

Or you could just go into each folder and download only what you need. I should add that it's approaching 00:30 in my time zone and I really need to get some sleep...! Which also means there's no rush to do this, I'm just very grateful for your help.

Edited June 8, 2022 by BrendanC

[markse68]

26 minutes ago, vlaiv said:

Yes, but I'm actually saying that you should really perform pixel math and see what you get.

Apparently Siril now has pixel math too Vlaiv but i’ve not used it nor know how to

Mark

[Adam J]

On 06/06/2022 at 14:29, ollypenrice said:

• The scope isn't up to the job     Edited: I don't think it's the scope but Vlaiv is right about light leaks and reflections. My doubts come from having seen so many threads about over-correcting flats. They afflict all kinds of optics.

Its not the scope, I have had a NASA APOD with the 130PDS. I did blacken the secondary edges, though I did not put anything over the primary end or flock it. 

Adam 

[Pitch Black Skies]

Do you still not put anything over the primary end Adam? Just wondering if it's really necessary. Congrats on NASA APOD! That's a fantastic achievement.

[vlaiv]

11 hours ago, BrendanC said:

It comes to 312MB unfortunately, and I don't want to break your bandwidth, so if you'd prefer, say, just 5 each of the flats, let me know.

That is really not much. My monthly quota is 200GB, but wife and I recently took a liking to Netflix and it being a streaming service - well, eats up some of it (I did limit it to 2mbps as soon as I realized how much data full hd stream can gobble up in no time).

It's downloaded now, and will report my findings when I have a look at it.

[BrendanC]

Cool. I also took some more sky flats in the early morning (cos I couldn't sleep) so let me know if you'd like me to upload them too. 

[vlaiv]

@BrendanC

Something is wrong with your files - namely with master dark.

Did you include master dark from 50s or 150s exposure instead of shooting dedicated darks with same exposure settings as sky subs?

Master dark you supplied has higher mean ADU value (by far) than sky flats you supplied.

Actually, never mind that - I just saw that you used same exposure length from sky and panel flats and master flat dark seems to match that exposure length so it can be used for both. I'm now going to do it like that.

There is quite a bit of over correction in the result I got:

However, I'm concerned about quality of the data.

Look at this:

This is stack of your sky flats without any alteration (no calibration of any kind - just regular average) - and that file has dust shadows inverted!

This cannot happen regularly and it must be consequence of some sort of data manipulation.

Here is what you need to do - ditch APT and switch to NINA, repeat the procedure, this time paying attention so that you :

1. Take sky flats of proper exposure length (ones you posted are way too short and their value is 300 out of 65000 or about 1/200, while your regular flats are about 20000 out of 65000 or about 1/3 - which is good)

2. Take again panel flats like you did

3. Take associated darks for sky flats (matching gain, offset, exposure length)

4. Take associated darks for panel flats (again matching gain, offset, exposure length)

take again 10 of each - but this time, post all files, don't create masters to save bandwidth (just to make sure something does not happen out of ordinary when stacking them).

It is important that you shoot with ASCOM drivers using NINA instead of APT - I'm afraid that APT does something weird like "automatic calibration" when taking images - that you don't know of and that messes up your entire calibration procedure after.

 

[BrendanC]

Are you sure they're not just out of focus stars? 

[BrendanC]

Actually, no need to respond.

@vlaiv, you've been incredibly helpful throughout all of this, but I've been through so much pain with this camera, and it looks like there's more to come, so I've decided to sell. I'm going to invest in something a bit easier, like an ASI533. If I still have problems with that, well, I won't know what to do, but fingers crossed I won't.

Thanks again.

Edited June 9, 2022 by BrendanC

[vlaiv]

1 minute ago, BrendanC said:

Are you sure they're not just out of focus stars? 

Good point - haven't thought about that.

I've seen similar dust particle in flat produced with flat panel - and concluded that it is the same thing, but you are quite right - it is much more likely that it is out of focus star, especially if sky flats are taken later in the evening.

[vlaiv]

1 minute ago, BrendanC said:

Actually, no need to respond.

@vlaiv, you've been incredinbly helpful throughout all of this, but I've been through so much pain with this camera, and it looks like there's more to come, so I've decided to sell. I'm going to invest in something a bit easier, like an ASI533. If I still have problems with that, well, I won't know what to do. 

Thanks again.

Maybe do just that last test with NINA and ASCOM drivers and then move on to selling the camera? Just in case?

[BrendanC]

Honestly Vlaiv, I can't face it. This has been playing on my mind for four months now. Right from the very start, I could tell something wasn't right, and I've tried so many things now that I'm just going to admit defeat. The ASI533 has great reviews, including from Cuiv the Lazy Geek who is in a heavily light-polluted city, plus I could consider an L-Pro dualband filter for narrowband stuff.

Thanks again.

[david_taurus83]

On 09/06/2022 at 13:26, BrendanC said:

Honestly Vlaiv, I can't face it. This has been playing on my mind for four months now. Right from the very start, I could tell something wasn't right, and I've tried so many things now that I'm just going to admit defeat. The ASI533 has great reviews, including from Cuiv the Lazy Geek who is in a heavily light-polluted city, plus I could consider an L-Pro dualband filter for narrowband stuff.

Thanks again.

Though I understand your frustrations (I had a newt when starting and had the same issues with flats) I have to disagree with your reason of thinking as the camera is not at fault here. I think you may still have issues if you simply swap cameras as you are not addressing the issue with your flats first.

[markse68]

On 09/06/2022 at 13:10, vlaiv said:

It is important that you shoot with ASCOM drivers using NINA instead of APT - I'm afraid that APT does something weird like "automatic calibration" when taking images - that you don't know of and that messes up your entire calibration procedure after.

Hi Vlaiv, I never heard this before- is it really true? Is it something that can be turned off? Seems a really bad feature if if it's true!