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ZWO1600MM - Some novice questions

teoria_del_big_bang

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RolandKol

RolandKol

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Posted

I also target to have around 1-0.5sec by adding or removing paper to panel.

ZWO Representative on ZWO forum assured me, Flats can be as short as possible as short subs have no bad effect as short Bias...

but I avoid going shorter than 0.3 anyway :)

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RolandKol

RolandKol

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3 minutes ago, teoria_del_big_bang said:

Sounds a stupid question as I think the answer is in my question but I take it that if I manage to take flats for all filters at same exposure I only need take one set of Dark Flats for all filters?

Sounds like yes..

but I just now noticed that you have the same exp on all filters... What a joy!!!

However, - I never managed to get the same exposure on all!!!! sounds strange...

Is it for LRGB? or NB?

if LRGB 2 sec... a bit too long... remove some paper, but on another hand... if 2 sec is actually for all... maybe leave as it is... quite nice universal exposure for flats and DarkFlats....

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RolandKol

RolandKol

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Hmm, really expensive one....

But if it enables to use the same exposure for all filters!

Probably worth money! :)

if it's not some kind of APT error....

I would download SGP pro and test Flat Assistant on it also.

Or maybe try changing APT Flat aid target ADU to 15k and see what happens?...

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teoria_del_big_bang

teoria_del_big_bang

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It is a nice light panel but still tend to think if I do not vary the light intensity then surely the exposure time should change.

I have installed SGP pro but just need to get to grips with it before the trial runs out and decide to move to it or not so can try that later. I can also try with the reduced ADU target as well.

Thanks for all the advice.

The panel was 2nd hand by the way from this forum so did not spend that much ? 

Steve

 

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RolandKol

RolandKol

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7 minutes ago, teoria_del_big_bang said:

It was too good to be true.

Despite APT being programmed to use all the filters the filter wheel was not indexing and all flats were with the L filter. So one problem solved but not sure why wheel did not work it always has before.

Steve

 

APT is on quite rapid Update schedule at this moment, as once they introduced auto meridian flip, they have quite a lot of bugs....

maybe you are facing one... if you are able to download version before Meridian Flip (v3.5xx), - it was quite stable

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RolandKol

RolandKol

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P.S. I would expect L to be around 0.5s only because I do not want it to fall shorter than ZWO suggested Bias 0.3s,

but it is just my "precaution"... it does not mean it is the correct way to do.

L should actually be the shortest Flat from all the filters you have...

Initially I had them somewhere around 0.02s or something... 

And as I recall, Vlaiv does not bother and does Flats as short as possible... it allows to collect a lot of subs quickly, and if in his case it works, - why not.

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vlaiv

vlaiv

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Yes, no way L and NB filters can have same exposure time, NB filters often let in about 1/40 - 1/100 of light from full spectrum of Luminance. Depends on bandwidth of filters, 3nm are "the longest" ones (let in the least light from 400-700nm range).

You can roughly estimate needed exposure time for your NB filter compared to L by dividing 300 with bandwidth of filter. 3nm will need x100 exposure, while 7nm one will need 300/7 = ~ x43 more exposure. This is just estimate because QE of sensor is not uniform and width of filter is FWHM of transmission curve rather than regular width.

Flats work with even seriously short exposures. I use about half a second for NB and, and L/RGB is order of few ms. I get no banding, which means that I have pretty decent LED panel. I did have issues on one occasion, but that was due to dodgy power connector - it was creating flickering of LEDs (not seen by eye - too fast, but was noticeable on 5-10ms exposures). Fixed it with soldering iron.

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teoria_del_big_bang

teoria_del_big_bang

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Okay I think I found the issue with filter wheel.

I am pretty sure all down to USB connection issues. Just could not get wheel to change filters when it should. It would to begin with but after maybe 3 changes just stopped. The APT does not recognise it has lost communication so just carries on saying it is changing the filters but wheel just stays where it is.

USB has been a millstone round my neck since I started with imaging. I thought I had bottomed it but obviously not.

As always I have a dedicated USB3 cable from camera to laptop but all others go through a hub.

When I disconnected the wheel and using same cable go direct to laptop it has worked time after time so I assume the very expensive hub I have has some issues???? And although I have 2 USB2 and 2 USB3 ports on laptop it is not enough without a hub (mouse takes one port away ).

Anyway will now continue to see if I can successful flats.

Thanks for the help especially @vlaiv and @RolandKol 

Steve

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vlaiv

vlaiv

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I sorted all my USB issues by using quality USB 3.0 powered hub, and running everything thru it. I also made sure to use quality USB3.0 cables.

Prior to this, I had spontaneous disconnects of various equipment (two different cameras, ....). Now I run 1 USB 3.0 lead from ASI1600 to hub, and another from HEQ5 to hub (that one is USB2.0). Guide cam is connected to ASI1600 USB 2.0 hub with short cable (that comes with ASI1600). All is working fine at the moment.

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teoria_del_big_bang

teoria_del_big_bang

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Okay sorry but I am now back to the original issue I had with banding. Below shows the test run for taking flats with all filters. I think the exp times look somewhere what is to be expected. To shorten the time from yesterday I have removed the paper layers I had to get exp time lower from the 2 sec for Luminance filter I had yesterday..

large.flats1.jpg.2e23f8e236fbf35ffdb80099cdc021da.jpg

 

But when I look closely at the faster exposures I can see banding. large.Dark_Flat_BLUE_Bin1x1_0.07125s_G139__-20C_2019-04-07_12-23-02.jpg.45457ba6265b808969acecb292d4e72a.jpg

With the longer ones such as the NB ones it looks much better.

large.Dark_Flat_HAlpha_Bin1x1_4.0625s_G139__-20C_2019-04-07_12-27-17.jpg.52b5674a4843bd1f5575fc065d2f00df.jpg

I take it that the one with banding is no good and I need to get rid of that banding, I guess by making the exposure time longer.

Steve

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ollypenrice

ollypenrice

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I'm going to disagree slightly with one or two earlier posts, based on practical experience. The posts in question are right, 'by the book,' but I'm tempted by shortcuts where they work!

1) I usually find that my luminance flat will work perfectly well for all filters. Very occasionally I'll get a dust particle on one filter which requires a dedicated flat. The luminance is by far the most important layer to flatten perfectly and since it will, by definition, determine the brightnesses of the RGB layer, it will rectify mild imperfections in the RGB flattening that might arise from the use of one flat for all. I suggest you give it a try. If you find that 'flats per filter' do a better job than 'L flat fits all' then do it by the book. If, like me, you find it rarely makes a scrap of difference, you can take your choice. I think if you look at my images you'll find my backgrounds are pretty flat. I measure them carefully during processing using Photoshop's Colour Sampler tool. Most deviations from flatness come from vignetting and dust closer to the sensor than the filterwheel.

2) Refocus between filters? Most good filters are parfocal and any deviation in focus will be generated by imperfect colour correction in the optics. How much difference there is in focus per filter depends on the specifics of your setup and you can easily measure it. Just use your preferred focus method to get an optimal focus in green and then try that position in red and blue. Do you need to make a significant adjustment for the other filters? If so you'll need to refocus. If not, is it worth it? Given that you can successfully halve your resolution in RGB by binning 2x2 how badly is a very slight focus error going to affect your result? Again, it is luminance which needs to be as perfectly focused as you can manage because it will define your LRGB resolution.

I mention point 2 because it might affect your decision on shooting order. The textbook way to shoot is to do luminance and blue at the highest elevation and red and green at the lowest. (Better still, only shoot at high elevation but let's not pretend we're going to do that other than with a robotic setup under good skies!) If I'm totally confident in the sky I'll do that, but if there's a risk I'd rather compromise and get something complete in the can. So the psychological priorities and the technical ones make different demands. Your choice. (In high res imaging there's another factor: if the seeing is good shoot luminance. If it's bad shoot colour.)

I don't want to encourage bad practice but, given that you are suffereing from complexity overload, some effective shortcuts might be a help at this stage...

Olly

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RolandKol

RolandKol

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52 minutes ago, teoria_del_big_bang said:

Okay I think I found the issue with filter wheel.

I am pretty sure all down to USB connection issues. Just could not get wheel to change filters when it should. It would to begin with but after maybe 3 changes just stopped. The APT does not recognise it has lost communication so just carries on saying it is changing the filters but wheel just stays where it is.

USB has been a millstone round my neck since I started with imaging. I thought I had bottomed it but obviously not.

As always I have a dedicated USB3 cable from camera to laptop but all others go through a hub.

When I disconnected the wheel and using same cable go direct to laptop it has worked time after time so I assume the very expensive hub I have has some issues???? And although I have 2 USB2 and 2 USB3 ports on laptop it is not enough without a hub (mouse takes one port away ).

Anyway will now continue to see if I can successful flats.

Thanks for the help especially @vlaiv and @RolandKol 

Steve

As per USB...

Why you dont use the USB slots in the camera?

My guidercam and FilterWheel cables are plugged into ASI1600 USB hub which is plugged into the external HUB and all works Perfectly!

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vlaiv

vlaiv

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Posted
1 hour ago, teoria_del_big_bang said:

Okay sorry but I am now back to the original issue I had with banding. Below shows the test run for taking flats with all filters. I think the exp times look somewhere what is to be expected. To shorten the time from yesterday I have removed the paper layers I had to get exp time lower from the 2 sec for Luminance filter I had yesterday..

large.flats1.jpg.2e23f8e236fbf35ffdb80099cdc021da.jpg

 

But when I look closely at the faster exposures I can see banding. large.Dark_Flat_BLUE_Bin1x1_0.07125s_G139__-20C_2019-04-07_12-23-02.jpg.45457ba6265b808969acecb292d4e72a.jpg

With the longer ones such as the NB ones it looks much better.

large.Dark_Flat_HAlpha_Bin1x1_4.0625s_G139__-20C_2019-04-07_12-27-17.jpg.52b5674a4843bd1f5575fc065d2f00df.jpg

I take it that the one with banding is no good and I need to get rid of that banding, I guess by making the exposure time longer.

Steve

Yes, could be due to LEDs flickering due to power supply or something. Maybe try another PSU for panel, or simply use longer exposures that smooth flickering out.

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