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ZWO 5 position FW and moon light leakage problem

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#1 BoskoSLO

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Posted 22 September 2019 - 06:02 AM

Is anyone having an issue with moonlight bypassing the ZWO 7nm 31mm narrowband filters and getting onto the asi 1600mm pro sensor?

My imaging train: ASI 1600mm Pro > ZWO 5 pos electric FW > 21mm spacer > TS 16mm OAG> 0,79x flattener reducer>focuser>telescope

 

I just recently switched to using 31mm NB filters from ZWO. Before I was using the 2inch 12nm Astronomik Ha filter that I screwed directly into the flattener and it worked great with no stray moon light effecting the image quality.

Because I have the 5 pos FW I can only mount 5 filters so I temp. replaced the green and blue with OIII and SII so my filter wheel looks like this ( L,R,Ha,SII,OIII).

So that's that. I have been testing the filters for the past 2 nights and realized that the moonlight, even at only ~50 illumination has found its way into my camera sensor. I have checked the time where my frames are starting to get brighter and brighter and it matched with the moon rising above horizon.

 

So i'm confused now. Isn't the idea of narrowband filters to image during moon light and in light polluted cities? in a bortle 4 zone and with a 55% illuminated moon the 300seconds frames are quite washed out, I can't even imagine during the full moon or inside a city, the image would be completely washed out.

 

before moon rise:

https://i.imgur.com/uOT8oky.jpg

 

after moon rise:

https://i.imgur.com/NPfpR1P.jpg

 

I was also looking at vignetting to identify the source of light leakage but the thing is that the whole frame is evenly illuminated. Flat frames look decent enough with minimal reflections. I also used a flashlight to shine down the telescope tube to locate the source but nothing  obvious was found. And the air gap between the camera frontal plate / window and the filter surface is <1mm. So how come there is so much moon light in my frames? Is it maybe passing trough the luminance filter that sits next to the OIII filter, but wouldn't a lot of people have the same issue?



#2 happylimpet

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Posted 22 September 2019 - 07:07 AM

if its evenly illuminated it isnt light leakage - that always shows patterns/rays/structure.

 

You'd expect the level to increase after moonrise. the moon is a broadband source so theres light at all wavelengths, including your narrowband filter bandwidth.


Edited by happylimpet, 23 September 2019 - 03:39 AM.

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#3 BoskoSLO

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Posted 22 September 2019 - 07:54 AM

if its evenly illuminated it isnt light leakage - that always shows patterns/rays/structure.

 

You'd expect the level to increase after moonlight. the moon is a broadband source so theres light at all wavelengths, including your narrowband filter bandwidth.

I see OIII is the one filter that gets effected the most by the moon as it scatters the blue light more in the atmosphere. That's why SII is slightly better and Ha even better(even at 12nm).

So if that's the case that means that the remaining frames that are somewhat brighter even before moon rise is probably NINA corrupting the files.

NINA started to corrupt more and more of my light frames, sometimes even merging 2 pictures together and downloading them as one, leaving black lines across the images, failed to download images, crash without a log,.... Could possibly effect the background brightness a bit. I had 3 good nights with NINA behaving and now it's failing fast. did some test images during daytime with SGP and it seem to work just fine there so the next time I will go back to SGP.



#4 ks__observer

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Posted 22 September 2019 - 08:57 AM

I get light leakage through my ZWO filter.

I always put a strip of blue tape over the filter change point.



#5 Rich139

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Posted 22 September 2019 - 09:06 AM

Yep when I had light leakage using the Zwo filter wheel it was like a sunburst across my subs. I now put an eyemask across the gap so I can change filter easily then put it back.

#6 BoskoSLO

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Posted 22 September 2019 - 11:00 AM

I get light leakage through my ZWO filter.

I always put a strip of blue tape over the filter change point.

you mean the 2mm holes for filter positions?



#7 ks__observer

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Posted 22 September 2019 - 11:27 AM

you mean the 2mm holes for filter positions?

Where you turn the wheel to change filter position.



#8 BoskoSLO

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Posted 22 September 2019 - 11:45 AM

Where you turn the wheel to change filter position.

Oh you are talking about the manual filter wheel. I use the electric version




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