My flats is not good - Forums

Hi,

Just got a new ZWO ASI 1600MM Cooled Pro. I have take flats which has a strange pattern. They are captured using a Gerd Naumann flat panel. My telescope is a Boren Simon 200mm f/3.6. Attached is a a ZWO filterwheel with Astrodon filters, 1.25". The flats are captured for L Serie 2 filter, lengt of exposures is 0.6 giving an average of 25000 ADU. The flats, 20 are calibrated by use of dark-flats, 20 at same gain, 76-12, and exposure time as flats. Processed in Pixinsight.

I can see the same pattern but not so dominat on the HA flats captured for Gain 300-50.

Link to Image

Any idea what is wrong?

There's obvious vignetting, as 1.25" filters are too small at that F-number - but I assume that's not what you mean

As for the structures in the image, can you check single exposures for a (horizontal) intensity pattern? The camera might be sensitive to flickering light due to the rolling shutter. Also, try using an additional filter (white T-shirt or alike) to reduce intensity, and increase exposure time. That would decrease the influence of the rolling shutter.

Looks like the pattern of the flat panel that you are using, but I could be wrong. I had the same issues with panels of Gerd Neumann, after I switched to a different panel it worked perfectly fine.

Thanks both for the tips. It seems that this is not only for me a post on the zwo forum describes the same issue.

Link to post

Nick, did you have the same problem as me with the Gerd Neumann panel on a ZWO camera? Any preference for another panel?

I am not sure but I think the pattern is on the lights too. Difficult to see with what I have captured

Erik

Hi Erik,
My friends and I (but also a lot of other astroimager) usually take flats at 15000 ADU. Another thing…probably 0.6" is too short, try to reduce light intensity and to take longer exposures.
Sorry for my english :-)

Thanks Vittorio, I will try with ADU 15000 and something that can reduce the intensity.

A question, are there others that used a Neumann Panel that get good flats with the ZWO 1600 camera. If so tips to ADU and exposure would be nice to get.

I use a tracing light pad panel from Amazon (that is used for tracing art work) on my GT102. I use the middle intensity, and 4 layers of white t-shirt, I go for an exposure of about 1-2 sec and get great results.

https://www.amazon.com/LitEnergy-Light-Panel-Ultra-Thin-Tracing/dp/B06VWBG73Y

I have tested with T-Shirt with Neumann panel and T-Shirt and a lamp as light source, 20000ADU at more that 2 sec. exposure time. Both gives the same pattern. My conclusion is t hat there must be something wrong with the camera. Maybe bad/missing coating. Any other opinions?

Erik

Why the camera and not the filters

Do you see the pattern also without any filter? And how is your filter wheel oriented? Is the threaded side of the filters towards the camera?

The filters have been used without problems with other cameras, and yes the threaded side is towards the camera. I dont. think it is possible to mount them wrong way if inserting them from the inside. Sorry for my Norwegian English.

I have tested with HA and L filter, same pattern, exactly at the same place.

Erik

I too use the Gerd Naumann flat panel with the ASI1600MM-C successfully. However the panel comes with layers of filters and I suspect you could use another filter to reduce the light.

Try this, take a white T-shirt and fold it so that there are FOUR layers covering the end of your scope, stretch tight and use bungie chort or large rubber band to keep it tight, point at the day time cloudless sky and set the ADU to 10000 (Sam with ZWO recommended this ADU) your histogram should be to the left of center with no dark clipping.

If you still have the same lines…..I am clueless - however I do think this will clear things up.

Hi and thank's, I did some more test for ZWO on different telesopes, different light sources, with/without filter, with/without density filter on the lightpanel but I got the same patterm. I got ZWO to give me a replacement so I will have a new one in the start of next week. Hopefully a "perfect" one.

Is 10000ADU enough to give a good calibration?

Yes on 10000, that is what SAM recommended.

Hi Edward, thanks again. Are there other readers that has an opinion to the low ADU level, 10000ADU? I assume that a to low intensity of the flats would actually not compensate for what is should.

I have had a Starlight Xpress H9 for many years there has never been any problem with flats. I have used the same panlel as now for ZWO camera. The camera is more sensitive but patters like the one that's on my camera is in my opinion a "defect" which is makes use of flats a problem. The camera should therefore be defined as "defect" and replaced which ZWO has done.

I understand! When I first got the ASI 1600 camera I sent Sam an email and ask him what EDU I should use, he said 10,000 would work great so I’m not used to anything else cents and it works great just like Sam said!

I understand! When I first got the ASI 1600 camera I sent Sam an email and ask him what EDU I should use, he said 10,000 would work great. So far so good!

I would try calibrating the flats without dark frames and see if that changes anything…

Sam, with ZWO, Recommended using 10,000 ADU.

Do you notice any errors in the calibrated lights when you calibrate with these flats? I have noticed strange patterns, especially in my OIII, when the flats are very aggressively stretched, but they calibrate OK as long as I follow a good procedure and use dark-flats.

As far as the ADU target, I typically do 14,000 ADU.

Nico Carver:
Do you notice any errors in the calibrated lights when you calibrate with these flats? I have noticed strange patterns, especially in my OIII, when the flats are very aggressively stretched, but they calibrate OK as long as I follow a good procedure and use dark-flats.As far as the ADU target, I typically do 14,000 ADU.

Nico very interesting your using 14,000 ADU I don't have any issues with my Calibration Frames and use 26,500 ADU. I will give it a go using ADU this low. do you know what the benefits to your calibration frames are using ADU this low.

I Use SGP flats wizard to set my exposure lengths.

Thanks

Dear friends,
probably, but I'm a novice, we have to talk not only about ADU but also about time of exposure. A lot of good astroimagers told me that exposures too shorts aren't good.