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russellhq

Help, Strange Looking Narrowband Flats

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I was getting set up tonight and was taking some practice flats and got some odd results with the narrowband flats. They showed a bright band around the edge of the frame which was not present in the G and L flats. All flats were taking with an exposure to get approx. 22000 ADU.

I think this may just be an issue with the light source, And I've read that it's not absolutely necessary to take flats for all filters. So I might just stick with the Lum flat and apply to all images?

Here's the flats with a screen stretch.

Luminance

post-6495-0-29750700-1411753531_thumb.jp

Green

post-6495-0-23987200-1411753538_thumb.jp

Ha

post-6495-0-36415100-1411753542_thumb.jp

OIII

post-6495-0-68521900-1411753534_thumb.jp

SII

post-6495-0-10654100-1411753527_thumb.jp

Also, here's a picture of my set-up and flat panel (Gerd Numann).

IMG_20140926_175850.jpg

IMG_20140926_175905.jpg

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They look fine. Mine are the same with an Atik 460EX, and they were similar with my 16HR. No idea why they look like this, but they work fine for me, which is what counts. I would check to see how well they work for you before worrying about it too much.

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Agreed, try them first.

Do be careful with the wires on the Neumann panels as they leave the panel and enter the power supply. The cables are too rigid and have broken at both ends on the two panels that I have here. So that's four breakages and two dead panels. I'd reinforce them with epoxy, maybe, but it's too late now, for me, since both are scrappers. Not happy!

Olly

Edited by ollypenrice

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I was getting set up tonight and was taking some practice flats and got some odd results with the narrowband flats. They showed a bright band around the edge of the frame which was not present in the G and L flats. All flats were taking with an exposure to get approx. 22000 ADU.

I think this may just be an issue with the light source, And I've read that it's not absolutely necessary to take flats for all filters. So I might just stick with the Lum flat and apply to all images?

Here's the flats with a screen stretch.

Luminance

attachicon.gifAutosave Image -001L.jpg

Green

attachicon.gifAutosave Image -001G.jpg

Ha

attachicon.gifAutosave Image -001Ha.jpg

OIII

attachicon.gifAutosave Image -001OIII.jpg

SII

attachicon.gifAutosave Image -001SII.jpg

Also, here's a picture of my set-up and flat panel (Gerd Numann).

IMG_20140926_175850.jpg

IMG_20140926_175905.jpg

If you use filters then you will need flats for each filter- why? you may ask. Each filter could have dust particles in different places which would not be removed by having  one flat alone. So, time consuming but a necessary evil.

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Agreed, try them first.

Do be careful with the wires on the Neumann panels as they leave the panel and enter the power supply. The cables are too rigid and have broken at both ends on the two panels that I have here. So that's four breakages and two dead panels. I'd reinforce them with epoxy, maybe, but it's too late now, for me, since both are scrappers. Not happy!

Olly

I broke mine, too. Was an easy fix though. Simply remove the ring (at least in my case it wasn't glued) and reconnect the broken band mechanically. Do something to secure the cables. Possibly add a plug. Reassemble. Took all of ten minutes and works better then before (I inserted paper to get the thing darker).

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Your Ha and OIII would benefit from flats to even out the dust motes and any other irregularities, but as others have said if they're all clean then using one flat for all filters can be considered, but I am curious why the artefact occurs with only those two filters?

Does the Ha have a narrower bandwidth than the others or have some different physical properties to the others (thickness, mounted vs unmounted etc...) which could cause different reflections ?

Were the exposures significantly longer or did you have to screen stretch more? Either could be highlighting the same properties that actually exist in all other flats just not immediatly apparent. A quick check would be to compare the ADU values for the HA edge within a similar range to the central areas?

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