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Problem with Flats


Kenza

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Hi!

A couple of nights ago I tried taking flats with my Ipad and a white cotton shirt. The outcome was that every image I took turned out completely black no matter what the exposure was ( 1,5, 10 sec). The scope was pointed vertically and the ipad placed on top (white screen was on) with the shirt in between. Just to make sure that everything was ok with the camera ( Atik 4000M ) I took a shot of the sky and everything was fine. Does anyone know what the problem might be?

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  • 3 weeks later...

You were right Ibbo, I was overexposing it. Last night I tried again with success. For the LUM filter i had to take it down to 0.09 sec in order to get an ADU of 20000. As for the H alpha the exposure had to be 20 sec. Here is an example of the two flats stretched in pixinsight.

Does this look ok to you? I mean in terms of acquiring a proper flat image.

 

5af6b79f7d898_Flatframeexample.thumb.jpg.e4bad1ed9d9f1a2816999973befb9c7c.jpg

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It's probably better to dim the light source more and increase the exposure time rather than have really short exposures.

I remember getting confused by Maxim many years ago finding that increasing the exposure made the image go black, no mention of this effect in the instructions as I recall :icon_scratch:

Dave

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29 minutes ago, Davey-T said:

It's probably better to dim the light source more and increase the exposure time rather than have really short exposures.

I remember getting confused by Maxim many years ago finding that increasing the exposure made the image go black, no mention of this effect in the instructions as I recall :icon_scratch:

Dave

I can put a black T-shirt instead ?

i also searched the manual but there is nothing on black images. It is confusing. They should mention it in the manual

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1 minute ago, happy-kat said:

If using your ipad as the light source then the app lightbox is good.

Thanks, i’ll try it. I just use Notes as a light source but i guess lightbox is better.

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