Flat frames not when I take them

[Newfie]

Quick pointers in the right direction, is there an obvious reason why my flat frames look like this. I have used a light panel and thought I had the histogram somewhere near where it should be, but they look more like a Zebra crossing than a flat frame. Apologies in advance for what may seam like an obvious fix to correct this !

 

[wimvb]

Can it be that the flat panel "scans" like a TV set? In that case, try with a longer exposure time.

[Adreneline]

Hi. I had a very similar experience using a Huion Adjustable Lightness 17.7 Inch (Diagonal) LED Animation/Artcraft/Tatoo/Quilting/Tracing Light Box - A4 - purchased from Amazon (I use it for macro photography of transparencies and negatives and works really well - and no, I'm not a secret tattoo artist!). In the end I gave up trying to use it to create flats with my Atik 414ex and just went for the uniform gray sky day (plenty of those round here) and a white teeshirt over the end of the scope - which gave what I thought were very good results.

Adrian