Re: [APML] What's Wrong with these Pictures?

[Philip Perkins <philip@astrocruise.com>]

Bobby, Kevin,

To me it looks as though the trailing might be due to field 
rotation.  Where was the guide star - off to the top left?  If so, this 
might fit - look at the trailing in the bottom left, bottom right, and top 
right corners - it seems to radiate around that point.  Field curvature 
tends to cause elongation going outwards, away from the centre of the frame.

Apart from the extreme corners, the vignetting could largely be overcome 
within PhotoShop.

--Philip


At 08:19 11/08/02 -0500, you wrote:
>1) Was the GR200 hypered?
>2) Was it the old formulation that's has been accepted as an excellent astro
>film, or the changed emiulsion as recently reported?
>3) You've got some severe vignetting that has allowed much more green
>response in the center of the frame as compared to the outside of the frame.
>Doing a lasso in the middle of the frame with feathering to allow a proper
>levels adjustment for the uneven illumination will bring out much more red.
>I've e-mailed you a copy showing this adjustment.
>4) The long stars are radiating around the center of the frame. I think
>that's a flat field issue due to the focal reducer aggrivating an allready
>curved field, not a field rotation issue.
>5) Warm film, bad processing or chemicals? I don't think so but how could
>one know for sure?
>Bobby Middleton


Philip Perkins - philip@astrocruise.com
Wiltshire UK & Luberon France
Astrocruise - http://www.astrocruise.com


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