IMPORTANT! Long time exposures without purpe corner!

Started Oct 19, 2005 | Discussions thread
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Nordstjernen
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IMPORTANT! Long time exposures without purpe corner!
Oct 19, 2005

Long time exposures with the D7 and D5 (> 30 sec) leaves a purple glow in the upper left corner of the frame. Frustrating? You bet! With manual dark frame subtraction in Photoshop I get far better results than without any noise reduction. But still not good.

Here are some really good news.

Frank, a fellow on this forum, have found a solution that really works! Check out Frank’s WinMRW raw file converter! 3 min exposures, 5 min, 10 min – don’t worry. His raw converter does the job! Just make sure that you make a dark frame with the same exposure time and udner the same conditions as the “light frame”. A dark frame is an exposure where absolutley NO light enters the camera. The information in this frame is subtracted from the “light frame”and viola, the purple glow is gone.

A few months ago, when I entered this forum with some of my 7D astro photographs, Frank contacted me and asked if I would try a very early version of his raw converter for D7 files. The software includes true dark frame subtraction at raw level, and both linear and non linear conversion. I was thrilled!

I have worked with this WinMRW converter for a while, and the software works so well (do not judge it by its early stage interface) that other KM users really should know about it. This raw converter is actually the best thing that have happened to my astrophoto life since the KM D7.

Frank’s web site: http://www.my-spot.com/astronomy.htm

This 30 minute exposure (5 min x 6) shows the North America Nebula (ngc7000) in Cygnus. Full frame, no cropping ... no purple glow!

First picture: A full frame 5 minute single exposure of the Andromeda galaxy, converted straight with Dimage Master. Lots of destroying purple glow – as with raw conversion in PS CS.

Second picture: The same frame converted straight with Frank’s WinMRW. Not only is the purple glow gone, the conversionis also shows much better colors.

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