IMPORTANT! Long time exposures without purpe corner!

Started Oct 19, 2005 | Discussions thread
my-spot Regular Member • Posts: 372
WinMRW Software

Sorry about the fact I didn't reply until now. I have hinted about the fact that I have been working on a RAW Converter for a while and I'm very pleased Nordstjernen has found it useful and is using it to produce his awesome shots. I contacted him after he posted some astrophotos to see if he would "alpha-test" my little program.

I started to write WinMRW after I found I didn't like how the 7D and available software at the time (Dec 2004) handled highlights. So I came up with a fairly good routine to correct / reconstruct blown highlights. One thing led to another and before long I was rewriting Bayer decoders and incorporating color profiles. Anyway, the point is it started out as a converter for "normal" photography. The dark frame feature was added after a night of being frustrated by doing dark frames the "normal" way. The user interface is very basic and leaves much to be desired but my focus has been on the best possible conversion not a fancy interface.

I would love to get a small number (

Nordstjernen wrote:

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:

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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