IMPORTANT! Long time exposures without purpe corner!

Started Oct 19, 2005 | Discussions
Nordstjernen
Nordstjernen Veteran Member • Posts: 6,876
IMPORTANT! Long time exposures without purpe corner!

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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santoguapo Senior Member • Posts: 1,674
Wow! Very cool!

I have only done a little astrophotography. Next time I will try this method.
--
Cheerio...
Rich

Nordstjernen
OP Nordstjernen Veteran Member • Posts: 6,876
For more than astro-photographers

I think this new raw converter will please all KM photographers who want to explore long time exposures -- i.e. night photography in general.

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mdl50
mdl50 Veteran Member • Posts: 3,211
Re: to which telescope did you attach ...

.... the 7D, which magnification did you use?
Mario.

Nordstjernen
OP Nordstjernen Veteran Member • Posts: 6,876
Re: to which telescope did you attach ...

For both pictures I have used my excellent Minolta Apo 400 mm f/4.5 at full aperture (less than 90 mm effective aperture). The camera was put on a Losmandy G-11 equatorial mount.You don't need a big telescope to reach light years ahead.

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Scooob Regular Member • Posts: 231
Re: IMPORTANT! Long time exposures without purpe corner!

This is GREAT news but I don't see any link to download the software...

Regards,

Marc

Anything through the lens can be beautiful
http://www.pbase.com/mmb14

tomes Regular Member • Posts: 221
Re: IMPORTANT! Long time exposures without purpe corner!

I second that. Looked on several pages of his website, and found nothing.

Also, what is the equatorial mount you are talking about?

imarollingstone Veteran Member • Posts: 3,642
I third that, where do we find this? nt

tomes wrote:

I second that. Looked on several pages of his website, and found
nothing.

-- hide signature --

Shawn

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PhotoTraveler Forum Pro • Posts: 11,700
Sounds good, but

Sounds good, but guessing by the name its windows only.

Also doing a dark frame for an hour would really drive one nuts after an hour shot, heck just a 10 minute shot drives me nuts, and waiting for the camera to do it's thing for a few minutes drives me nuts.

Maybe KM can built something into the cameras in the future, maybe like not letting it happen in the first place.

Purple fringe of doom is very dependent on many things, thus why at time you can get shots into the minutes without it. other times you get it for sub 30 second shots.

Nordstjernen
OP Nordstjernen Veteran Member • Posts: 6,876
Software

Please wait for further information about this software. I tought Frank's web page had an e-mail option, but there is not.

This equatorial mount is a tracking device wich is used to follow the motion of the star (compensate for Eart's rotation). This is used with telescopes, and is needet for astrophotography. If not used., the stars will make trails within a few seconds with telephoto lenses.

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Nordstjernen
OP Nordstjernen Veteran Member • Posts: 6,876
In fact this is a quick and efective solution

With this software you can spit the total exposure time into several shorter excposures, i.e. 5 minutes. At the end of the session (or in the middle, if you like) you make just ONE dark frame exposure. This dark frame can be used for ALL the pictures from this session. Really a time saver!

A dark frame is needed to remove noise. It also removes the purple area. Actually, this shows how efective the dark frame noise reduction is.

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santoguapo Senior Member • Posts: 1,674
How long is the longest shot you actually take?

Do you have a typical shot length? 1 minute? 5 minutes? I haven't ever tried the shot-stacking technique, but shot a bunch of 1 min exposures the last time I was in Colorado (dark skys) and have yet to stack them.
--
Cheerio...
Rich

Nordstjernen
OP Nordstjernen Veteran Member • Posts: 6,876
Re: How long is the longest shot you actually take?

To bring the information/sky background away from the left side of the histogram, I am using 5 minutes at ISO 800 and aperture f/4.5 (max with my 400 mm glass). Even 3 minutes works well, and 30 sec exposure time is not too bad at this relative slow aperture! Still, I will explore longer exposure time, but not more than 10 minutes, I think. I will also try ISO 1600.

Many exposures that brings a total of 30 to 60 minutes seems to give very good results when the conditions for observation is good.

According to the histogram 5 minutes is a good balance between info/noise level (data) and tracking time/turbulent air (real world conditions). With a f/2,8 lens 2 minutes shold work really well at ISO 800.

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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: 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.

Craig Davis Regular Member • Posts: 219
I wonder if something similar happened here.

I was wondering where the purple tinge came from in this lightning shot.

I haven't done a dark frame subtraction as I have no idea how to do it in PS SC. I disabled the Noise Reduction in camera because it slows down the shots too much.

I'd like to give the software a try some time in the future. I'll make sure next time I'm taking the lightning pics that I get a dark frame shot.

Nordstjernen
OP Nordstjernen Veteran Member • Posts: 6,876
Over exposure, I think

Seems like your photo is overexposed (exif: 42 seconds at f/5.6 ISO 100), and that the all over purple cast is the object's color (the clouds).

If the photo was made at late twighlight, and not complete darkness, this purple color cast is not unexpected, I think. When I darkened your shot I could hardly isolate the purple light in the upper left corner.

This defect shows up just in the upper left corner, stronger the longer exposure, and it is best seen against dark backgrounds.

When you expose up to 30 seconds I will strongly recommend to use the camera's own noise reduction to get the best results. For longer exposures the mentioned raw converter should be VERY useable, and a real time saver.

If I forgot to mention: This raw converter also does an impressive job with ordinary photographs (where dark frame subtraction is not needed).

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bracket Senior Member • Posts: 1,360
Re: WinMRW Software

very interesting to hear about your software. I don't own a KM 7D yet, but I wondered if your software would work also for a Dimage A2, since the RAW format may be similar? If so I'd really like to try it out.

greetings,
bracket

my-spot Regular Member • Posts: 372
Re: I wonder if something similar happened here.

I looked at the histogram and it looks like a white balance issue, maybe as an issue with the lightning effecting it...

Craig Davis wrote:

I was wondering where the purple tinge came from in this lightning
shot.

I haven't done a dark frame subtraction as I have no idea how to do
it in PS SC. I disabled the Noise Reduction in camera because it
slows down the shots too much.

I'd like to give the software a try some time in the future. I'll
make sure next time I'm taking the lightning pics that I get a dark
frame shot.

Craig Davis Regular Member • Posts: 219
Re: Over exposure, I think

You are correct it was a little over exposed. I didn't get the settings quite right. I did notice it was more of a balanced purple haze rather than just the top corner.

I'll contact Frank in the hope that he may let me have a play with his program to see if it helps me with the long exposures.

Thanks for taking a look at it for me.

Regards

Craig

Nordstjernen wrote:

Seems like your photo is overexposed (exif: 42 seconds at f/5.6 ISO
100), and that the all over purple cast is the object's color (the
clouds).

If the photo was made at late twighlight, and not complete
darkness, this purple color cast is not unexpected, I think. When I
darkened your shot I could hardly isolate the purple light in the
upper left corner.

This defect shows up just in the upper left corner, stronger the
longer exposure, and it is best seen against dark backgrounds.

When you expose up to 30 seconds I will strongly recommend to use
the camera's own noise reduction to get the best results. For
longer exposures the mentioned raw converter should be VERY
useable, and a real time saver.

If I forgot to mention: This raw converter also does an impressive
job with ordinary photographs (where dark frame subtraction is not
needed).

Craig Davis Regular Member • Posts: 219
Re: I wonder if something similar happened here.

Frank thanks for the feedback. I'll have a play with the WB and see what I think.

Regards

Craig

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