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Cookbook CCD Images
Images and Text by Jan Wisniewski
Updated with more notes February 20, 1999
For color imaging I first tried RGB dichroic + IR-blocking
filters from Edmund Scientific. They work great, but there are
two problems:
1) each of them lets through only approximately 1/3 of the
spectrum, so signal-to-noise ration is not great. Red frames are
best in that respect, because of the highest sensitivity of CCD
in that range. Blue frames are
usually noisy - which can be remedied by taking more exposures
through blue before stacking them together with Multi245.
2) In my experience, however, green exposures were the worst -
that probably results from the gap in coverege around 480-550nm.
Unfortunately, that means that the light of ionized oxygen
never gets through and it is impossible to get proper images of
planetary nebulas (dichroic filters have very "sharp"
bandpass so there is no "leakage" like with classical
Wratten filters - however more then 90% of the light inside bandpass
goes through the dichroic filter, compared to about 40% for the
Wratten filter). Both of the above difficulties are taken care
of once I switched to dichroic cyan, magenta and yellow filters
(also from Edmund Scientific).
Richard Berry modified his QColor program to handle these filters.
His Cookbook webpage contains a detailed description http://wvi.com/~rberry/cookbook.htm.
Shorter exposures are OK to get a nice signal, as each filter
allows through 2/3 of the spectrum and the cyan filter lets through
the ionized oxygen band. An additional advantage comes during
assembly of the final color image. To achieve that, CMY images
are mixed and split to creat RGB intermediates and in Berry's
QColor software it is easy to play with corresponding coefficients
until the image looks right. I prefer to get star images in the
natural color range as that takes care of light pollution, CCD
color-sensitivity etc. In effect nebulas and galaxies have the
right appearance and are not surrounded by green or magenta stars!
Editor's Note: Since this article was originally introduced
Jan has added some notes from his January RASC Meeting presentation. Additional notes ...
Click on image for full file image |
Helix Nebula image was taken on Oct. 19, 20 &
21, 1998. Two
separate frames were assembled, each using W (12 or 13 x 4min.)
and CMY (9
x 4min.), then mosaic was merged with PhotoPaint 8.
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Click on image for full file image |
M1
Image was taken on Sept. 26, 1998 (am) from my
backyard observatory in Sooke, BC using Cookbook 245 LDC CCD
camera on Ultima 8 f6.3 telescope, autoguided with Cookbook 211
LDC camera on piggybacked 500mm f8 telephoto lens. It is composed
of W (10 x 4 min.) and CMY (6 x 4 min. each) integrations processed
with Multi245, AIP245 and QColor, as well as PhotoPaint 8.
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Click on image for full file image |
M16
Image was taken on June 20, 1998 (am) from my backyard
observatory in Sooke, BC using Cookbook 245 LDC CCD camera on
Ultima 8 f6.3 telescope, autoguided with Cookbook 211 LDC camera
on piggybacked 500mm f8 telephoto lens. It is composed of W (6
x 2 min.) and CMY (3 x 2 min. each) integrations processed with
Multi245, AIP245 and QColor, as well as PhotoPaint 8.
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Click on image for full file image |
M17
Image was taken on June 22, 1998 (am) from my backyard
observatory in Sooke, BC using Cookbook 245 LDC CCD camera on
Ultima 8 f6.3 telescope, autoguided with Cookbook 211 LDC camera
on piggybacked 500mm f8 telephoto lens. It is composed of W (6
x 2 min.), CM (4 x 2 min. each) and Y (3 x 2 min.) integrations
processed with Multi245, AIP245 and QColor, as well as PhotoPaint
8.
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Click on image for full image |
M33
Image is a mosaic of 4 frames taken on Sept. 20,
21 & 23, 1998 from my backyard observatory in Sooke, BC using
Cookbook 245 LDC CCD camera on Ultima 8 f6.3 telescope, autoguided
with Cookbook 211 LDC camera on piggybacked 500mm f8 telephoto
lens. Each frame was composed of W ( 8 or 9 x 4 min.) and CMY
( 4 x 4 min. each ) integrations processed with Multi245, AIP245
and QColor, as well as PhotoPaint 8. Mosaic assembled with PhotoPaint
8. |
Click on image for full image |
M57
Image was taken on June 19, 1998 however cyan,
magenta and yellow filters were used instead of RGB. Following
exposures
were combined as above: W (6 x 2min.), CMY (3 x 2min. each).
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Click on image for full image |
Veil Nebula
Image is composed from mosaic of three frames,
each
composed of W (6 x 4min.) and CMY (4 x 4min.) exposures taken
on July 28 &
29 and Aug. 2, 1998.
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Click on image for full image |
M101
Image was taken on April 28 & 29, 1998 with
8" SCT f6.3 and Cookbook 245 LDC. It is composed of white
exposures (taken through IR-blocking filter only, elswhere listed
as "W" - 8 exposures, 4 min.each.), red (R = IR-blocking
+ red dichroic filter, 4 x 10 min.), green (G = IR-blocking +
green dichroic filter, 5 x 10 min.) and blue (B =
IR-blocking + blue dichroic filter). Those where processed with
Berry's Multi245, AIP245 and QColor software, as well as PhotoPaint
8. |
Jan Wisniewski
http://astrosurf.com/jwisn/
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