A Pair of Planetary Performers - AstroPhoto Insight

A Pair of Planetary Performers - AstroPhoto Insight
Tim Easterday
Over a year ago I finally had the opportunity to purchase a decent astrophotography rig. This was after
more than two decades of enjoying this hobby with just
my eyes, and sometimes a pair of binoculars. Like many
of us, I spent a long time obsessing over what items to
purchase while still keeping within my budget. It was truly
“analysis paralysis” for a while, but I eventually came up
with a list of equipment that would serve my needs both
in deep-sky photography and planetary imaging. One of
these items was a dedicated planetary camera. My criteria required that this camera be not only a good imager
for the planets and the moon, but also a good guide cam
for long-exposure work with my DSLR. Therefore, I
needed a camera with a high frame rate, good sensitivity,
and longer exposures than typically found in PC webcams. At the time (summer of 2006) there was a lot of
talk about these little “blue cubes” from The Imaging
Source that delivered a 30 fps frame rate with good sensitivity and exposures up to 30 seconds. About the same
time they announced a firmware upgrade to 60 fps –
even better! Given my budget, this seemed like the perfect choice for my needs, as the next step up in planetary
cameras was much too expensive to consider.
The next choice was between the color “DBK” version
or the monochrome “DMK” version, with the edge in sensitivity obviously going to the mono version. For longexposure photography I would need maximum sensitivity
in the guide camera because of my light-polluted skies in
Atlanta. With that in mind I called up the nice folks at TIS
and placed my order for the DMK 21AF04. I figured I
could later save up enough money to get a filter wheel
and some good-quality filters for color planetary imaging.
The choice in resolution was strictly a budgetary concern
for me. The DMK 21AF04 resolution of 640 x 480 pixels
is plenty for the planets and adequate for guiding at
longer focal lengths when using a reducer.
AstroPhoto Insight December 2007
The Imaging Source DMK 21AF04
At the time I purchased my DMK 21AF04 they were
not including the C-mount to 1-1/4” adapter that is necessary to use this device in a telescope. No big deal – these
are easily found on Ebay and cost $20. Since then TIS
has started including the adapter. They have also created
a website and blog dedicated to astronomical use of
these cameras (the website can be found at http://
www.astronomycameras.com/en/products/ and the blog
c a n
b e
f o u n d
a t
h t t p : / /
www.astronomycamerasblog.com/). The cameras are
available directly from TIS or from many different resellers. One other required accessory that is not included is
the FireWire cable that connects the camera to your computer. Here’s where you need to be careful: most laptops
have a 4-pin FireWire port. The cameras from TIS have 6
-pin ports on the back. What’s the difference? Power.
Laptops do not usually have the extra 2 pins that supply
DC power to the device. Fortunately there are power supplies and special cables with a DC power jack available
from TIS. Another route, the one I chose, is to purchase a
powered FireWire hub, a 6-pin to 6-pin cable, and a 4-pin
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Figure 1 — The DMK 21AF04 FireWire Camera
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to 6-pin cable. The hub allows for future expansion in
case more astro devices come out in the future that support the IEEE 1394 FireWire standard. Recently TIS has
introduced a line of USB 2.0 cameras on their main website. This should simplify the computer connection for
those who don’t have IEEE 1394 ports on their computer,
or don’t want to spend the extra money on power supplies or FireWire hubs.
The DMK 21AF04 camera is one solid piece of equipment. When it arrived I was impressed by the quality construction. It feels heavy and well built. Isn’t it funny how
the heavier weight of an object somehow translates to
better quality in our perception? In this case it’s true. The
camera comes with a thick metal base that is tapped for a
tripod mount. The 5mm thick C-mount ring unscrews to
allow the use of CS-mount lenses. This is necessary because of the 12.5mm backfocus requirement of CSmount lenses, while C-mount lenses require a 17.5mm
backfocus. Connection to a telescope is made via the
(now included) C-mount to 1-1/4” adapter. After using the
DMK for a few months I purchased a C-mount to T-thread
adapter that I now prefer to use. I find this method of connection more solid and easier to change from my photo
adapter/reducer combo for guiding to my filter wheel for
color imaging (yes, I finally purchased that filter wheel +
filters!).
This camera uses the Sony ICX098BL CCD sensor
with 640x480 pixels, each measuring 5.6µm square. The
same ICX098 family also includes the ICX098BQ sensor
used in the DBK/DFK 21AF04 models as well as the Celestron NexImage, older Philips ToUcam pro webcams,
and the newer Philips SPC900NC webcam (more on that
later). If the convenience of a color camera is something
you prefer, go for the DBK model camera. The DBK series does not have an internal IR-cut filter, so you need to
supply your own. The DFK series does have the IR-cut
filter but it cuts off steeply at the 656nm wavelength of Halpha emissions - just in case you ever want to do some
deep-sky imaging. If more pixels are your fancy, step up
to any 31AF03 model which features 1024x768 pixels
each measuring 4.65µm square, or the 41AF02 models
which feature 1280x960 pixels also measuring 4.65µm
square. Keep in mind the slightly larger pixels of the
21AF04 models will offer higher sensitivity over the larger
resolution models.
As the cameras go up in resolution, the maximum
frame rate decreases. The 60 fps frame rate is only available in the 640x480 resolution models. High frame rates
are necessary to freeze the turbulence in the atmosphere. Moments of good seeing can then be captured
more effectively amid the shifting & shimmering image we
typically see when viewing a planet or the lunar surface
under high power. Even though the DMK 21AF04 is capable of 60 fps, I find myself rarely using such a high
frame rate. It takes a pretty bright object to get a good
exposure at 1/60 second or faster. I usually only use
those short exposures for lunar imaging. When using
color filters a longer exposure is normally required so the
frame rate drops.
Speaking of exposure, not long after I got my DMK
camera TIS came out with a long-exposure upgrade designated as the “AS” version. This upgrade extended the
maximum exposure time to 60 minutes – more than
enough for just about any deep-sky imaging. It was about
this time that I was fighting an issue of some very bright
stuck pixels on my DMK. TIS was nice enough to exchange my camera for an “AS” version. Now my camera
was a real “triple threat” – capable of great planetary
work, long-exposure deep-sky imaging, and a pretty darn
good guide camera too. The long-exposure mode presented a new challenge, and yet another opportunity to
buy more stuff (which we all love doing, right?). Now I
needed a guide camera to have any chance of actually
using the DMK’s long exposures. Enter the Philips
SPC900NC color CCD webcam, which at less than $60
at the local Sam’s Club seemed like a good bargainpriced guide camera.
Figure 2 — The Philips SPC900NC with telescope
adapter
The SPC900NC webcam was the successor to the
very popular ToUcam 840K and shares the same Sony
ICX098BQ color CCD sensor used in the older ToUcam
model. As I mentioned earlier, you’ll also find this sensor
in the 21AF04 color versions from TIS, as well as the Celestron NexImage. I never owned the ToUcam but I did
own the NexImage for a few months and had a chance to
compare it briefly with the SPC900NC. Even though the
two cameras used identical CCD sensors, there was
something different in the electronics. The AVI files and
final stacked images from the NexImage always looked
noisier to me. Within a week of purchasing the
SPC900NC, I put the NexImage up for sale. This Philips
webcam has already been replaced by newer models
with larger CMOS sensors, but you can still find them
online.
This webcam comes ready for mounting on your laptop or PC, complete with a focusable lens assembly and
a large bracket to clip on a notebook screen. None of that
is useful for planetary imaging and must be removed. The
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AstroPhoto Insight December 2007
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lens is pretty easy to remove and reveals the Sony CCD
sensor sitting on a small pair of stacked circuit boards. An
adapter is required to mount the camera in a telescope’s
focuser tube. Just like the DMK adapter, you can also
find these on Ebay for around $20, or a little more expensive elsewhere.
The Philips SPC900NC has a resolution of 640x480
pixels. The pixels are covered by a Bayer matrix which
filters red, blue, and green to separate pixels. In this configuration, each 4x4 square of pixels contains one red,
one blue, and two green filters. Naturally this camera has
the strongest response to the green portion of the light
spectrum. Overall you can expect this type of camera to
be less than half as sensitive as a monochrome model.
However, the convenience of one-shot color imaging and
the price are hard to beat for anyone just getting started
with planetary imaging.
Beware of the advertised specifications you’ll find on
many websites. Many online stores are using the default
specs straight from the manufacturer. This can be misleading for the beginning astronomer. The camera is often labeled as a “1.3MP camera” capable of “90 fps.” Obviously 640x480 does not equal 1,300,000 pixels. That is
an interpolated mode specifically for snapshots – useless
for webcam imaging. The 90 fps frame rate spec is also
misleading. You will never realistically want to use more
than 30 fps in AVI mode and even then you are pushing it
for this less-sensitive camera on a slower USB 1.1 connection. It’s better to start off around 15 fps and see what
kind of image you can get.
A Little Bit about Bit Depth
It should be mentioned that both the Philips
SPC900NC and all the DMK/DBK/DFK models are 8-bit
cameras. This means that there are 2^8, or 256 possible
levels ranging from pure black to pure white. Higherpriced planetary cameras can output 12 bits, or 4,096
possible levels. However, that kind of resolution is best
for solar H-alpha imaging or extremely detailed lunar imaging. Eight bit data is acceptable for typical planetary
images and the results will make most of us very happy.
You’ll find 16-bit resolution on the typical deep-sky CCD
imagers such as my newly acquired Meade DSI Pro, but
these cameras just aren’t made to deliver high frame rate
video. They excel at what they were made for – very dim
objects. The TIS cameras with long-exposure capability
are capable of some decent entry-level deep-sky work,
but the 8-bit images will never be able to compare to a
true 16-bit camera.
The Cameras in Action
The DMK 21AF04.AS is very easy to setup and get
running for the first time. Many great products suffer from
being bundled with poor software, but that is not the case
here. The camera comes with a licensed copy of IC Cap-
ture.AS. The more I use this program, the more I love it.
All the controls are laid out very sensibly across the top of
the screen and you can enable only the controls you
need and hide the rest. You can setup a particular configuration and save it for future use. Toggling the Recording Control Dialog pops up the Record Video File
window where you setup the file format, location, and
naming convention. IC Capture can automatically increment the filename when recording multiple video files.
Time stamping is also available if you don’t mind your
filenames getting longer. I would suggest that you go into
the filename menu and type in something meaningful
every time so you can remember later what was recorded.
At first the choice of recording format may seem quite
daunting but it’s really simple. Clicking on the Codec Setting button in the Record Video File window brings up a
choice of media container type and video compression
type. Choosing media container is easy – AVI is the only
choice and the format needed when opening the file in
Registax. Choosing the video compression method can
be confusing because of the different settings and the
sheer quantity of codecs available. For best image quality, compression of any kind should not be used. While
compression saves on file space, it can degrade the quality of the file and may introduce artifacts. I tried every codec I had on my system and most would not even allow
video recording. Those that would were not compatible
with Registax. Therefore, I always choose an uncompressed format. You’ll eat up a lot of hard drive space but
it’s necessary to get the best results. For monochrome
imaging the only format needed is Y800. This is an 8-bit
per pixel format. The other uncompressed formats are
RGB24, RGB32, and UYVY. These are color formats and
only applicable to a color camera like the DBK & DFK
models. Below the uncompressed format selection,
there’s another choice labeled “Unspecified” which I believe defaults to Y800. I compared files taken with the
Y800 format and the Unspecified format and for the same
number of frames both had the same file size. Both
worked in Registax as well.
Before you begin recording you must set up the
proper exposure. This is where my favorite feature comes
in - the live histogram. The histogram indicates the number of pixels at each of the 256 available levels. I always
have “Visualize Zeros” checked and the graph scale set
to logarithmic. What you are looking for here is an image
that is neither underexposed nor overexposed. With the
Visualize Zeros option, keeping a bit of yellow at each
end indicates a good exposure level (Figure 3). I then
adjust gain and exposure until I get a good-looking image
and a properly exposed histogram. At that point it’s time
to begin recording. It’s important to always go back and
adjust the histogram when changing filters, moving to
different objects, or even just moving to a different part of
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AstroPhoto Insight December 2007
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Figure 3 — IC Capture screen shot with the DMK 21AF04.AS
the lunar surface. I have also found the histogram useful
for attaining the best focus. As you move the focuser, the
histogram will maximize on the X-axis when proper focus
is reached.
The Philips SPC900NC is another story when it
comes to bundled software. The included VLounge software only records in MPEG compressed format, making
it useless for planetary imaging. Fortunately there’s good
software out there to record AVI files with this camera
and the best part is that most of them are
free. I’ve tried QCfocus, AMCap, and K3CCD
Tools 3. The first two are free but K3CCD
Tools will cost you $49.99 for the full version.
K3’s software does a whole lot more than just
video capture and is well worth the price (and
it also works well with the TIS FireWire cameras). But for just recording a few video files I
prefer QCfocus. Actually I use a combination
of QCfocus and another program called
WcCtrl. This is because QCfocus only allows
the camera’s standard adjustment sliders for
gain, brightness, gamma, etc. These sliders
do not have any numerical reference and
there’s no way to save a preset for future
use. WcCtrl has adjustment sliders with numbers and allows settings to be saved to a preFigure 4
set file. And you can run both programs at
the same time. I use WcCtrl to fine-tune my
AstroPhoto Insight December 2007
exposure while viewing the live image in QCfocus.
Recording files in QCfocus is very simple and the program allows automatic filename incrementing similar to
IC Capture. Here again you must make a choice for the
recording format. There are three formats possible: I420,
IYUV, and YUY2. The first two are the same format according to FourCC.org but YUY2 is a higher bit-depth
format and takes up more file space. Beyond the format
there is not much else to set in QCfocus if
continued >
— QCfocus and WcCtrl screen shot with the
Philips SPC900NC
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you are using WcCtrl too. The only setting to change is to
turn off auto exposure in QCfocus first before trying to
adjust the exposure in WcCtrl. Otherwise you will not be
able to turn off auto exposure in WcCtrl.
Stacking up the Results
This summer was pretty poor for imaging of any kind,
but I managed to get a couple of good nights with clear
skies (but poor seeing) to test out both cameras. Saturn
was at a low but acceptable altitude late in the spring and
became my first choice for a target. At that time I did not
have a filter wheel yet which limited me to strictly monochrome imaging with the DMK camera. This was not a
problem – I didn’t need any extra complications during
my first attempt at planetary imaging. I was instantly impressed with the results from the DMK 21AF04. The AVI
files taken with IC Capture looked awful for the most part
due to the turbulence in the atmosphere, but the DMK
was able to capture those microsecond-long moments of
good seeing. Divisions in Saturn’s rings became visible
as did some banding on the planet’s surface. The Philips
SPC900NC was then popped in for some color imaging.
Compared to the DMK the image was not quite as sharp
and detailed, and showed some sort of noise pattern of
bands going across the entire frame. I still don’t know
what is causing the occasional noise pattern but I suspect
it is due to either overexposing the video capture or pushing the levels of the final image a bit too much. As an
experiment, I combined the DMK image as a luminance
layer over the SPC900NC color image. Overall not too
bad for my first try.
Figure 5 — A comparison of Saturn images
Later in the summer it was on an even more challenging target – Jupiter. The fast rotation of this gas giant
means you have to be pretty quick. Making it even more
challenging was the fact that I was using a manual filter
wheel with LRGB filters on my DMK camera for the first
time. On the SPC900NC I just used a Baader UV/IR
blocking filter. I recorded 300 frames with the DMK for
each of the LRG filters and 200 frames for the blue filter.
Each time I adjusted the gain and exposure to get the
histogram looking right. Each separate video file was
stacked and processed in Registax and then saved as a
TIF file. The images were then processed just a little
again in Photoshop with the final LRGB combine performed in Images Plus. Overall it was a LOT of work to
get a color image. Using the SPC900NC I recorded 300
frames, stacked & processed in Registax, then performed
some final adjustments in Photoshop. This took me just a
fraction of the time as the LRGB processing. I’m sure the
final results could be better (I am just beginning to learn
Registax and image processing) but I was pleased with
my first try at Jupiter and happy to catch Jupiter’s moon
Io transiting the planet. The Philips SPC900NC actually
produced a pretty good image – not quite as good as the
DMK but a lot less work. The colors and banding details
seemed sharper on the DMK image. Also, Io disappeared
on the SPC900NC final image but mostly remained on
the DMK image, albeit with a bit of color shift due to my
slowness with the filters.
Figure 6 — A comparison of Jupiter images
Finally, I chose a bright 18-day old Moon for another
comparison. For both cameras I just used a UV/IR blocking filter. It was not ideal conditions with poor to average
seeing, although the skies were crisp and clear due to a
cold front passing through the day before. I picked a couple of interesting features to try out each camera. The live
image at 1/30th of a second exposure rate was a boiling
mess most of the time but there were some very brief
moments of stable images. I recorded about one thousand frames for each camera on each feature. I eliminated nearly half of the frames in Registax and processed all the video files in a similar manner with minimal
post-processing. Different capture programs were used
as mentioned earlier, so exposure settings were not exactly the same, but pretty close. I was surprised to see
such a good result from the Philips SPC900NC. I have
done quite a bit of lunar imaging previously with the DMK,
but never with the Philips webcam. On this night the
SPC900NC performed very well in poor imaging conditions with final images just as good, if not a little better
than the DMK. My past imaging efforts with the DMK
were much, much better, so it may just be a case of poor
seeing leveling the playing field.
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AstroPhoto Insight December 2007
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when the seeing is good. My DMK is a keeper that will
remain an important part of my imaging setup for a long
time.
I mentioned earlier that the SPC900NC had already been replaced by multi-megapixel CMOS imagers.
This seems to be the trend as CMOS performance gets
better and better, while the sensors get bigger and bigger. Eventually I’ll get my hands on some of these newer
CMOS webcams and see how they stack up. With these
sensors being mass produced much more than CCD’s,
the choices for astrophotographers should get more interesting & hopefully cheaper. I welcome that change, and
hope it helps us all enjoy this wonderful hobby even
more.
Figure 7 — A comparison of lunar images
Summing it all up
For anyone getting started in planetary imaging,
the Philips SPC900NC is an ideal entry point at a
very affordable cost. The convenience of a oneshot color webcam saves time in post processing
and requires very little investment in additional
equipment to get good color images. Basic software to support this camera is free and easy to
use. More advanced software like K3CCDTools v3
will get you many more additional features for not
much more money. Regarding its use as a guide
camera (the original reason why I bought it) I have
found that the SPC900NC probably won’t meet my
needs because guide star selection becomes difficult with the lower sensitivity and lack of a long exposure mode. However, there are instructions
posted on the Internet for a long-exposure mod and
it does not look too difficult. Some online shops sell
these cameras already modded. If not for the
(unplanned) purchase of a Meade DSI Pro, I probably would have performed the long-exposure mod
myself by now. I’ll still keep this camera around for
when I just want some quick color shots without all
the extra fuss of filters.
For anyone who wants to take the next step up,
the DMK series from The Imaging Source with their
monochrome CCD sensors offer more sensitivity,
better throughput performance, and awesome bundled software. Color imaging will require an investment more than the camera itself to get good results, but it’s worth it if you want the best images
possible in this price range. Larger apertures will
benefit even more from these cameras as the increased sensitivity should help pick out more detail
AstroPhoto Insight December 2007
Tim is a 1992 graduate of Purdue University with
a B.S. in Electrical Engineering Technology. He is
currently a senior project manager for the Intelligent Switchgear Organization, LLC. He has enjoyed observational astronomy and reading astrorelated books most of his life, but caught the astrophotography bug in 2006. Tim lives in Buford,
GA with his wife and many, many pets.
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