From: "Milton Aupperle" <milton@outcastsoft.com>
Date: July 26, 2008 5:04:43 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Preliminary Grasshopper GRASS-145SM-C Mono Camera Review
Hi Folks;
I just purchased a large format EXHAD Grasshopper Point Grey Research
Camera, the GRASS-145SM-C monochrome model. I'll likely be eating
craft dinner and spending zero money on anything but the basics for
the next 6 months, but it looks like it's worth the money (a bit under
$3K USD).
For size comparison, here are two pictures of the camera with a TIS
Mono Camera, a Flea2 PGR camera, the Grasshopper and a 1.25" eyepiece
(ruler in one shot has major dimensions in centimeters).
http://groups.yahoo.com/group/Astro_IIDC/files/Other/TIS_Grasshopper_Flea2Top.jpg
http://groups.yahoo.com/group/Astro_IIDC/files/Other/TIS_GRASSHOPPEr_FLEA2_Side.jpg
The GRASS-145SM measures 44x29x58mm in size, weighs about 3 ounces,
has two FireWire 800 / 1394B interfaces (also works with FW400 / 1394A
cameras too) and uses a Sony EXHAD ICX285 2/3" 6.45 micron square
pixel CCD. This is the same CCD used in the StarLight Express HX9
series of cameras, except it runs at much higher frame rates via
FireWire (runs at up to 15 fps in 16 bit mode at 1384x1036 pixel
sizes). The A/D converter delivers 8 or 16 (14 bit true) video and
sensitivity wise, it should be about 250% more sensitive than my color
Flea 640x480 Super HAD camera. Here is more technical information on
the Grasshopper camera from Point Grey Research:
http://www.ptgrey.com/products/grasshopper/index.asp
The Camera has Region of Interest control, so you can set it to any
size you want from as small as say 64x64 pixels to as large as 1384 x
1036 pixels. The Gain / Brightness control run from 64 to 746.
I've only run some preliminary dark frames tests so far, as the camera
only arrived yesterday. My main concern with the camera was how much
the amp glow will affect imaging, which has been an issue with the
Flea and the Flea2 cameras when I exceeded about 5 minute exposures.
My first test was not very encouraging, as shown in this first test image:
http://groups.yahoo.com/group/Astro_IIDC/files/Other/GRAS14S5M_Uncooled5MinExpGain64.jpeg
However I had been running the camera at 15 fps or faster initially
for about 1 hour, so the camera was "warm" at around 30 to 35°
centigrade. At higher temperatures it's not that unexpected to see a
lot of noise and hot pixels for longer (>30 seconds) exposures. For
live imaging in 16 bit mode the quality should be really great. I
should be able to do some nice large UV cloud imaging with it of venus
and also some very fast imaging of Luna and the Planets at high frame
rates.
I then attached my "Mark2" peltier camera cooler (see images of it in
the AstroIIDC Files "Other" folder) and cooled the camera down to
around 15 degrees centigrade, which is about 12 degrees below ambient.
I then put the camera in a dark closet and wrapped the lower end of
the camera in a dark cloth so that there was no ambient light hitting
the sensor. I attached a digital thermometer sensor to the camera case
to monitor the camera's external metal case temperature.
This first cooled image is a 4 minute dark frame and the camera case
was 19 centigrade.
http://groups.yahoo.com/group/Astro_IIDC/files/Other/GRAS14S5M_4MinExpos200Gain19C.jpg
Notice that there is virtually no amp glow (completely even image
background) and other than a hand full of hot pixels the image looks
good. For comparison's sake, have a look at the uncooled and cooled
results for my Flea Super HAD color camera as show in the last 3 pages
of this .pdf file.
http://groups.yahoo.com/group/Astro_IIDC/files/Other/Cheap_Peltier_Camera_Cooler_MJA.pdf
I then tried a cooled 8 minute exposure
http://groups.yahoo.com/group/Astro_IIDC/files/Other/GRAS14S5M_8MinExposGains20018C.jpg
and then a cooled 15 minute exposure.
http://groups.yahoo.com/group/Astro_IIDC/files/Other/GRAS14S5M_15MinExpos200Gain19C.jpg
In the 15 minute exposure, you can see that there is a small amount of
background glow on the upper left corner, which rises to around 6,200
out of 65,535.
I also ran a 20 minute test, which has slightly higher noise, but much
less than my Flea camera would ever do.
If the weather cooperates (thunderstorms now and rain tomorrow) I
should be able to do my first light tests on an astro object early
this week week and will post my results.
I expect that when using it during the summer outdoors (ambient temp
20 to 10° centigrade), I should be able to get the camera down to the
0 to 5° Centigrade range which will drop the hot pixels and other
noise even lower. During the winter (-10° to -25° ambient temperature)
noise will not be an issue at all. This camera would be ideal for a
HyperStar system (something I'd love to have if I win the lottery)
during the winter months as it will block less light than the
secondary would.
I'll keep you all posted on my progress.
Milton Aupperle