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Subject: [M]: RE: [MAPUG]: PICTOR 416/1616
From: Michael Hart
Reply To: mapug@shore.net
Date: Wed Oct 02 01:08:25 1996

On 9/29/96, Keven Dougherty wrote:

>Thanks to all who replied - my original posts on this must have not gotten
>through. I'm now wondering if those of you who have been succesfully using
>the Pictors have some tips they can share. The manuals are not very
>helpful, and the software is very much first generation and poorly
>documented. For example:

>- Determining exposure times...do you use the 'auto' feature and then take a
>another set of images with different exposure lengths manually determined?

The "auto feature" in PictorView 2.0 works, as does using experience with CCD
cameras to determine exposures. For bright objects, I take a 1 minute 2 X 2
binned image (light from 4 pixels combined). For dim objects, I take a 3 minute
2 X 2 exposure. I then use the PictorView utility to measure pixel brightness.
Since a CCD camera is essentially linear, if the area I'm interested shows a
brightness of 2,000 and the brightest object shows a reading of 10,000, I can
expose for at least 6-1/2 minutes before filling the wells. I can over-expose
25-50% before blooming occurs.

All this is similar to using a light meter on a SLR camera rather than using the
automatic averaging settings. This manual method allows me to set the best
exposure times for long exposures. While many objects can be imaged with
my 12" in 1-3 minutes, the "keepers" are those with adequate signal-to-noise
ratio (increases with longer exposures) and image scale (using conventional
wisdom f-ratios reduces exposure, but severely limits image information).

>- Dark frames... do you regularly take dark frames? If not, under what
>conditions do you?

With the PictorView 2.0 software, you can automatically take and subtract
dark frames. If you use automatic temperature (designated coldest in software)
control, you would want to use the automatic dark frame setting to enable your
dark frame to have the same chip temperature as the image. But, this means
a half hour exposure takes ties up the camera for 1 hour. For images of a few
minutes, I often use the auto setting.

For longer images, I manually set the chip temperature to match the
temperature of dark frames that I took earlier and averaged. The two stage
cooling in the Pictor 416/1616 allows a 40 degree C. differential. I manually
select a temperature setting that is about 30 degrees C. lower than ambient
which will produce the desired temperature at 75% power.

- Flat frames... same as above?

Flat frames are necessary for photometry and useful in situations where the
object brightness is close to background levels (such as in the city) and for
resolvable objects such as planets. Many CCD books say flat frames are a
must, since pixel sensitivity varies on the chip. My Kodak CCD chip has a
maximum of 5% difference and 1.7% difference in the center 2/3 of the chip.
Dust specs and optical induced variations are only 0.4% difference on my
setup. The ultimate way to take a flat frame is fairly complicated- 50-70%
pixel saturation through a diffused light source, 6 or more averaged to reduce
noise, use the same optical setup as the image, use the same exposure
for planets, etc. The raw image is then divided by the flat which corrects
pixel to pixel variations to about 0.1%.

Since optical induced variations amount to only .4%, I use a master flat
for about 1/2 of the images I take. I can't usually see the 1.7% change
averaged over 2/3 of the chip and often have to look closely to see a 5%
change over the entire chip. Flats for the Kodak KAF series CCD chips
should probably be considered optional. Still, I use flats for my keepers.
I can't imagine how one would implement the automatic flat setting in
PictorView 2.0 at a star party.

>- File types...I have discovered incompatiblility in some of the file types -
>fo you have a preference when saving an image in one type or another?

For full compatibility, save as or convert to a 16 bit tiff file. The fits format
used by PictorView 2.0 is non-standard, but records image info such as
temperature and optional user details.

- Mosaic's... any tips for making these work well? Also, it appears you
can't image process the component images in IP2000 - any ideas?

For fun, I took a mosaic of the moon last night. PictorView 2.0 stores
mosaics as individual images with index files to tell the software what
files to load. Basic contrast stretching can be done in PictorView 2.0
on the complete mosaic image. Change the .m_ extension to .tif and
open as an 8 bit file in IP-2000. Process the individual images and
assemble with a good high end program such as Micrografx Picture
Publisher or Photoshop.

I "stitched" together six images in 10 minutes that look like one big
image. The result looks VERY good. I may consider some of the large,
bright objects that I usually photograph with a camera.

>- Motion calibration / Head rotation... can you just do the head rotation and
>go with the motion calibration it performs as a second step?

Motion Calibration calibrates the Pictor to the scope setup. It tells the
software how far to move the YOUR scope and in what direction.
Successful motion calibration enables the Pictor to auto-center,
mosaic and autoguide. Done improperly, the Pictor will behave poorly
when accessing features that depend on motion calibration. Done well,
the Pictor will seem amazing! For best results, orientate the Pictor
parallel to the declination axis.

Motion calibration of the Pictor should be done using a moderately
bright star at the declination you intend to image at. For general use,
point the scope at a star opposite Polaris at about 45 degrees above
the horizon. Too bright a star will cause blooming and errors, too
dim will increase calibration times considerably. Watch the Pictor
control box for frequent exposure and direction changes which
indicate all is well. In a few minutes, the software will indicate
successful motion calibration. This information is permanently stored
and includes head orientation information.

Head rotation is used tell the Pictor software where the head is
oriented. You will need to do this to enable features such as auto-
centering. You DO NOT have to perform motion calibration unless
you are imaging in an area significantly higher or lower than where
you last motion calibrated the Pictor.

>- IP2000...many many questions, but just for starters, when you first load a
>file, you get the histogram window that has several options before the image
>is displayed, like std dev., threshold, min/max, full scale. These appear
>to not be documented ibn terms of their effect on subsequent processing,
>although they do change the data. Any thoughts?

If you haven't used image processing software before, you probably
feel intimidated with Spartan documentation. I HAVE used and own a lot
of image processing software. Probably the most important is histogram
equalization. You must adjust the image to enable your monitor to DISPLAY
it. Experience will serve you better than documentation- experiment and
read about CCD imaging techniques.

>This is just a partial list of questions I still have after some time with
>the 416 - and I wonder if a 'Useful Tips ' list would be helpful for others.
>I believe Meade could do themselves a great favor by improving the
>understanding of their products in this area, but perhaps I'm more alone on
>this issue. If there is an interest in doing so, I'd volunteer to assember
>everyone's suggestions / tips into a single document, but for now, I'd very
>much appreciate everyones' ideas on these and any other areas that they think
>helpful.

>Thanks in advance.

Meade is relatively new to CCD imaging. Meade's niche is producing good
performing equipment for a very reasonable price. Perhaps the new
7" Mak isn't optically as good as a Questar. Perhaps other CCD cameras
seem to work better due to design and/or extensive tech support. WordPerfect
used to offer UNLIMITED FREE technical support, but cost $500/copy.
Now, WordPerfect goes for less than $100 with little support. Meade
continues to be a leader in bringing good products to the masses for a
reasonable price.

Michael Hart
mhart@netexpress.net