Jeff,

I have a 216XT and went through exactly the problems you did. It is a
learning process but now I am having a lot of fun with it. I just want you
to know, first, there is a light at the end of the tunnel and it is in focus
and full of real stars. Ok, enough of waxing poetic.

First, you didn't say how long your exposure was, but based upon your
results, I would say that it was too long for a moon shot (especially if you
are shooting without a neutral density, i.e. "Moon", filter). In other
words, your shots were overexposed. You will get results like that from
overexposed shots and the results are from a phenomenon known as linear
blooming, I think, which I will repeat again in the next paragraph. If you
shoot daylight or directly at the moon, first stop down your scope using an
aperture mask (an aperture mask is a fancy way of saying that you put a
cover over your scope except for a small hole that makes your scope aperture
smaller. This effectively increases your focal ratio also, but that isn't
important for this particular experiment except that it will reduce the
amount light coming through your scope and increase contrast). The SBIG
manual suggests (I got this info from the Meade customer service person of
all folks!) that you shoot through a pinhole aperture.

For my first outing, I shot a daylight shot into a shaded glen of trees
using an 80mm f/5 (Celestron 80mm WA, which I usually mount on top of my
bigger scope, a 10" LX-50 SCT f/10). My aperture mask was a piece of
cardboard taped over the front of the telescope with a hole in the middle
from a standard paper hole punch as you find in an office or school. My
exposure time was (if I recall correctly) about 1/100 second or less
(probably less). If you are shooting at the Moon, I would use similar
settings because the Moon (even harvest Moon) is extraordinarily bright and
the CCD is very, very sensitive. Your shots that you are describing are
exactly what I got when I was overexposing my shots (it is a linear blooming
effect that you are getting, basically, where the pixel wells are
"overflowing").

If you are using a larger aperture scope, such as an 8" or 10" SCT, you can
put a piece of cardboard with a very tiny, tiny hole in it to one side of
the central obstruction over the front of your scope to accomplish the same
type of aperture mask.

The Scotch (or Magic) tape method of trying to get an initial focus works ok
with daytime or Moon shots, but little else. You will get a rough focus
with it usually, unless you are lucky and get it perfect the first time. I
used the daytime shots to simply get used to the software and equipment and
get an idea of focusing. I also didn't have to worry about tracking
something. I also used the daytime shots to start setting up my parfocal
eyepiece. I found an eyepiece that works quite well without the extension,
but with the focusing collar.

Go ahead and do a dark frame for the daytime shots (although it may not be
necessary because of the significant contrast of the shots) just so you can
get use to how it works and the differences between the raw and dark frame
subtracted images.

My next foray into using this animal, once I got past the overexposing
stage, was to take my first night shots. In this case I used the 80mm
again, and shot on an undriven mount in order to get star trails. I really
didn't use the focusing mode, rather I just took a series of 15 to 30 second
shots into an area of the sky that had lots of stars (near, but not in the
galactic plane). I achieved focus rather quickly and was able to detect
very sharp star trails even without subtracting a dark frame, although
without dark frame subtraction I had the noise "snow" all over the star
trails. For my 80mm, when I achieved focus I marked the barrel of the
focusing tube with a pencil, as well as verified the focus of my parfocal
eyepiece. So now, for the 80mm scope I had two focusing references: the
parfocal eyepiece and the mark on the tube. I would later use a graduated
marking on my focuser for the 10" scope as a similar reference. The
parfocal eyepiece works in either scope (or any scope), by the way, since it
is... well... parfocal.

Another problem that I had, which you may encounter in Seattle also (I live
in Southern Louisiana), is the formation of dew on the glass cover over the
CCD chip. This happens where the humidity is moderate to high and the
ambient temperatures are relatively warm. You are, after all, cooling the
chip down significantly, so dew is a normal reaction. Symptoms of this
problem are: 1)You will not be able to achieve focus when your eyepiece and
markings say you are in rough focus and; 2) Your images may show either
linear blooming or just a whole lot of "snow", even more than a normal dark
frame. When these things happen, take your camera out and look at the CCD
chip. If there is dew, it will be visually evident on the glass cover over
the chip. If you run ambient temperature air from a hair dryer (set to the
"cool" setting) over the glass cover for a few minutes, you should be able
to visually see the dew retreat and disappear. Immediately put the camera
back in the telescope and your camera should remain stable from that point
on. If you change scopes, you may have to do it again. WARNING: Do not
run air over the CCD on the "Warm" setting from your hairdryer as this may
cause a "thermal shock" to the chip (I understand that Apogee has some
warnings about this). Use cool ambient temperature air. It will take a
while, but it should work.

It should be noted that if you take your camera out or change it, and you
are needing to also take flat fields (which I use for serious DSO imaging),
you will need to take your flat fields after you have returned the camera to
the telescope since there is a potential that the focal path has changed
slightly.

So, in summary, you are probably overexposing your shots and for the Moon,
need to also put an aperture mask over the end of the scope. Be aware that
after you get started and the CCD settles down to its low temperature, you
may have dew form on the glass cover to the chip. You may start getting
similar results to your overexposed images, or a lot of "snow", and you will
suddenly lose all focus. And, as always, before starting any imaging or
beginning calibration images, let the camera "settle down" into its
temperature setting (i.e., about 10-15 minutes).

I hope this helps. If you have any other questions, please feel free to
ask.

Clear Skies,
David

----- Original Message -----
Sent: Wednesday, October 03, 2001 1:49 AM
Subject: [M]: Problems with 216XT


> I took advantage of a clear night and the full harvest moon to try out my
> 216XT for the first time.
>
> I followed the CCD tutorial as described in the manual, using the "scotch
> tape" method to achieve focus before attaching the CCD.
>
> All the images were nothing but noise. Mostly like 50 vertical white lines
> about a pixel or two across. Sometimes nothing but black, but pressing the
> left/right arrow keys a couple of times would display solid white on the
> right 1/2, and solid black on the left 1/2 of the image. Nothing even
close
> to an image.
>
> I tried subtle focusing in and out many times, but the images were always
> pretty much the same noise.
>
> I had essentially the same results using MaximDL and PictorView.
>
> Any ideas? Just symptoms of poor focusing perhaps?
>
> Jeff
>
>
>

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