Sky & Telescope - April 2025 - 66

Gear Improvement
Most cameras I've tested started out with a ½-inch to
1-inch circle, and then after adjustment, I was able to get the
circle of projected beams to less than ¼-inch pretty easy, and
with some care less than 1
rotation slowly, and keep adjusting the screw pairs until the
size of the circle is minimized. The first time you do this process,
it may take some time, but with repetition the routine
becomes more intuitive.
Testing Square and Non-symmetrical
Cameras
Some newer astronomy cameras today come in square housings,
and some have a sensor offset from the center of the
camera housing. Some older CCD cameras had more exotically
shaped bodies. To test these, mount a 2-inch focuser
tube on the top of a camera holder that's either 3D-printed or
scavenged from an extension tube or old Barlow. The camera
is then installed with its 2-inch nosepiece in place and
rotated in the focuser tube to perform the testing. Be sure
to include this additional offset when creating your sensor
simulator so that the laser is properly aimed.
If your camera has a built-in shutter, you'll need to connect
the power and USB to a computer to open the shutter
during testing. It's also advisable to remove external filter
wheels or off-axis guiders because they can introduce their
own tilt errors. If you trust your filter wheel to be machined
accurately, then move it to an empty filter slot with no
filters for the test. By routing the cables up and over the top
you can spin the camera about a full turn without twisting
the wires too much.
Final Testing at the Telescope
After aligning the sensor as best you can indoors, install
the camera on your telescope or camera lens to do a final
check by imaging a rich starfield and reviewing the result
on screen. Zoom in on the corners of the frame to have a
critical look at the shapes of the stars there. While field flatness
can also be measured by software such as PixInsight, or
/8-inch. Repeat the six-point camera
COLLIMATING ADJUSTMENTS Nearly all recent astronomy cameras
include three or four sets of push-pull screws to allow adjustment of the
tilt of the camera. Here the pull bolt is a larger cap screw than the push
bolt next to it.
CCDInspector, it's really what you can see at full resolution
in your images that matters the most.
With this simple, home-built alignment rig, you can
ensure your camera is going to give you the sharpest possible
images as long as your astrograph or camera lens is well collimated.
And if you do have an issue with a tilted focuser, you
can be certain you've at least eliminated the camera as the
problem and can address that issue separately.
It's a good idea to retest your cameras annually since
adjustments can loosen in normal use. With some practice,
you can test a camera and adjust it in less than 10 minutes.
The sharp images possible with a properly aligned camera can
be quite dramatic, resulting in photos that can inspire awe
and admiration from your family and astro-imaging friends.
¢ CHRIS SCHUR operates a pair of high-altitude observatories
in northern Arizona where he routinely pushes the limits of his
equipment. Visit his website at schursastrophotography.com.
SHRINKING CIRCLE Left: The first round of testing produces a wide circle, revealing sensor tilt. Right: After a few rounds of adjustments, the
circumference of the laser's path should become very small. At this point, your sensor should be parallel to the front plate of your camera.
66 APRIL 2025 * SKY & TELESCOPE

http://www.schursastrophotography.com

Sky & Telescope - April 2025

Table of Contents for the Digital Edition of Sky & Telescope - April 2025