Sky & Telescope - January 2025 - 65

at a 2.6-arcsecond pixel scale. Using 2× Drizzle processing in
PixInsight, the resulting pixel scale is boosted to 1.3 arcseconds,
and most stars look round when closely examined. I use
this imaging system for large objects, like the North America
Nebula, NGC 7000, or the Andromeda Galaxy, M31. For
wide-field, deep-sky images and for nightscapes, field of view
(how much sky fits on the camera sensor) is more important
than pixel scale, since the intention isn't to see individual
stars, galaxies, and nebulae up close. When the vastness of
the Milky Way or the foreground in a nightscape shot is most
important, image scale doesn't matter much at all.
Optimizing Your System
If you'd like to determine the pixel scale for your optics and
cameras, there's a great online tool that does the math for
you. The Astronomy Tools website hosts the CCD Suitability
Calculator (https://is.gd/CCDsuitability), which, despite its
name, also works with CMOS cameras. It lets you select from
many models of cameras and telescopes in dropdown lists or
input custom information about your equipment, including
camera binning and telescope focal reducers. Simply enter the
values in the calculator, choose your typical seeing conditions,
and the app immediately determines the pixel scale.
It also provides information regarding the suitability of the
setup for high-resolution imaging. It's interesting to explore
how various kinds of equipment or operational settings affect
pixel scale. The documentation includes a discussion of how
the Nyquist theorem is used (with slight modifications) to
complete the assessment.
Based on my own experience with a wide range of telescopes
and cameras, about 0.5 to 2 arcseconds per pixel
resolves the majority of small-scale detail that conditions
allow on most every clear night, assuming you have accurate
collimation, focus, and tracking.
Get the Most from Your Conditions
The quality of the data we acquire depends on things we
can control just as much as on things we can't. Local seeing
conditions are largely beyond our influence, but we can select
equipment to perform reliably given our specific situation.
Focusing on image scale when you next upgrade your telescope
or camera can help ensure you'll be able to get as much
fine detail in your photos as possible. And it will help you pick
a combination that can produce round, not square, stars -
even the tiny ones.
¢ Contributing Editor RON BRECHER currently photographs
the night sky at 0.4 arcsecond per pixel from his home
observatory in Guelph, Ontario. He displays his images at
astrodoc.ca.
GALACTIC SURFBOARD The spiral galaxy M108 in Ursa Major shows a wealth of detail in this high-resolution portrait recorded at 0.4 arcsecond
per pixel. Note the many pinkish HII regions and mottled dust lanes not visible in lower-resolution shots, as well as several much
farther galaxies visible in the background.
sk yand tele scope .o r g * JANUARY 2025 65

https://www.is.gd/CCDsuitability http://www.astrodoc.ca http://skyandtelescope.org

Sky & Telescope - January 2025

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