Sky & Telescope - April 2025 - 71

ideal benefit as well because putting one
of these filters in line changes the back
focus by the thickness of the filter's
glass, usually about 1 mm or more.
All this sounds like it would be quick
to dial in and start imaging, and I had
a full-frame color camera on hand that
I was anxious to try with this scope. In
practice I found that I had to experiment
quite a bit to find the optimal spacing
with both adapters. I made sure I started
with the minimum recommended spacing
of 55 mm between the camera and
the reducers. I anticipated adjusting the
spacing by as much as 1 mm when using
with an UV/IR blocking filter or a light
pollution filter. However, I had to spend
a good bit of time adjusting the spacing,
refocusing, and then evaluating the
corners of images to see how the change
affected the star shapes. Corner stars
showed significant distortion initially,
looking bloated and cross-like rather
than round. The goal was to minimize
these to acceptable levels. With each
spacing change, refocus was necessary
and, just like finding focus, I could
clearly see the correction in the corners
of the images get progressively better,
and then start getting worse.
This brings me to the performance
of the scope with a full-frame sensor.
The scope is described as capable of
illuminating a full-frame (24 × 36 mm)
detector, but marketing being what it is,
you may not get quite what you expect.
I would say the scope's corrected field
coverage is closer to full frame than to
a cropped sensor, but it's no match for
any of my premium refractors. I could
adjust the spacing such that stars at the
edges of the field were close enough to
being round that they could be corrected
with software in post processing
or cropped out after stacking. This
level of performance was the same
with both reducers, although the 0.75×
flattener was substantially better than
the 0.92× model, most likely because it
was designed specifically for this scope
rather than for a range of optics. The
stars in particular degrade quite rapidly
at the very corners where you can see
chromatic aberration and distortion.
Again, this is only in the extreme corners
of the field of view.
I also tried the scope with a monochrome
sensor, though not a full-frame
unit. I used the Player One Poseidon-M
with an APS-C-size detector and did
some imaging with a Chroma 3-nanometer
hydrogen-alpha filter. The 28-mm
wide field was well-corrected from
corner-to-corner. No optical distortions
were visible at all in this smaller field.
Final Thoughts
For visual use, the Airy Disk 106mm is
a fine scope. The build quality and the
focuser are excellent, and the instrument
looks and feels like a high-quality
telescope. The views were quite satisfactory
to me as well, and better than
many refractors I've tried at this price.
For twice the money, the next tier of
refractor quality will give you a solid
and noticeable incremental improvement,
but certainly not twice as good.
As an astrograph, I did find the " full
frame " claim to be a bit of a stretch,
particularly with the 0.92× flattener.
The horizontal and vertical edges from
such a sensor were decent enough and
can be easily corrected in processing.
Both the optional 0.92× flattener / reducer
(left) and 0.75× (right) have built-in extensions
with index marking that allow precise adjustment
of the spacing between your camera and
the rear element of the corrector.
The corners, however, were truly bad
on the 0.92× flattener, showing badly
distorted stars. Corners with the 0.75×
reducer were much better but not
perfect. On the other hand, if you typically
work with smaller sensors, this
is an excellent scope even with these
limitations. Given that it's one of the
lower-cost refractors of this size on the
market, I'd consider it a great value.
¢ If Contributing Editor RICHARD S.
WRIGHT, JR. could only keep one telescope,
it surely would be a high-quality
refractor.
This image of The Andromeda Galaxy, M31, was captured with the Airy Disk 106mm and dedicated
0.75× reducer and a full-frame Player One Zeus camera. With this combination the outer 1/8
of the field required some cropping to remove distorted stars in the corners of the frame.
sk yand tele scope .o r g * APRIL 2025 71

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