Criteria Reflector Refractor CAT

Criteria

Reflector

Refractor

CAT

Cost

Cost least per inch

Cost most per inch

In the middle, not
as inexpensive as a
reflector, not as
expensive as a
refractor.

Image Quality

Can produce very
good to excellent
images

APO Refractors tend
to have the best
image and contrast

Can produce very
good to excellent
image

False Color

No false color

An ACHRO
refractor will
produce false color
on bright objects,
APO which cost
$$$$ will eliminate
false color

No false color

Contrast

Will have some
contrast loss do
to
secondary mirror

Refractors provide
the best contrast.

As the secondary
mirror tends to be
larger, the loss of
contrast is more
than the other types

Coma (seagull
shaped stars at the
edge)

Fast scopes (F5 and
below) tend to have
more Coma. A coma
corr
ector is needed
for visual

For visual generally
not an issue, for AP
will need a focal
reducer to eliminate
coma

For visual generally
not an issue, for AP
will need a focal
reducer to eliminate
coma. Coma is
more pronounced
compared to a
refractor

Collima
tion
(aligning of
mirrors or lenses)

Must be done
regularly

Usually never done,
may also be
impossible for a user
to adjust

Rarely needed,
holds collimation
well.

Mounts available

Alt
-
az, dob or
equatorial for smaller
scopes (under 8”)

Alt az and
equatorial, rarely
included in the cost
except for
inexpensive Achro
scope.

Alt az (up to 16”)
equatorial (up to
20”)

Largest Size
commercially
available

50”

8” (Note: Several
companies make
larger scopes to
order, the largest I
have seen is
currently 10”

)

20”

Eyepieces

Fast scopes need
Fast scopes need
SCT’s (F10+) are
good quality
eyepieces

good quality
eyepieces

very forgiving of
eyepiece quality.

Ability to do AP

Smaller scopes
possible, large scopes
on Dob mount are
limited to webcams,
long term ex
posures
are not possible. RC’s
are excellent for AP

APO’s have the
highest quality
image for given
aperture. Usually
recommended for
beginners.

SCT’s are not
recommended for
beginners, fast
Schmidt Newtonian
and Mak
Newtonian are
excellent imaging
scopes.