Paul's 20" dobstuff and his review of the telescope on Cloudy Nights:
I purchased the telescope in early 2022 as a
retirement present to myself. I purchased the mirror from Hubble
Optics, and the rest of the scope was custom built by Dennis at
Dobstuff. My reason for getting a 20” f/3.3 was because it was the
largest telescope that I could reasonably carry in my vehicle while
also allowing me to observe without a ladder or step stool. I love
the simplicity and ease of assembly of Dennis’ design.
How
good is the Hubble Optics mirror?
Very good. My only caveat is
that although the manufacturer claims that cooling fans are not
needed due to the sandwich mirror design, I found that adding cooling
fans significantly improved the views.
How well does a GSO
coma corrector work at f/3.3?
Well. I was concerned that it
would not work well at this fast focal ratio but I was pleasantly
surprised that it does work well.
Is it a big improvement over
my previous 14.25” telescope?
Yes! Objects are bigger and
much brighter. It is a big improvement. Many more objects are visible
as well.
What eyepieces do I use?
I love 100°
eyepieces and they are all I use; a combination of Explore Scientific
and APM. My lowest power 20mm eyepiece gives me a 5.5mm exit pupil
which is perfect for my dark adapted eye and it gives me a 1.1°
field of view. Then I go to 14, 9, and 7mm. Rarely do I ever go above
that since the 7mm gives me 263X magnification.
Does it fit in
my vehicle?
Yes, barely. I have a Honda CR-V and it barely
fits in the rear. I use some rubber straps to hold the altitude
bearings down during transport. Since the telescope is too heavy for
me to lift by myself, the included wheelbarrow handles are a must and
I use 7ft wheel chair ramps to load it.
Best
Feature:
Digital Setting Circles (Nexus-II with Sky Safari
Plus). These have really transformed my observing sessions as I can
find and observe so many more objects in one night. I find that I
don’t need a finder anymore. I just use my laser to find the
alignment stars and calibrate the setting circles at the beginning of
each observing session. I find objects that I want to look at using
Sky Safari running on my iPad and then slew the telescope until the
bullseye is on the target. The objects are almost always in the view
on the first try!
Disadvantages:
With an f/3.3 scope,
collimation is critical. As I move the telescope around the sky it
does not keep perfect collimation. Usually I collimate at a 45°
angle which is good enough for most deep sky objects from low to
medium power. But when I want to use high power on a planet or the
moon, I collimate right before at the location of the object in the
sky. With my barlowed laser collimator, this only takes me about a
minute to do.
In summary I am extremely happy with this
telescope and wouldn’t have done anything differently if I had to
do it all over again.
