Paul's 20" Dobstuff Telescope .. A Review

 

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.