Showing posts with label weight. Show all posts
Showing posts with label weight. Show all posts

Monday, July 18, 2011

Counterweight

With the vast variety of accessories, starting from a different weight eyepieces, the OTA center of gravity might shift considerably towards the open end. Which is often perceived as the altitude bearing failure and usually addressed by a sort of adjustable braking system over the altitude semi-axes hubs, plus a habit of applying and undoing it. In my opinion  that just consumes observing time and neglects the dobsonian construction principle: "simplicity - first".

Luckily enough the Zhumell Dob OTA material is a plain steel which is naturally ferrous. The solution came in a snap. An old steel (also ferrous) counterweight scavenged from my old cheap refractor mount (4.2 lbs), a couple of strong neodymium magnets harvested from a broken hard drive, and a stripe of blue masking tape for scratches prevention - all were sticking to each other almost by themselves.

Thursday, July 7, 2011

My Zhumell 12" dob specifications

Apperture - 305 mm (12 inch)
Focal Length - 1500mm
Focal Ratio - f/4.93
Star Diagonal - 1.25 Inches (32 mm)



Finderscope - 8x50
GoTo - No

Weight Complete - 75 lbs (34 kg)
Total height - 63 inches (160 cm)
OTA length - 60 inches (152.5 cm)
Base height - 27 inches (68.5 cm)
Base diameter - 25.5 inches (65 cm)


Aperture Gain - 1900
Visual magnitude limit - 14.2
Max FOV - 1.9 deg
Resolution - 0.38 - 0.68 sec
Maximal Magnification - 300
Optimal Magnification - 150
Minimal Magnification - 42
Absolute Maximum Magnbification - 750


See the great Telescope Equations site for the underlying theory and formulas.