Thanks, Mitch... "fmhill"
Ken Fiscus Stargazing since 1980 Now observing from a green zone. Z12 on custom mount, Atomic EQ platform, 100% flocked, OMI primary, Astrocrumb filter slide with O-III, NPB, Skyglow filters. Focuser & spider rotated 45 degrees, new springs & Bob's Knobs, Telrad & 9x50 straight finder 35 & 24 Pans, TV 13,7,5 T6s Custom Orion XT10 with piggyback XT4.5 Round Table EQ Platform
Quote:"I'm wondering about the feasibility of building an equatorial mount for a dobsonian telescope."
14" f/4.8 Obsession Clone w/ ServoCat/ArgoNavis Apogee RA-88 Binocs
Equatorial Newtonians, 20" and 14" "The purpose of life is to be defeated by ever greater things." - Rielke
LX200 ACF 10" Antares 105mm 10 " DOB Home built Canon T4i New Observatory...Norse Star....
The Cheapest Astronomer in the World gets excited by Jupiter. Builds dob, builds eq platform, arranges to borrow webcam...
Quote:I'm wondering about the feasibility of building an equatorial mount for a dobsonian telescope.
Quote:A major reason that Alt-AZ mounts have become so popular for all types of scopes over the last 30 years is because they are more comfortable to use, eyepiece orientation does not change, the observer does not get tangled up in the mount the way can with a GEM or fork mount.
Quote:Quote:A major reason that Alt-AZ mounts have become so popular for all types of scopes over the last 30 years is because they are more comfortable to use, eyepiece orientation does not change, the observer does not get tangled up in the mount the way can with a GEM or fork mount.Agreed that alt-az mounts are more comfortable than an equatorial without a rotating tube. But once you have a rotating tube, it's a tremendous convenience. On my 14" Newtonian pictured above, observing positions are comfortable no matter where it is pointed. If the eyepiece is a little low or high, just rotate the tube a little (obviously this doesn't work at the zenith, but the zenith height happens to match my standing height closely).
Quote:I see two problems with the split-ring or horseshoe mount. The first is size. On the JMI split-ring scopes, the outer diameter of the ring is twice the mirror diameter and it's hard to see how it could be made smaller. This impairs portability and the ring can get in the way when observing near the zenith. The second problem is that the ring restricts the length of the mirror box. This can make it difficult to balance the scope without using counterweights behind the mirror. Ball scopes have the same problem. The 200-inch Hale telescope gets around this problem by suspending the tube from an additional pair of arms, making it even larger (500 tons of steel, not a problem if you don't have to load it into your vehicle!)For these reasons, I've chosen to use fork mounts for my big Newtonians, like the 14" pictured above. The outside width of the fork is about 50% greater than the mirror width. Within limits, you can make the fork as long as needed to balance the tube and provide enough range below the equator. They probably don't have as much stability as a split-ring or Dob, but vibration is low enough that it is not a significant problem.
Quote:It's been really great reading all the comments and ideas presented in this thread because I am evaluating my options for "equatorializing" my 20" f/4 Obsession. Thanks!
George RoffeKingwood, TX