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Posts Made By: Dick Jacobson

March 12, 2003 12:04 PM Forum: Deep Sky Observing

Best way to cool down a scope?

Posted By Dick Jacobson

When I will be observing from my driveway, I take my 14" Newtonian outside just after sunset, uncover the front end, and point a 12" desk fan at the open back end blowing at high speed. This seem to work very well; by the time it's nice and dark, the mirror is nice and cool.

April 7, 2003 12:34 PM Forum: Equipment Talk

Discovery trip report

Posted By Dick Jacobson

I think there will soon be a better alternative to solid tubes or truss tubes. I sawed the tube of my 14" in half, attached a couple aluminum bars, and ended up with a scope that snaps together in seconds and avoids the complications of a truss tube. More details are in the Dobsonians forum.

April 14, 2003 11:19 AM Forum: Telescope Making

Truss or tube?

Posted By Dick Jacobson

For a 10" scope I think a solid tube would be preferable, though f/8 is very long and cumbersome. I've owned 10" f/5.6 and 14" f/4.5 solid tube scopes and have been very happy with them, never any dew problems, easy to set up though quite an effort to lift and carry. I've never owned a truss scope so can't claim to be an authority.

About a year ago I sawed my 14" Sonotube in half, attached some aluminum bars, resulting in a much more portable scope that snaps together in seconds, doesn't need alignment, and is simpler and cheaper than a truss. I think most scopes in the range of about 10 to 16 inches will be built this way in the future. There is some more discussion of this in the Dobsonians forum.

April 15, 2003 09:03 AM Forum: Telescope Making

Piano wire spider

Posted By Dick Jacobson

I've thought about using videotape but have never tried it. Vibration could be a problem.

April 25, 2003 07:25 AM Forum: Telescope Making

What Size Mirror to Purchase (Make)?

Posted By Dick Jacobson

I love my 14" f/4.5 Newtonian from Discovery Telescopes. It's short enough to observe at the zenith while standing on the ground. The Sonotube was pretty heavy at 87 pounds so I sawed it in half, attached some aluminum bars and came up with a more portable scope that snaps together in a few seconds (see some discussion in the Dobsonians forum under "Tube to Truss"). Globular clusters are gorgeous; galaxies are still rather faint at this aperture. I previously had bought a 6" Mak-Newt for planetary observing but have found that the 14" usually does better.

June 11, 2003 08:33 AM Forum: Equipment Talk

Straight Correct Image Finder

Posted By Dick Jacobson

I don't know of any 9x50 straight correct image finders, but I made a similar one out of an old pair of 7x35 binoculars. In my opinion, it far out-performs any finder on the market (though a larger aperture would be helpful). It took a fair amount of tinkering, and since the binoculars have no cross-hairs I drilled a hole at the focal plane and inserted a small screw to mark the center of the field. The screw is easily visible in dark skies without illumination. If you're interested, I could write more details.

I've used conventional (inverted image) finders and a Telrad; it seems to me that the correct-image straight-through finder combines the best features of both. You can see much fainter stars than with a Telrad, yet can easily relate the finder view to the naked-eye view or the star atlas (held right-side-up).

June 16, 2003 10:17 AM Forum: Telescope Making

cutting aluminium

Posted By Dick Jacobson

Harbor Freight Tools sells a special metal-cutting bandsaw for $200. It works great on steel and aluminum. The blade runs at a much lower speed than a wood bandsaw, which is what you need for cutting metal without a coolant or lubricant.

June 17, 2003 10:28 AM Forum: Telescope Making

HVHC Plywood

Posted By Dick Jacobson

Rockler Woodworking sells "Finnish Birch" which is a high quality hardwood core plywood. I see they have a store in St. Louis. They sell it only in 24" x 30" sheets or smaller. I used it for an equatorial mount; it's beautiful material and well worth the high price.

June 19, 2003 10:43 AM Forum: Equipment Talk

Vehicle Recommendations

Posted By Dick Jacobson

VW Passat Wagon. 30+ MPG, great handling, solidly built, roomy on the inside yet compact on the outside, highly rated by Consumer Reports and other magazines. AWD available if you need it (I don't, even in Minnesota!) On the negative side, more expensive than some competing wagons.

Wagons in general are great for hauling long narrow things like telescopes. Lower floor height than some other vehicles so lifting is easier. If you need to carry something on the roof, wagons are ideal because you don't need to lift as high and the center of mass is lower.

July 28, 2003 11:01 AM Forum: Equipment Talk

How I avoided aperature fever

Posted By Dick Jacobson

Couldn't resist jumping in on this to brag about my 14" split-tube scope. About a year ago I sawed my 87-pound, 14" Discovery in half. Attached a couple of aluminum bars; now the two halves snap together in a few seconds, no collimation needed. Granded, the lower half is still hefty at 67 pounds but it's an awful lot easier to handle than the original tube. I can load it in my car without lifting the weight of the mirror (see photo). I also built an equatorial mount; the original cradle is on wheels and is used now only for storing the scope and wheeling it around the garage and driveway.