Posts Made By: Doug Tanaka

Rob, I was waiting to see whether anyone would answer your specific question, but since no one has, I'll give you what info I can. I don't have the 7mm S-W, but I do have the 5mm-8mm variable S-W. I absolutely love this eyepiece. The only comparison I can give is to a 5mm Takahashi LE and a 7.5mm Tak LE. The Taks are brighter, with the color of both Jupiter and Saturn closer to white, while the S-W is closer to a yellowish tan. But I can't discern any difference in detail. I live in the Pacific Northwest and rarely get skies steady enough for a serious test, but I did get one really steady night last year when I was able to see the festoons between Jupiter's N and S equatorial bands and the view was the same in both. In fact, I preferred the S-W because it wasn't as bright and therefore more comfortable. Another reason I preferred the S-W is because I use it in a 12.5", f/6 Dob and the AFOV of the Taks is pretty small, so I have to move the scope a LOT! The wide FOV of the S-W is such a treat, although it isn't quite as sharp at the edge (but the Taks have zero there so who cares).

I have heard that the S-W line requires a little more in-travel to reach focus than your normal eyepiece, so be forewarned. The only eyepiece I have that requires more in-focus travel is a 10mm Nikon adapted from a microscope eyepiece. The S-W is also pretty long, so it looks pretty odd, and rather heavy, although I don't know about the 7mm. Hope this helps.

Doug Tanaka

Today marks the tenth anniversary of the death of Robert Burnham Jr. For those who have never done so, read the article at

http://www.phoenixnewtimes.com/issues/1997-09-25/feature.html/page1.html

Let's pay tribute to a man who gave amateur astronomy so much and got back so little.

Doug Tanaka

I don't know what you'd do with other scopes, but I was concerned about the same thing with my 12.5" Dob. In the past my primary mirror would ocassionally dew up but once I mounted two small fans to blow air over the surface it has never dewed up. This worked so well that I decided to do the same with the secondary mirror. I had a homemade system using resistors but was concerned about the heat. On really bad nights it would still dew up. I mounted another small fan next to the focuser, pointed at the secondary, and haven't had any dew since. To me it's the best solution because it also gets the optics to ambient temperature faster.

Doug Tanaka

The only thing I might be able to help you with is the epoxy issue. Quick set epoxy doesn't bond well and doesn't get much stronger after about 15 minutes. It's great for some things but not for what you're doing. I'd try using JB Weld. It has a longer cure time and sets much harder. You should probably make sure the mating surfaces are really clean by wiping with acetone to get rid of any traces of oil (like from your hands). Good luck.

Doug Tanaka

Rob,
I also have a 12.5" f/6 with a curved spider and have glued the secondary with silicone adhesive. I have rebuilt the spider assembly twice (from curved vanes to wire and back to curved) and from experience the silicone is a bear to remove. My only concern for you would be how the silicone adhesive will adhere to the semi-endgrain of a 45 degree cut dowel (mine is glued to carbon fiber). To be safe I'd sand the cut smooth, apply a thin coat of slow-set epoxy and then lightly sand again when the epoxy cured. This would give a better surface for the silicone to stick to.
Make sure to clean both surfaces with acetone before gluing, to remove any oils that may have come off from your hands. You might also want to glue a piece of string to the back of the secondary mirror and loop it or tie it to the spider (inside of the secondary's shadow) for your own ease of mind. I did this when I first built my scope but on the last rebuild I omitted it when I realized how strong the RTV adhesive really is. Good luck to you.

Doug Tanaka

Just about everything you need to know can be found at Chuck Shaw's website and Jan van Gastel's website .
I'm just putting the finishing touches on my own platform, built from the info on these sites. One main difference in my approach was how I made the conical sectors. Once I figured out the circumference I cut them straight using a circle cutting jig on a bandsaw, then I cut the angle to match my latitude using a tablesaw. The arc was smooth enough off of the bandsaw that I could glue an aluminum strip right to it without any sanding. It saved the time of making a jig for the whole platform and trying to true the sectors with a belt sander. Good luck on your project.

Doug Tanaka

Stuart,

I made a baffle using black ripstop nylon. It is very lightweight. For support I sewed in some 1/8" bamboo-like reeds. The whole thing weighs almost nothing and when I'm done for the night it rolls up into a very thin tube that fits into my eyepiece case.

Doug Tanaka

John,

I live right across from you on Bainbridge Island and use a 12.5" Dob. Granted it's darker over here, but I also use it in Vancouver, BC which blows Seattle out of the water for light pollution. You should get in touch with the Seattle Astronomical Society, . They have over 200 members and when the weather is clear they hold star parties at Green Lake, among other sites. Right, good luck this time of year.

Other than the fact that the 4" APO would be more grab-and-go, the 11" StarMaster would give the better views. Good luck.

Doug Tanaka

Dan,

I live in the Pacific Northwest, too, and have hooked some resistors to a 3.5" ETX. I took a wild guess and shot for 3W for the objective and on most nights this was fine, although dew would build up on really bad nights. Based on that, if I were you I'd go for about 5W on the objective, especially if you can control the heat (for that matter you might want to make it 6W).

For eyepieces 1.5W seems to be OK, but I tried going up to 2.5W and found that it didn't hurt the image at all (possibly because the heat is at the end of the optical train). The added bonus is that observing when it's freezing or below makes for a very cozy eye socket!

Doug Tanaka

The on/off knob is a variable pot that should intensify the light the farther you turn it from the off position. If you have a volt/ohm meter you could check to see that it actually works. Is this a new unit? If used, perhaps the battery was replaced by one with a higher voltage so the light is always on max. The size of the dot remains about the same, although max brightness does make the dot appear slightly larger.

Doug Tanaka