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Posts Made By: David Tarshis

January 24, 2004 10:40 AM Forum: Film Astrophotography - Imaging and Processing

Power at prime focus?

Posted By David Tarshis

What would be the power of my ed80 with a OM-1 at prime focus? I know how to do this with eyepieces, but don't have a clue with a camera. Thanks.

January 25, 2004 09:27 AM Forum: Film Astrophotography - Imaging and Processing

Adapter?

Posted By David Tarshis

I have a meade t-adapter that will fit my sct. Is there such a thing to adapt this to a refractor, or will I have to buy a new t-adapter (om-1/ed80)? Thanks

March 13, 2004 09:49 AM Forum: Equipment Talk

Sliding counter weight for ed80 on Bogen 410?

Posted By David Tarshis

I would like to be able to balance my ed80 on my Bogen 410 head (3233 tripod). Is there such a thing? Or what else can I do? I do have rings and rail from Orion. Thanks.

March 27, 2004 12:18 PM Forum: Equipment Talk

Planner?

Posted By David Tarshis

I am going after all the Messier objects. I have Starry Night backyard, and it works ok, but my question is, is there a planner out there the will suit my needs. Is it worth the upgrade to SN pro? I just came back from a vacation from semi dark skies and was able to bag some messier's that I haven’t been able to see from my light polluted house. After coming back home and going to the computer, I realized that I probably could have done better if I had some kind of plan. I missed a lot of objects just not knowing what to expect at the eyepiece. I took my travel scope (ed80) and left the 9.25 at home. I had my atlas 2000 and some charts I printed from SN backyard. I guess what I'm looking for is something that can tell me what messier's to go after for the time of year, and what magnitude the objects are so I don’t skip over them like I'm sure I did. I caught m3, 94, 51, 65, and 66 the other night with no problem. It was 101, and the grouping abound m80 I had trouble with. Ursa minor was not visible to the naked eye, but Kocab and Pherkad were visible. Well, maybe not so dark sky, but better than where I live. I’m using Pentax ep’s, 10.5, 14, and 21 with a 2.5 powermate and a 9x50 CI Orion finder. I also have some Ultima’s 18, 35, and 42. I was at Eagle Crest Resort with the wife and kids, just a few miles from Redmond Oregon. The nights were clear, don’t know quite how to judge transparency and seeing yet. Still trying to get a feel for judging magnitude as well. That’s why I mentioned ursa minor. Thanks Dave

April 8, 2004 10:30 AM Forum: Equipment Talk

Which camcorder?

Posted By David Tarshis

My son broke our 10 year old sony camcorder on xmas. He's 2, how mad can you get. So now I'm in the market for a new one. I've seen some of the pics here people have done with "hand held" cams. Very nice. Does it make any difference what camcorder? Is there one that works better in low light than the next? Any pointers when picking one out? Thanks DaveT

April 9, 2004 10:05 AM Forum: Telescope Making

About to make my first scope with John Dobson

Posted By David Tarshis

I'm taking a class here locally with John Dobson sitting in. Very cool. I choose a 12-inch mirror to polish. I guess I can make any f/l I want. My question is, what would be criteria for choosing the right f/l? I already have a Orion ed80 and celestron 9.25. Thanks DaveT

April 14, 2004 11:59 AM Forum: Equipment Talk

Need parts for controller

Posted By David Tarshis

I have a vixen controller thats not working. I'm looking for someone who might have one thats not working, tucked away thats forgotten about that they want to get rid of (for a reasonable price), thanks. Here is a pic of the controller I have:
http://www.astromart.com/viewad.asp?cid=264158
I have placed an ad in classifieds, if this is too redundant, I'll remove this post. Thanks DaveT

April 17, 2004 01:27 PM Forum: Telescope Making

April 22, 2004 09:33 AM Forum: Telescope Making

First night with John Dobson (long)

Posted By David Tarshis

Please be patient, English was never one of my better skills. But I will attempt to post my progress on my 12.5 mirror here. Tuesday night was the first night. We all gathered in the basement of a church. This church is in rural Battleground, Washington. It is converted to an astronomy shop. The only one in greater Portland. Seans Astronomy Shop. We had made these benches to grind on. I sit low enough on it to allow my body weight to add pressure as I grind. I straddle the bench with the mirror in front of me. My good friend Dan and I arrived in the rain, slightly late, with these bulky benches, (they’re small enough to fit two of them in the back of Dan’s Civic). We go down these stairs, with benches in hand, there is about a dozen or so people with these home made benches of all different styles, getting situated, looking for a good place to set up, and there in the middle of the room is this little old man, white hair in a pony tail, helping people set up their benches. This is John Dobson. He looks like a ‘60’s throw back. He’s all of about 5’6-8”, 100 lbs dripping wet. His pony tail splits his shoulders. After I pay up and get my mirror and tool, I get the wrong size and have to wait my 12.5. Dan is doing an eight inch mirror. While everyone is securing the tool to their bench, John want’s the attention of the room. At first people are eager to hear his words, and the room quiets. He starts out with a couple of instructions, and a couple of stories. I get the feeling that no one here has ever done this before. The instructions are quick and short. He ask’s if there are any questions, and it’s quiet as a church, or in this case, a church basement. After about a minute, the questions start. Someone asked about “dunking”. I didn’t hear the whole question, but I did hear the response, “these aren’t doughnuts, these are mirrors”! We get turned loose. (cont)

April 24, 2004 01:07 PM Forum: Telescope Making

Mirror grinding question

Posted By David Tarshis

I'm in the rough grinding process of my 12.5 (60 grit). I am one inch from the edge. When I check the f ratio I get about a f6.3-6.9. I am using 2 methods. Sun check I get 67 inches, which calculates to f6.3, when I do a sagitta check, I get about f6.9 [F = r²/(4D)], D=. 095 r=5.25 (I’m only calculating the part of the mirror that has been ground, approx 10.5) which comes out to f6.9. My question is, when I go to parabolize, does the f ratio change? I want about f7-f8. I was told to go the depth of a dime and a penny (.110). Do I keep grinding with the 60 with the MOT until I get the .110? If I do, I’m afraid the f ratio will be to fast. My next class is Tuesday night, I was wanting to keep up with the 6-10 inch mirrors that are done with the rough grinding. I elected to do some grinding outside the class. I don’t want to have to go back and correct any errors so I’m asking the experts here. I am also using a 10 inch tool. Don't know if that is going to make any difference. Thanks, DaveT