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Equipment Discussions >> Refractors

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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: You ever go to the Reflector forum by mistake? new [Re: csrlice12]
      #5545306 - 11/29/12 10:51 AM

Quote:

Just remember, they come over here looking for finderscopes.......




Only if "they" are looking for a modest sized finder scope.

A good sized finder scope

Jon


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snommisbor
scholastic sledgehammer
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Reged: 06/15/09

Loc: Cedar Park, TX
Re: You ever go to the Reflector forum by mistake? new [Re: Jon Isaacs]
      #5545372 - 11/29/12 11:35 AM

Zowie!!! You need a cherry picker to observe with that. I bet that pulls in some detail.

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Jon Isaacs
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Re: You ever go to the Reflector forum by mistake? new [Re: snommisbor]
      #5545383 - 11/29/12 11:44 AM

Quote:

Zowie!!! You need a cherry picker to observe with that. I bet that pulls in some detail.




The 12.5 inch Finder is probably no slouch either..

Jon


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csrlice12
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Loc: Denver, CO
Re: You ever go to the Reflector forum by mistake? new [Re: Jon Isaacs]
      #5545433 - 11/29/12 12:10 PM

You know, it is possible the big dob is the finder for the little one...........might have a wider FOV.....

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Jon Isaacs
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Re: You ever go to the Reflector forum by mistake? new [Re: csrlice12]
      #5545449 - 11/29/12 12:23 PM

Quote:

You know, it is possible the big dob is the finder for the little one...........might have a wider FOV.....




Not really... The relative lengths of the tubes tell the story as far as TFoV goes...

Jon


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saemark30
Pooh-Bah


Reged: 02/21/12

Re: You ever go to the Reflector forum by mistake? new [Re: Jon Isaacs]
      #5545557 - 11/29/12 01:37 PM

No but staying here can be an expen$$$ive mistake.

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Mark Costello
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Loc: Matthews, NC, USA
Re: You ever go to the Reflector forum by mistake? new [Re: Jon Isaacs]
      #5545589 - 11/29/12 01:55 PM

True, but IMHO it belongs on its own mount. It looks to me like using it in its current position to find things for the main scope would be an ergonomic nightmare. A finder would be better off near the eyepiece IMHO. Also, the finder there probably has a focal length of a whopping 1500 millimeters. That would limit its use as a finder. Why not a 4.25" or 6" Starblast tube near the eyepiece....

Edited by Mark Costello (11/30/12 09:31 AM)


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galexand
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Reged: 07/10/12

Loc: Bloomington Indiana
Re: You ever go to the Reflector forum by mistake? new [Re: Jon Isaacs]
      #5546174 - 11/29/12 08:17 PM

Okay now that I've gotten over my vertigo looking at that picture..that looks like a regular dob, right? So you've gotta stand at the bottom, line it up within the tiny view of the 12.5", and then run up the ladder and hope you can still find it in the 40"? I guess you could always have a buddy on the ground operating the finder scope for you.

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Jon Isaacs
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Re: You ever go to the Reflector forum by mistake? new [Re: Mark Costello]
      #5546686 - 11/30/12 05:54 AM

Quote:

True, but IMHO it belongs on its own mount. It looks to me like using it in its current position to find things for the main scope would be an ergonomic nightmare. A finder would be better off near the eyepiece IMHO. Also, the finder there probably has a focal length of a whopping 1500 meters. That would limit its use as a finder. Why not a 4.25" or 6" Starblast tube near the eyepiece....




Mark:

This is my thinking:

- Balance is always a problem with Dobsonians, if the 12.5 inch were near the eyepiece it would probably add 50lbs of weight which would require a stiffer stronger structure plus probably a few hundred pounds of counter balances in the base... not a good thing. Even a Starblast and an eyepiece and rings would "only" weigh 6 lbs or so but that would still cause significant balance problems.

- That's a 40 inch F/5, that means the focal length is about 200 inches and the maximum field of view is less than 0.5 degrees, the 12.5 inch is there just to get close.

With a scope that requires a ladder, particularly a tall ladder, one actually points the scope from the ground and then climbs the ladder. With a scope that tall, 10 degrees represents about 3 feet of motion of the focuser, you'd have to climb down, reposition the ladder, climb back up, look through the scope, climb back down. With my 25 inch F/5, I position the scope with the Telrad while I am standing on the ground.

Jon


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Mark Costello
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Re: You ever go to the Reflector forum by mistake? new [Re: Jon Isaacs]
      #5546870 - 11/30/12 09:41 AM

I can't believe that I miswrote the finder focal length as 1500 meters! Zounds! I meant 1500 millimeters! I corrected my post in that respect.

Well, Jon, you make some good points, as usual. I still believe a 4-6" short tube reflector would make a better finder with a capacity to get a 3-4 degree field of view with a reasonable eyepiece. A magnifying finder in the back would best be a reflector for comfort.


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simpleisbetter
Carpal Tunnel
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Reged: 04/18/11

Re: You ever go to the Reflector forum by mistake? new [Re: snommisbor]
      #5546904 - 11/30/12 10:14 AM

"You ever go to the Reflector forum by mistake?"

Nah, I go there on purpose all the time. Years back on my old CN user account (when I owned my last dob), I did once go to the Cats forum and forgot the "reflectors" I was reading about weren't newts, and replied as if the OP's scope were a newt...


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: You ever go to the Reflector forum by mistake? new [Re: Mark Costello]
      #5546994 - 11/30/12 11:19 AM

Quote:

I can't believe that I miswrote the finder focal length as 1500 meters! Zounds! I meant 1500 millimeters! I corrected my post in that respect.

Well, Jon, you make some good points, as usual. I still believe a 4-6" short tube reflector would make a better finder with a capacity to get a 3-4 degree field of view with a reasonable eyepiece. A magnifying finder in the back would best be a reflector for comfort.




I suspect Steve Swayze probably doesn't need a short tube refractor to find his way around the sky. Even a duffer like myself, a Telrad is fine for finding my way around the sky with my 12.5 inch if the skies are sufficiently dark. My 12.5 inch scope is capable of a nearly 2 degree TFoV with a slightly oversized 7.6 mm exit pupil.

jon


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snommisbor
scholastic sledgehammer
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Reged: 06/15/09

Loc: Cedar Park, TX
Re: You ever go to the Reflector forum by mistake? new [Re: simpleisbetter]
      #5546998 - 11/30/12 11:21 AM



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David E
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Loc: North Carolina
Re: You ever go to the Reflector forum by mistake? new [Re: csrlice12]
      #5547045 - 11/30/12 11:54 AM

Quote:

You know, it is possible the big dob is the finder for the little one...........might have a wider FOV.....




Of course it would. It's got a bigger opening to allow in more field of view.


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: You ever go to the Reflector forum by mistake? new [Re: David E]
      #5547259 - 11/30/12 01:48 PM

Quote:

Quote:

You know, it is possible the big dob is the finder for the little one...........might have a wider FOV.....




Of course it would. It's got a bigger opening to allow in more field of view.




It's got the bigger field to mow, that for sure... One thing that is not so obvious about such scopes is how much room the require. A 25 inch F/5 covers a circle about 20 feet in diameter, you don't want anything inside that circle or it may get hit. A 40 inch F/5 covers a circle about 10 meters in diameter or 33 feet...

Jon


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Meadeball
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Reged: 10/22/12

Loc: Midlothian, Virginia
Re: You ever go to the Reflector forum by mistake? new [Re: Jon Isaacs]
      #5548234 - 12/01/12 02:55 AM

How you gonna move that danged Dob when you're trying to center something in the finder? What a nightmare.

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csrlice12
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Reged: 05/22/12

Loc: Denver, CO
Re: You ever go to the Reflector forum by mistake? new [Re: Meadeball]
      #5548792 - 12/01/12 01:21 PM

With it's self-contained cold fusion reactor of course......

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GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: You ever go to the Reflector forum by mistake? new [Re: Jon Isaacs]
      #5548829 - 12/01/12 01:46 PM

A friend of mine has observed through a 40 inch dob...said it was crazy good. Had to use an orchard ladder to look through it.

Considering the 30 inch I looked through wasn't even in that good of shape, I can only imagine what a high quality 40 inch would be like.

Good stuff.


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JMW
Pooh-Bah


Reged: 02/11/07

Loc: Nevada
Re: You ever go to the Reflector forum by mistake? new [Re: GOLGO13]
      #5560040 - 12/07/12 10:06 PM

I camped next to a 40 inch home made dob this summer at the Oregon star party. The guy made the mirror out of fused plate glass. It weighed about 800 pounds and he needed a winch to load or unload it from the trailer. Fun to look through but we ended up mostly on very faint objects that were still on the edge of perception. He was looking for a permanent dark site to keep it at. It was a little too much hassle to transport. The ladder was a 16 foot Tallman astronomy ladder modified to have wheels to easy positioning.

Edited by KWB (12/08/12 02:17 PM)


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Jon Isaacs
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Loc: San Diego and Boulevard, CA
Re: You ever go to the Reflector forum by mistake? new [Re: JMW]
      #5560408 - 12/08/12 04:48 AM

Quote:

I camped next to a 40 inch home made dob this summer at the Oregon star party. The guy made the mirror out of fused plate glass. It weighed about 800 pounds and he needed a wench to load or unload it from the trailer. Fun to look through but we ended up mostly on very faint objects that were still on the edge of perception. He was looking for a permanent dark site to keep it at. It was a little too much hassle to transport. The ladder was a 16 foot Tallman astronomy ladder modified to have wheels to easy positioning.




Was it this scope:

Steve Swayze's 40 inch Dob

If so, it is hard to think of anything Steve Swayze builds as "Homemade."

Jon


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