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Equipment Discussions >> Refractors

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jrbarnett
Eyepiece Hooligan
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Reged: 02/28/06

Loc: Petaluma, CA
Re: You ever go to the Reflector forum by mistake? new [Re: Jon Isaacs]
      #5523380 - 11/16/12 07:49 PM

"Newtonians have very lax collimation tolerances because there is only one curved surface so they can be collimated by the owner in the field in a moment are two."

Only if you're looking at blobs (DSOs). Even slight decollimation of a Newt kills it for planetary work. Moreso the faster the Newt.

Slow doublet refractors, on the other hand suffer the least from miscollimation errors. So long as both elements are in the same backyard, that's good enough for planetary viewing.

- Jim


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Scott in NCAdministrator
80mm Refractor Fanatic
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Reged: 03/05/05

Loc: NC
Re: You ever go to the Reflector forum by mistake? new [Re: RGM]
      #5523470 - 11/16/12 09:09 PM

Quote:

I wander around CN because of my various scopes, but I consider this forum as home, followed by EPs.



+1


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TileArt
member
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Reged: 09/13/12

Loc: Fort Collins, Colorado
Re: You ever go to the Reflector forum by mistake? new [Re: Scott in NC]
      #5523529 - 11/16/12 10:00 PM

I wandered in there once. Ran away when I read something about ladders. That's all I need, something else to drag out to the back yard in the middle of the night.

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Sky Muse
sage


Reged: 10/26/12

Loc: De Soto County, MS
Re: You ever go to the Reflector forum by mistake? new [Re: TileArt]
      #5523552 - 11/16/12 10:22 PM

I thought it was the refractor forum, too, until it was too late.

I "received" fully three crates of tomatoes and a four-vane spider.

Alan


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wormstar
Pooh-Bah


Reged: 11/23/09

Loc: Central Ct
Re: You ever go to the Reflector forum by mistake? new [Re: Sky Muse]
      #5526489 - 11/18/12 05:08 PM

"one time at band camp...."

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cloud_cover
professor emeritus


Reged: 08/17/10

Loc: Restaurant at the End of the U...
Re: You ever go to the Reflector forum by mistake? new [Re: csrlice12]
      #5527244 - 11/19/12 01:35 AM

Quote:

Quote:

No one sends a Newtonian to the factory to be collimated, it happens with refractors all the time...

Jon



Yes, but you can easily collimate a Dob. Collimating a refractor...good luck with that; maybe if you start now, you'll be ready by tonight....




Nah, my NP-101 was nicely collimated in the daytime with an artificial star within 1 hour But that was alignment between front and back elements, similar in a sort of way to collimating the primary and secondary of a Newt.
On the other hand, I agree: if the individual elements of a doublet or triplet need to be collimated, it will be difficult, at best to do-it-yourself.


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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: jrbarnett]
      #5527368 - 11/19/12 06:07 AM

Quote:

"Newtonians have very lax collimation tolerances because there is only one curved surface so they can be collimated by the owner in the field in a moment are two."

Only if you're looking at blobs (DSOs). Even slight decollimation of a Newt kills it for planetary work. Moreso the faster the Newt.

Slow doublet refractors, on the other hand suffer the least from miscollimation errors. So long as both elements are in the same backyard, that's good enough for planetary viewing.

- Jim




Ho hum...

The collimation tolerances in a Newtonian are lax by comparison with other designs. Sure a Newtonian needs to be accurately collimated but accurate collimation in a Newtonian which would provide text book images would be unacceptable in other designs.

Consider the 6 inch F/8 Newtonian versus the 6 inch F/8 refractor. The Primary tilt spec is about 4mm for the Newtonian... Imagine one of the lens elements of the refractor were off center by 4mm...

Long focus Newtonians, an F/15 Newtonian has a coma free region of 74mm... Collimation tolerances are about half that... Try that with a refractor..

One curved surface means that centering is not critical...,

Jon Isaacs


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GeneT
Ely Kid
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Reged: 11/07/08

Loc: South Texas
Re: You ever go to the Reflector forum by mistake? new [Re: Jim Romanski]
      #5528584 - 11/19/12 07:02 PM

Quote:

It's really weird there. They talk about seeing Stephan's Quintet and the Horsehead Nebula. Like anybody can really see that stuff.






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GeneT
Ely Kid
*****

Reged: 11/07/08

Loc: South Texas
Re: You ever go to the Reflector forum by mistake? new [Re: FaronD]
      #5528588 - 11/19/12 07:06 PM

Quote:

I stumbled in there a couple of times. I whistled and snuck out real fast.




Reflector owners are not embarrassed by discussions of size.


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csrlice12
Postmaster
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Reged: 05/22/12

Loc: Denver, CO
Re: You ever go to the Reflector forum by mistake? new [Re: tomcody]
      #5529771 - 11/20/12 10:30 AM

Quote:

By mistake? NO.. but I have gone there to escape the numerous "whats the best refractor for under $XX.." threads that keep coming up.
Rex




For the "Wht's the best reflector for under $XX"? Guess for either, the answer is, which one will you use??


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jrbarnett
Eyepiece Hooligan
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Reged: 02/28/06

Loc: Petaluma, CA
Re: You ever go to the Reflector forum by mistake? new [Re: Jon Isaacs]
      #5529865 - 11/20/12 11:17 AM

There are no f/15 Netwtonians. There are, however, many f/15 and slower refractors. On the other hand, the trend is for fatser Newts. f/5 is now "slow" and f/3.x and f/2.x are becoming increasingly common. Thus the "average" Newtonian today is exceptionally demanding of collimation for planetary work. That not uncommon f/15 achromat, on the other hand, really isn't.

Regards,

Jim


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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: jrbarnett]
      #5530705 - 11/20/12 05:48 PM

Seems like there is a trend toward faster refractors as well. Especially on the Apo side of the market. Certianly faster scopes are a benefit to both types of scopes for usability. F15 refractors need quite a mount, and can be like using an long reflector with ladders and or contortions.

Those fast newts are common to keep people's feet on the ground with HUGE aperture. 15 inch refractors may cause some interesting mounts/setups.


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jrbarnett
Eyepiece Hooligan
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Reged: 02/28/06

Loc: Petaluma, CA
Re: You ever go to the Reflector forum by mistake? new [Re: GOLGO13]
      #5530814 - 11/20/12 06:52 PM

"F15 refractors need quite a mount, and can be like using an long reflector with ladders and or contortions."

Not so much, really. A 4" f/15 works just fine on a CG5-GT with the 16" Orion pier extension. A smaller f/15 or slower works well on pretty much any mount.

4" f/15 on a CG5 with pier:



2.4" f/16.7 on a CG5 with Orion pier extension:



The same 2.4" on an alt-az mount:



I use the same setups (pier, pier extension and alt-az) with a 76.2mm f/15 as well. Really not even remotely comparable to the ladder hassles with a big f/5 Dob.

Regards,

Jim


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Jon Isaacs
Postmaster
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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: jrbarnett]
      #5530830 - 11/20/12 06:59 PM

Quote:

Quote:

"F15 refractors need quite a mount, and can be like using an long reflector with ladders and or contortions."




Not so much, really. A 4" f/15 works just fine on a CG5-GT with the 16" Orion pier extension. A smaller f/15 or slower works well on pretty much any mount.

4" f/15 on a CG5 with pier:







The photo pretty much proves the point that a 4 inch F/15 requires a substantial mount and may require contortions and a stool. Just how high is the eyepiece when viewing the horizon? To my eye, it is not quite as nimble as an NP-101 or Traveler on a Portamount.

Jon


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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: jrbarnett]
      #5531013 - 11/20/12 08:47 PM

That was still a substantial mount for a 4 inch scope. Look how it gets for a 6 inch F15.



This 6 inch F10 reflector doesn't look so bad...not too different a situation.



I think we should be comparing scopes of similar aperture with at least a semi-close F-ratio.


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Deep13
Carpal Tunnel
*****

Reged: 01/25/05

Loc: NE Ohio
Re: You ever go to the Reflector forum by mistake? new [Re: GOLGO13]
      #5531024 - 11/20/12 08:52 PM

No, on purpose.

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David E
Post Laureate
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Reged: 05/25/06

Loc: North Carolina
Re: You ever go to the Reflector forum by mistake? new [Re: snommisbor]
      #5544356 - 11/28/12 06:31 PM

Quote:

I just went to the Reflector forum thinking I was in the Refractor forum and I'm thinking, "Man, there are a lot of new post I didnt see an hour ago." And then I started reading a new post and after a few lines I was thinking, "What am I reading?" Looked up and saw I had accidentally gone into the Reflector Forum. Thought that was funny and just wonder if anyone else had done that and how long did it take to realize. I'm in the wrong place.




Yeah, I've done that before. Started reading about collimation and coma and I'm like, what are they talking about? They really should separate those two forums on opposite sides of the web page.


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csrlice12
Postmaster
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Reged: 05/22/12

Loc: Denver, CO
Re: You ever go to the Reflector forum by mistake? new [Re: David E]
      #5545123 - 11/29/12 08:59 AM

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

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sg6
professor emeritus


Reged: 02/14/10

Loc: Norfolk, UK.
Re: You ever go to the Reflector forum by mistake? new [Re: csrlice12]
      #5545142 - 11/29/12 09:13 AM

Who cares about a 10" reflector?


Link

Translation manages to still say Mirror when it is a Lens.

Edited by sg6 (11/29/12 09:14 AM)


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orion61

*****

Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: You ever go to the Reflector forum by mistake? new [Re: sg6]
      #5545194 - 11/29/12 09:51 AM

I don't know I just went through there where they are talking about actually useing their equipment, not just looking at it in the daytime and cutting down other people.
enjoy your daytime hobby.
Gee I wonder why Hubble is a reflector? even with its optical flaws, I wonder why they didn't put a refractor up there?

Edited by orion61 (11/29/12 09:56 AM)


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