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Equipment Discussions >> Reflectors

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GeneT
Ely Kid
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Reged: 11/07/08

Loc: South Texas
Re: Why the Need to Collimate Newts in the First Place new [Re: rmollise]
      #5668051 - 02/07/13 10:58 PM

Quote:

The other side is that a Newtonian that must be collimated is simple to make. AND collimation is a five minute process at worst unless you are a collimatoholic.




This is true. I just make collimaiton part of my set up. It is easy and I now do it without thinking (my wife says I do a lot of things without thinking. )


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Atl
professor emeritus
*****

Reged: 04/13/12

Re: Why the Need to Collimate Newts in the First Place new [Re: GeneT]
      #5668160 - 02/08/13 12:04 AM

Use concrete, rebar, and 6 inch thick mirrors...maybe a titanium spider and the need to collimate vanishes.

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beatlejuice
Pooh-Bah
*****

Reged: 04/05/11

Loc: Hamilton, ON,Canada
Re: Why the Need to Collimate Newts in the First Place new [Re: FirstSight]
      #5668323 - 02/08/13 04:01 AM

The OP's original question:

Quote:

rather the angle I'm interested in is why hasn't it seemed feasible (at least so far) to improve the overall structural design of reflectors to mostly eliminate their vulnerability to miscollimation for an indefinite duration, once it's been initially set?




I was sure that the engineers amongst us would have come up with somewhat of a more technical answer than those that have appeared so far. Perhaps it's just that talking about and tinkering with collimation is something that we really don't want to do without and the loss of this cerebral process to a permanantly collimated reflector would be devastating to many of us. (If it can be done, I don't want to know about it!)

Eric


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jpcannavo
scholastic sledgehammer
*****

Reged: 02/21/05

Loc: Ex NYCer, Now in Denver CO!
Re: Why the Need to Collimate Newts in the First Place [Re: beatlejuice]
      #5668388 - 02/08/13 06:44 AM

Another - and clearly there are many - issue that arises is the mirror cell. Refractor objectives are typically circumferentially "locked" into their cells. Consider instead a large newtonian that is "floating" on a complex layered structure. This introduces a number of potential mechanical variables. So, for example, merely unloading and loading the mirror into its cell will often create the need for re-collimation.

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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Why the Need to Collimate Newts in the First Place new [Re: jpcannavo]
      #5668855 - 02/08/13 12:03 PM

It's mostly a matter of weight. If I scaled the 4" refractor here up to the 12.5" size, my scope would weigh around 300+ lbs because the entire structure would have to be beefed up to handle the weight of the tube, etc.
Yet, my scope is 80 lbs total and can be broken down for transport, with no part over 40 lbs.
When I carefully assemble it at a dark site, it's out of collimation because even though I put everything together in exactly the same way, even tiny changes make a difference to collimation.
I can envision having a permanently-mounted scope that never went out of collimation. It wouldn't be light, nor would it be cheap.
I can envision having a portable scope that never went out of collimation. It wouldn't be light for its size, and it would be small in size.

But, alas, we usually want to move them, which puts an upper limit on the weight. So we take a disassembled scope to the field and assemble it there. In the 20-30 minutes it may take to put it together and connect everything, if we spend 5 minutes collimating and observe for, say, eight hours, is it not a 5 minutes well-spent?


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Jon Isaacs
Postmaster
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Why the Need to Collimate Newts in the First Place new [Re: Starman1]
      #5668885 - 02/08/13 12:16 PM

Quote:

If I scaled the 4" refractor here up to the 12.5" size, my scope would weigh around 300+ lbs because the entire structure would have to be beefed up to handle the weight of the tube, etc.






My 12.5 inch F/6 Equatorial weighs right at 300lbs but that includes the mount... It's not what I would call portable.

Jon


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dan_h
Carpal Tunnel


Reged: 12/10/07

Re: Why the Need to Collimate Newts in the First Place new [Re: Jon Isaacs]
      #5668927 - 02/08/13 12:36 PM

Question: ( I know absolutely nothing about this one)

How often is a large professional observatory scope aligned? Do they check it for every exposure? Is it remotely adjusted so that continuous adjustments are possible? Or is it ridgid enough that collimation can be set and left?

dan


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Why the Need to Collimate Newts in the First Place new [Re: dan_h]
      #5669114 - 02/08/13 01:53 PM

Quote:

Question: ( I know absolutely nothing about this one)

How often is a large professional observatory scope aligned? Do they check it for every exposure? Is it remotely adjusted so that continuous adjustments are possible? Or is it ridgid enough that collimation can be set and left?

dan



The 60" at Mt. Wilson is collimated when the freshly-recoated mirror is put back in the scope (the mirror is 1900 lbs) and pretty much that's it.
One of my biggest disappointments with that scope was that it was out of collimation when I spent a night looking through it.


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