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Equipment Discussions >> ATM, Optics and DIY Forum

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Scout92
member


Reged: 12/20/11

Loc: Hoquiam, WA.
eBay Mirrors
      #5550234 - 12/02/12 12:07 PM

Astronomy supernewby here, and I have a quick question. Is a Meade 4.5 in. f/4 spherical primary from ebay worth the $24 to by it?

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kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

Re: eBay Mirrors new [Re: Scout92]
      #5550238 - 12/02/12 12:10 PM

A f4 should be parabolic so no

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Scout92
member


Reged: 12/20/11

Loc: Hoquiam, WA.
Re: eBay Mirrors new [Re: kfrederick]
      #5550241 - 12/02/12 12:13 PM

whould it be good for anything?

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orlyandico
Postmaster
*****

Reged: 08/10/09

Loc: Singapore
Re: eBay Mirrors new [Re: Scout92]
      #5550277 - 12/02/12 12:36 PM

burning ants?

those were made for a type of telescope called a "Bird Johnson" where there is a corrector lens in the focuser which (attempts) to correct for the short, spherical primary. This design is only found in the cheapest of telescopes.. and you can guess why.

that said this - http://www.cloudynights.com/classifieds/showproduct.php?product=69629

at $75 is actually worth building a scope around.

but if you really want to build a telescope for cheap, this is a better choice -
http://www.surplusshed.com/pages/item/l3002.html

not quite $25. or this (would result in a shorter telescope but one with more chromatic aberration)
http://www.surplusshed.com/pages/item/l2196.html


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Andy Taylor
Twisted, but in a Good Way
*****

Reged: 09/24/08

Loc: Epsom - UK
Re: eBay Mirrors new [Re: Scout92]
      #5550278 - 12/02/12 12:36 PM

Carton mirrors

Check these out. Sheldon has loads of good quality stuff and is a great guy to buy from.

PM him to see if he has something suitable. Carton stuff is top quailty.

I'd avoid ebay.


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Scout92
member


Reged: 12/20/11

Loc: Hoquiam, WA.
Re: eBay Mirrors new [Re: orlyandico]
      #5550296 - 12/02/12 12:50 PM

Oh man! I was just at that site looking for a 76 mm lens to make a copyscope and didn't see anything like that so I bought a 70mm from eBay! Oh well live and learn thanks for the link. Lol...I might get one there anyway so I ca make 2 scopes, be good practice!

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Scout92
member


Reged: 12/20/11

Loc: Hoquiam, WA.
Re: eBay Mirrors new [Re: Andy Taylor]
      #5550298 - 12/02/12 12:52 PM

Thanks for the tip!

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Ksearles62
member


Reged: 11/26/11

Loc: Medical Lake WA
Re: eBay Mirrors new [Re: Scout92]
      #5550388 - 12/02/12 01:55 PM

Don't feel bad. I bought one of the f4 mirrors from ebay for project. Now I have a nice paperweight. Live and learn

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dan_h
Carpal Tunnel


Reged: 12/10/07

Re: eBay Mirrors new [Re: Andy Taylor]
      #5550397 - 12/02/12 02:01 PM

Quote:

Carton mirrors

Check these out. Sheldon has loads of good quality stuff and is a great guy to buy from.

PM him to see if he has something suitable. Carton stuff is top quailty.






Sheldon does have some good stuff at reasonable prices. These mirrors don't fall into that category. Our local ATM club just received a number of the 4" f6 mirrors. It is my understanding that they were not top quality. It is a case of you get what you pay for.

dan


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Tom and Beth
Post Laureate


Reged: 01/08/07

Loc: Tucson, AZ
Re: eBay Mirrors new [Re: Scout92]
      #5551289 - 12/02/12 11:42 PM

Quote:

Astronomy supernewby here, and I have a quick question. Is a Meade 4.5 in. f/4 spherical primary from ebay worth the $24 to by it?




Only if you consider the "mirror" as a blank that is already ground and sorta spherical. If it's been coated you CAN pour a pitch lap and re-figure it.


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edsplace
sage
*****

Reged: 11/02/11

Re: eBay Mirrors new [Re: Tom and Beth]
      #5551681 - 12/03/12 08:58 AM

You can find Meade 4.5" F/9 mirrors on eBay. I built a reflector that was carry on luggage for airlines on trips for a trip to Hawaii. The scope worked wonderful!

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Ksearles62
member


Reged: 11/26/11

Loc: Medical Lake WA
Re: eBay Mirrors new [Re: edsplace]
      #5552050 - 12/03/12 01:28 PM

Now that I own a set of the 4.5 f4 ebay mirrors, is there anything I can do with them besides burn ants? I already have a different mirror set on the way for a PortaBowl project

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Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: eBay Mirrors new [Re: Ksearles62]
      #5552057 - 12/03/12 01:33 PM

test their figures, maybe flex it to a parabola

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hottr6
Carpal Tunnel
*****

Reged: 06/28/09

Loc: 7,500', Magdalena Mtns, NM
Re: eBay Mirrors new [Re: Scout92]
      #5552243 - 12/03/12 03:12 PM

Despite all the good suggestion here, please consider if you are going to build or buy a cell for the mirror. New cells for 4" and 4.25" mirrors are non-existent today. Cells for 4.5" are plentiful, both used and new. If you go with the 4" mirror, you will have to build the cell yourself.

The main problem with buying used small mirrors are the coatings; it will cost at least twice as much as the used mirror to have it re-coated by the labs.... if they will even do it.


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mikey cee
Postmaster
*****

Reged: 01/18/07

Loc: bellevue ne.
Re: eBay Mirrors new [Re: hottr6]
      #5552449 - 12/03/12 05:21 PM

Sheeesh finally someone who knows the difference between "calvary" and "cavalry"! It's like screeching chalk on a blackboard to my enlightened ears. Mike

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kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

Re: eBay Mirrors new [Re: mikey cee]
      #5552679 - 12/03/12 07:41 PM

Maybe have Ed Turco correct your spherical f4 or Mark Harry

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dave brock
professor emeritus


Reged: 06/06/08

Loc: Hamilton, New Zealand
Re: eBay Mirrors new [Re: kfrederick]
      #5553209 - 12/04/12 01:03 AM

Does Mark Harry need correcting?
Sorry, couldn't resist.

Dave


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Al8236
Pooh-Bah
*****

Reged: 08/18/10

Loc: 48.9173N 122.1390W
Re: eBay Mirrors new [Re: dave brock]
      #5553275 - 12/04/12 02:54 AM

Ta da dum!

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nytecam
Postmaster


Reged: 08/20/05

Loc: London UK
Re: eBay Mirrors new [Re: Ksearles62]
      #5553373 - 12/04/12 05:38 AM

Quote:

Don't feel bad. I bought one of the f4 mirrors from ebay for project. Now I have a nice paperweight. Live and learn


This is the ATM Forum so you can do better than just burn ants Could make a Lensless Schmidt out of one - same mirror in Meade scope here



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Scout92
member


Reged: 12/20/11

Loc: Hoquiam, WA.
Re: eBay Mirrors new [Re: mikey cee]
      #5554140 - 12/04/12 03:01 PM

Well Mikey I should know I was a scout for 16 years!

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