Clive Gibbons
Mostly Harmless
Reged: 05/26/05
Posts: 13421
Loc: Oort Cloud
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Just for curiosity sake, I measured the magnification of my Questar's built-in Barlow lens.
Did so by noting the time it took for Arcturus to track across the field of a 12.5mm Ortho ocular. Then, timed the event with the Barlow in place.
The result was 1.91x
The Questar manual says this should be "approximately" 2x.
That's close enough. 
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A few telescopes of dubious value.
Understanding wife, two curious cats and one sadly departed.
"Semper ubi sub ubi"
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Billydee
super member
Reged: 01/23/08
Posts: 183
Loc: Winter Haven, FL
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Not all built-in Barlows are the same. That is why the manual states "approximately".
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Les
professor emeritus
Reged: 04/22/06
Posts: 730
Loc: Maryland
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Yes, the built in Barlow can be anywhere from 1.6x to 2x. Mine measures 1.875 as per the lab report. Often a good idea to delay selection of eyepieces until the Barlow power is known.
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Les
Canon 10x42L IS
Oberwerks BT80/45, Helix Hercules mount on Oberwerks Standard Tripod
Swift 8x44ED Ultralite
Questar 50th Anniversary Model, 501 head on Manfrotto 475 tripod
Stellarvue SV90T 90mm Fluorite refractor Bogen 3236/Televue Tele-Pod Head
Questar 7 Astro
Vixen GP-DX on Baader Surveyor Tripod
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Matt Looby
scholastic sledgehammer
Reged: 07/09/03
Posts: 828
Loc: Wadhams, NY
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Hi Guys,
I measured the barlow of the 1989 Q 3.5 to be 1.63x which is very practical.
Matt
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CN GALLERY
6" F/8 Newtonian
3.5" Mak-Cass
7x50 Binolux Binoculars
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Clive Gibbons
Mostly Harmless
Reged: 05/26/05
Posts: 13421
Loc: Oort Cloud
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Funny thing was, I was expecting the power to be a little over 2x.
Like 2.2x or thereabouts.
Most of the regular Barlows I have measure a bit higher than their stated power.
1.9x is fine by me.
Guess it's not a bad idea for Q owners to check what power their built-in Barlow generates.
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A few telescopes of dubious value.
Understanding wife, two curious cats and one sadly departed.
"Semper ubi sub ubi"
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Billydee
super member
Reged: 01/23/08
Posts: 183
Loc: Winter Haven, FL
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Makes one wonder. You would think that Questar would order 200 Lens at some fixed value (say 1.75x) and then when they needed more they order 200 lens at (say 1.80x) due to other production changes. It appears that they just order lens and use what comes as long as it fits a rather wide set of values. Wonder why?
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Billydee
super member
Reged: 01/23/08
Posts: 183
Loc: Winter Haven, FL
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Question? The actual power is the focal length of the Ota divided by the focal lenght of the focuser lens. Since the mirror can be moved in the OTA that changes the focal lenght of the OTA. This makes the focuser's power a non-fixed value. Is this the reason that Questar states the barlow value as 'approximate"?
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NeilR
member
Reged: 02/18/08
Posts: 75
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You would have to ask Questar to divine their statement but I think it is a fact that many of us have come up with very different measurements, all measured at infinity timing the passage of stars across the field of view. That difference goes beyond the variations and or approximations in eyepiece focal length (not mentioned here) and focus distance.
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Les
professor emeritus
Reged: 04/22/06
Posts: 730
Loc: Maryland
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According to the Company 7 website, the Barlow power is a function of the production lot.
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Les
Canon 10x42L IS
Oberwerks BT80/45, Helix Hercules mount on Oberwerks Standard Tripod
Swift 8x44ED Ultralite
Questar 50th Anniversary Model, 501 head on Manfrotto 475 tripod
Stellarvue SV90T 90mm Fluorite refractor Bogen 3236/Televue Tele-Pod Head
Questar 7 Astro
Vixen GP-DX on Baader Surveyor Tripod
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gschnelk
member
Reged: 12/11/08
Posts: 16
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Hi
Thank you for waking me up. The "specs" for my barlow is 1.7X. I thought of some esoteric methods of measuring my barlow's power but it seemed like a lot of trouble. I smacked my self in the forehead and said,"Of course, time it".
Thanks
Gary
Thanks for
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ColoHank
professor emeritus
Reged: 06/07/07
Posts: 507
Loc: western Colorado
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1.7X for my 2007 scope, just what Jim told me at the time of purchase.
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Questar 3.5 standard - pyrex and BB coatings
Powerguide II
8mm, 12mm, 16mm, 24mm and 32mm Brandons
modified Bogen 3030 w/ homebuilt wedge
Homebuilt Galileo scope and very large and ugly homemade tripod
other odds and ends, including iPod Touch with StarMap Pro (what a marvelous combo)...
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"Nothing exists but atoms and empty space. Everything else is opinion."
Titus Lucretius Carus 99-55 B.C.
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Matt Looby
scholastic sledgehammer
Reged: 07/09/03
Posts: 828
Loc: Wadhams, NY
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You know a 1.9x barlow is perfect for the Brandons...
Matt
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CN GALLERY
6" F/8 Newtonian
3.5" Mak-Cass
7x50 Binolux Binoculars
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