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Stacked Barlows??

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#1 sslcm56

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Posted 20 October 2013 - 10:30 AM

I read a post the other day where someone had stacked their barlows for a 4X mag. I have also read where you can take the element off a GSO barlow and screw it onto an EP for a 1.5X mag. SOoooo if I put the GSO element onto my ES 2X extender I should get a 3.5X mag ? 1250/8.8= 142 X 3.5= 497X mag. Is that right? I mat just keep the GSO balow after all.

Thanks
Steve

#2 youngamateur42

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Posted 20 October 2013 - 10:59 AM

My grandpa once told me of a story of one of his best friends who had built an 8" F/12 Newtonian that was an amazing scope- he still tells me one of the best that he's ever looked through (this story takes place in the late 1950s). It was just past first quarter moon so the crater Plato was in prime viewing position. At the floor of this crater are numerous little "cratelets", small impact craters only a few miles wide, and less. This night was one of the clearest with some of the best seeing he had ever seen. Well, the zoomed in on this crater with his shortest focal length eyepiece (my guess maybe 5mm or so. Then he proceeded to attach every Barlow lens he owned. When they were all in the focuser it extended well over a foot from the focuser. This telescope was so good and the seeing was so good that he could have easily put on more magnification, but he quite literally ran out of power!

#3 sslcm56

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Posted 20 October 2013 - 11:59 AM

I live in a very red zone that should possibly even be a white one. I might have about 45% of the sky available to look at. I can't wait to try the barlow thing on the moon and Jupiter.

#4 SteveNH

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Posted 20 October 2013 - 12:22 PM

Great story! I imagine he must have seen something like this, where I used two stacked 2x shorty barlows for the capture (image is not as sharp as what I thought I saw visually - so yes, it works):

Attached Thumbnails

  • 6148432-Plato 20121105_1216_03_g3_b3_ap16.jpg


#5 sslcm56

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Posted 20 October 2013 - 12:41 PM

I'm really glad that it works but are my calculations correct? Will I really get 497X mag with a GSO element screwed onto my ES 2X?

#6 Steve OK

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Posted 20 October 2013 - 02:21 PM

Maybe, but it seems that if one Barlow is 1.5x, and the other is 2x, that you would get a net 3x, rather than 3.5x. I think they would multiply, rather than add.

Steve

#7 StarCurious

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Posted 20 October 2013 - 02:31 PM

I too have a GSO 2" ED 2X Barlow, which is a combination of the lens and a 50mm extension tube. By replacing the 50mm with a 80mm extension tube, I get a 2.6X Barlow. By stacking the tubes together with only one Barlow lens, I should get 3.6X. That is my understanding from this:

http://en.wikipedia....iki/Barlow_lens

You can get extension tubes from Astronomics:

https://www.astronom...=extension tube

and if you bought the Apertura, you probably already have the 35mm extension tube.


#8 SteveNH

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Posted 20 October 2013 - 02:55 PM

Maybe, but it seems that if one Barlow is 1.5x, and the other is 2x, that you would get a net 3x, rather than 3.5x. I think they would multiply, rather than add.

Steve

Yes, they multiply when you stack. eg., 2x barlow and 3x barlow = 6x.

#9 jgraham

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Posted 20 October 2013 - 08:35 PM

An alternative to stacking Barlows is to use an extension tube to increase the spacing between the Barlow lens and eyepiece. If I recall right the amplification scales linearly with the lens/eyepiece separation.

#10 Jon Isaacs

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Posted 21 October 2013 - 05:13 AM

An alternative to stacking Barlows is to use an extension tube to increase the spacing between the Barlow lens and eyepiece. If I recall right the amplification scales linearly with the lens/eyepiece separation.


John:

I believe you are correct. The simplest model in stacking Barlows is that you multiply the magnifications, i.e. a 1.5x and a 2x = 3x.

But it's not that simple because the magnification of a Barlow is not fixed but rather depends, as John has said, on the distance between the lens and the focal plane.. So, the actual geometry would need to be understood.

Jon

#11 jrbarnett

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Posted 21 October 2013 - 10:25 AM

Vavavavoom! That Barlow is STACKED!

:lol:

- Jim


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