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Equipment Discussions >> Refractors

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DavidNealMinnick
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Reged: 03/06/06

How small is too small? new
      #5872705 - 05/19/13 10:28 PM Attachment (73 downloads)

Borg makes some small EDs, down to 45mm. This is the Pocket Borg, a 25mm f/7 achromat.

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DavidNealMinnick
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Reged: 03/06/06

Re: How small is too small? new [Re: DavidNealMinnick]
      #5872709 - 05/19/13 10:29 PM Attachment (35 downloads)

Focus is achieved by sliding the lens section.

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DavidNealMinnick
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Reged: 03/06/06

Re: How small is too small? new [Re: DavidNealMinnick]
      #5872712 - 05/19/13 10:31 PM Attachment (51 downloads)

With diagonal.

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DavidNealMinnick
sage
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Reged: 03/06/06

Re: How small is too small? new [Re: DavidNealMinnick]
      #5872715 - 05/19/13 10:31 PM Attachment (35 downloads)

Cell.

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DavidNealMinnick
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Reged: 03/06/06

Re: How small is too small? new [Re: DavidNealMinnick]
      #5872716 - 05/19/13 10:32 PM Attachment (37 downloads)

Handy.

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DavidNealMinnick
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Reged: 03/06/06

Re: How small is too small? new [Re: DavidNealMinnick]
      #5872722 - 05/19/13 10:34 PM Attachment (44 downloads)

Where do I attach the finder?

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

Loc: NC
Re: How small is too small? new [Re: DavidNealMinnick]
      #5872839 - 05/19/13 11:37 PM

Now that's small. I don't recall ever seeing a scope that was dwarfed by a Plossl before!

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Koala117
sage


Reged: 05/11/13

Re: How small is too small? new [Re: Scott in NC]
      #5872849 - 05/19/13 11:44 PM

Wow, that's just tiny!

What would one use this for, if not a finder scope? That is.. with a 25mm it's what, 7x magnification. Would the light-gathering ability be worth-while?

I did try to google it but only found the 45mm. What would this cost? Not that I'd buy one, I'm just curious. o:


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: How small is too small? new [Re: DavidNealMinnick]
      #5872856 - 05/19/13 11:48 PM

Quote:

Borg makes some small EDs, down to 45mm. This is the Pocket Borg, a 25mm f/7 achromat.




David:

Have you tried it yet?

Jon


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Astrojensen
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Reged: 10/05/08

Loc: Bornholm, Denmark
Re: How small is too small? new [Re: Jon Isaacs]
      #5873064 - 05/20/13 03:39 AM

I've tried my WO 72ED stopped down to 25mm and it's possible to see surprisingly much. From a dark sky, many Messier objects and even quite a few NGCs are visible.


Clear skies!
Thomas, Denmark


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Derek Wong
sage
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Reged: 04/27/08

Loc: Glendale, CA
Re: How small is too small? new [Re: DavidNealMinnick]
      #5873066 - 05/20/13 03:50 AM

Quote:

Borg makes some small EDs, down to 45mm. This is the Pocket Borg, a 25mm f/7 achromat.




This is a nice little scope, would love to hear about it. See here for a photo of it with an erecting prism:

http://www.tomytec.co.jp/borg/products/detail/summary/9/1

If you put an Ethos 13 in the diagonal, you could carry the setup by the eyepiece...

Derek


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csrlice12
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Reged: 05/22/12

Loc: Denver, CO
Re: How small is too small? new [Re: Derek Wong]
      #5873300 - 05/20/13 09:21 AM

.....and, it's reversable, you can look thru either end!

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chaoscosmos
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Reged: 01/26/13

Loc: Mission Viejo CA
Re: How small is too small? new [Re: csrlice12]
      #5873533 - 05/20/13 11:35 AM

Why? oh why? I say.

Edited by chaoscosmos (05/20/13 11:36 AM)


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Koala117
sage


Reged: 05/11/13

Re: How small is too small? new [Re: Astrojensen]
      #5873715 - 05/20/13 01:04 PM

Quote:

I've tried my WO 72ED stopped down to 25mm and it's possible to see surprisingly much. From a dark sky, many Messier objects and even quite a few NGCs are visible.





Hi, Thomas =)

I wonder: Would that be an equal comparison? That is to say, wouldn't your 72 have a much longer focal ratio, and as such, have much more magnification? Or am I misunderstanding what 'stopped down' means... (which is possible since I'm still learning!)


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t.r.
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Reged: 02/14/08

Loc: Upstate NY
Re: How small is too small? new [Re: Koala117]
      #5873774 - 05/20/13 01:28 PM

Thats ridiculous...I too ask, Why???

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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: How small is too small? new [Re: Koala117]
      #5873827 - 05/20/13 02:00 PM

Quote:

Quote:

I've tried my WO 72ED stopped down to 25mm and it's possible to see surprisingly much. From a dark sky, many Messier objects and even quite a few NGCs are visible.





Hi, Thomas =)

I wonder: Would that be an equal comparison? That is to say, wouldn't your 72 have a much longer focal ratio, and as such, have much more magnification? Or am I misunderstanding what 'stopped down' means... (which is possible since I'm still learning!)




The 72ED probably has a focal length of about 430mm, this 25mm scope is F/7 so it has a focal length of 175mm, so indeed, using the same eyepiece, the magnification would be considerably greater with the stopped down 72mm. You would have to use different eyepieces if you wanted to do a side by side comparison.

I have to think a 25mm scope is more of a curiosity than a practical tool. One could increase the aperture to 35mm and keep the focal ratio at F/5 without compromise.

Jon


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Koala117
sage


Reged: 05/11/13

Re: How small is too small? new [Re: Jon Isaacs]
      #5873853 - 05/20/13 02:09 PM

Quote:

The 72ED probably has a focal length of about 430mm, this 25mm scope is F/7 so it has a focal length of 175mm, so indeed, using the same eyepiece, the magnification would be considerably greater with the stopped down 72mm. You would have to use different eyepieces if you wanted to do a side by side comparison.

I have to think a 25mm scope is more of a curiosity than a practical tool. One could increase the aperture to 35mm and keep the focal ratio at F/5 without compromise.

Jon




Ahh, okay! I understand a little better now. =)

I did manage to find a picture/article of it that someone else posted on the internet, for those interested:
http://digiborg.wordpress.com/2012/08/27/pocket-borg-h2b-rocket/


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csrlice12
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Reged: 05/22/12

Loc: Denver, CO
Re: How small is too small? new [Re: Koala117]
      #5873951 - 05/20/13 03:15 PM

could you swap out the focuser for 2" eyepieces??? Think of the FOV!! Put an old nonwaterproof ES82 30mm on it!! (truely doubtful you'd see anything, but hey, we can all imagine!)

A serious question though, what was this "scope" designed for???


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Astrojensen
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Reged: 10/05/08

Loc: Bornholm, Denmark
Re: How small is too small? new [Re: csrlice12]
      #5874091 - 05/20/13 04:04 PM

Quote:

could you swap out the focuser for 2" eyepieces??? Think of the FOV!!




I'm saying only two words: Field curvature!


Clear skies!
Thomas, Denmark


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Astrojensen
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Reged: 10/05/08

Loc: Bornholm, Denmark
Re: How small is too small? [Re: Koala117]
      #5874120 - 05/20/13 04:12 PM

Quote:

Hi, Thomas =)

I wonder: Would that be an equal comparison? That is to say, wouldn't your 72 have a much longer focal ratio, and as such, have much more magnification? Or am I misunderstanding what 'stopped down' means... (which is possible since I'm still learning!)




As Jon already pointed out, aperture for aperture, the comparison is fair, but the eyepieces will need to be of much longer focal length in order to get comparable magnifications. Also, the stopped down scope with the longer focal length is more or less guaranteed to have superior optics, especially in terms of color correction, but also most likely much better spherical correction.

With the optics stopped down to 25mm f/17.2, my WO72 has an absolutely perfect star test and double stars (the ones it can resolve that is!) are amazingly perfect. I've never seen so crisp low-power fields either. A bit dim, but extremely sharp. Quite lot of things visible, if one care to look.


Clear skies!
Thomas, Denmark


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