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geekgroupie
sage


Reged: 01/07/12

Loc: Puebo, CO
owning a nexstar
      #5837578 - 05/03/13 01:56 AM

I got asked this question about my NexStar and I don't know the answer.....

What's your shortest focal length eyepiece and what mag. does it provide?

Can ya'all help me out? I really wanna learn this. I'm sure the answer is easy, like uh-duh, hee hee

Edited by geekgroupie (05/03/13 02:02 AM)


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Tel
Postmaster
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Reged: 03/31/06

Loc: Wallingford England
Re: owning a nexstar new [Re: geekgroupie]
      #5837645 - 05/03/13 04:22 AM

Hi Lucy,

If you view the specifications contained in the manual for your Nexstar 8SE, you'll find that it suggests a "Highest Useful Magnification" of X480. This equates to the use of a ca. 4mm eyepiece by reason of the standard formula:

Magnification = Focal Length of the Telescope divided by the Focal Length of the Eyepiece.

Thus: 2032mm / 4.2mm = X480

In reality, however, and under good seeing conditions, it's doubtful whether you will be able to employ an eyepiece of a focal length much shorter than 8mm, which will produce a magnification of ca. X250 albeit on the very best of clear seeing nights, (those which occur approximately once every ten years!), the use of a 6mm might just be possible, giving you a magnification ca. X340.

Overall therefore, the specified, X480 is unrealistic and in any event, high magnification is only a small part of what astronomical observing is all about !

Hoping this helps,

Best regards,
Tel


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ben2112
Cloud Magnet
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Reged: 07/12/12

Loc: North Charleston SC
Re: owning a nexstar new [Re: Tel]
      #5837654 - 05/03/13 04:44 AM

Tel - You are so right about mag being a small part. When viewing planets, I like getting as high of a magnification as I can, but for DSOs, I like more of a wide field view.

The highest magnification I have been able to use is a 6mm. It was on a very cold super dry night. The seeing was great and the object was basically straight up. But most nights, I use a 13mm and on occasions, it's a 10mm.


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Tel
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Reged: 03/31/06

Loc: Wallingford England
Re: owning a nexstar new [Re: ben2112]
      #5837680 - 05/03/13 06:01 AM

Hi Ben,

I experience the same as you with my Nexstar 8i OTA. When vieweing planets, the moon, close double stars and globulars, I tend to hover between a 13mm (Baader Hyperion), a 10mm, (I think it's an Antares Orthoscopic?) I bought some 10 years ago, and a 9mm of unknown make which while good on occasion, does suffer from some degree of "kidney beaning" !

I don't possess an 8mm !

Best regards,
Tel


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ben2112
Cloud Magnet
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Reged: 07/12/12

Loc: North Charleston SC
Re: owning a nexstar new [Re: Tel]
      #5837769 - 05/03/13 08:09 AM

Mine came in my eyepiece kit. I am going to upgrade to a Baader one down the road..

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Midnight Dan
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Reged: 01/23/08

Loc: Hilton, NY, Yellow Zone (Bortl...
Re: owning a nexstar new [Re: ben2112]
      #5837824 - 05/03/13 08:47 AM

Quote:

I got asked this question about my NexStar and I don't know the answer.....

What's your shortest focal length eyepiece and what mag. does it provide?




Since you were asked this about *your* NexStar, then the answer has to come from you. Look at your eyepieces and see which one has the smallest number on it. That's your shortest focal length eyepiece.

As Tel said, the magnification is the focal length of the scope divided by the focal length of that eyepiece. So if your eyepiece is, say 10mm, then the magnification is 2032/10 = 203x.

If you're interested in the maximum magnification that the scope cis capable of, and what eyepiece accomplishes that, then Tel has provided that answer of 480x with a 4mm eyepiece.

But, the fact is, you will almost never reach that magnification. Magnification is limited on most nights by the atmospheric stability, known as "seeing". On almost any night, I can use my 13mm EP and see things at 150x. Only about half the nights I view allow me to use my 8mm to get to 250x. Its only on rare nights of perfect seeing, about 2-3 nights a year, that I can use my 5mm to reach 400x.

Last night I was able to get out and observe for a couple of hours (finally some clear weather here!). The seeing was not very good and I never used any eyepieces with greater magnification than my 13mm (150x). Yet, there were plenty of targets to see, and many of them actually needed lower magnification for best viewing. I used my 21mm (97x) and 36mm (56x) quite a bit last night.

-Dan


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Bob Griffiths
Getting Grouchy
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Reged: 10/10/05

Loc: Frederick Maryland
Re: owning a nexstar new [Re: Midnight Dan]
      #5837888 - 05/03/13 09:27 AM

The HIGHEST power eyepiece I even bother to carry in my eyepiece case that I use for my 8i is an 8.5 mm Pentax (XF60 degree) ..which yields 239x ...And BABY it sure does not spend a lot of time in the diagonal..

On those extremely rare nights ( in my case once every 10 years or it seems like it as Tel noted) with a 13 or 15

Bottom line I use anyone of my 26 31 and 35 mm individual eyepieces more then I do my 8.5 and 10 COMBINED

Magnification is just NOT the name of the Game...

Bob G


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geekgroupie
sage


Reged: 01/07/12

Loc: Puebo, CO
Re: owning a nexstar new [Re: Bob Griffiths]
      #5838824 - 05/03/13 05:52 PM

Thanks

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