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Practical highest magnification for a 102 mm ED for double stars

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#1 dhkaiser

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Posted 21 June 2020 - 03:46 PM

Posted this question in the refractor forum then realized it would be better here.  I'm the new owner of a Lunt 102 ED, my first quality refractor. While awaiting a mount I'm thinking do I need another eyepiece?  I own 3 Tele Vue eyepieces, Panotic 24 mm, Nagler 16 mm and a Nagler 9 mm along with a Tele Vue 2.5 x barlow.  The 9 mm with barlow takes the 102 mm to 198 x.  Assuming above average seeing can I realistically expect good views through this telescope over 200 x?



#2 Astrojensen

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Posted 21 June 2020 - 03:55 PM

A good 4" refractor in fine seeing is just getting warmed up at 200x. 

 

 

Clear skies!
Thomas, Denmark


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#3 ButterFly

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Posted 21 June 2020 - 04:02 PM

For double stars, after you start seeing the Airy disks, the detectability starts to go down as the star becomes spread out further at higher magnifications.  The brighter the stars, the higher the magnification before they fade away.  Poor seeing further spreads out the Airy disk.  Double double is a good test target becuase the pairs are fairly equaly matched in magnitude at about 2" apart.

 

For bright objects like the Moon and planets, you can go as high as you can until the image starts to break down.  Although no new information is gained after the resolution limit, the object still looks bigger.  The Moon is a good target to test where the image starts breaking down becuase it is so bright.

 

Of course, with higher magnifications, the exit pupil gets smaller.  Floaters in your eye may be a practical ;limit.


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#4 Robert Zebahl

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Posted 21 June 2020 - 04:21 PM

With average seeing, the view beyond 200x may not be the most pleasant. It also depends on the double star. For very close, sufficiently bright double stars with similarly bright components, magnifications up to 300x can make sense. Here it is then more about the detecting of irregularities of the diffraction disk.
If this looks appealing depends on the observer as well, of course.

 

With 4 inch aperture one can "easily" observe double stars up to an angular distance of 1 arcsecond and even less. Of course, there is no clean split here any more.


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#5 Astrojensen

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Posted 21 June 2020 - 04:21 PM

For double stars, after you start seeing the Airy disks, the detectability starts to go down as the star becomes spread out further at higher magnifications.  

That depends. It's certainly true in many cases, but in cases of extremely uneven stars, even fairly wide ones, you often need a lot of magnification to drive the companion as far away from the main star as possible. 

 

 

Clear skies!
Thomas, Denmark


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#6 MP173

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Posted 22 June 2020 - 10:26 AM

Responded on the Refractor forum, but will also post here.

 

Last Thursday, I was able to take my 6mm Plossl from Astronomics with 2x barlow to 236x for a very solid view of the Double Double.  Best night of seeing I could recall.

 

Not sure how much higher I could go.  

 

The problem is the quick movement of object across the FOV.

 

Ed



#7 dhkaiser

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Posted 22 June 2020 - 10:52 AM

Responded on the Refractor forum, but will also post here.

 

Last Thursday, I was able to take my 6mm Plossl from Astronomics with 2x barlow to 236x for a very solid view of the Double Double.  Best night of seeing I could recall.

 

Not sure how much higher I could go.  

 

The problem is the quick movement of object across the FOV.

 

Ed

That can be a problem.  Today I expect delivery of a Celestron Omni CG-4 German equatorial mount and two axis drive.  Total coast about the same as a high end Tele Vue eyepiece.



#8 Steve Cox

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Posted 22 June 2020 - 12:15 PM

I've taken mine up to 270x quite often when I used to own the TV 8mm Plossl and 3x barlow.  These days, I use my TV 3-6 Zoom at 3mm if the seeing allows.


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#9 MP173

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Posted 22 June 2020 - 02:24 PM

Dan:

Where are you in Indiana?

I am in Valparaiso.

 

Went to school in Southern Indiana.

 

Ed


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#10 dhkaiser

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Posted 22 June 2020 - 03:21 PM

Dan:

Where are you in Indiana?

I am in Valparaiso.

 

Went to school in Southern Indiana.

 

Ed

Ed, I'm in Columbus.  I was raised in north central Indiana.



#11 dhkaiser

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Posted 24 June 2020 - 05:13 PM

Update...  I was able to borrow a friend's 7 mm and 4.8 mm naglers and used them last night on some double stars.  I was impressed with the 7 mm and ordered one.  I think it will fit well in the double star observing program.  Thanks to all who commented.


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#12 nerich

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Posted 24 June 2020 - 08:16 PM

Update...  I was able to borrow a friend's 7 mm and 4.8 mm naglers and used them last night on some double stars.  I was impressed with the 7 mm and ordered one.  I think it will fit well in the double star observing program.  Thanks to all who commented.

Congrats! Enjoy. Looking forward to hearing some observing reports that take advantage of it.


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