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Barlow an existing or buy a new EP?

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#1 vvars

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Posted 12 August 2020 - 03:26 PM

I got a 8mm plossl eyepiece. Getting double the magnification which option is better, buy a same series 4mm eyepiece

or barlow my existing one?

My barlow is a cheap one: https://www.astrosho...ow-lens/p,54273

and the usage of 4mm will be planetary (300x, got relatively good skies).



#2 Shorty Barlow

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Posted 12 August 2020 - 03:39 PM

Well, I suppose it boils down to getting a better Barlow or getting a 4mm eyepiece. Bear in mind 4mm Plossls and orthoscopics have very short eye relief. 

 

https://www.teleskop...iverguetet.html

 

https://www.firstlig...-eyepieces.html

 

These above are good for the money.

 

med_gallery_249298_10131_285539.jpg

 

A 4mm DeLite is more expensive, but ultimately worth it.


Edited by Shorty Barlow, 12 August 2020 - 03:43 PM.

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#3 sg6

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Posted 12 August 2020 - 03:41 PM

Althugh I rather dislike them I expect a barlow is the better, for the reason that you actually double the effective focal length and so the 8mm plossl maintains it's 5mm or 6mm eye relief.

 

If you found a 4mm plossl you would be wearing the eyepiece like a contact lens.

 

There was a question once:

What is the use of a 4mm plossl?

Best answer was stand a golf ball on it and take a swing.

And having bought a 4mm plossl it is more use as a golf tee then an eyepiece.

 

If a 4.5mm would do I would be tempted by an ES 52 at 4.5mm.


Edited by sg6, 12 August 2020 - 03:43 PM.

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#4 Lazaroff

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Posted 12 August 2020 - 03:44 PM

You would almost certainly dislike the very short eye relief of a 4mm plössl. I suggest you try out your 8mm + 2X barlow combination and see what you think of it. I use a barlow that was much cheaper than that and it's just fine.

 

You might be interested in this ongoing forum:

 

https://www.cloudyni...a-barlow-lens/ 


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#5 vvars

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Posted 12 August 2020 - 03:48 PM

My bad, didnt post the exact specs, it's a 9mm uwa SW improved design, eye relief 16mm, not a plain plossl,

https://www.firstlig...-eyepieces.html

so i think there won't be an eye relief problem



#6 JGass

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Posted 12 August 2020 - 03:59 PM

You already have the barlow, so why not try it with the 8mm and see how you like that combo first hand?

 

If the nosepiece of the barlow will thread onto your 8mm, you could also try that out for a combination that might give effective 1.5x boost (a guess).



#7 vvars

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Posted 12 August 2020 - 04:01 PM

Thanks for the advices, and Lazaroff that thread is really helpful :)



#8 havasman

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Posted 12 August 2020 - 04:16 PM

My bad, didnt post the exact specs, it's a 9mm uwa SW improved design, eye relief 16mm, not a plain plossl,

https://www.firstlig...-eyepieces.html

so i think there won't be an eye relief problem

Barlows are not essential bits of kit but special purpose tools. One fine purpose is to preserve the eye relief of a longer focal length eyepiece while getting the magnification of a shorter focal length eyepiece. A 4mm Plossl will have short eye relief. So using a Barlow fits the mission here. I have a Barlow specifically for the same reason and use it with a 9mm eyepiece if I think I need really high magnification and it remains comfortably useful.


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