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Old 08-10-2020, 11:06 AM
mandragara (Richard)
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mandragara is offline
Join Date: Oct 2020
Location: Sydney, Australia
Posts: 30
Barlow drawbacks vs dedicated eyepiece?

Hi all,

First post here.

Just three basic questions about barlows and how they impact seeing.

Firstly, do barlows reduce brightness beyond the usual brightness reduction you get with magnification + the additional light absorbed by the glass of the barlow? As in, do they scatter some light outside of the FOV of the eyepiece?

Secondly, please consider the following three situations:

A) Looking through a 4.5mm eyepiece

B) Looking through a 9mm eyepiece + 2x barlow

C) Looking through a 22.5mm eyepiece + 5x barlow

My understanding is that (A) is superior, as there is less glass between your eye and the sky (and possibly other reasons depending on Q1). But how much better is (A)? Also, comparing B and C, which is superior\inferior and why?

Lastly, how do you compare barlow specifications between brands? Televue want 4x the price compared to GSO for a 2X barlow, but how do you compare the two based on specs? If a telescope cost 4x the price, there would be lots of detail as to why one costs more.

Many thanks,
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