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Stock eyepiece vs BST


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A 30mm eyepiece in an f5 scope will give an exit pupil of 6mm. Under urban/suburban light pollution this size exit pupil may not darken the background sky sufficiently. You will have to judge this based on the brightness of the background sky when using your current 25mm eyepiece. 

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17 minutes ago, Ricochet said:

A 30mm eyepiece in an f5 scope will give an exit pupil of 6mm. Under urban/suburban light pollution this size exit pupil may not darken the background sky sufficiently. You will have to judge this based on the brightness of the background sky when using your current 25mm eyepiece. 

That’s interesting to know. I basically have minimal light pollution and have a bortle 4 sky.  I’ll check when I next use the 25mm, thanks.

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38 minutes ago, Dinoco said:

That’s interesting to know. I basically have minimal light pollution and have a bortle 4 sky.  I’ll check when I next use the 25mm, thanks.

My sky is like yours (I live in a village on the edge of the greenbelt) and the 30mm Vixen gives me a dark enough background, as does a 25mm NPL and a 19mm TeleVue Panoptic.  

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