Astro Imp Posted December 23, 2013 Share Posted December 23, 2013 As I understand it a Barlow doesn't alter the focal length of the EP but increases the focal length of the OTA thereby giving greater magnification.As the properties of the EP are not changed why does a Barlow extend the eye relief available. Link to comment Share on other sites More sharing options...
ronin Posted December 23, 2013 Share Posted December 23, 2013 I have no idea, but a year or so ago people said that the barlow effectively gave a shorter eyepiece (= longer focal length of OTA) while maintaining the eye relief, now I have noticed that it extends the eye relief in a few posts.So there has been a change in the final result, from same eye relief to greater eye relief.I am not sure where from. Link to comment Share on other sites More sharing options...
swamp thing Posted December 24, 2013 Share Posted December 24, 2013 I believe It changes eye relief because the Barlow lens alters the angle of the light cone hitting the field kens of the eyepiece.Edit. It lengthens eye relief. Not quite sure how one calculates how much though, I believe its down to Barlow length, but not totally sure. Link to comment Share on other sites More sharing options...
Joves Posted December 24, 2013 Share Posted December 24, 2013 Is it that a Barlow extends the eye relief or that it allows you to use a longer focal length EP at higher magnification, which typically have longer eye relief, without changing its properties? Link to comment Share on other sites More sharing options...
swamp thing Posted December 24, 2013 Share Posted December 24, 2013 Is it that a Barlow extends the eye relief or that it allows you to use a longer focal length EP at higher magnification, which typically have longer eye relief, without changing its properties?Barlows extend eye relief. Link to comment Share on other sites More sharing options...
Joves Posted December 24, 2013 Share Posted December 24, 2013 I didn't know that. Cheers. Link to comment Share on other sites More sharing options...
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