Quote:
Originally Posted by Scoper
Hi all,
The reason for the increase in eye relief is because the barlow, after intercepting the light-cone, narrows the cone, therefore increasing the focal ratio of the optical system as a whole. In doing so the exit pupil is pushed back but if that is the case then the eye relief of a given eyepiece must be variable.
Cheers again
Malc
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"Ok. The convergence of the light cone is reduced; the angle of the cone is made less steep by the barlow; that is what i meant by it being narrower. "
I wasn't meaning to be rude Malcolm, it's just that neither of those 2 quotes above really make sense (not saying you don't
know what you mean; just that it isn't correct to call a beam that diverges (expands) as "narrower" whether you say "the convergence of the light cone is reduced" or "the angle of the cone is made less steep...")
I've found myself (without really taking the time to check various eps like you've just done) that eye relief is enhanced with the use of a barlow: which is why I made my original comment: but I wouldn't disagree with your trials that found that the longer f/l eps showed this more markedly - I haven't tried what you've just done, and I accept your results.
I'd just like to hear/see some optical science/illustrations that explain the situation; to be able to get my head around it all from a logic aspect, that's all.
Best regards, Darryl.