2 inch SWA's - 32mm or 38mm ?

[John]

TBH I've never quite got my head fully around this exit pupil thing

I'm contemplating the purchase of a 2 inch eyepiece and, as my budget is limited at the moment, I have been looking at the 2 inch SWA 70 degree FoV eyepieces on offer branded Rigel and clones. From the reviews I have read, for what they cost, they will perform reasonably in my scopes but I'm torn between going for the widest possible field (ie: the 38mm) or the one that keeps closer to the optimum exit pupil (ie:the 32mm). As a middle aged bloke I reckon my optimum exit pupil will be around 5-6mm - the 32mm will be around that (slightly over in my F4.7 newtonain) wheras the 38mm would be well over that in both scopes.

What is the effect of using an eyepiece that exceeds the optimum exit pupil V's the benefits of one that stays more or less within it ?.

Thanks,

John

[GazOC]

If the exit pupil is too large you are cutting down the effective aperture of your scope. Its OK if you have a large scope and just want a 'finder' eyepiece but you shouldn't do it otherwise IMHO.

[John]

If the exit pupil is too large you are cutting down the effective aperture of your scope. Its OK if you have a large scope and just want a 'finder' eyepiece but you shouldn't do it otherwise IMHO.

Thanks Gaz,

Is that because your own iris is effectively stopping the scope down ?.

John

[GazOC]

yes mate.

[FLO]

You might also find THIS interesting.

[John]

You might also find THIS interesting.

Thanks Steve, useful link. Tele Vue have a number of interesting articles like this on their site - I'd forgotten about this one.

John