Re: ATM Does a Barlow change eye relief ?

["Richard Schwartz" <richas@earthlink.net>]

Eye relief is a property of the eyepiece.   A barlow does not change that
any more than stopping down your mirror or changing the focal length of the
mirror.

So what is preferable... a 10 mm eyepiece with a barlow, or a 5 mm eyepiece
without one?   Answer: the 10 mm eyepiece has greater eye relief.

. . . Richard

----- Original Message -----
From: "N. Foldager" <nf@dadlnet.dk>
To: <atm@shore.net>
Sent: Thursday, August 16, 2001 10:21 AM
Subject: ATM Does a Barlow change eye relief ?


>
>
> Has a Barlow lens any influence on the eye relief of a certain
> eyepiece?
>
> If, for example:
>
> F of the objective is 1200 mm
> F of the eyepiece is 10 mm
> eye relief in this configuration is 20 mm,
>
> Would the eye relief be changed, if just we insert a Barlow and keep
> everything else constant?
>
> How to measure eye relief accurately?
>
> Best regards,
>
> Niels Foldager
> Copenhagen
> Denmark
>