RE: [ATM] Eyepiece in question

["Ellen Mackenzie" <mackenzieconsulting@sympatico.ca>]

You should have noted also that all Erfle eyepieces are not the same. I
Think what is important here is what the telescope image field diameter is.
With a field of view of 1 degree 18 mm is performing at the limit of his
telescope. Of more importance, is his image clear, bright and crisp to the
edges. If he is unhappy with the math I'll gladly take it off his hands. 20
mm is a rather short focus for an Erfle with 32 being the more common size
seen around.

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Wouter van Reeven
Sent: Monday, November 29, 2004 8:29 AM
To: Maingot Fabrice
Cc: atm@atmlist.net
Subject: Re: [ATM] Eyepiece in question


Hi Maingot,

On  0, Maingot Fabrice <Fabrice.Maingot@ipcms.u-strasbg.fr> wrote:
> I got an Erfle eyepiece of focal length f=20mm;
> I measured the field stop : d = 18mm.
> The telescope has a focal length F=1103mm.
> 
> I compute the angular field of view :
>    FOV = 2 atan(d/2F) = 0.93 deg
> so the apparent field of view :
>    AFOV = F/f * FOV = 51 deg !!
> 
> An Erfle has rather 70 deg of field. Is there
> a problem with my equations, or this eyepiece
> will not suit well with that scope ?

There's nothing wrong with your calculations. To get a 70 degrees fov you'll
need a field stop of 24 mm. So despite this eye piece being an Erfle, it
does have a 51 deg fov.


Clear skies!

Wouter van Reeven

-- 
Black holes are where God is dividing by zero.
_______________________________________________
ATM mailing list http://www.atmlist.net/


_______________________________________________
ATM mailing list http://www.atmlist.net/