Doh, you’re right. It’s diameter of 30mm, F4 and 120mm focal length.
Sent from Mail for Windows 10
From: MAIN@ESPMC-Eight.groups.io <MAIN@ESPMC-Eight.groups.io> on behalf of Wes Mcdonald <wesmcd6@...>
Sent: Thursday, June 13, 2019 2:01:58 PM
Subject: Re: [ESPMC-Eight] Expected tracking times *Unguided
It's the focal length ratio. The 30mm guider has a focal length of what, 150mm?100?. Your 400 mm lens has a FL of 400. Ratio about 3.5 to 4.
Wes, Southport NC
PMC-8, ES ED 127, 10" LX200GPS, Astro-Tech 8" Newt, ETX-90
Polemaster, Orion ST-80 and SAG
Electrical Engineer, Retired