Your browser is no longer supported

For the best possible experience using our website we recommend you upgrade to a newer version or another browser.

Your browser appears to have cookies disabled. For the best experience of this website, please enable cookies in your browser

We'll assume we have your consent to use cookies, for example so you won't need to log in each time you visit our site.
Learn more

Backing focal


I beg to differ with Peter J Felton's when he says: 'A hemisphere does not have a focal point and would lead to a poor signal'. (NCE 14-28 December) The focal point of a hemisphere (whether concave or convex) is on the focal plane half way between the hemisphere and its centre of radius. Satellite TV dishes are hemispherical as are car mirrors and give perfectly good signals or images.

Graham Pennells, Whitby Bird & Partners,

Have your say

You must sign in to make a comment

Please remember that the submission of any material is governed by our Terms and Conditions and by submitting material you confirm your agreement to these Terms and Conditions. Please note comments made online may also be published in the print edition of New Civil Engineer. Links may be included in your comments but HTML is not permitted.