Decided to stop buying telescopes?

1. If you are interested in wide field objects, notice that the light
gathering power increases as the square
of the aperture, but the maximum true field possible varies inversely with
the square of the aperture. A 20 inch scope
will show objects four times as brightly as a 10 inch scope, but will have
one-quarter of the maximum true field.

The area of the Field of View will be 1/4. The angular FOV will be 1/2.

Jon

Bill Meyers wrote, in part:
A few thoughts that may help:
1. If you are interested in wide field objects, notice that the light
gathering power increases as the square of the aperture, but the
maximum true field possible varies inversely with the square of the
aperture. A 20 inch scope will show objects four times as brightly
as a 10 inch scope, but will have one-quarter of the maximum true
field.

Bill is correct with respect to the *area* of the field of view. The true field
of view produced by an eyepiece is often described in terms of field
*diameter*, which varies directly with any change in focal length. For example,
an 8.8-mm Meade UWA eyepiece shows a 39 arcminute diameter field in my 10-inch,
f/4.5 at 129X. In a 20-inch, f/4.5 that same eyepiece would produce a 19.5
arcminute diamter true field of view: one-half the field diameter and
one-quarter the field area.

Regards,

Bill Ferris
"Cosmic Voyage: The Online Resource for Amateur Astronomers"
URL: http://www.cosmic-voyage.net
=============
Email: Remove "ic" from .comic above to respond

Hello, Bill,
Yes, you are right and I should have stated it more precisely. Thanks for the
clarification.
Bill Meyers

Bill Ferris wrote:

Bill Meyers wrote, in part:
A few thoughts that may help:
1. If you are interested in wide field objects, notice that the light
gathering power increases as the square of the aperture, but the
maximum true field possible varies inversely with the square of the
aperture. A 20 inch scope will show objects four times as brightly
as a 10 inch scope, but will have one-quarter of the maximum true
field.

Bill is correct with respect to the *area* of the field of view. The true field
of view produced by an eyepiece is often described in terms of field
*diameter*, which varies directly with any change in focal length. For example,
an 8.8-mm Meade UWA eyepiece shows a 39 arcminute diameter field in my 10-inch,
f/4.5 at 129X. In a 20-inch, f/4.5 that same eyepiece would produce a 19.5
arcminute diamter true field of view: one-half the field diameter and
one-quarter the field area.

Regards,

Bill Ferris
"Cosmic Voyage: The Online Resource for Amateur Astronomers"
URL: http://www.cosmic-voyage.net
=============
Email: Remove "ic" from .comic above to respond