Updated 23 June 1999

Amateur Astronomer's Notebook

CCD Imaging Topics

Meade Pictor 216XT Field of View w/ Celestron C-11


This page will illustrate the size of the field of view of the Meade Pictor 216XT CCD camera when used with a Celestron C-11 telescope. The purpose is to show just how small an area the CCD camera can cover.

Celestron C-11

My particular model of the C-11 is the CG-11 (all Celestron 11 telescopes have the same optics however). The C-11 optical system is an 11" F10 system "as is"; in the metric system the unit is a 280mm F10 system (focal length is 2800mm).

When used with various focal reducers, the C-11 optical system may be altered as follows:

The Field of View... Not Very Big!

The field of view of the C-11 when used in various configurations (focal reducers) is as listed below:

  1. When used without a focal reducer: 2800mm F10: FOV = 3'59" x 2'53"
  2. When used with an F6.3 focal reducer: 1764mm F6.3 system: FOV = 6'19" x 4'43"
  3. When used with an F3.3 focal reducer: 924mm F3.3 system: FOV = 12'3" x 9'0"

To get a feel for just how big these fields of view really are, consult the diagram below. The large circle represents the typical size of the full Moon (30 minutes of arc wide). Rectangles A, B and C below correspond to the areas 1, 2 and 3 in the above list.

As you can see, even with an F3.3 focal reducer, the fields of view are quite small. Consider also that a standard 35mm film format can easily contain the Moon's entire image when the C-11 is used at F6.3! The diagram above helps to illustrate why locating targets is one of the tricky things when it comes to CCD imaging. It's not so bad if you have a flip mirror unit (or a properly aligned high power finderscope)... if you are running without one of these features you will encounter more difficulty acquiring your target.

Note: The "match" of the Pictor 216XT CCD camera is nearly ideal when the C-11 is used with an F3.3 focal reducer (this applies to deep sky imaging).

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