From: Milton Aupperle <milton@outcastsoft.com>

Date: January 26, 2009 10:13:21 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] chip size, Flea 2...

Sony is correct in the size of the CCD dimensions. Sony is accounting for the gap between pixel elements, which Astro Planner doesn't know about. In fact we don't know what the gap is, because it's not published anywhere that I know of. We can only estimate what it is, which should be about 1.5278 microns.

What Astro Planner does is multiply the number of pixels by the size in microns, so they come up with 4795.2 microns wide, which is 4.7952 mm and rounded is 4.80 mm.

From my own measurements on my Flea (7.4 micron pixels), for an image size of 640x480 (you don't get the extra 8 pixels in real use) the dimensions were 4.736 x 3.55 mm. You can then use the formula:

Width in minutes arc = (4.736 * Focal Length in MM ) / 3438.0

Height in minutes arc = (3.55 * Focal Length in MM ) / 3438.0

to calculate the FOV. So Astro Planner should be quite close.

Also as soon as you stop using prime focus, your "guessing" at what the actual focal length your actually getting with a Barlow or Focal Reducer.

HTH..

Milton

On 26-Jan-09, at 4:59 PM, Mark Gaffney wrote:

Hi Milton, The Sony site you`ve directed me to gives a chip size for

the ICX424AQ chip used by the Flea 2 as 5.79mm (H) x 4.89mm (V).

However, when I enter the details for the Flea 2 into Astroplanner`s

(v2) Imagers window in "Resources", (7.4um x 7.4um & 648(W) x 488(H)

as number of pixels) I`m getting a reading of 4.80 mm(W) x 3.61 mm(H)

for sensor size. Which of these would be more accurate? Mark.