From: Mark Gaffney <markgaffney@mac.com>

Date: January 26, 2009 10:33:54 PM MST

To: Astro_IIDC@yahoogroups.com

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

Thanks Milton, The way I`ve done it is to multiply my scope`s focal length (2350mm) by whatever reduction factor I`m dealing with (0.63x or 0.3x & 0.6x for the Mogg reducers) & entering the adjusted FL as a new entry for the scope. I have lots & lots of different entries in the FOV indicator window of The Sky 6 for different configurations. I was getting a disparity in size of FOV there, with these 2 measures ( the Sony one & the Astroplanner one). I`ll keep using the Astroplanner one now I guess. Mark.

On 27/01/2009, at 4:13 PM, Milton Aupperle wrote:

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.

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