strangeness about ToUcam CCD size information

[themos]

The 740K ToUCam I have contains the ICX098BQ chip (I think).

In http://www.pk3.org/Astro/astrophoto_ccd_comparison.htm I see the specs:

ICX098BQ

Color

Diagonal=4.5mm(Type 1/4)

Pixel size=5.6µm x 5.6µm

Effective pixels=659x494

These numbers don't all make sense together. The image that I get is a 640x480. The pixels are square so the diagonal of 640x480 is 800. That means that the scale is 1/4 inch : 800 if the image diagonal is REALLY 1/4 inch. But at that scale each pixel comes out to (1/4 inch* 25400µm per inch)/800 = 7.9375 µm per pixel.

That gives for the sides

640*7.9375= 5.08mm

480*7.9375= 3.81mm

which makes the diagonal 6.35 (1/4 inch).

But what's the 5.6µm then? And why is the "chip size" on Sony's PDF file for the chip given as

Chip size: 4.60mm (H) × 3.97mm (V)

One resolution of this puzzle is that the "1/4 inch diagonal" is fictional. This means that the diagonal is 800*5.6 = 4.48 mm , less than 1/5-inch.

Does anybody KNOW EXACTLY what's going on?

thanks

[Milamber]

Where do you get 1/4 *inch* from?

[themos]

Where indeed!

So, it's 1/4 of nothing in particular...

[bern]

1/4", 1/3" etc are a throwback to an old system, from the days of Vidicon vacuum tubes used for TV, they aren't the actual sizes of the chip these days.

bern

[themos]

You know, I'm pretty sure I saw the " notation attached to the 1/4 in some web pages. Anyway, it's good to know for real the actual size of the thing.

[GazOC]

1/4", 1/3" etc are a throwback to an old system, from the days of Vidicon vacuum tubes used for TV, they aren't the actual sizes of the chip these days.

I didn't know that. "Live and learn" as they say...

[zootlewurdle]

I had a very similar puzzle recently when I looked up the specs of my DSI Pro 2.

Pixel size: 8.3 by 8.6 microns

Chip size, 5.59mm by 4.68mm (8mm diagonal, type 1/2)

Effective pixels, 752 by 582

5.59mm by 4.68mm gives a diagonal of ~7.2904mm, so this seems wrong.

8.3 microns * 752 = 6.2416mm

8.6 microns * 582 = 5.0052mm

Both those numbers are out. However, both those numbers give a diagonal of 8.0006mm.

It's also a Sony chip. Seems a bit confusing!

[Tinners]

Aren't we taking for granted that we have zero gap between pixels here?

[themos]

I've always assumed that "pixel size" does not refer to the active size but the distance from one to the next which would include any dead zones.