Misunderstanding pixel size

[m37]

Right, Canon EOS1000D Horizontal is 22.2mm with 3888 pixels. 22.2/3888=0.0057. Pixel size is quoted everywhere as 5.7 microns.

DMK21 is 4.6mm horizontal with 659 pixels. 4.6/659=0.0069 but everything says 5.6 microns.

I am confused. What am I missing? Is there a gap between the pixels of 1.3 microns? Why is this not present on the DSLR chip?

cheers

[Merlin66]

Hmmm.

My DMK21 is recorded as 2.8 x 3.7mm

659 x 494 pixel matrix of 5.6micron pixels......

""

The ICX098BL 

• Image size: Diagonal 4.5mm (Type 1/4)

• Number of effective pixels: 659 (H) × 494 (V) approx. 330K pixels

• Total number of pixels: 692 (H) × 504 (V) approx. 350K pixels

• Chip size: 4.60mm (H) × 3.97mm (V) -NOTE this is not the same as the active area!

• Unit cell size: 5.6μm (H) × 5.6μm (V)

""

[Guest]

Right, Canon EOS1000D Horizontal is 22.2mm with 3888 pixels. 22.2/3888=0.0057. Pixel size is quoted everywhere as 5.7 microns.

DMK21 is 4.6mm horizontal with 659 pixels. 4.6/659=0.0069 but everything says 5.6 microns.

I am confused. What am I missing? Is there a gap between the pixels of 1.3 microns? Why is this not present on the DSLR chip?

cheers

I have no idea what you are asking or saying??..

[pete_l]

There are two issues here.

Taking the basic chip dimensions divided by the number of pixels attribute gives you the "micron number" you refer to. This is really the distance between the centres of adjacent CCD pixels. That number is good for calculating the resolution of a CCD / telescope combination, in terms of arc-seconds per pixel.

As you suggest, the sensitive part of individual pixels do not butt up against each other (unless you're willing to sell your house and buy a back-illuminated CCD). That means that some pixels will hit the sensitive part of the CCD in one of the pixels and get detected. Others will fall between the cracks: the space taken up with the CCD wiring and actual detectors, themselves. How big these gaps are will depend on the technology of the CCD sensor.

One technique that Sony use in their sensors is to place a "microlens" over each pixel, and it's associated "gaps". That will focus the photons that would have failed to be detected onto the light-sensitive parts of a pixel, thus increasing the chances of it being detected and therefore the overall sensitivity of the CCD.

Since these concepts are glossed over by marketing blurb (esp. in DSLRs where the only thing people care about is having far too many pixels to ever be able to see them all ) you won't see terms like Quantum Efficiency used in the technical data if you ask someone in Curry's about the specifications fof a new DSLR

[stoffe]

M37 here is your nice lens in your avatar

http://petapixel.com/2013/02/10/the-infamous-hal-9000-was-built-around-an-nikkor-8mm-f8-fisheye-lens/

Here is some information about DSLRs sensors and QE.

http://sensorgen.info/

[m37]

Thanks guys

@ Merlin - That's me misunderstanding the spec sheet then! Cheers mate.

@MagnaMan - I was asking about the apparent disparity between the spec sheet and my actual images regarding physical chip size / number of pixels = pixel size. Turns out only part of the chip is active and contributes to the image.

@Pete - Thanks man, that's cleared up a lot for me. I am totally going to go to Currys and ask about QE though

@Stoffe - Thanks for the QE link, been looking for that info for ages to help with my flats. Also, HAL sees us through a Nikon lens? I always hoped it would be a Pentax!

cheers y'all