Hello there, I am currently debating whether to buy a digicam, and have been trawling the web for information. There are a few technical points in the operation of these marvels that I would very much like explained. 1) How does the shutter operate on cameras with LCD viewfinders? I would have thought that the CCD had to be constantly exposed to get the data for the viewfinder. How, then do shutter timings come into play? 2) How is colour seperation performed in the CCD. Various articles have informed me that it is done by a filter in front of the CCD that has red, green and blue spots in front of each sensor element. One article however statet that such a filter was only used on higher end cameras. If so, how do the lower end cameras manage? 3) How are pixels counted in digicams? Is each pixel in a 1024x768 the combined result from three sensors, one for each of the primary colors? Or does a 2,1 megapixel camera really have only 0.7 megapixels for each colour? 4) What are the (technical) differences between CCD and CMOS sensors? I have read that CCD's give better picture quality, but in what way and how much?

Thanks in advance for any information.

Kari Vssurarson

-- Kari Vssurarson (kari@ejs.is), July 14, 2000

Answers

If you do some searching on this forum with the search function, you'll find the answers to nearly all of your questions.

Yes, there are colored filters placed over the ccd or cmos sensor elements. Typically, you really only have 1/4 the advertised resolution of the camera. Interpolation techniques use blocks of 4 pixels to build the rated resolution of the camera. Search for LCD or color filters, or similar, and you'll probably find the previous posts concerning this.

The shutter question is interesting. I think the shutter is normally open to provide video for the LCD display. My guess is that upon fully pressing the button, the shutter(if there is a mechanical one) is actuated(closed) and the CCD is blanked(or purged of data) then the shutter is opened for an exposure then closed and the contents of the CCD are read out. The shutter must then be reopened and LCD video resumes. You can see the LCD blank for a portion of a second and hear the shutter click. That's my story and I'm sticking to it... :-)

Hope that helps somewhat. If you read the old posts and still have questions about color filters, etc., fire away. I'm sure that I and others would be glad to help.

-- Gerald M. Payne (gmp@surferz.net), July 14, 2000.