p.5

 

To do this, you just need one cirlce like the one depicted below, but using the two is better. The circle was made in such a way that when it covers exactly 10% of picture width, the numbers show the hundreds of lines per picture width. You need to print out the circle(s) or, if you don't have a good printer, send me an e-mail, so I will arrange sending you the two copies for $5, shipping included.

Procedure 1. Fix the circle on any wall. A sunny wall would be optimal since you don't need a tripod, alternatively use flash. 2. Check in the viewfinder whether the circle is on the center and covers (very roughly) 1/10 of the frame height. You may fix another circle at the frame's edge, so you'll get the data for the center and the side at the same time. 3. Make a photo on the auto focus mode. 4. Download it onto a computer. 5. Find out what is the thinnest line is still visible, check with the chart on the left; let's call this number "L". 6. Count the number of pixels of the entire circle diameter image, call it "D". 7. Find out at what resolution mode have you made the picture and read the entire picture height (in pixels), call it "R". 8. Do the math: The Corrected Line Widths (in 100's, call it "W") _______________W = 0.1 * L * R/D 9. Ideally, the value of W should be equal to R/100, if it's not (and usually it isn't) the lens of your camera is not matching the resolution of the sensor and, in fact, your camera resolution is: The Real Camera Resolution = Sensor Resolution (in mega pixels) * (100 * W/R)2

Example The picture on the left shows an exapmpe how to calculate the Real Camera Resolution. It is sold as a 3.1 M pix camera, but in fact it is only 1.9 M pix. And don't even think that this is the really bad camera. Most other snap-shots perform even worse! I hope I have convinced you of the importance of camera testing before you actually buy it. I personally own Canon A70, and use it only in its 1.9 M resolution mode. It makes an excellent 1.9M pix camera with its 1600x1200 pixel resolution.

 

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