Resolution Test Chart – Siemens star

The resolution of a photography image depends on the sensor or film material and on the lens. Proclaiming the sensor delivers crisp images and its data is not corrupted by software demosaicing etc. the resolution of the lens is limiting image sharpness.

How to test your lens

The basic procedure is to take a photo of a test chart with fine detailed patterns of individual sizes. Larger objects will be visible whereas smaller pattern will diminish details into blurry gray.

One chart is the Siemens star wich consists of n black and white sectors. All lines concentrate in the middle where dueto the limited resolution a gray circle occurs. It’s diameter d to the image size gives the resolution l:

lt

I made a  Siemens star with 314 sectors which simplifies the calculation:

l314t

Example

IMG_0963_0966

lens: Pentacon 300mm at F4.0, d = { 200, 300, 400 } pixels

camera: Canon 1000D, Sensor is 22.2 mm wide with 3888 horizontal pixels

resolution: l = d / 100 = { 2, 3, 4 } lines/pixel;

d * [ 3888 pixels / 22.2 mm ] = { 350, 525, 700 } L/mm

(some times d is given in LP/mm ,line pairs, one black and one white line; 1 LP/mm = 2 L/mm)

As stated above. With modern cameras and increasing Sensor Pixel count, the image resolution limiting factor is the optics, especially when using old film camera lenses designed for larger image circle. It is similar to a soundcard sampling with 384 kHz while the audio signal is just 20 kHz. The signal’s resolution or bandwidth stays still low.

c)langhans


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