Basic Photography Examination: Brief Introduction to the Photometric Principle of Exposure Meter?

Exposure meter is the main tool for measuring light intensity, and its basic working principle is to convert light signals into displayable electrical signals to represent the intensity of light.

A selenium photocell exposure meter.

Principle:

When the selenium photocell receives different intensities of light, it will generate different intensities of current, and the corresponding intensity of light will be displayed by galvanometer.

Description:

1, low sensitivity, difficult to detect in weak light.

2, the volume is large

Second, cadmium sulfide photoresistor exposure meter (Cds)

Principle:

When cadmium sulfide photoresistor is exposed to different intensities of light, its resistance will change accordingly. Through the external battery, the corresponding light intensity will be displayed on the ammeter.

Description:

1, sensitive to low light.

It is more sensitive to red light than the naked eye.

3. It has a memory function for strong light. When measuring a scene with high brightness, immediately measure a scene with dark color, and the value is obviously higher. It usually takes 1~2 minutes to return to normal.

Three, silicon photovoltaic cell exposure meter (SPD, SPC)

Principle:

When the selenium photocell is irradiated by different intensities of light, it will generate different intensities of current. Through special power supply and signal amplification circuit, the corresponding light intensity will be displayed on the galvanometer.

Description:

1, sensitive to low light.

2. No memory effect

It is sensitive to blue light and needs to be corrected by a filter.