Then again, some will state the sensitivity with AGC on but not what the AGC gain is. Camera specmanship is too vast a subject to expand on in this article but suffice to say the f-number of the lens is a most important consideration. In simple terms the smaller the f-number the more light is passed to the sensor, therefore f1.2 is better than f1.8. The percentage of light passed by different apertures is listed in table 1. This shows the percentage of light falling on the lens that is passed to the sensor.
Some manufacturers specify camera sensitivity as that on the faceplate or sensor.
In these cases use these ratios to convert to the light required on the lens. An example taken from distributors catalogue shows two 12mm auto iris lenses, one f1.4, and one f1.2. Another consideration is, how efficient is the lens at passing the maximum amount of light. There are several factors that determine the efficiency of a lens and of course they all cost money. This is generally only available from the manufacturer.