Does any one know the document number for an ASTM for Light Loss Testing (if there is one)?

Does any one know the document number for an ASTM for Light Loss Testing (if there is one)?
Can you provide some details or context? Describe the conditions.

Sorry for the delay in responding.


We manufacture enclosures for the CCTV industry. One of the requirements is a specific f stop or light loss. We currently use a black box and light loss controller to calculate the amount of light loss.

Also, how is f stop converted to a light loss %?

Thanks in advance for any help.

Sorry for the delay in responding.


We manufacture enclosures for the CCTV industry. One of the requirements is a specific f stop or light loss. We currently use a black box and light loss controller to calculate the amount of light loss.

Also, how is f stop converted to a light loss %?

Thanks in advance for any help. Mshell,

If I understand, you're asking what is the attenuation of the light for different f-stops?

If that is the case, the F stop is equal to the ratio of the Diameter of the aperture to the focal length of the lens (focal length/diameter). There are standard f-stops like f1.0 f1.4, f2.0, f2.8......f22 ad infinitum. The amount of light is double when you go down from one standard f stop to the next lower or 1/2 when you go up a standard f-stop. The reason it is inversly proportional, is because the area of the aperture (a circle) increases as the f stop decreases.

Look at A Tedious Explanation of the f/stop (http://www.uscoles.com/fstop.htm) for a more detailed (and probably clearer) explanation. You will also be able to calculate the percent difference in light for non standard f-stops after reading this.

Thanks Al,

This site has helped. :thanx: