Re: [Leica] Re: UV filter for Noctilux-measurable light loss?? or any lens

[Henry Ambrose <digphoto@telalink.net>]

>>Anyone else have any thoughts on whether a UV filter cuts out a measurable
>amount of light?

It will make any difference that you could measure with any normal camera 
meter. 
Or see on film.

The idea that a filter will have a greater effect in low light "available 
darkness" is not correct. The reasoning that you already have only a few 
units of light to work with does not fly. The filter's exposure factor 
holds what ever the combination you set on the camera or the existing 
light level. (exception to colored filters and light, a different subject)

To get "normal" exposure the film is still receiving its standard dose of 
units of light. For instance, if you render Zone VI exposed skin on a 
negative, that area of film got its full dose of light whether the 
negative was exposed in full sun or in a coal mine by candlelight. (full 
dose defined by film speed and density desired)

Demonstrate for yourself:
Set your camera on a tripod facing a blank wall. Expose some film both 
with and without your filter, making no other adjustment to the camera. 
Write down what you did for each frame. Develop the film. Look at it. Now 
you KNOW.

If you want to carry this further do the above inside with the light 
level adjusted to high and low. (turn the lights on or off and make 
exposures with appropriate settings)

This will also PROVE whether a given filter (or combination of filters) 
vignettes or not.
Try it at different apertures this time especially if you're stacking 
filters.

Exposing one roll of film this way can answer this question. You'll not 
have to wonder again. You could test several filters with one 36 exp. 
roll!


Happy testing,
:)

Henry