Filters and Exposure

Think the light is starting to glow a little - while going over exposures of past images in my head, I realized that one reason that some of my images may not 'sing' is that the exposure is all wrong. When using filters I tend to take the light meter and hold a filter in front of it to get the exposure settings...now it all made sense until this morning when it dawned on me that the exposure I was getting would be for 18% gray..Right? I was trying to get the correct exposure using the filter, when actually the correct exposure would be the unfiltered reading + the filter factor ? Is this correct?

So if using a filter with a factor of +2 then a reading of say f/16 at 125 would need and adjustment to either f/16 at 30 or f/5.6 at 125?

Is the light coming on or is it about to go out? :confused:

Thanks in advance for the input...

yes. I tend to take the meter reading and then set the exposure and then add the filter corrections. I don't use the filter that much.


lee\c

With a filter factor of 2 you would open the lens 1 stop or multiply your shutter speed by 2, (in your example, 2/125 or 1/60).

But yes, I would definitely determine my best exposure and then apply the F.F. (though some will disagree) unless I was just doing general shooting with the filter in place and using a through the lens meter.

also - some of the "newer"-type films (ie T-max) can need a slightly different filter factor to the older- type emulsions. I did have a link to a site that gave all the filter factors for diffent films but i cant find it now - sorry. Either way, I reckon its best to meter then apply the factor, rather than through the filter.

Another way of doing this is to meter an object without the filter...(the sky for instance) then meter through the filter on the same object. I do this when I use reflective spot metering. Obviously when I use incident metering then I use filter factors.

The reason that this will enable you to more accurately determine the effects of the filter is that "filter factors" do not have the same effect on different colored objects. In other words a #25 Red may have an 8 (3 stops) effect on a blue sky...but it would have a far different effect on a red fence, for instance. It would have another effect entirely on green foliage.

A yellow number 12 will have one effect on the sky and another effect on yellow straw.

That is why when one is attempting to visualize how a scene will render the information gained by metering without and then with the filter is very informative.

A study of a color wheel will help in understanding the effects of filters...same colors lighten...opposite colors darken.