cross-polarizing on lights and camera

[Mark Woods]

can anyone walk me through the steps of positioning my polarizing filters to red uce reflections on a glossy black painting i'm photographing? i assume i put the polarizing filters over the two lights first, and then one on the camera. but w hen i put them on the lights, how do i orient them? and do i look at the results of different orientations from behind the lights, or behind the camera? then, w hen i go to put a filter on the camera, do i orient it with the light-filters pr esent or absent? what is the right sequence for all this? and then, do i just ad d two stops of exposure to compensate for the filter on the lens, and take an in cident reading off the painting once the filters are in place over the lights? t hanks.

mark

[Ellis Vener]

You orient the filters on the light in the same direction, say vertical. The fil ter on the lens would then be rotated to the polarized axis is horizontal. In ot her words the angles need to ba at right angles to each other. How i do it is set th e filters on the lights and then while looking through the camera (with the filt er mounted) I rotate the filter till the reflections disappear. Using electronic fl ash I take an incident reading (I read at each corner and in the center of the p ainting to ensure even coverage and adjust the position ofthe lights until all readings are within 1/10 of a stop of each other) and then subtract the filter factor of the polarizer. And then I .Polaroid.

[Mark Woods]

thank you so much, ellis.

let me make sure i understand, though. it does not matter how the two on-light filters are oriented, so long as they are oriented the same as one another and perpendicular to the axis of the filter on the lens? so there is no need to be twisting and turning the two on-light filters to see their effect on the glare: just make sure their axes of polarization are either both vertical or both horizontal (these are equally good, i suppose? no reason to prefer "both vertical" over "both horizontal"?). then i can go to the camera, put a polarizing filter on it, and rotate THAT filter to reduce glare/reflections. and the maximum reduction will occur when it's axis of polarization is perpendicular to the axes of the two on-light filters.

and regarding the exposure: it seems i should take the incident reading WITH THE FILTERS ON THE LIGHTS, with the meter at the position of the painting but pointing towards the camera, and then add two stops of exposure to compensate for the on-camera filter, then shoot a polaroid to test, and perhaps bracket the chromes, and perhaps run one and hold the rest so i can push or pull as needed. does this sound right? any improvements you can recommend? thank you again.

mark

[Carl Weese]

Mark,

An extra consideration--you may not want to completely eliminate the flare because this can leave the painting flat and lifeless-looking. The surface of a painting is an important part of its 'presentation' and using maxiumum cross-polarization can work against you. I usually adjust the lens polarizer until most of the obscuring flare is gone, but leave just a bit of "shine" as seems appropriate for the actual surface treatment of the painting in question.---Carl

P.S.---my wife is a painter so I get to do a lot of this....

[Ellis Vener]

let me make sure i understand, though. it does not matter how the two on-ligh t filters are oriented, so long as they are oriented the same as one another and perpendicular to the axis of the filter on the lens? s o there is no need to be twisting and turning the two on-light filters to see th eir effect on the glare: just make sure their axes of polarization are either both vertical or both horizontal... then i can go to the camera, put a p olarizing filter on it, and rotate THAT filter to reduce glare/reflections. and the maximum reduction will occur whe n it's axis of polarization is perpendicular to the axes of the two on-light filters.

Yes.

<I> and regarding the exposure: it seems i should take the incident re ading WITH THE FILTERS ON THE LIGHTS, with the meter at the position of the painting but pointing towards the camera, and then add two stops of exposure to compensate for the on-camera filter, then shoot a polaroid to test, and perhaps bracket the chromes, and perhaps run one and hold the rest so i can push or pull as needed. does this sound right?</ I>< P>That's right. Do you know what the filter factor of your camera filter is? Mak e sure you keep the camera well shielded from flare from the lights.