The use of filters and filter factors are sometimes not well understood. This is a perfect example of the apparent confusion that exists. The use of filters in black and white photography is for the purpose of affecting contrast. In this case the unfiltered exposure value of the green foliage and the red roses were probably very near each other. If a photograph were made without the use of a filter the print values of the green foliage and the red roses would have been near each other. By using a red filter the blossoms were rendered lighter and the foliage is darkened. Conversely if a green filter such as a 58 would have been used the blossoms would have been darkened and the foliage would have been lightened. The use of a filter factor and how it applies to the manner in which colored objects are rendered are of only approximate value in determining the rendering of these objects. In this case had a 23 or a 25 red been used the effects would not have been so severe. The only way, of which I am aware, that one can determine more nearly the effects that filters have on colored objects is to meter through the filter with a meter that has the spectral response of the modified Zone VI.
In this case the effects that this 90 red filter produced are perfectly predictable. It created enough contrast between the roses and the foliage that the development of the film was too extreme for the film to contain the contrast range. The characteristic curve of the film and it's inherent properties were violated.
If you wish to continue to use the 90 red filter on this subject matter, you will need to compensate by giving at least three stops more exposure (to gain detail in the foliage) and reduce development to reduce contrast. This would probably be on the order of at least a minus 4 development. This would probably require a water bath or another means of compensating development. The results would be better using a less severe filter.
The use of an orange filter may have very little effect in lightening the rose blossoms, just as a yellow would. The orange would however darken the foliage.
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One slight correction ... the use of a "red" filter does not really "lighten" red colored areas; it simply darkens all else - especially blue (and to a large degree - green).
I'm not familar with a "90 Red", but it may be too severe for this application - but all that is dependent solely on the "vision" and intent of the photographer.
Try a less "severe" filter - Red 25, or orange ... or yellow....
On the image you highlight 2 zones (both v and vi). If as in the senario mentioned you placed the leaves at zone v and the roses on zone vi. In my calculations to get the image that you have, only a major change in light conditions to the Zone v leaves could have caused the 'blow out' that you have. The leaves should have become a zone iii.5 with the red filter(Darker than original placement). Was there a change in light?
Not that I recall, but it is a good point I hadn't considered. The leaves did have direct light falling on them from the rear. I suppose if the sun had poped out of the overcast it would have thrown off the Z-V reading a great deal and while the roses were shadded they did not change to the degree of the leafs...
[quote="Bruce (Camclicker)"]I was shooting a group of roses - deep red - with lush green leaves around and behind the main subject. It was a low light/low contrast morning and had rained earlier, the flowers and leaves were showing rain drops. I metered on the green leaves and placed them on Z-V, the flowers fell about Z V-1/2. I wanted to use a red filter (#90, factor of 5) and opened up 2-1/2 stops. It was a close up shot and I wanted to use a shallow DOF to capture the Bokah in mid tones and the subject roses sharp and with *etched* detail. The exposure after filter factoring was 1/4sec @ f-4.5
After considering your data, observing you print, and reading other posts, I wish to offer a possible explanation of some of your resuts. First the subject roses were backlighted, which always makes it hard to get a meaningful luminescent determination with reflective meters. I use a spot meter for similar situations and compare the reading with an incident reading. In many cases, I have found very high, almost specular readings from light reflected from leaves back lighted in a way very similar to those in your print. It is hard to realize this just by observing the scene or reading with an averaging-type or other reflective meter. You have to admit that the leaves were pretty much over exposed and this could be the reason. Second, your #90 filter, I believe, is the "viewing" filter intended for making a color scene appear monochromic to the observer. I recall that they give an overall brown appearance. I have no idea how b&w film would be affected - sorry.
If possible, in the future you should probably try an incident light metering and use a fill-in flash to bring the foreground up to the desired zone. I would also recommend that you minimize the use of color filtration in such a scenario and explore the use of polarizing filtration to cut down reflective possibly specular light from the leaves - easily said after the fact, right?
As far as DOF affecting exposure - I'll have to say not probable except in cases of in-camera metering that can get confused when metering scenes with high background luminances.
Truly, dr bob,
You haven't read the question thoroughly enough: He DID use a spotmeter (Pentax V). Also, the "90" filter is not a wratten designation, but a B+W type number entirely unrelated to the Wratten codes...
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