Can DOF affect Exposure?

Discussion in 'Exposure Discussion' started by Bruce Osgood, Jun 20, 2003.

  1. Bruce Osgood

    Bruce Osgood Membership Council Council

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    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

    The lens was Zeiss VS 80-200 at about 85mm.

    The film was 35mm Pan F+ rated at EI 40.

    The development was: small tank (one roll); DD-X 1:4; 22-c @ 5:30.

    The results are: Blownout midtones - unprintable even burning at 2X base exposure. The subject roses look good and are quite interesting to me. They are in the area of my intent.

    My questions come down to:
    1) While trying to capture Bokah with a shallow DOF would/could luminosity be scattered to a point different than indicated by a spot meter (Pentax V)?
    2) Did I simply process the film incorrectly?
    3) Did I incorrectly apply the filter factor (factor of 5 = 2-1/2 stops)?
    4) Given the subject to film plain distance of less than 1 meter should I have compensated for that in exposure also?

    The weather conditions for today and tomorrow are the same as they were a couple of days ago (and weeks before that) when I took the picture and I would like to try it again.
     
  2. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    I think (4) is a possibility, if you were using an external meter. At 1m, magnification with an 85mm lens is about 1:10, so you need to add 1/3 stop, and if you were closer, you would need to add more. Of course, if you were using the camera's internal meter, it would compensate automatically.
     
  3. Ole

    Ole Moderator Staff Member Moderator

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    1) No, but... The spotmeter doesn't focus close. It will be influenced by the surroundings.

    2) Seems a bit too bad to be mere processing?

    3) That sounds about right to me.

    4) Yes, but failing that would lead to underexposure.

    I have tested the bokeh of an old (1934) Heliar 150mm by shooting the same scene at f:4.5, f:16, and f:45 adjusting the shutter time accordingly. The exposures were identical - incidentally proving that the shutter is still reasonably accurate.

    Wrong exposure is the likely culprit - check your meter. And also have a look at how it behaves close up...
     
  4. Annemarieke

    Annemarieke Member

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    My Minolta Spotmeter F does not work properly within 1m30cm. I guess your Pentax V might have the same problem.

    Try measuring the roses from farther away. If the Pentax is a 1° meter, this will work OK.
     
  5. Aggie

    Aggie Member

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  6. Eric Rose

    Eric Rose Subscriber

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    Your meter does not read deep red very well. Most meters don't. I usually put a grey card in the scene and meter off that if possible. The same problem happens if you put a red filter in front of the lense on the spot meter. For some reason they are not linear in their response to color.
     
  7. Donald Miller

    Donald Miller Member

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    The one thing which you reported that I tend to question is:

    .

    The reason that I question that statement is that I have heard of blown out /blocked highlights and I have heard of underexposed shadows but I have never heard of blownout midtones in my life.

    If the shadow detail is there and the highlight highlight detail is there then the midtones need to be there as well. Perhaps if one knew which end of the spectrum you feel is missing then a direction might be more readily addressed. The matter of metering this scene is the same as always. Expose for the shadows and develop for the highlights.

    Additionally you failed to account for the effects of the red filter on the green foliage. It darkens it as it is the opposite of green. Filters lighten like colors and darken dissimilar (opposite) colors in a print.

    .

    The red filter lightens the color of the red roses and that is why you got some exposure on the blossoms (I am assuming here) but no printable exposure on the green foliage.
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  8. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Here's another thought:

    An overcast morning at EI 40 should give you about f:5.6 at 1/40 sec., so make it 1/30 sec. to account for the magnification factor, and adding 2.5 stops for filter factor gives you f:4.5 at 1/8 sec., so you should have been in the ballpark, exposure-wise.

    Could you post a scan? Like Donald, I'm a bit unsure about what you mean by "blown out midtones."
     
  9. Bruce Osgood

    Bruce Osgood Membership Council Council

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    See Chritique Gallery
     
  10. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Looks like the dark red filter lightened the roses substantially, and now they're hard to print. The green leaves should look virtually black with that filter. My strategy would be to increase the overall exposure to get detail in the highlights, if that is possible, and dodge to get the shadows, maybe using a lower contrast grade.

    This might also be a neg to try some pre-flashing on to get the highlight detail, but there are others here more experienced in that technique than I am.

    Next time, try a lighter red filter.
     
  11. Aggie

    Aggie Member

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  12. lee

    lee Member

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    looks to me like the development was blown and over done. Maybe time or temp.

    lee\c
     
  13. Donald Miller

    Donald Miller Member

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    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.
     
  14. Ed Sukach

    Ed Sukach Member

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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....
     
  15. Robert

    Robert Member

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    Ya which #90? Kodaks would be the viewing filter. That doesn't look red to me. I just looked-) Do you mean a #29?
     
  16. Bruce Osgood

    Bruce Osgood Membership Council Council

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    B+W - 090 - 5X
     
  17. philldresser

    philldresser Subscriber

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    Bruce

    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?

    Phill
     
  18. Bruce Osgood

    Bruce Osgood Membership Council Council

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    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...
     
  19. dr bob

    dr bob Member

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  20. Ole

    Ole Moderator Staff Member Moderator

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    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...
     
  21. Ed Sukach

    Ed Sukach Member

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    Got it .... From the B&W catalog: "Filters Special Effects Acessories From the Pros to the Pros":

    The filter is a B&W090 "Light Red" - equivalent to a Wratten 25 or Hoya R25.
    The filter factor is given as 5 - requiring a filter correction of 2 1/4 stops- close enough to the 2 1/2 used.

    All I can say is "That is what happens when a B&W090 is used to photograph roses".
     
  22. dr bob

    dr bob Member

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    Thanks for the edification. I have no knowledge of B+W filters. Rereading the original post I don't see any referal to the brand of filter. I have often wished to see a comparitive chart of the various filters. There have been some implied work (A. Adams - Schaffer Vol I e.g.) but where is a comprehensive list?

    Truly, dr bob.