Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,455   Posts: 1,570,545   Online: 886
      
Page 3 of 8 FirstFirst 12345678 LastLast
Results 21 to 30 of 80
  1. #21

    Join Date
    Dec 2004
    Location
    Milwaukee, Wi
    Shooter
    35mm
    Posts
    3,242
    I believe that a spot meter could be used to determine an SBR if one was trying to make it function as an incident meter by reading of, for instance a gray card in the shadow and in the lit area of the scene and determining the difference in f stops between the two. It would, in my opinion, be sort of cludgy because one would have to be very careful in reading the card...the angle between the meter and the card etc and one would also be introducing some fare in the reading by using the spotmeter. I believe the single largest problem in the incident approach is the freedom from flare in using the meter while there is bound to be some in reality. I believe the spotmeter suffers from having flare that is very likely to be different the the camera/lens combination, not to mention color sensitivity different from the film, and the need to bias your reading through experience that you have gained, when reading dark areas at various distances.

  2. #22

    Join Date
    Mar 2003
    Location
    Greenville, SC
    Shooter
    Large Format
    Posts
    4,813
    Images
    5
    Quote Originally Posted by jdef
    Sandy, HP5+ is available in ULF sizes, for the time being, at least. HP5+/DRU 3min/70F paper ES 1.7 = SBR 4. DRU is a non-staining developer, so I think it might be possible to increase the contrast for UV processes with a staining developer like Hypercat. HP5+ developed in Hypercat 1:200 for 8 min/70F with continuous agitation shows an SBR of 6.6 for a paper ES of 1.7. I'm not sure where HP5+ got the reputation for low contrast, but I've never found that to be true.

    Jay

    Jay,

    HP5+ has had a reputation for low contrast among platinum and palladium printers for many years. People often compared results with TRI-X and found that by comparison HP5+ gave much less contrast. This is in part due to the fact that when these films are developed to the contrast necessary for pt./pd. the curve of HP5+ tends to shoulder slightly while that of TRI-X rises.

    About 2.5 years ago there was a change in HP5+ that made it much more suitable for alternative printers. Ilford made no mention of the change but several experienced pt./pd. printers soon noticed and commented on it, and I confirmed it for myself in both film tests and field work. Simply put, the new Ilford HP5+ is capable of a much higher CI than the old one.

    You are correct in the assumption about the effect of stain. An HP5+ negative developed in a staining developer has a much higher effective printing contrast for UV sensitive processes than for blue and blue/green sensitive processes.

    BTW, you should understand a couple of things about my plotting procedure. It is based on the assumption that the process has a log exposure scale of 1.75, which is about right for AZO #2 and for processes such as carbon, kallitype and palladium, and I always incorporate a small factor for flare into the data. If you use my assumptions for ES and flare in your plotting I think you will find the same thing I have found, i.e. there is no film/developer combination available for ULF workers that will give the CI that is needed for a SBR value of very much below 5. Dick Arentz gives data in his new book for film/ developer combinations useful for SBR values down to 4.2, but his assumption is for a process ES with a maximum of log 1.6.

    In any event the TRI-X versus HP5+ comparison is pretty much a moot issue at this point because the former is only available by special order and Ilford just announced that it would no longer supply HP5+ in ULF size.


    Sandy

  3. #23

    Join Date
    Jul 2003
    Location
    Missouri
    Shooter
    Large Format
    Posts
    171
    Claire,
    I use both incident and spot meter with the Zone Dial by Davis. One side is for incident readings and the other for zone system. After taking a reading with either you just turn the thing over and it tells the SBR and that is how I determine dev. I seem to have better luck with the incident side but at times the spot meter come in handy.
    Wm Blunt

  4. #24

    Join Date
    Sep 2002
    Shooter
    Large Format
    Posts
    4,530
    SBRs from a curve can be obtained by a geometry formula. G=ES/SBR which is nothing more than the Tangent. This is in the book, at least in the 2nd edition.

    Spot meter readings can be converted to SBRs by the following formula:

    SBR=(7*(D-N))/D

    where:
    D= spread
    N= N number (development)

    This I got from Phil when I first started using the BTZS.

  5. #25
    Ole
    Ole is offline
    Ole's Avatar
    Join Date
    Sep 2002
    Location
    Bergen, Norway
    Shooter
    Large Format
    Posts
    9,282
    Blog Entries
    1
    Images
    31
    [QUOTE=Jorge]...
    Spot meter readings can be converted to SBRs by the following formula:

    SBR=(7*(D-N))/D

    where:
    D= spread
    N= N number (development)
    ...QUOTE]

    Let's see: I have a scene with a spread from EV3 to EV17, that's a spread of 14. I developed it to N-3 or something like that - compensating developer by inspection so I don't really know.

    SBR=(7*(14-(-3))/14) gives 17/2, or 8.5

    Another scene, EV4 to EV6 (flat and dim), given a N+2 development:

    SBR=(7*(2-2))/2 is 0?

    Sorry, the formula doesn't work as written...
    -- Ole Tjugen, Luddite Elitist
    Norway

  6. #26

    Join Date
    Mar 2003
    Location
    Greenville, SC
    Shooter
    Large Format
    Posts
    4,813
    Images
    5
    Quote Originally Posted by Claire Senft
    I do get a bit confused with the way that you use the SBR terminology Sandy. Coirrect my thinking: SBR is BTZS Incident system terminology. An SBR of 5 is a flatly lit plane without any lighting variation. I get that impression that when you say SBR 5 that you are referring to 5 stops of difference in lighting ratios between lit and shadowed areas instead of no difference. I am no stickler for terminology but if each of us means something different when using the same term the communications of concepts and ideas can get quite muddled.

    I also believe that SBR is a term that applies only to a scene.
    Yes, SBR is indeed BTZS terminology that is based on and anticipates incident readings. SBR is not a corruption or misuse of the terms LSLR because they are not the same thing, though in some cases they may indicate the same or similar values. As has been pointed out before, a SBR reading is based on a reading of the intensity, or illuminance of the light that falls on the subject. LSLR is based on the brightness or luminosity of light reflected from the subject and is measured with a reflectance meter. Moreover, if you read carefully the pertinent sections in Beyond the Zone System it should be clear that SBR and SLR are not used to mean the same thing.

    When I speak of the 5-stop range I do so within the context of the way Davis describes it, i.e. it is based on the presumption that the maximum subject luminance range of any object in a glare-free, shadow-free area, and that is evenly illuminated, is about five stops. SBR is a concept that ensues from his assumption that the subject luminance range can be estimated by adding the illuminance range (which is the difference between readings measured with an incident meter in the most brightly lit area of the scene and in the shadow areas of the scene) to the 5-stop luminance range. In other words, the SBR system of metering does not give us LSLR, but an estimate of it. In fact, it is impossible to directly measure LSLR with an incident meter at all.

    My response to Kirk in the other thread offered a means of getting around the obvious fact that we can not directly measure SBR values below 5 when there is no difference in intensity in the light falling on the subject in different areas of the scene. The only way to do that is to fudge the issue by simulation.

    At some place in Beyond the Zone System Davis mentions that he used the term SBR to avoid confusion with SLR, which was widely used at that time to mean a single lens reflex camera. Strictly speaking he did not need to make that clarification at all because SBR as he uses ther term is not the same as subject luminance range, or LSLR. The term SBR only has meaning within the specific reference of the BTZS system of exposure and development, which is built around the use of an incident meter and attempts to provide a fast and reliable method of *estimating* the subject luminance range.

    In fact, to say that SBR is a corruption of NSLR is a contradiction in logic, for as Stephen Benskin correctly notes, “subject luminance range can be measured with a spot meter. In fact, you can only assume the range with an incident meter.” SBR is not NSLR. It is a term used with very precise meaning within the framework of a specific system or method for exposure and develoment. It incorporates some of the assumptions of NSLR but it is clearly not the same thing since, as I belive we all agree, it is impossible to measure NSLR directly with an incident meter since it is based on luminance readings. So, far from confusing terms, Davis shows much greater precision in the use of terminology than some of us contributing to this discussion, and I include myself, sadly, in the group.


    Sandy
    Last edited by sanking; 04-16-2005 at 01:58 PM. Click to view previous post history.

  7. #27

    Join Date
    Sep 2002
    Shooter
    Large Format
    Posts
    4,530
    [QUOTE=Ole]
    Quote Originally Posted by Jorge
    ...
    Spot meter readings can be converted to SBRs by the following formula:

    SBR=(7*(D-N))/D

    where:
    D= spread
    N= N number (development)
    ...QUOTE]

    Let's see: I have a scene with a spread from EV3 to EV17, that's a spread of 14. I developed it to N-3 or something like that - compensating developer by inspection so I don't really know.

    SBR=(7*(14-(-3))/14) gives 17/2, or 8.5

    Another scene, EV4 to EV6 (flat and dim), given a N+2 development:

    SBR=(7*(2-2))/2 is 0?

    Sorry, the formula doesn't work as written...
    huh......good try but you rnumbers are not realistic, go out on the field and try it and get back to me...

  8. #28

    Join Date
    Sep 2002
    Shooter
    Large Format
    Posts
    4,530
    Quote Originally Posted by jdef
    In the interest of concensus and precision, how do we refer to SBR values as a function of development, If everytime I give SBR data derived from a film test someone remarks that SBR only applies to the scene? Is there no way to discuss this data without getting into these kinds of terminology debates?

    Jay
    The reason that referring to SBRs as function of development is not good is because it assumes a fixed ES. For example go back and read the posted results from Kirk's numbers. When I used an ES of 1.45 his SBR was 3.6, when I used an ES of 1.05 his SBR was 2.6. So if you say " I developed this film to an SBR of 9", you also have to specify the ES so that we are all talking about the same results. OTOH if you say " I develop this film to a G bar of .76" then regardless of the ES we are individually using, we all can relate the results to our own experience.

  9. #29

    Join Date
    Jun 2004
    Location
    Portland, OR
    Shooter
    4x5 Format
    Posts
    3,268
    Quote Originally Posted by sanking
    SBR is a concept that ensues from his assumption that the subject luminance range can be estimated by adding the illuminance range (which is the difference between readings measured with an incident meter in the most brightly lit area of the scene and in the shadow areas of the scene) to the 5-stop luminance range. In other words, the SBR system of metering does not give us LSLR, but an estimate of it. In fact, it is impossible to directly measure LSLR with an incident meter at all.
    Jay - you need to remember the above - it's key to the BTZS meter with an incident meter. Davis is making an assumption in order to devise a simplified metering system. There's nothing wrong with making an assumption like that - and by many accounts, it works really well for many types of situations.

    My question in the other thread was to find out what happens (incident metering-wise) when a subject fell outside of the conditions that the basic assumption covered.

  10. #30

    Join Date
    Jun 2004
    Location
    Portland, OR
    Shooter
    4x5 Format
    Posts
    3,268
    Quote Originally Posted by sanking
    At some place in Beyond the Zone System Davis mentions that he used the term SBR to avoid confusion with SLR, which was widely used at that time to mean a single lens reflex camera.
    Wouldn't SIR - "Subject Illumination Range" have been appropriate if Davis modified the system to not include the addition of "5" to the difference of all readings?

    (But then it doesn't matter, as Davis is free to use any terminology he wishes. It is his system, after all.)

Page 3 of 8 FirstFirst 12345678 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin