Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 69,982   Posts: 1,523,883   Online: 1073
      
Page 1 of 3 123 LastLast
Results 1 to 10 of 22
  1. #1
    Christopher Walrath's Avatar
    Join Date
    Dec 2005
    Location
    Milton, DE, USA
    Shooter
    4x5 Format
    Posts
    6,980
    Blog Entries
    29
    Images
    19
    Wirelessly posted (BlackBerry9000/4.6.0.167 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102 UP.Link/6.3.0.0.0)

    Ian brought something I had NEVER before considered. Could someoe please explain to me how and why there would be reciprocity on underexposures of short duration? Would this occur with small apertures and s/s less than one second as well with general films?
    Thank you.
    CWalrath
    APUG BLIND PRINT EXCHANGE
    DE Darkroom

    "Wubba, wubba, wubba. Bing, bang, bong. Yuck, yuck, yuck and a fiddle-dee-dee." - The Yeti

  2. #2
    Mike Wilde's Avatar
    Join Date
    Aug 2006
    Location
    Misissauaga Canada
    Shooter
    Multi Format
    Posts
    2,939
    Images
    29
    My sort of non sceintific short duration exposure reciprocity explanation- you need something like 4 electrons to hit the film spot and transfer their energy to turn a halide to a pending elemental state (latent image formation). When exposires are really short, there is not a good cahnce of 4 electrons to make it though while the shutter is very briefly open.

    My long duration reciprocity failure explanation - some of the electron charges recieved fade away before enough come together to give the 4 electron equivalent and make the speck suitable to turn metallic once developed.
    my real name, imagine that.

  3. #3
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,934
    Images
    65
    Chris;

    There is both LIRF (Low Intensity Reciprocity Failure) and HIRF (High Intensity Reciprocity Failure). Any film can fail under low intensity light with long exposures or at high intensity light with short exposures.

    PE
    Last edited by Photo Engineer; 07-07-2009 at 05:29 PM. Click to view previous post history. Reason: Parentheses.

  4. #4

    Join Date
    Jul 2007
    Location
    Netherlands
    Shooter
    Medium Format
    Posts
    5,686
    Quote Originally Posted by Christopher Walrath View Post
    Ian brought something I had NEVER before considered. Could someoe please explain to me how and why there would be reciprocity on underexposures of short duration? Would this occur with small apertures and s/s less than one second as well with general films?
    It's called the "intermittency effect", and occurs when exposure times get very short. You may find info on the net about that if you search using that as key words.
    Not very noticeable when you add exposures in the "will our shutters do" range.

    It's not a case of "reciprocity", by the way.
    Rather of "reciprocity (law) failure". Yet that only indirectly.
    So it would perhaps be better to say that it has nothing to do with reciprocity at all.

    (It's neither the low nor high intensity effect PE mentioned, but the phenomenon that when exposures get short, the sum of such short exposures is not equal to one single exposure of the same total duration.)

  5. #5
    MattKing's Avatar
    Join Date
    Apr 2005
    Location
    Delta, British Columbia, Canada
    Shooter
    Multi Format
    Posts
    12,098
    Images
    60
    Chris:

    I assume you are asking about reciprocity failure when using shorter (not shirter ) exposures.

    You probably know all or most of this, but here goes:

    The effect that light has on light sensitive materials is generally a function of exposure, which is actually made up of two components:

    1) the intensity of the light striking the materials, and
    2) the length of time that the light strikes the material.

    For most materials we work with, in the ranges we most commonly work with them, to a very great extent the light intensity and duration work in a reciprocal relationship - i.e. if you double the duration and halve the intensity, the exposure is the same, and the resulting density on the material is the same as well.

    This reciprocal relationship only applies however over a range of light intensities. If you go outside that range, and the intensity is either so much greater, or so much less than the more commonly encountered intensities, then the corresponding change in the duration of the exposure won't have sufficient effect to result in the same density on the light sensitive materials - i.e. we have reciprocity failure.

    We generally tend to speak in terms of duration of exposure when we discuss reciprocity failure, because we are usually faced with a given light level (which we cannot control) and we are attempting to deal with it by adjusting the duration of the exposure (which we can control).

    All this is pretty well understood by most here, but we sometimes overlook the following:

    a) no light sensitive material evidences perfect reciprocity over any range - it is always at best close; and
    b) there is no such thing as a perfect shutter or iris aperture - all exposures involve at least some change in intensity over the range of an exposure.

    In the example Ian referred to in the other thread, wherein there were several exposures of 1/5 of a second, the difference due to reciprocity failure between the exposure at 1/5 of a second at one f/stop and the exposure at 1/10 of a second at the next f/stop might be too small to be obvious, but it would be real. If one used 5 such exposures, then the differences would add together and may as a result become quite significant.

    There are other factors to keep in mind however. In that example, the (in)accuracy of the shutter or the iris diaphragm of the lens may very well have a larger effect.

    Matt

    EDIT: As indicated above in Mike Wilde's and Q.G.'s posts, there is another effect that one encounters with very short exposures - not the ones in the 1/5 of a second range that I assume Chris was asking about

  6. #6

    Join Date
    Jul 2007
    Location
    Netherlands
    Shooter
    Medium Format
    Posts
    5,686
    Good explanation of reciprocity.
    Also a good explanation of why the intermittency effect (the thing alluded to in the thread about multiple exposures) has only very indirectly to do with the assumptions that led to the reciprocity law.

    In reciprocity law issues, both Matt's #1 and #2 are supposed to be in balance, and problems/failure occurs when they no longer are.

    In the intermittency thingy, intensity is not a variable. The #1 and #2 here are total duration and frequency, or rather 'helpings'.

  7. #7
    richard ide's Avatar
    Join Date
    Nov 2005
    Location
    Markham, Ontario
    Shooter
    Multi Format
    Posts
    1,214
    IIRC some Literature (I believe from Kodak) gave minimum exposure information. Exposures of very short duration were not sufficient to generate a latent image in the emulsion.
    Richard

    Why are there no speaker jacks on a stereo camera?

  8. #8
    Christopher Walrath's Avatar
    Join Date
    Dec 2005
    Location
    Milton, DE, USA
    Shooter
    4x5 Format
    Posts
    6,980
    Blog Entries
    29
    Images
    19
    Wirelessly posted (BlackBerry9000/4.6.0.167 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102 UP.Link/6.3.0.0.0)

    Well, I am indeed referring to multiple short exposures. For instance, I have 140mm lens on my 4x5 that has s/s's of 1/100, 1/50, 1/25, B and O for focusing. If my metering requires a 1/6 second exposure. In order to acheive this, I would need to expose the scene at 1/25 about four times plus a fraction more to get the same exposure. But by doing so I am making four exposures that were two stops underexposed each. What if I need to acheive 1/3 of a second? That would be eight exposures underexposed by three stops each.

    By my understanding this repeated underexposure might add up to deeper shadows due to the inability, or rather inaccuracy, of the photons to repeatedly strike all of the halides in a local area of the negative in a uniform manner, thus providing increased contrast in the higher negative density values and evident in the lower print values as well.

    Did I get it right? More or less?
    Thank you.
    CWalrath
    APUG BLIND PRINT EXCHANGE
    DE Darkroom

    "Wubba, wubba, wubba. Bing, bang, bong. Yuck, yuck, yuck and a fiddle-dee-dee." - The Yeti

  9. #9
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,934
    Images
    65
    I did not consider that you meant the intermittency effect.

    In this latter effect, 10 exposures of 1/100 second does not equal 1 exposure 0f 0.1 second. This means that several short exposures are not additive and do not equal an exposure equal to the sum of all of the exposures. It is due to two effects, one rather esoteric involving the formation of the latent image and the other due to straightforward reciprocity failure. So Intermittency is the approximate "sum" of two effects.

    PE

  10. #10
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,133
    I don't have anything else to add to what Matt King wrote but sometimes a picture is worth a thousand words. This 3d graph shows the effects of both very short exposures and the effects of very dim light (This is an older diagram, the Log E axis would be Lux in SI units). The areas where useful "reciprocity" exists are on the two slopes A and B. The rest of the points on the surface show little or no reciprocity and are not useful for most photographic purposes.

Page 1 of 3 123 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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