Luna-Pro sbc light meter compared with Olympus E-P1 for accuracy

Discussion in 'Miscellaneous Equipment' started by noparking, Oct 27, 2012.

  1. noparking

    noparking Member

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    I recently purchased an old Gossen Luna-Pro sbc light meter. It seems in excellent condition with case and manual. The internal battery test indicates as good; and the meter is correctly zeroed with the battery removed. When I went to check its accuracy by comparing exposure readings with my Olympus E-P1 the exposure values reported by the light meter in reflective mode (i.e., spherical diffuser moved to the side) are way off. (I have to adjust the exposure factor from 1 to 4 to get the Goessen reflective value to match the E-P1's). Here's the odd part, when the Gossen is in incident mode (i.e., spherical diffiuser is inline with light sensor) the exposure reading of the Gossen matches ~ that of the E-P1.

    The E-P1 is giving a reflective light reading; and the fact that the light meter exposure value in incident light mode matches the E-P1 is purely coincidence, correct? The light meter readings should be close to the E-P1's reading when in refective mode, correct? If I'm to use this meter as-is, I'll need to use it in its incident reading mode as a reflective light meter as a workaround?

    - Jeff
     
  2. BradS

    BradS Subscriber

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    What the &@?! Is an E-P1? Why do you assume that the meter inthe E-P1 is calibrated for film?
     
  3. bdial

    bdial Subscriber

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    If you're just pointing the meter and the camera randomly at a scene they would be pretty unlikely to agree. The camera is probably using some sort of matrix algorithm and is basing it's reading according to the needs of the sensor, not a piece of film.
    If you meter from something like an evenly lit wall from a few inches, making sure you don't have a shadow on it, they may be a little closer. If you have a grey card, that would be the ideal target. That the meter and the camera agree when in incident mode is an indication that your comparison technique for the reflective reading may not be valid.
     
  4. noparking

    noparking Member

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    I assume it's calibrated to match the ISO sensitivity of 100 that I had the camera (an light meter) set to.
     
  5. MattKing

    MattKing Subscriber

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    There are at least two different ISO specifications for light sensitivity - one for film and one for digital sensors.

    If you want to see if there is a useful correspondence between how the metering system in the E-P1 reads light and how your Luna-Pro SBC reads light, you need to take reflected light readings with each of them from something like a large, evenly lit, monotone wall that has a consistent colour and reflectivity throughout.

    Make sure that the angle of acceptance of the Luna-Pro SBC and the E-P1 are approximately the same, and that both are pointed at approximately the same point on the wall, and in the same direction.

    Make sure you are metering manually with the E-P1.

    If possible, try this at a number of different light levels.

    The readings may either match, or if they are different, the difference may be constant. If so, that will tell you how to use one meter and compensate to obtain the same results as the other.

    If the difference is not constant, you won't be able to use these interchangeably. In that case, most likely the metering in the E-P1 includes a built in adjustment to take into account the peculiarities of that system.
     
  6. Diapositivo

    Diapositivo Subscriber

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    1 to 4 EV of difference?

    Maybe you know it but I would like to clarify: one uses incident light metering and reflected light metering in different ways.

    Incident light metering: the light meter is placed in front of the subject, the cell with the dome pointing toward the camera.

    Reflected light metering: the light meter is placed near the camera, the cell without the dome pointing toward the subject.

    If the subject is of average brightness (reflectivity) you should have more or less the same exposure always.

    For an accurate comparison you should measure, while in reflected light metering, a grey card without projecting your shadow on it, filling the entire frame with the grey card. That should give you a value which is very close to the incident light metering.
     
  7. ic-racer

    ic-racer Member

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    I have not heard of the E-P1 meter, so I'd go by the readings on the Luna Pro.
     
  8. MartinP

    MartinP Member

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    Send the meter back to Gossen for servicing then you'll have a meter (and an impressive calibration chart) that works with no doubts, and it won't cost much either unless the innards need to be replaced. There is no sensible way to draw conclusions in a comparison between a digicam and a lightmeter without knowing exactly what is going on to make each reading, and that is unlikely to happen with the digicam.

    EDIT:
    I just went to check the Gossen website for servicing details to add to this post, and found that non-digital meters are no longer being serviced! This is relatively recent as my Lunasix was calibrated by them about two years ago. Unfortunately the OP will have to compare his meter to some clever light-source in a third-party repair-shop and then hope no parts need replacing.
     
    Last edited by a moderator: Oct 28, 2012
  9. benjiboy

    benjiboy Subscriber

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    This is about the third thread on this subject in as many weeks, and as I keep writing on this forum, I.S..O. 100 on a digital cameras inbuilt lightmeter that is designed for that individual cameras sensor, it is not the same as I.S.O. 100 on a hand held lightmeter intended for use with film, this is bourne out by tests carried out in the U.K Professional Photography Magazine a few years ago who did extensive tests on this subject.
    The only hand held lightmeter I know that is programable for digital camera sensors is the Sekonic L-758, watch this it should help to explain why you get different readings http://www.youtube.com/watch?v=_7SZ58CugpY
     
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  10. Chan Tran

    Chan Tran Member

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    without flaming you for comparing a light meter to a digital camera meter I honestly don't know why unless I have both your meter and your camera with me for a while then I can tell you what's going on.
     
  11. benjiboy

    benjiboy Subscriber

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    Please read my previous post Chan.
     
  12. andrew.roos

    andrew.roos Subscriber

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    Hi Jeff

    The fact that when using the SBC like an reflective meter, but with the lumisphere set in the incident position, gives readings that match the E-P1, is just coincidence. It makes sense though because you say you need to set compensation to 4 and I believe that the SBC comp dial gives filter factor (not stops) so this means the meter will read 25% of the value that it would read with the compensation set to 1. The lumisphere is designed to give the same reading as if you were using reflective metering on an 18% gray card - in other words, when misused as a reflective meter, it should read about 18% of the real value. This is close enough to the 25% given by your exposure comp as to give an almost identical reading. I would not use the lumisphere for reflected light measurements though, since it will give you a 180% (hemispherical) field of view, which won't match your camera FOV (unless using a 180 degree fisheye!).

    I'm not going to weigh in on the EP-1 as a light meter debate, but you might find Ctein's discussion of ISO useful. He's an experienced analog photographer and printer, as well as a digicam user. You can find it on TOP at http://theonlinephotographer.typepad.com/the_online_photographer/2012/09/why-iso-isnt-iso.html.

    Andrew
     
    Last edited by a moderator: Oct 29, 2012
  13. benjiboy

    benjiboy Subscriber

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    Light meters and sensors even in different makes and models of digital cameras give different readings at I.S.O 100 because the meter is designed for that particular models individual sensor.
     
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  15. noparking

    noparking Member

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    1. I do not own an 18% grey card, but I want to own one now.
    2. My understanding is that pointing the meter from the position of the camera at the subject is reflective; pointing the meter from the position of the subject back at the camera is incident
    3. I made two additional comparision measurements this evening, but which I need to do over.
    4. I have been using the exposure readings from the E-P1 to set the exposure on a Technika III for the past five (5) months. Using this methodology the exposures seemed reasonably close to me. That's the main reason I thought to compare the sbc with the E-P1.
    5. From the manual, p. 12: "For example, assume that a filter with filter factor of 4x is being used which represents a change of 2 stops. By moving the index mark of the EF ring to a position opposite the number 4, the meter readings will automatically be compenstated for the 2 stop difference."
     
    Last edited by a moderator: Oct 29, 2012
  16. bdial

    bdial Subscriber

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    Incident readings are done using the white dome on the meter, without it you're reading reflected light.
    For incident readings, you would usually point the meter towards the camera, though sometimes toward the light you're looking to expose for. Otherwise, for reflected readings point it at the surface or scene you want to measure. The incident readings and reflective readings will (should) match if you're metering a greycard, or at least be within 1/2 stop or so.

    What sort of result does the Gossen give you if you do an incident reading in full sun for 100 ISO? Should be in the ballpark of 1/100 sec @f/16...
     
  17. Diapositivo

    Diapositivo Subscriber

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    Pointing the meter from the position of the camera at the subject with the dome off is reflective; pointing the meter from the position of the subject back at the camera with the dome in front of the cell is incident.

    Your exposure problems might be due to the incorrect usage of the dome.
     
  18. noparking

    noparking Member

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    I had the opportunity to take test readings with the SBC using a subject (an 11 story office building) I originally photographed on 29-Jul-2012 @12:31 p.m. this past week around 11:15 a.m. I believe the light intensity was very close between the days. (In retrospect, the photo shot in July, which was taken at 1/60 sec @f/11, was over exposed. I ultimately reduced brightness -20 in PS to correct.) The sbc meter registered just under 1/125 sec @f/16 in both reflective (from camera/no diffuser) and incident modes (stood in the front of the building facing the direction of where the shot was taken using the spherical diffuser for the incident reading).

    So my thought is, if I had this meter on the day of the shot, I probably would have chosen a setting of 1/250 sec @f/11 (a difference of two f-stops) and the picture would not have been over exposed (but maybe slightly under exposed). I'm looking forward to giving the sbc a try at my next shoot.

    Thanks all for the feedback and links regarding ISO. It has been enlightening.
     
  19. wiltw

    wiltw Subscriber

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    Aim your EP1 at an 18% grey card that fills the view, and note the reading. Now, in the same light, aim your Gossen meter in reflected metering mode at the same grey card and note its reading. Now, in the same light, aim the incident light hemisphere of the Gossen meter toward the camera lens position, and note its reading. If the three are not within about 0.66EV of each other, one of the meters (likely the Gossen) is in need of calibration.

    The 'digital calibration' vs. 'film calibration' is a bunch of hooey!!! I can aim a Minolta one-degree flashmeter at a grey card, I can aim my Canon digital camera at a grey card, I can aim my Olympus OM-1 at the same grey card, and they all agree with my Minolta Autometer Vf in incident mode. I just did it, to make sure I am not making false claims!
     
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  20. pdeeh

    pdeeh Member

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    I occasionally use a digital camera for "spot" metering when using film (as I don't own a spot meter) ...

    I've read a few times (on APUG) that the metering of digital cameras and that of handheld meters is different and incompatible. The implication is that using a digital camera to meter for film will inevitably produce exposure errors. Presumably, therefore, using a handheld meter with a digital camera will inevitably also produce exposure errors?

    Yet there are dozens of models of meter still being made and sold ... are they only being used with film ?

    I've looked at a few user manuals for current handheld meters, and none of them have said that they cannot be used with digital cameras ...
     
  21. Chan Tran

    Chan Tran Member

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    I agree with you there. Another thing I have found is that, I have a Nikon Coolpix 5000 and its meter isn't very good. If I use my F5 on matrix and use the reading of the F5 and set it on the Coolpix I would have good exposure but if the F5 produces bad exposure on film.
     
  22. benjiboy

    benjiboy Subscriber

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    I have written previously my assertion is based on extensive tests carried out by the U.K Professional Photography Magazine using a Minolta Autometer Vf with various DSLRs and types of film, the tests were extensive and the conclusion irrefutable.
    The 'digital calibration' vs. 'film calibration' is a bunch of hooey!!!, and they used to believe the World was flat.
     
  23. noparking

    noparking Member

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    Picked up an 18% gray card yesterday and performed your test with direct sunlight ~7:15 a.m. and got these results:

    E-P1 = 1/60 sec @f/16 (does not provide 1/3 stop detail)
    SBC reflective = 1/60 sec @f/16 +2/3
    SBC incident = 1/60 sec @f/16 +1/3
     
  24. wiltw

    wiltw Subscriber

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    Given that noparking's test reflects what I said it would, is sufficient to demonstrate the earlier point that I made about comparing film vs. digital meters!
     
  25. pentaxuser

    pentaxuser Subscriber

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    Ben, can you link us to the test you refer to?. The body to which you refer has either got it right and the fact is that wiltw's test and noparking's execution of it is simply luck or the body had got it wrong( seems unlikely) or there is a way of reconciling these apparent opposite conclusions which may be the most likely explanation.

    Thanks

    pentaxuser
     
  26. Diapositivo

    Diapositivo Subscriber

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    I hope nobody thinks that a digital body will give random exposure values just because it has a digital sensor.

    The exposure reading of a digital camera is not exactly matching the exposure in the FILM-ISO standard - OK - but it is not without correlation to light :wink:

    0.66 is not a small mistake and certainly it cannot be considered satisfactory for slide film use. But once one gathers - after a little experimentation - that his digital camera is yielding results which are let's say 0.66 EV "more" than what would be appropriate in the FILM-ISO standard, then one compensates and the reading is reasonably accurate along all its EV range.

    The greatest source of exposure mismatch is probably the "matrix" or "pattern" camera metering as that will introduce some "guessing" by the camera regarding which part of the image is the one the photographer would - likely - consider the important one. So that is never comparable to an external light meter reading which averages the scene in front of him.