Luna-Pro sbc light meter compared with Olympus E-P1 for accuracy
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?
What the &@?! Is an E-P1? Why do you assume that the meter inthe E-P1 is calibrated for film?
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.
I assume it's calibrated to match the ISO sensitivity of 100 that I had the camera (an light meter) set to.
Originally Posted by BradS
There are at least two different ISO specifications for light sensitivity - one for film and one for digital sensors.
Originally Posted by noparking
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.
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2
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1 to 4 EV of difference?
Originally Posted by noparking
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.
I have not heard of the E-P1 meter, so I'd go by the readings on the Luna Pro.
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.
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 MartinP; 10-28-2012 at 12:10 PM. Click to view previous post history.
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
Last edited by benjiboy; 10-28-2012 at 04:30 PM. Click to view previous post history.
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.