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

[wiltw]

Folks need to consider that the len's RATED aperture may in fact NOT be true to its real aperture size. And the light transmission of the lens might be less efficient due to the use of less expensive coatings. So unless the lens is identical in all the testing, it would not be surprising that a meter reading does not match between two different brands of cameras, both with supposedly f/1.8 lenses. Magazines like Modern Photography and Popular Photography used to pose the ACTUAL max aperture (vs. the manufacturer's rating), for example the Olympus 100mm f/2 might really measure as f/2.1, and pass less light to the meter.
I have taken two different f/2.8 lenses for my digital camera, and I have seen about 1/3 EV difference in the level of light seen by the meter, at the so-called same f/2.8 setting when both lenses were set to same FL to capture the same field of view!

Add to the meter comparison issue the fact that the ISO equation also allows variability due to the manufacturer chosen C value and K value for incident and for reflected meter calibration. So even if the same lens is mounted on two different camera bodies, the readings from their meters may not match.

So in practice, while 0.33EV might be the standard of variability allowed within the ISO equation itself, the fact that the lens passes different levels of light due to actual vs. rated aperture and due to transmission variability, adds more range to the variability of results.

 

[Chan Tran]

Although digital, color negative film, color transparency film, B&W film, polaroid film all should be exposed differerently, the meters on all these cameras should give the same readings. Or else the meters are wrong.

 

[noparking]

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

For the record, the test above was done with the camera in aperture priority mode (f/16) and a Tiffen 40.5mm uv filter attached. I just re-did the test without the uv filter

E-P1 Auto exposure mode
-----------------------------
E-P1 = 1/320 sec @f/10
SBC-R ~ 1/320 sec @f/8
SBC-I ~ 1/320 sec @f/9

E-P1 Aperture priority mode
-------------------------------
E-P1 = 1/125 sec @f/16
SBC-R = 1/125 sec @f/16 +1/3
SBC-I = 1/125 sec @f/16 +1/3 (this time reflective and incident readings matched - I have no explanation why)

 

[Arvee]

All my Gossen meters read 1/3 to 2/3 stop more light than my other meters. Judging from your numbers the Luna Pro is just fine. Take it out and shoot a roll; you'll see it's okay. You may have to make a slight adjustment in your development for the tiny bit of underexposure but I doubt you'll be able to detect it.

 

[Diapositivo]

Noparking, you should find in your E-P1 manual the way to choose the metering pattern: something like "average", "center-weighted", or "matrix" (where "matrix" can be called "pattern" or something to that effect).
Then you should choose "center-weighted" or "average". The default choice is probably "matrix".

Auto-exposure (full auto, that is normally called "Program" mode or whatever P in PASM means) or Aperture priority do not have any influence in how the light reading is performed so there should not be any difference in exposure between the two automatic modes (or any other exposure mode).

When reading the light reflected by the bloody grey card a small different in the angle between card and light meter (or camera) matters. In your first example you got a 1/3 EV of difference (f/8 and f/9) while in the second example you had the same reading between incident and reflected light reading. I suppose the first time you did not have the exact same angle, or maybe you were projecting some shadow by mistake.

Be wary when doing this kind of experiments of the shadow you, the photographer, project on the grey card or on the light meter. It's easy to make this mistake. You'll see that if you repeat your measures with great care, you'll probably obtain very coherent results.

I don't use grey cards any more. The "caveats" in their use are many: angle between light source, camera, and light meter, mistakes due to shadows, mistakes due to "mirror effects" (reflectivity of the card at certain angles) and general clumsiness and difficulty in use. Incident metering works MUCH better and is MUCH faster

 

[MattKing]

There is a difference between the ISO standard for film and the ISO standard for digital, but that probably isn't the biggest problem with using any camera (not just digital cameras) to meter for another camera.

The biggest problem is that cameras are systems themselves, and each part of the system can add variation.

For instance, if there is a marked difference between the light transmission of the lens (the "T-stop") and the aperture of the lens (the f stop) then reading the f stop will introduce variation.

If the shutter speeds vary in accuracy between the two cameras, and the reading obtained using the digital camera is adjusted or exposure, then the difference in the two shutters will introduce a variance.

The exposure systems in digital cameras are designed to give good exposure with a system that is more like slide film than negative film. The ISO standard for film is oriented toward negative film. Differences in films often require us to develop separate and distinct EIs for films that have similar ISO ratings.

It is no doubt possible to, through care and experience, develop a customized approach to making use of the information from a digital camera's meter (or any other camera's meter) to expose film in another camera, but the differences between the two systems do make it necessary to both be very careful about metering technique (such as using a standard focal length on a zoom lens) and to be very precise about using the right EI - customized to that particular combination of cameras, lenses and film.

 

[benjiboy]

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

I can't give you a link because I read it in the actual magazine about four years ago that I still have somewhere but can't lay my hands on at the moment, but I can assure you that Professional Photographer did extensive test with E6 and C41 film and several different DSLR camera sensors using a Minolta Autometer 1V F hand held light meter and the test results convinced me, anyway this isn't really a subject for a forum dedicated to film photography, and I only read the article out of interest since I let the digiheads worry about such matters, because I don't own a DSLR

 

[benjiboy]

There is a difference between the ISO standard for film and the ISO standard for digital, but that probably isn't the biggest problem with using any camera (not just digital cameras) to meter for another camera.

The biggest problem is that cameras are systems themselves, and each part of the system can add variation.

For instance, if there is a marked difference between the light transmission of the lens (the "T-stop") and the aperture of the lens (the f stop) then reading the f stop will introduce variation.

If the shutter speeds vary in accuracy between the two cameras, and the reading obtained using the digital camera is adjusted or exposure, then the difference in the two shutters will introduce a variance.

The exposure systems in digital cameras are designed to give good exposure with a system that is more like slide film than negative film. The ISO standard for film is oriented toward negative film. Differences in films often require us to develop separate and distinct EIs for films that have similar ISO ratings.

It is no doubt possible to, through care and experience, develop a customized approach to making use of the information from a digital camera's meter (or any other camera's meter) to expose film in another camera, but the differences between the two systems do make it necessary to both be very careful about metering technique (such as using a standard focal length on a zoom lens) and to be very precise about using the right EI - customized to that particular combination of cameras, lenses and film.

I agree with this post entirely Matt, very well written.

 

[Chan Tran]

For the record, the test above was done with the camera in aperture priority mode (f/16) and a Tiffen 40.5mm uv filter attached. I just re-did the test without the uv filter

E-P1 Auto exposure mode
-----------------------------
E-P1 = 1/320 sec @f/10
SBC-R ~ 1/320 sec @f/8
SBC-I ~ 1/320 sec @f/9

E-P1 Aperture priority mode
-------------------------------
E-P1 = 1/125 sec @f/16
SBC-R = 1/125 sec @f/16 +1/3
SBC-I = 1/125 sec @f/16 +1/3 (this time reflective and incident readings matched - I have no explanation why)

The E-P1 gave the same readings in both modes.
The SBC gave different readings first time and second time and the differerences are 2/3 and 1 stop. I think there is something wrong with the SBC readings.