In-Camera Metering Accuracy
I've had a Nikon FE2 for several years that wants to overexpose my pictures so I usually shoot on manual mode using a separate hand-held incident meter. Checking the Nikon's meter against my incident meter and a grey card, and comparing it to my Olympus OM-2 and a couple of Pentax cameras with accurate meters, the FE2 is overexposing by exactly one stop.
I took the FE2 to a local repair shop and the fellow checked it out and said the meter was right, but it might be a 1/4 stop off. That didn't seem right, so I took it to a different shop and that fellow said it's close, but about 1/2 stop off. I still think it's a full stop off.
So my questions:
Is the testing equipment used in camera repair shops only accurate within 1/2 or 3/4 stop? I have no idea how their equipment functions, but presume there must be some sort of calibrated light source.
Does the testing equipment need to be calibrated periodically?
Why is the FE2 off when it is probably my newest camera?
And for those of you who also have inaccurate camera meters do you get it fixed, or do you just determine how much off it is and adjust ISO accordingly, or simply shoot in manual mode using a separate meter?
Bench equipment tends to be more accurate than microminiaturized portable equipment.
However, when you have your own equipment all agreeing within some unstated tolerance, except the FE2, trust your four pieces over the two shop pieces.
Just how close are your four pieces agreeing? (HH meter, OM-2, two pentax)
Measurement is fundamentally a statistical activity and that needs to be fundamentally understood before progressing.
Last edited by Monito; 07-11-2011 at 11:03 PM. Click to view previous post history.
An incident meter should measure an amount of light that is 1/2- to 2/3-stop lower than the amount measured off of a gray card, so it will recommend an exposure that lets in that much more light than the gray card. In other words, the way to use a gray card in place of an incident meter is to take a reading from the card, and then open up 1/2- or 2/3-stop from that reading. I don't like doing this, so when I shoot using a gray card, I move my EI down two notches.
Aside from the possibility of flat-out inaccuracy, different cameras will also give different readings because they may use different metering patterns, and because they may use different values for middle gray.
In general, you are going to get "correct" readings all the time with an incident meter. But an in-camera meter compromises ideal readings for convenience.
The easiest way around all these variables is to simply pick one meter that will be the "master." The incident meter is a good choice to be the "master" meter. Have it serviced by a competent technician who specializes in meters specifically. (Industrial Light Metric is a good place to have this done in Los Angeles.) Then figure how to make all the other cameras conform to that meter. You can use the EC dial if your camera has it. If not, you can change the EI.
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I have an OM2 that reads 3 stops under my main meter, and my other OM2's meter, and various other meters I have lying around.
I just make sure I adjust the film speed dial when I put film in it.
The problem with adjusting the iso dial or some other standard is older Cds meters (not sure about selenium) can respond non linearly (may be accurate in bright daylight but off in low light).
Imo it's better to use a meter you know is at least reasonably accurate throughout it's entire range.
You can get Cds cells replaced fairly easily these days...
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For calibrating/testing, I find it very useful to tape a piece of white paper to a window, then hold a camera's lens up directly on the paper to measure.
Put a hand-held (non-incident) meter as close to the paper as possible.
This assumes that the outside light isn't changing rapidly, such as on a windy, cloudy day, but gives very accurate and repeatble results for comparing different meters, regardless of their measuring angles or patterns.
M6, SL, SL2, R5, P6x7, SL3003, SL35-E, F, F2, FM, FE-2, Varex IIa
I think the problem lies in the different reading patterns of the different cameras. How do you compare the cameras? Do you just point them in front of you and see how they measure the scene? The camera which weights more the sky (less prevalence to the centre) will give you a reading which is "closer" (higher EV).
In order to compare the two readings you should find a uniform wall in uniform light (uniform shade, uniform sun light) and then measure and compare (the wall must cover the entire frame).
If the error is linear, compensating the ISO should work as most lightmeters don't actually change anything during measurement when you change the ISO, they just measure a light intensity, which is then converted in an exposure value which depends on the ISO.
First it was my newest camera that has the exposure meter off so newer doesn't mean much. My F5 that I bought new had to be sent back to Nikon for calibration twice before it's accurate. The first time to a local repair facility that work for Nikon and the second time to Nikon Mellville, NY.
I only have access to service manual for the Nikon F5 and F3 and in the F5 manual, Nikon recommends the Kyoritsu EF-8000 and it's a shutter, exposure and meter tester all in one. The calibrated light source is relatively small and the camera under test has the lens literaly touch the light source. The light source is adjustable for a range of brightness but I am not sure how much adjustment is available.
I forgot what's in the F5 manual but in the F3 the calibration is done at LV14 and LV9
Although we don't have calibrated light source we can say simply assume that one or more of our meters are accurate. To compare meter like others have said we must eliminate the difference in metering pattern. To do that I would point the camera or meter to an evenly illuminated surface and preferably of neutral color. I have the camera close to the test surface to make sure the entire screen is filled with the test surface. I have the lens focused at infinity, I don't want to focus on the test surface. Do this at the least 2 different brightness levels to check for linearity. This is eaiser done with the test surface being backlit like paper on window because the camera or meter won't cast shadow on the test surface.
Of course this will be a problem if the meter used as standard is an incident meter. If this is the case then you will need a larger surface and it would be difficult to get it lighted evenly and the surface should be of that a good gray card and the diffuser on the meter should be a flat diffuser and not a dome.
There's no saying that any of your equipment is dead-on, so you're comparing it to camera that would likely show their own errors once they hit the repair shop. I calibrate meters to my shutter tester and advise customers that if they have a box full of cameras (that they never use) the overhauled camera will likely not match them, and not matching all his other "stuff" is not grounds for a "rework". Meters are check at 4 light levels. John
Thanks for the replies and comments. My primary meter is a year old Sekonic L-308 incident meter, which appears to be accurate. Slide film (and b&w negative film) processed using this meter seem to be correctly exposed.
I walked out in the back yard one day last week and thought "This looks like a sunny 16 day" then got the meter and confirmed it was sunny 16 on the nose. That's a good test, right?
At that same time, I aimed the FE2 around and couldn't point it at anything in my yard to display a sunny 16 reading. The ISO needed to be adjusted anywhere from one to two stops higher depending on the subject. My OM2 and ME Super easily returned a sunny 16 reading. These are my primary slide film cameras and have historically produced properly exposed slides under normal conditions, except when expected such as backlit scenes.
I suppose the best way to confirm the FE2 metering is to load a roll of slide film and make test pictures under a variety of lighting conditions and various EI settings and then look at the results.