Light meters, how do they work?

[p.giannakis]

A few months ago, i bought an old Olympus OM-2n. First film came out grossly overexposed, i realized that the LR44 batteries don't go down very well with this model. I since purchased the right SR44w batteries and before i put another film in it, i tried to test the meter against 2 of my most reliable AF SLRs - the Canon EOS 5 and the Nikon F4s. I also had a hand held Calcu Light XP that measures incident light.

Of course, none of the cameras agreed on a meter reading. And not only that but the OM-2n seems to generally agree with the newer cameras in good light but in low light it seems to overexpose by 1 stop when compared to the Canon and by 1/2 when compared to the Nikon.

Then with the newer AF cameras set on Average metering, i used them as light meters and transferred the reading on my Canon EOS 10D and took a series of pictures to see how they compare.

Here they are:

All cameras with their 50mm lenses.

Now, am i right to believe that the OM-2n is accurate?

Another thing is this; I understand that the differences in readings between the Nikon and the Canon are down to the algorithms they use but why did the meter readings seem to be the same regardless using Matrix or avarage metering (i.e. Canon gave same readings when in matrix and in average metering and Nikon ave same readings when in matrix and in average metering)?

Any ideas?

 

[Ronald M]

F stops can be off best to use 4-8 middle values

Shutter may be off

monitor may be off use measured value should be 128-128 128 RGB you should also use MacBeth Color checker or other devices Never a grey card

Metering patterns can be different

in the end, use a fudge factor that makes the pic turn out . They may, and probably will, be different for each camera.

I would say the top two are closest.

 

[x-ray]

Most meters are based on an average reflectance of 18%. Matrix and similar types of metering are seeing a weighted area and compensating for things like bright sky in the top of the frame and such. I believe Nikon said at one time they had 100,000 different patterns programmed in. What matrix metering does is analyze the bright and dark areas in the frame and compare them to a known data base and come up with an exposure. It tries to overcome bright and dark areas the would throw off the average 18%.

Early attempts to do this were center weighted readings. Every camera manufacture had their own pattern of weighting.

It's not unusual to find meter reading to not be linear. I have several older meters I sent to Quality Light metric to get calibrated and they're not linear compared to a digital meter I have that I consider to be the standard. As Ronald mentioned I use a fudge factor when i go to the low scale on a couple of my meters.

Based on your scans, I'd also agree the top two are the best exposures but it's hard to say without viewing your film on a standard light box or even better using a densitometer. To me the Nikon is the best.

Really it comes down to how your negs or transparencies look and how they scan or print. Everyone has different idea of what the perfect image is.

 

[kuzano]

I like the last part of Ronalds post.

Experimentation and fudge factor.

Certainly there are various technically correct answers.

But in the real world, there are so many variables.

what you've proven so far is no two camera's and meters are consistently the same.... NO MATTER HOW MUCH MONEY YOU SPEND ON THEM!!!

The variables are:

The cells used in the meter, from early selenium (no batteries) to current. CDS, and Blue Chip just a couple. Changes over time

Batteries... Alkaline (crap for camera's because of no steady discharge curve), Silver Oxide, Lithium, etc. Discharge curve really messes with consistency of readings. I get the best results on my OM2 and OM4 with 357 batteries.

Mode of reading the subject view... spot, evaluative, center weighted.

Even more goes on. Manufacturer distinctions.

For me, both for film and digital, the solution is often a fudge factor for each camera. Find the metering for the best images. I don't have any camera's that I don't end up dialing in a bit of Exposure Compensation to get image I like. Both sides of 0.

The science will drive you crazy, and the best solution is to use camera's and film you know the results from.

I have a good friend who has shot large format using the SAME camera, the SAME film emulsion, and the Same trio of lenses for years. He's always likely to have the SAME meter with him whenever he is shooting. He RARELY uses the meter. He simply knows that much about his unchanging equipment and film. Even then, film can slightly change per batch of manufacture even for the same ASA and emulsion.

I pity those gearheads who just must have the newest, bestest, "gonna make me a photographer" camera to hit the market. How do they ever master their equipment?

If you are going to be constantly changing camera's, one constant can be a handheld meter that you come to know VERY WELL!

But Hey!!! There's always PhotoShop to make your pictures good. Just shoot RAW and BLAZE AWAY!!

 

[David Hughes]

Hi,

Film has quite a wide fudge factor built into it, and then the printing will compensate.

Luckily, slide film is not so tolerant and that's the acid test for me...

Regards, David

 

[Spanik]

The images you sowed are what exactly? If they are scans from negatives then how where they treated? Same if they are scans from prints. You have a lot of other variables before we can start to discuss the cameras.

 

[p.giannakis]

The images you sowed are what exactly? If they are scans from negatives then how where they treated? Same if they are scans from prints. You have a lot of other variables before we can start to discuss the cameras.

The pictures provided are taken with a DSLR after transferring the meter readings from the above mentioned cameras.

 

[dmc]

Sunny 16🙂

 

[FrozenInTime]

Sunny 16🙂

For Britain :

Occasionally sunny 8 ; becoming cloudy 4 ;-)

 

[Spanik]

The pictures provided are taken with a DSLR after transferring the meter readings from the above mentioned cameras.

Ah, that wasn't clear at all.

Well if I take the outdoor scene, then the difference between 1/400 and 1/600 isn't that large. Less than a stop so it can be anything even just aging or basic accuracy of the meters. The Calcu however is clearly overexposing (to my taste anyway).

I assuma that the second series is a grey card. Then the Canon and Nikon "look" the most correct with again the Calcu clearly overexposing. I'm always surprised at how dark an 18% grey card is.

 

[Chriscrawfordphoto]

Have you considered that maybe some of the meters just need recalibrated? Meters do go out of calibration over time. All of my handheld meters match EXACTLY because I send them in for yearly calibrations.

 

[Bill Clark]

There are a number of variables with photography. I will mention a few. Film ISO can vary fom batch to batch. I usually used film from the same batch number when photographing a gig. Temperature can vary battery output as well as shutter speed. During process of film temperature can vary from roll to roll. Chemicals can vary depending on things like re-use, same chemicals for more than 1 roll. Then, for print, many processing variables. This is built into the film system as the scientists who developed film and chemistry put a pretty good amount of variance into the system.

With digital exposure I used the histogram to give an indication if I was exposing on either side if the wall. Since I used RAW capture I had some variance to work with.

Nohing is dead on or perfect with photography. That's what makes it so much fun as it's an adventure for me.

 

[David Hughes]

Hi,

Here are some links about exposure and exposing:-

http://www.shutterfreaks.com/Tips/Exposure/exposure111.pdf

http://www.photographers-resource.co.uk/downloads/Photography/EV_Guide.pdf

http://www.fredparker.com/ultexp1.htm

http://www.brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/PHOTO_EXP_CALC_HIST.html

http://www.photomemorabilia.co.uk/Johnsons_of_Hendon/JoH_Exposure_Calculators.html

http://www.photomemorabilia.co.uk/Ilford/Exposure_Meters.html

Just my 2d worth and I hope you find them interesting.

Regards, David

 

[Benjamin Marks]

There is a lot of wisdom in -- and quite a bit of experience behind -- the posts above. I think the goal is for you to have good control over _your_ process. I would define "good control" as "giving you the results you want on a predictable basis."

So: what does this mean in context? Work with the camera and take notes about what you are doing. Make sure you test it in a variety of lighting setups. Take notes. See what adjustments you have to make in each situation in order to get the results you want with your process. Be brutally honest with yourself about whether your highlights and shadows have the detail you want. Keep in mind that your light meter is only one of about 15 variables in the equation . . but at least it is one you can test and have control of. (some of the others: film freshness, film transport and storage before it got to you, your own film storage, light meter accuracy, shutter speed accuracy, freshness of development chemistry, pH of local water, freshness of development chemistry, paper, accuracy of your scanner, calibration of your monitor, ambient room light, color of your walls, cataracts in your eyes, blahblahblah)

In my case, I have a large number of cameras in different formats ranging from 8x10 to Olympus half-frame and everything in between. Some shutters are electronically controlled, some are mechanically timed. Some are ancient (Kodak Supermatics from the 1950's, Leica IIIa's from the 1930's, Nikon F's from the 1970's), some are more modern (Leica M6, Nikon F4, Copal shutters from the 1990s). For me, it made more sense to use an incident light meter (Gossen Luna Pro-F) and to standardize my development and printing processes to its values across a variety of platforms. This works well for the kind of photography I do and allows me to get pretty consistent results. FWIW, I also have a shutter tester, but I really think that piece of gear is overkill. When I depart from this approach, it is with a couple of cameras whose meters I trust based on long experience (Leica M6, Nikon F4s).

For your results above, I agree that the Nikon or Canon gray cards look about right on my monitor, but man, in the world of digital there are sooooo many variables between your click of the shutter and my click of the mouse that it makes my head explode.

You also asked, "I understand that the differences in readings between the Nikon and the Canon are down to the algorithms they use but why did the meter readings seem to be the same regardless using Matrix or avarage metering (i.e. Canon gave same readings when in matrix and in average metering and Nikon ave same readings when in matrix and in average metering)?" If your question is about the gray card, it is because a correctly calibrated meter will provide the same reading of an evenly exposed gray card that fills the frame regardless of the algorithm or meting pattern used. That is actually the point of the gray card: to have a standard point of reference when so many other variables are local. So the answer is: because their meters are properly calibrated.

Think about what a gray card is: it is like you took a checkerboard where half the squares were pure white and half the squares were pure black and mixed the reflectances evenly together. The reason why cameras have "averaging" meters or "Matrix Metering" or whatever fancy name they want to use for it is that the world is not, in fact, like a gray card. Outdoors, during the day, with a level horizon, the ground reflects and the sky "shines". Unless there is a body of water in the picture or it is dusk, or you are in a forest, or your subject is standing in front of a sheet of window glass. . . . or a thousand other common exceptions. Your job is to figure out how your meter and camera interpret those scenes and use your brain to tell the camera what it is supposed to be doing. Which takes me back to testing and note taking.

Live. Learn. Win!

 

[Rob-F]

Have you considered that maybe some of the meters just need recalibrated? Meters do go out of calibration over time. All of my handheld meters match EXACTLY because I send them in for yearly calibrations.

Not only that, but all brands don't necessarily use the same standard for what is a "correct" exposure. My Nikon FE2s both give about 1/4 to 1/3 stop more exposure than my Leicas. I had the dealer send both Nikons to Nikon for a check. They were both returned with a note that they were within spec and needed no adjustment. To get the same exposure as I get with an M6 or M7, I'd have to expose Velvia 100 at 125 with the FE2.

 

[MRohlfing]

When using the Olympus OM-2n take into account that the camera has actually two metering systems. In automatic mode it starts metering after the mirror is up and 2 SBC sensors read the reflected light off the shutter curtain and off the film.

The needle in the viewfinder is operated by a completely different metering system (2 CdS sensors)