Testing light meters.

I am normally rather laid back about posting on this blog. I don’t bust a gut trying to get two posts a week out there, I post things when I feel I have something worth saying (and the pictures to support it). Recently, I have been thinking about how metering, exposure, measuring chemicals, temperature and processing all have an effect on the final quality of your images. I wanted to address that by writing about those aspects and pointing out areas which need to be thought about. My first idea was to write about light meters and make a comparison between different types, and this research is shown below. But I realised that all of the other aspects were so important that I had to post the other topics either at the same time, or shortly after. I have decided to write all of the articles in one go, then publish them here in short succession, so here is the first;

Meters and metering.
How reliable is your meter or your metering method? I thought I had my technique all sorted and knew what I was doing, but recently I was using a Nikon F4 camera and the in camera meter was giving me readings which I wasn’t convinced were correct. I checked it against a light meter app on my phone and there was quite a difference. As I wasn’t too far from home I decided to go back and check against my trusty Lunasix F analogue meter. The surprise was that I now had three different readings!

I decided to do a proper test, using a number of cameras, meters and a couple of phone apps. The following results show that you shouldn’t just believe that your meter is always correct. Also, an accurate meter is only any use if you use it properly, so make sure you give that some thought too.

Screen Shot 2015-05-31 at 23.56.54
The following cameras, meters were compared in various lighting conditions and under varying levels of daylight;
Gossen Lunasix F Analogue meter

Sekonic digital

Sekonic analogue

Pentax Spotmeter (analogue)

Pentax LX camera

Nikon F4 camera

Minolta Dynax 9 camera

To establish a base line of exposure, I used a digital meter: the Sekonic L-308S. I painted a large piece of card grey and positioned it in a variety of locations at different times of the day. I used white card for the higher values. I didn’t want tungsten lighting to throw in another variable, so these were all daylight readings. I will be writing a separate post on metering and shooting under tungsten light at a later date.
After spending a number of days compiling this data, I noticed that the readings did vary in places, though not as much as I had expected. My original problem of three different readings was down to two factors: Firstly, I was using a Nikon F4 with a non Ai fitting lens, which meant that I had to press the depth of field/stop down button to take a TTL reading. I have since discovered through these tests, that this is inaccurate most of the time. The second problem was that the battery in the Lunasix-F was nearly dead, so it wasn’t reading correctly.

So before these test readings were complete, I had solved my original problem, but I thought that I would post the information anyway because there are a few discrepancies. As I said, these readings were taken from a large grey board in less than scientific circumstances and readings taking under scenic conditions could vary more, depending on angle of view and colour sensitivity.

Out of interest, I also later compared two iPhone metering Apps: myLightMeter and Light Meter. Both are using the same hardware and probably the same, or similar software, but as this is not my area of expertise, I have no real evidence, and only refer to how useful they actually are, and how close the readings were compared to the Sekonic digital. Before I began this second phase of testing, I did a little research and discovered another App which was getting good reviews; FotometerPro. This proved to be the best of the three, but still had its limitations. I have not included the phone readings here, the phone apps will be covered in a later post.

So, to the testing,..

You might think that after a few decades of dedicated monochrome photography, I might have a workable, reliable metering system, and to a large extent this is true, but when working with a number of cameras, unexpected variations show themselves in wrongly exposed negatives, sometimes months later (by the time I get round to processing them), and it is not always possible to remember how the frame was metered. My trusted method is to take an incident reading, and apply that to the camera. I don’t usually rely on camera meters unless I am working really quickly. My second method of establishing a reading is to take a reflective, or spot reading from the shadows and underexpose by two stops. More on this in a later post, or read an earlier post on metering;  thewebdarkroom.co.uk/2011/04/21/using-light-meters-intelligently/

I had suspected that one or two of my cameras gave unreliable readings, but hadn’t put the time aside for proper testing until now. I already knew that the meter in my Pentax LX was exactly one stop out, so when shooting I always set the ASA to the number above. The readings in the table are with the ASA setting altered to give the reading I would normally get. The results are as follows. The x denotes correct, or matching exposure.
Table.

Screen Shot 2015-07-08 at 23.53.45

So it would appear that some meters are good at the lower light levels and inaccurate as levels increase, and some others have this problem in reverse. There are blips in the readings and I can’t understand these, as I was very careful about measuring consistently and did them a number of times over.
A slight inaccuracy in a meter is not a huge problem if it is the only one you use. If you have tailored your reading method and processing to give the results you prefer, then why worry? The problem will come when you take a reading with another camera, another meter, or rely on someone else’s exposure.
I think the important message from these comparisons is that we should never assume that our equipment is properly calibrated. This kind of test or comparison should always be undertaken when buying a new meter, or camera. The variations I found are not too far from ‘correct’ for normal black and white work, apart from the Pentax, which I have already allowed for. But they could make a big difference if you were shooting transparency. I did discover though, that metering through old lenses on the Nikon F4 was not a good idea.

Another factor which needs to be mentioned is the accuracy of your shutter. If your meter is giving you readings which lead you into overexposure, and your shutter is firing slower than it should (a leaf shutter problem mainly), then the combined overexposure could be very significant, and if your processing is out, you could be making the situation even worse!

My next post will cover the topic of how your metering method might be more of a problem than the accuracy of your meter and how you can remedy that.

3 thoughts on “Testing light meters.

  1. Thomas Binsfeld

    Thank you for that, Andrew!
    I was aware of that problem and preferably use one light meter with all different cameras I have.
    30 years ago I only owned an old rangefinder Leica with no buit in light meter. So I always had to use my Lunasix meter and took reflective readings and corrected them by estimation if I had other than midtones. I used this combination of meter, camera and measuring method over a long period. The negatives of this period are very constantly exposed!
    An other fact I noticed is that built in meters of modern cameras often comensate for difficult lighting situations by a system which measures more than one area and weight these differently (I don’t know the english technical term for that, in german it is called “Mehrfeldmessung”).
    I have this in my Rolleiflex 6008 and it confuses me more than that I benefit from it!
    Kind regards,
    Thomas

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  2. keith

    If you could choose only one lightmeter Andrew, which one would it be and why?
    I look forward to more blogs soon.

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