Monthly Archives: July 2015

Is your metering method causing you problems?

Following on from my previous post on comparisons between meters, I thought it important to point out that HOW you use your meter has a significant effect on the exposure you get on the film. There are basically two ways to meter a scene, but a few variations on how those measurements are actually taken and interpreted;

The two main ways of taking a light reading are Reflective and Incident. Reflected readings are measurements of how much light is falling ON THE SCENE and Incident readings are measurements of how much light is falling ON THE METER. Spot meters measure small areas, but are still reflective types and when you take a reading through the camera lens (TTL metering), you are also taking a reflected reading. The trouble is, your choice of subject, or the angle that you shoot from, will influence the brightness that the camera reads. For instance, If I point my camera at a bunch of trees from thirty feet away, I will probably get a reasonable reading from the camera. If I then walk up to the nearest tree and lie underneath it, pointing the camera up through the branches at the sky, I will get quite a different reading, even though the light levels are the same.

In another scenario; I have in front of me two garage doors. One of them is painted black, and the other is white. If I stand some distance away, my reflective reading will average out the lights and darks, giving me an exposure somewhere in between. If I then walk towards the garage doors and take a reading from each, I will have TWO OTHER readings, even though the light levels are still the same.

This kind of subject influenced reading happens on sunny beaches, snowy landscapes, stage photography, night photography, or whenever you photograph any object, scene or person with a predominance of dark tones, or light tones. Given the infinite range of everyday lighting situations and possibilities for error, it is amazing that most shots come out at all. The reason they do, is because film is so forgiving, especially if you are scanning from your negatives and working on the images in photo-editing software. When I say film, I am referring to black and white, or colour negative films. Colour transparency film is far less forgiving and needs more careful metering.

The other method of metering  I mentioned was the incident reading. With this, there is usually a white plastic cone which goes over the light cell and this then allows the meter to read the light falling on the meter, and this is not affected by the tone of the subject. Incident readings are a quick and very accurate way of establishing a reading and are correct in most situations. If used in a back lighting situation, they will favour the shadow tones and give you an exposure which will show the lit areas as overexposed, so use them intelligently.

There is one rule when taking incident readings, and that is that you must point the cone from the scene towards the camera, -not towards the light source. The reason the white thing is a cone, and not a flat disc, is so that in side lighting, one side will be lit and the other shaded, the meter can then average them out. If you point the meter at the light source, it will not take shaded areas into account and you will have an underexposed shot.

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If you have a meter with the facility for taking both types of reading, you can take two readings beginning with an incident, then decide if the reflective is giving you a proper mid tone. I usually take an incident and check that against a reflective reading off the grass, or tarmac on the road, both of these are very close to mid grey.

In certain weather conditions, fog for instance, or snow scenes on a grey day, the light remains constant for a number of hours and one meter reading will be sufficient for many shots. Take one incident reading and the light will be the same for every shot.

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Spot metering. The spot meter is an excellent invention, but needs careful thought when being used. Typically it will take a reflected reading from a small area, indicated by a circle in the viewfinder of the meter. Anything outside of this area will not be metered, though they do pick up a bit of stray light if you have areas of brightness nearby, or are pointing into the light.

Some people think that all you have to do is take one reading from the shadows, and another from the highlights and put your setting right in the middle. This can be done, but it will depend on how high your bright areas go. Are you reading off a white painted door, or the clouds nearest to the sun? A far more accurate way to do it is to read the exposure for the darkest tone that you would like detail in and underexpose from that reading by two stops.

The important thing to remember is that exposure determines shadow detail and development determines highlight detail.

Just let that sink in a bit; Exposure determines shadow detail and development determines highlight detail. There is no shadow detail that can’t be rendered on film if given enough exposure. Leave the shutter open long enough and the film will record light that your eyes cannot detect. Okay, we’ve got that, but what about contrast? Well, if you have exposed so that the shadow detail will produce some pale greys on the negative, but you have areas where a lot more light reached the film, say for instance, a gap in dark woodland with a sunlit area beyond, this area will have obviously received an excess of light. This will only become unprintable if you keep it in the developer long enough for it to go to black. You don’t want that, you want a dark grey that you can print through, so the answer is to cut back the developer so that this doesn’t happen. I’ll be covering this subject in my next post.

Metering through the camera lens (TTL). This is a quick and practical way to get your exposures pretty close to correct as long as you understand a few things; What you point the camera at for the picture, doesn’t have to be exactly the same thing you point it at to take a reading. For instance, if you were shooting tall buildings in the city from ground level, you would most likely be pointing the camera up and getting lots of sky. Point the camera at the building, excluding sky, take the reading and use that for the up shots. If you are shooting a band on stage, exclude the lighting rig from the frame when you take the reading, then set it and fire away.

For street shooting, a 35mm camera is ideal, but you won’t have time to take a reading as you compose the shot. Think about the tonality of the scene, take a reading from something typical, then set it and forget it.

Metering in low light.

Metering in situations where there is low, even light only requires a good incident reading, a reciprocity chart and a tripod. Metering in situations where there are areas of deep shadow, coupled with hotspots of intense light, such as a concert needs a different approach. Uprating is commonly used in these situations, but this creates negatives of higher contrast, requiring very careful metering. Whenever I see images online and the photographer is claiming that the film was rated at 12500 ASA / ISO or some such high number, my first thought is; Yes, but where did you meter from? If the shots are taken at a concert, or some dark restaurant or club, there will be areas of deep shadow and very bright spots of light. In that kind of situation, a 12500 ASA reading from dark clothing in the corner of the room will give pretty much the same exposure settings as a 400 ASA reading from a well lit face. TTL metering will give you a result, but if the shot is important, then a carefully taken incident reading would be better.

Outdoors in changeable weather conditions: If you have one of those days when the sun is in and out every two minutes messing up your readings, remember that the exposure will only drop by one to one and a half stops when a small cloud comes over. Proper storm clouds will take much more light away, but a typical British summer day with fleeting clouds is easy to meter; If you meter the grass for the sunny areas, the shadows from the clouds will be 1.5 – 2 stops darker than mid grey, but if you meter for the grass when the cloud comes over, the sunny patches will be 1.5 – 2 stops brighter than mid grey. Meter the scene according to the look you are after.

Go out and try these methods and let me know how you get on. If there are any other lighting situations you are having difficulty with, then please leave a comment or question.

 

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.

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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.

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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.