Metering Mode and Histogram – Learn How to Never Miss A Great Moment Again

Metering Mode and Histogram – Learn How to Never Miss A Great Moment Again

metering mode and histogramIn the last photography 101 tutorial, I have discussed the concept of the three elements that make up the exposure triangle. In this post, I am going to talk about metering mode, the way in which camera determines the exposure. In order words, how to let the camera know where to expose correctly. In most cameras, there are mainly three types of metering which you can use. I will also discuss how do you know if a image is correctly exposed, as well as the use of histogram and its advantages.

Metering Mode in Camera

There are three different metering modes in a DSLR. Different metering modes meter the environment in different way. They are namely, average metering, centre-weighted average metering and spot metering. Metering mode is the way that you tell your camera how and where to meter the ambient environment.

Average Metering

average meteringIn this metering mode, the camera will use the light information coming from the entire scene and averages for the final exposure setting. The camera gives no weighting to any particular position of the metered area. This mode works great if the contrast is not too high. The brightest part and the darkest part in the scene can be all presented by the camera. If the contrast is too high which the camera cannot present all, or the subject is in the shadow or highlight part of the whole image, the camera would expose not to what you want.

overexposed lighthouse

If the scene has a super high dynamic range, you may get white clipping and black clipping at the same time. You need to go into the HDR (high dynamic range) field, if you want to reserve all the detail of the image, which is totally another story. I would create a dedicated tutorial later focusing on HDR topic, stay tuned for that. In the meantime if you find this case happen, you can try to recompose the image.

Centre-Weighted Average Metering

cetre-weighted average meteringThis mode is similar to average metering. The difference is that when using centre-weighted average metering, the camera averages the part in the centre circle only and ignores all other parts. You can set the size of centre circle, normally 6mm, 8mm and 10mm. (Please look up your camera user manual) This metering mode is commonly use by professionals. (I always use this mode too – so as to pretend professional :D ) It is because it can give a smaller part to mater which results in a more accurate exposed image.

Spot Metering

spot meteringThis is the last metering mode of cameras. Spot metering is something you can understand by its name. In this mode, the camera only measures a very small area, around 2%, of the scene. Camera will meter the focusing point. Many high grade DSLRs have several focusing points for you to select. In other words, the metering is easy and accurate because the focusing point and metering point are the same. It is great in portrait, marco and other topics.

AE-Lock Button

AE-Lock may be unfamiliar to many newbies. Many people even do not know this function after using their cameras for years. Actually this function is great and useful in many cases. By using AE-lock, you can recompose without changing the exposure of the photo. First let’s discuss what function this button can give us.

AE Lock Setting on D700This button is usually combined together with the AF-Lock. You need to set the usage of the function key manual first. There are a few choices to choose from in this function key in most cameras, they are:

  • AE and AF lock together. By using this setting, exposure value and focus will not change as you hold the button.
  • AE (auto exposure) lock only. This selection is to fix the exposure value by holding the AE/AF Lock button.
  • AF (auto focus) lock only. Similar to AE lock only, but this time only auto focus is fixed.
  • Keep AE lock. I use this one for most of the time. In this case the exposure value is fixed after you press the button. You can see that aperture value and shutter speed won’t change no matter how bright or dark you aim you camera to. The camera will not do metering again until shutter is released or the button is pressed again.
  • FV(flash value) lock. This is something about flash and I would not discuss here. Flash can be a huge topic which every photographer needs to put hard work into it. So please forget about this function at the meantime.

So, why is this button so powerful?

When you are shooting something that you want to do spot metering on the left hand side of the photo but focus on the right hand side of the photo, you can just use spot metering or centre-weighted metering to meter the left hand side. Then use this button to lock the exposure. Next you can recompose the photo without making changes to the exposure. This is great when you are shooting in very high contrast or when subject is not at the metering point.

Steps To Apply AE/AF-L Button

  1. Think about your composition first.
  2. Think about the exposure. Which area should be “correctly” exposed? Which areas should be highlighted or shadowed? Do you need to make any exposure compensation?
  3. Think about which type of metering mode you need to use. Are you going to use average metering or centre-weighted? Or do you need more accurate spot metering?
  4. Metering. Half-press the shutter or press the metering button.
  5. AE lock.
  6. Recompose the image.
  7. Focus and release shutter.

It seems that there are many steps to use this function. But it would definitely worth to know how to use. It will save you dozen of time to do “try and error” on exposure compensation. So, I suggest you to make sure how to use this button and figure out which setting you are the most comfortable to the button.

Histogram

When talking about to histogram, I think many of you learnt about histogram in math lesson when you were in primary school. And I think most of you have already forgotten what histogram is in math. Never mind, this is a simple concept in photography which let you know whether you capture a “correctly” exposed photo. First of all, let’s look at the below image and its corresponding histogram.

image with histogram

As you can see, this image has a nice dome shape in the histogram, which means the bright part and the dark part are evenly distributed. The first thing you need to know is there is a limit between the darkest part and the brightest part of a photo. Anything fall outside of the limit will become absolute black or absolute white, which is also called clipping. The left hand side of histogram represents the darker portion while the right hand side of the histogram represents the bright portion. The most left hand side means black clipping and the most right hand side is white clipping. You can never reserve any detail if some pixel become clipped. It is good to know that the black clipping is much less obvious than the white clipping. Therefore, photographers usually take a dimmer photo to prevent the highlight losing detail in a high contrast environment. Post process in digital darkroom can easily tune up the whole picture easily, of cause, with exchange of some noise.

Why histogram is so useful?

HistogramThis is a question many people ask about. In this digital world, I can look at the instant effect of the image. Why are you bordering about such an annoying histogram? Actually, what you can see in the preview screen on the camera is not accurate. It is similar to the experience that you cannot see your telephone screen under sunny day, or you found the screen too bright in low light area. Although the latest cell phone have a sensor and tune the back light of the screen. However, that leads us to aware that naked eyes are not good to tell whether the image is correctly exposed in some cases. A histogram is a great tool to prevent photographers making subjective mistakes. It also helps you to make sure that there is no die pixel, that is clipping, in the image.

I hope this post can give you enough information in how to use metering mode and the use of histogram. If you find this post useful, don’t forget click the share button below to share to your friends. By the way, I have just launched my gallery here. I will keep adding new photo into it. Hope you like it.