Wednesday, October 12, 2011

Fundamentals of Night Photography

So far I have only provided a bunch of numbers and terms in this blog, without actually explaining any of the basic principles behind them. Many of you will already be taking pictures in RAW format and developing them in Lightroom, CameraRAW or any other software capable of handling RAW formats. I thought, for those of you who already got a fair grip on the fundamentals of photography such as ISO, aperture, exposure time and focal length, providing the workflow and the settings of my pics might give you a spark of inspiration for your own work.

However, I would now like to begin with explaining some of the fundamental principles related to taking a picture. Sure, you can find countless photography tutorials online, but I thought it wouldn't hurt anyone if I put it in my own words. I'll try to keep it simple.

From the technical point of view taking a photo crucially involves considering three interdependent settings:
  • ISO rate
  • Aperture (f-stop)
  • Exposure Time (also called shutter speed, but this term is technically incorrect)

Depending on which lens you use these three settings may also be influenced by
  • Focal Length (Wideangle or Zoom)

Now let's look at them in detail, shall we?


ISO

ISO refers to how sensitive the camera sensor will react to incoming light. The higher you set the ISO the more sensitive the sensor will be, allowing for a shorter exposure time and / or a higher f-stop (smaller aperture). I will explain these in more detail below. As for ISO it is most important to understand that using a high number will result in so called noise - a grainy texture all over the image. Usually you don't want that.

However, sometimes you may want to agree to a compromise. Let's have a look at this picture:


14mm, f2.8, 1/13s, ISO 1600

It is obvious that these friendly chaps would be blurred if I had used an exposure time of some 30 seconds. In order to make the most of the available light I changed ISO from 200 (my usual setting) to 1600. My camera can handle high ISO numbers quite well, provided there are no black areas in the picture. But if you can, always use a tripod for night photography and provided that the subject does not move, use a low ISO rate!


Aperture (f-stop)

Further to a high ISO I used an aperture of f2.8 in the above image which, in spite of the small number, is called a fast or open aperture. In this case it is even the "maximum" aperture of the lens. Usually I use something around f11 for architectural photography. But don't get confused by the terminology, I just wanted to mention it. In the future I will only refer to it as high and low "f-stop".

Now what's the effect of using a low f-stop like f2.8? The lens will allow for more light to come in at any given time, thus reducing the required exposure time! However, and this really is the essence of photography as such, a low f-stop will only produce a sharp image in the exact distance of the focal plane. In simple terms it means that only the object you have focused on will be sharp, anything in front of it or behind it will be somewhat blurred (the look of the blur is called "Bokeh"). In the above picture you will barely notice the effect, as it increases when using zoom lenses. Wideangle lenses hardly show this effect at all. I will not go more into detail about the reasons for this now, but I will show you an image which was taken at a focal length of 50mm with a low f-stop. It shows you what I mean by referring to the "focal plane":


50mm, f2.0, 1/8000s, ISO 200

Since low f-stops allow for shorter exposure times it comes very useful for handheld available light photography, for example taking pictures at a friend's party. What's more, low f-stops are a great thing to play around with when you take portraits! However, I do not recommend using low f-stops for architectural or landscape photography. Sometimes it might be useful, but usually you would want the whole image to be sharp. Therefore, use f11 or higher for taking pictures of buildings or landscapes. And don't forget to use an ISO as low as possible!

So what did we learn so far?
  • Use low ISO, if possible
  • For architecture and landscapes use a high f-stop (e.g. f11)

Exposure Time

If you could follow my explanations thus far you might now want to ask: "But what about the exposure time if I use low ISO and a high f-stop!?"

Well, that's a very good point! Let me tell you: For architecture and landscapes it is the least (and last!) thing to worry about - provided that you have a tripod! Go buy one now, if you don't already own one.

The longest exposure time you can set for any DSLR camera is 30s. I make use of that very often. As a matter of fact, most of the pictures I take range between an exposure time of 20 to 30 seconds. If you want to use longer exposure times you will have to set the camera to "Bulb" mode and use a remote shutter release. But for any kind of "normal" photography this is not required.


Summary

So what exactly should you do when you go out shooting architecture at night?
Here's my recipe:
  1. Make sure you shoot in RAW format so you can edit the image far better than in JPG format (my wife tends to use JPG for taking pictures of the kids and quite a few times I had forgotten to check on this setting before going on a photo tour around town - a bit frustrating!)
  2. Make sure ISO is set on 200 (or lower)
  3. Make sure you have picked an f-stop between f8 and f13
  4. Now check the display to see how long you will have to expose in order to get a nice picture. Anything below 30s goes!
  5. If the picture appears to be underexposed at 30s, use a lower f-stop, but try to keep it at f8 or higher. However, wideangle lenses can be used with f-stops as low as f4 (roughly) without showing too much blur.
  6. If even that does not work, go back and cautiously increase ISO.

Addendum: Focal Length

As I mentioned before, depending on the lens the settings of exposure time, ISO and aperture may be influenced by zooming. Lenses show information written on their barrel. One example:

Nikon 18-200mm f3.5-5.6

Looks terrible at first, doesn't it? Don't worry, it's not rocket science. This is just a lens which can be used at focal lengths ranging from 18mm (wideangle) to 200m (zoom). "f3.5-5.6" indicates the lowest possible f-stops within that range. Lenses offering the use of low f-stops are called "fast" lenses. The above lens is not very fast in that sense.

This particular lens enables f3.5 as the lowest f-stop at 18mm and for zooming in to 200mm the lowest f-stop changes to f5.6. This mainly happens due to the lens getting longer, thus making it harder for the light to reach the end of the tunnel (that's how I imagine it anyway). So when you set up perfect settings for 18mm, but then decide to zoom in to 100mm, your image will become underexposed!

This, however, depends on which lens you use. I am now a proud owner of a Nikon 24-70mm f2.8 lens. It is quite fast, but what is even better: The lowest possible f-stop stays the same all the way from 24 to 70mm! Nice.

That's it for now, folks! I hope I could give you some useful information. If you have any questions, please just drop me a comment! I'll be happy to help.

Further information about my photography:
Cheers,
Sebastian

8 comments:

  1. Hi Sebastian,

    many thanks for that little workshop of night photography here!
    I do understand many things a litte bit better now.
    But what about the VR that some lenses have. On or Off?

    Kind regards from Germany,
    Sebastian

    ReplyDelete
    Replies
    1. Hi Sebastian,

      Thanks for your comment. It is better to switch it off when you shoot from a tripod.

      Cheers,
      Basti

      Delete
    2. Thanks

      Cheers,
      Sebastian

      Delete
  2. hey sebastian,

    First of all, i would like to say thank you for sharing your expertise, skill and knowledge in taking photography to the higher level. I just notice that your night shots were taken in different locations. My questions is about the shotting locations, are these free to shot for photographers? Does tripod installations allowede special in high areas you sholt pic in szr and marina.

    since yours,

    steven

    ReplyDelete
  3. Loved this post. Thanks for sharing your day!

    ReplyDelete
  4. So happy to support your organization.

    ReplyDelete