How many times have we seen wonderful nocturnal images of cities, with those unreal lights whose transform common urban landscapes into misterious places, with fantastic lights and colours?
Now we have a fork in front of us: taking pictures in the "blue time" or true nocturnal photos. During the blue time (which lasts about twenty minutes), the sun is still rising, or setting, therefore we can still use a short enough shutter time and get pictures with both a beautiful blue sky and the city illumination on. Whiles in a nocturnal picture we will get a black sky (or at most with moonlight) and the city lights.
Luckly for us, April and May are the best periods over the year for such kind of of photos, because dawns and sunsets last longer and the weather is quite good. Often, better results can be achieved just after the sunset or before the dawn.
Let's start talking about nocturnal photography, what do we need? Our thrusted reflex camera and our lenses, a tripod (better if has a level), an electric torch, a notepad, a pen, spare batteries, film rolls or memory cards, a remote shoot control and a cronometer (a wrist watch is pretty good).
Very easily, our exposure time will be of the order of between ten second and some minutes! Therefore we will need to use "Bulb" (or B) time quite often, with the camera mounted over a tripod and the remote shoot control to avoid unwanted vibrations and movements during the long exposure time. Moreover, during such long exposures, it is a good practice to cover the viewfinder in order to avoid light infiltrations that could affect the exposimeter or even the image sensor. This is a quite uncommon likelihood, but why should we risk that?
If our camera does not have the B-time option (really a serious lack), we are forced to take pictures during the blue time or in few lucky nocturnal situations.
Now we have in front another fork. If we have a film camera, we have to remember that for exposure times longer than 10 seconds, the reciprocity law no longer holds, due to the Schwarzschild's effect (or lack of reciprocity). In other words, if the exposimeters indicates 10''@F/8, due to the lack of reciprocity the exposure will not be the same (or equivalent) at 20''@F/11. Then what can we do?
As a first reference, we can adopt the following values remembering that they can vary depending of the film used.
- from 10'' to 20'' + 1 stop
- from 20'' to 100'' + 2 stop
- more than 100'' + 3 stop
Of course, the transition between the above correction factors is not so marked. Remember that you can also use stop fractions.
Therefore, if our light meter indicates 10'' F/8, the correct exposure time should be 40'' F/11.
As a further complication, for exposure times longer than 10 seconds, color films are usually affected by color alterations, so it is highly recommendend to use always the same film type in order to predict its behaviour in such situations. Moreover, this could be a typical case where bracketing may not be a waste of film. The use of a negative color film is recommended for nocturnal photography, thanks to their wider exposure latitude (better tolerance of exposure errors).
If, instead, we have a digital reflex camera, the lack of reciprocity will not be a problem for us and we can follow the light meter indications. Moreover, we can see a preview of the image in the camera display and this is a great advantage over film cameras. However, digital cameras also have their drawbacks in nocturnal photography. In particular, digital image sensors performs worser during long exposure times, due to the additive effect of noise. In other words, the longer is the exposure time, the higher will be the noise level in the picture. In order to reduce this problem, some camera manufacturers have implemented the dark frame method: in practice, the camera takes two shoots, one of the real scene and the other is a dark frame, taken in the same condition of the first shoot, that contains only the noise. At this point, the camera software subtracts the dark frame from the first shoot, resulting in a quite effective noise canceling method (the hipothesis is that noise is almost the same both in the scene shoot and in the dark frame). If your camera does not have this function, you can still improve your image in terms of noise during post-processing, by using a specific software like one of the following:
http://www.neatimage.com it isn't free, it also is a Photoshop filter
http://www.picturecode.com download Noise Ninja
http://www.imagenomic.com download Noiseware
Do not expect miracles from these software, but they can actually improve your shoots.
It is not unusual to find some faulty pixels in an image taken with an exposure time of ten seconds or longer. They can be easily recognized as white/grey spots in areas where they should not be, or even red, green or blue dots.
There exist a free software that recognize dead pixel by analyzing your picture files, it is Dead Hot Pixel Test, and can be downloaded at: http://www.starzen.com/imaging/deadpixeltest.htm.
Hot pixels are damaged pixel, locked to a single color that are going to burn, while dead pixels are alreay burnt ones.
If you will find your camera has some dead or hot pixel, and it is still under warranty period, you should check your warranty conditions and try to get your camera repaired. Otherwise, don't worry about that, because dead and hot pixel can usually be noticed for exposure times longer than 1/15'' and they can be easily removed during post-processing.
As a further consideration, in the topic of nocturnal photography, we have to discuss about color balancing. If we will make use of daylight films, or daylight settings on our digital camera, as a result we will highlight the color of each light source in the scene, and we should be conscious that it would be almost impossible to compensate for all color casts (in the event we want to do so). As a reference for chromatic dominants, we can consider the following:
- Tungsten, halogen and street lamps give a red/orange colored light;
- Fluorescent lamps give a blue/green color cast;
- Sodium lamps give a reddish color.
Human eye hardly recognize such chromatic dominants (except for few extreme cases), therefore owners of digital cameras are advataged from this point of view.
Now that we knew our equipment and its limitations, can join the fray, let's choose a subject: a well illuminated building, a glimpse of our city as seen from above, a square, a statue, a street... whatever stimulates our fantasy, and let's start to work. on the contrary of what one might think, the best results are achieved with a sensitivity of 100 ISO and a pretty close apertures, F/8 or F/11, where F/11 should be preferred for telephoto lenses. It is, obviously, possible to use different aperture values, in order to achieve different effects. However, nocturnal photos should have good depth of field and sharpness.
You can find lots and lots of quite useless reference tables reporting time and apertures values suggested for several shooting situations, but they will be a waste of time and film for you, because nocturnal photography is a test-bench for your ductility as photographers!
Just keep in mind that if you include the moon in your scene, then you should use exposure times shorter than 1/4'',otherwise you will get the moon's shining path on your picture.
We have to choose the right focal lenght for our subject and, once we have found a good viewpoint, measure the light of the scene. It is recommended to measure exposure only, or almost only, on the brighest area of the scene and take note of the values, for example 1/8''@F/8, then measure a dark area of the subject that we want to be visible in the picture, suppose we get 8''@F/8. Now we can, at least initially, take the average value for the exposure time, and then 1" (1/8 - 1/4 - 1/2 - 1 - 2 - 4 - 8), hence set the camera to 1"@F/8. It is highly recommended to set bracketing with at least one shoot more with longer exposure time.
In order to enhance the accuracy of light measurement in those bright or dark points of the scene, to better isolate them from the rest of the scene during measurement operation, just point at them with a wide angle lens, a zoom set at 200mm, or simply get closer to that points.
If the light meter of your camera is not able to perform a light measurement, you can try to trick it by setting a higher ISO value, either in film or digital cameras; take the exposure measurement and then compensate it for the correct ISO value. For example, if the light meter cannot provide time values longer than 30''@F/8 100 ISO, first try to measure at higher apertures, say F/5.6 or F/4, if the light meter gives a valid reading, for example 30''@F/4, in order to compensate this reading for the correct aperture, we should set (30''@F/4 - 60''@F/5.6 - 120''@F/8) 120"@F/8. Then, if we are using a film camera, also have to compensate the latter value for the lack of reciprocity with an increment of +3 stops, and then it will be 960''@F/8!!!
Alternatively, you can set the sensitivity to the highest ISO value available, say 1600 ISO, in such a way the camera light meter should provide a reliable reading, let's suppose 15''@F/8, and then we will have (15''@1600 ISO, 30''@800 ISO, 60''@400 ISO, 120''@200 ISO, 240"@100 ISO) 240''@100 ISO F/8 (again, enhance this reading by 3 stops if you have a film camera, in order to compensate the lack of reciprocity).
You can easily recognize how quickly exposure times rise. It is quite common to deal with seconds and minutes, therefore a chronometer is needed in order to measure such long times, and a small electric torch could be very useful to allow reading the chronometer and to find things in our bag. With such long exposure times, a difference of the order of few seconds usually does not results in visible errors, therefore if you use bracketing set it to -1/+1/+2 stop relative to the exposimeter reading and with high probability you will get good nocturnal photos.
As a last recommendation, remember that in some cities it is forbidden to place the tripod on the ground, but not on the trash cans or the benches. Moreover, some buildings may be protected by copyright, therefore you cannot take pictures of them and show it to others, so try to find out about the situation before shooting. It could be useful to visit the place you want to photograph during the day. In my opinion, the better hours to take nocturnal photographies are those after midnight in working days, when cities are desert.
If you want to include people in your nocturnal pictures, take into account that with exposure times longer than 1/15'', they will appear as wakes or ghosts, unless they are still.
Also, beware of cars. If their lights point directly to the camera lens, your picture is definitively compromised, while if they move transversely with respect to the lens, their lights will produce shining paths on the picture.
A notepad and a pen can be useful in order to calculate the exposure value after several measurements in different points of the scene and, especially if you use a film camera, it could be the case of taking note fo each exposure value, in order to avoid the same errors next time!
It is a good practice ckecking the longest exposure time in the Bulb (B) mode on your camera, either film or digital one, in order to avoid malfunctions or faults due to overheating. It is obvious that this operation mode consumes lot of battery power, especially for digital cameras. Therefore it is highly recommended to have spare batteries in your bag and to wait some seconds, or few minutes, between successive shoots in bracketing mode, to allow camera electronics to cool down.
When using long exposure times and apertures smaller than F/11, light spots in the scene may produce a star-like pattern in the picture. This effect is due to reflections of light rays on the aperture strips, and differs from lens to lens. A similar effect can be observed in daylight photographies, if a strong light source, i.e. the sun, is included in the scene! Even with very short times and large apertures! Moreover, it is possible to achieve the same effect by placing a star-filter or a net (like mosquito-net) in front of the lens, in such a case the effect will produce a four-pointed star for each light spot, but the image will be soft. I personally do not appreciate too much this kind of effect, because it is quite unreal, but someone may like it.
P.S.: If you use a film camera, it could be useful having a compact digital camera with you, in order to make some test shoots. On top of this paper a picture of mine, entitled "Nel blu dipinto di blu", shooted during the blue time.
Article written by MambasoftSHARE