It is almost superfluous to reiterate it, but night photography is one of those areas capable of creating headaches even for the most experienced photographers, let alone those of us who have recently approached it.
Photographing at night is certainly not a walk … the hostile environment, the dark, maybe let’s put in a load of little experience, and here everything becomes decidedly complicated, especially finding the correct exposure.
I have seen photographer friends, not necessarily beginners, literally groping in the dark for tens of minutes before finding an exposure that satisfied them. I saw them get nervous, lose their patience and risk throwing away entire night sessions which, due to weather conditions and location, promised quite well.
A friendly rule of exposure
Personally, I tend to be wary of pre-packaged rules, but, I confess that when the conditions dictate it – and photographing at night falls right into this category – being able to resort to a rule that promises to speed up the times is certainly not a trivial matter!
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At night, calculating exposure is a trial and error process.
We start with a time/aperture pair, set the ISO, and cross your fingers (!).
On the basis of the result, then, the changes are made – someone relies on the display (more common choice, but less accurate), someone else checks the histograms, but, in fact, it is only after a series of attempts that we arrive at an exhibition that satisfies us.
This to proceed by trial and error is a common practice even for professionals and has nothing either shameful or disconcerting, except that, doing it at night and doing it with exposure times of even a few minutes, could really force us to invest a lot of time before being able to say satisfied in terms of exposure.
Let’s try to imagine the scene: we placed the camera on the tripod and composed it carefully, which is already critical in itself. We set the minimum sensitivity, let’s say ISO 100, to limit the noise as much as possible, and chose an average aperture, let’s say f: 8 or f: 11, which allows us to keep everything in focus and which exploits the sweet spot of our lens.
It is late at night and there is very little light around, it may take a shutter speed of even a few minutes. We set the timer to two minutes and activate the remote shutter.
No! All Black! We set six minutes and shoot again.
Better, but we’re not there yet… let’s try it in ten minutes…
Here! Here we are, here we are! Ten minutes can be fine.
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How long did it take us to reach a satisfactory result?
Eighteen minutes of exposure only, plus a few minutes wasted tinkering and heaven forbid that we have chosen to leave the noise reduction function on long exposures on, which practically doubles the working time of our machine.
Without even realizing it, we burned from a minimum of eighteen, nineteen minutes, to a maximum of thirty-six, thirty-seven minutes in the path that brought us closer to the exposure we had in mind.
We must learn to shorten the times: WE RELY on OUR CALCULATIONS TO THE RULE OF ISO 6400 .
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Exposing to the ISO 6400 Rule
The rule reminds us that AT 6400 ISO, THE SENSOR IS 64 TIMES MORE SENSITIVE THAN WHEN IT IS SET TO ISO 100 and, in this information, which might seem almost pedantic, hides the solution to our problems of slowness.
Follow the reasoning: in a minute there are 60 seconds, 60 and 64 are rather close values and, for our purpose, completely similar, this suggests that, with the same light, to get the same exposure at ISO 100 that I get at ISO 6400, I will have to multiply the time by 64, let’s be happy to multiply it by 60, approximating, and here it is:
- 1 second at ISO 6400 equals 1 minute at ISO 100;
- 2 seconds at ISO 6400 equals 2 minutes at ISO 100;
- 3 seconds at ISO 6400 equals 3 minutes at ISO 100;
and so on…
- 10 seconds at ISO 6400 equals 10 minutes at ISO 100
So what !?
And therefore we will no longer have to wait a few minutes to correct the exposure, but only a few seconds. That’s how:
- We set ISO 6400;
- We choose the diaphragm;
- Let’s set a shutter speed, which usually will be a maximum of a few seconds;
- We shoot;
- We check the result;
- We correct the shutter speed, if necessary;
- We shoot again;
- Once we have found the shutter speed that satisfies us, we lower the sensitivity to ISO 100;
- We transform the seconds of the shutter speed into minutes;
- We shoot;
- Let’s enjoy the result.
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I don’t get to ISO 6400!
Unfortunately, some basic models do not allow us to reach ISO 6400.
Do not worry: we set the sensitivity to 1600 ISO and divide the conversion seconds/minutes by 4 – unfortunately, the calculation is not as immediate as with ISO 6400, but of necessity a virtue, as they say …
- 4 seconds at ISO 1600 equals 1 minute at ISO 100
- 8 seconds at ISO 1600 equals 2 minutes at ISO 100
- 16 seconds at ISO 1600 equals 4 minutes at ISO 100
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