How to Calculate Exposures Longer than the Maximum Exposure Time? The typical long exposure night photography leads to increased noise captured by the sensor. A typical reader of our website, already have read our previous article How to Calculate Long Exposures in Night Photography.
In essence, we talked about using the Bulb Mode and get a longer time limit, which in many cases is set to 30 minutes. until a time limit which in many cases is set to 30 minutes. In this article on How to Calculate Exposures Longer than the Maximum Exposure Time, we will go in to some more details, we will use in-line clickable URLs linked to proper articles to help you more.
Basics on How to Calculate Exposures Longer than the Maximum Exposure Time
The typical long exposure night photography leads to increased noise (three important articles are – Noise in Digital Photography, Noise and Acceptable Values ??of ISO, How to Set ISO to Get Pictures Rightly Exposed Without Noise) captured by the sensor.
Therefore, as we saw in the old linked guide, more than in other cases it is necessary to use the value of the ISO as low as possible. But, we know (as written in the article on exposure triangle ) that when you lower the ISO, in order to have the same exposure; you need to increase the exposure time.
So, as you may have guessed, if we want to lower exposure time we have to increase the ISO. Always for the rules that govern the triangle of exposure, in order to obtain the same result, it can decrease the opening. Putting these elements together, we must understand that the technique that allows us to calculate exposures greater than the maximum time allowed.
First, we need to set the aperture to the lowest value possible. In this way, the sensor will capture a greater amount of light.
If the ISO is set to a minimum and the recommended exposure time exceeds 30 seconds (or the maximum value for your camera), the camera does not offer a precise exposure time. Then we apply this technique:
- We set the ISO to the maximum possible value (could be 3200)
- We read and annotate the suggested exposure time, which will probably be below the maximum value
- We set the ISO to the minimum value (which in many case it is up to 100)
- We calculate the number of stops separating the maximum value and the minimum value of ISO
- We increase the same number of stops the exposure time
- We put the camera in bulb mode
- Then we press the shutter button
- We look forward to the time calculated in step five and press the shutter button again to close the shutter.
How to Calculate Exposures Longer than the Maximum Exposure Time : Difference in Stop and Depth of Field
What we read so far on this article on How to Calculate Exposures Longer than the Maximum Exposure Time is that, this technique works around the exposure triangle.
To understand how to calculate the difference in stop; however we need an example. Suppose, the minimum value for the ISO on our camera is equal to 100 and the maximum value is equal to 3200. At each stop the ISO is doubled, then the difference between the stop equals to five, according to this scale: 100, 200, 400, 800, 1600, 3200.
Then we find the exposure time calculated with ISO equal to 3200 which must be increased five-stop to get the same exposure with ISO 100. Suppose that the exposure time was 15 to 3200 seconds. We have to increase five-stop, or multiply it by 2 for five times. The scale we get will be: 15, 30, 60, 120, 240, 480. So, we will have to keep the shutter open for eight minutes (480 seconds equals eight minutes).
As we know that a low value for opening leads to a shallower depth of field. If we are photographing a landscape, you probably want the portion of the frame in perfect focus, so we need to increase the aperture value. For rules resulting from the exposure triangle we have mentioned above, then we will have to raise the same number of stops and also the shutter speed to maintain a constant exposure. Fine tuning.
Calculate exposures that go beyond the maximum value calculated by the camera is quite laborious, even though the individual steps are quite simple. Also, since we will then close the shutter at the end of the exposure time, we will not be very precise.
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