Equivalent lectures

I hope, my stem readers, that you have practiced how to read the expose meters on your cameras. If you still have some doubts, please be confident enough to send me a comment.

When you master how to read the values, now you are prepared to make equivalent lectures. This means, that you are able to change shutter speed or ƒ numbers to accommodate your needs or the end result you wish, without changing the quantity of light that is going to get into the film. Maybe by now, you are going to be able to have an idea if you know what each light step means.

This is going to be a little bit more practical than before. First of all, lets imagine that a friend of us has a hand expose meter, and he (or she) measures the light on his face, and the displays says: s 1/250 @ ƒ 4.0. In this case we want to blow away the background, in other words, make it unfocused. How do we do that? Easy one! We just open the lens aperture, in this case we are going all the way to ƒ 2.0. If we write an scale:

ƒ numbers   1.4   2.0   2.8   4.0   5.6   8.0   11   16   22

Speed   15   30   60   125   250   500   1000   2000

Note: I did not write the 1/ of the speed

Each number is a step, in which I am going to let pass the double or the half of light, so if we are in ƒ 4.0 and we want to go to ƒ 2.0, how many steps are we moving? Just two steps, but in this moment we let enter four times the amount of light to make a perfect exposure, so what do we do now? We have speed in the other hand and as we are not worried about its effect, we are going to move it the same number of steps until it compensates the light we let pass with the aperture, this means we are going to move the speed to 1/1000, as it let passes four times less light than before, and so our new lecture is going to be 1/1000 @ ƒ 2.0 and we assure a shallow depth of field as we wanted to do the portrait of our friend.

This also applies to the case in which you are more concerned about the speed, for example not letting it go below 1/30. For example, we are in a place where the Sun is about to set, the shadows are very long and dark, but we found that some places where the lights still passes trough is interesting, we make a lecture with our camera, and it says: 1/8 @ ƒ 8.0, and also we do not bring any tripod, and there is not a table at sight. 

ƒ numbers   1.4   2.0   2.8   4.0   5.6   8.0   11   16   22

Speed   8  15   30   60   125   250   500   1000   2000

Note: I did not write the 1/ of the speed

We want to be safe about shutter speed, so we want to shot at 1/60, so from 1/8 to 1/60 are three steps, in which we will not let pass much light at all, like about 8 times, so what do we do next, is compensate with the ƒ number, the same number of steps, so we let pass more light to it, from ƒ 8.0 we head to ƒ 2.8, and this way we end letting pass the same amount of light as the original reading.

The next pair of images exemplifies the Equivalent lectures.

1" @ ƒ 8.0

1/15 @ ƒ 2.0

Contrast seems a little bit different on each… but as you can observe, both have similar amounts of light on them, the only difference is how I wanted to move DoF, so only the little turtle was in focus. As you can notice both values moved five steps, if I just moved one without compensating the speed that would be blank image.

The second part of the Triangle Exposure

Last entry was focused on ISO, what it meant and what considerations you should take. This time, I am going to explain about Shutter Speeds or in other words how much time we will expose the film.

In the history of photography Shutter Speed became after the aperture, but I think is easier to understand. Before standardized shutter speeds,  the photographer just put off a lens cap and wait a little time to just cover it again, something that today stenopeic photographers still do. As manufacturing technics advanced, and different ISO sensibilities became much wider, different shutter speeds appeared. Like many concepts in photography, shutter speed was determined by dobles and halfs. So if we take for instance, one thousand of a second the starting point, the double of light we need is: (1/1000)/2 (one thousand of a second divided by two) will equals 1/500. And so on.

1/1000

1/500

1/250

1/125

As long for this seems very straight forward, due the fact that 125/2 will equals 62.5, makes very specific to do mechanisms, they went to the easiest nearest value 1/60.

If you make the division:

1/62.5 = 0.016

1/60 = 0.01666667

so, its the same…

1/60

1/30

1/15

1/8

1/4

1/2

1"

Most old cameras will have a dial with this values, but those, will be without the "1/" and only show the denominator of the division, so you will see 1000, 250, 30, etc.  In later models, the ones with digital displays, will have medium values, for example: one between 1/60 and 1/30, 1/45. These are called half stops, and digital cameras will have thirds of a stop. Also this electronic cameras will have longer times programed, from 1 second (1") all the way to 30". Some old cameras will have different colored numbers. The most commons are:

• 60 Synchronization speed
• 30 or under, shutter speeds too low that are not recommended to shot the camera unless you use a tripod or other stable elements (like a table).
• In some cases only 1 comes in a different color, representing is 1 second

Most SLR, because not all (like the Canon T50) will have a B on the dial. This B means Bulb, this mode or selectable speed is a speed chosen by the photographer, more like the old days, and is used for longer exposures, longer that the slowest time that the camera let. The shutter will be open as long as the shutter button is pressed. But as mentioned with speeds slower than 30, you are going to need extra help, from a tripod, or something else that could keep the camera fixed. In the case of the B, is also recommended the use of a shutter release cord. Older cameras will have more standardized accessories, while electronic ones, in most of the cases, will only accept first party cords. The cord will have a block system, in which there is no need to be continuously pressing the shutter, just to remember when to release it.

As for some mechanical cameras, and all semi-automatic, you could choose freely the speed. In old cameras, some lenses had an A, mostly in green, in the aperture selection ring, and in the electronic cameras, there is a mode called Tv (Canon and Minolta) or just S in Nikon. So by now you are not going to worry about selecting the right aperture value. The next week topic.

There are two major effects created by the shutter speed, blur or still.

Blur

It is said, and it is true, that the whole Universe is in motion, but depending on which point of view we have chosen, things may be moving or may be still. Most of the times people think photography is just a moment captured, although, a photo is able to record the succession of moments in just one shot, it can illustrate trajectories.  This effect is going to give a sense of motion, and it is not very hard to achieve.

The only consideration we have to think about is the velocity of the object we try to photograph. For example: we see a juggler and he is doing some fancy stuff with his toys, we could try to have a sharp still image of his face but not of his toys. In this case his toys are moving way more faster than the juggler, he is standing still and just his hands are moving. The slowest speed in which I am able to shot without a tripod, is 1/30. So if he is standing still, and just moving his hands, the end result may be of some blur on his hands and his toys, while his face may seem still. If I would go with slower speeds, if I had the tripod, I could be in risk of making everything blurry, even the juggler. 

But in shiny conditions, if you are able to do it with sunlight, very long exposures will tend to "erase" the blur, as the original object you tried to blur is no longer in front of the camera, and the objects behind it will start to show in the image. The only sure blur that will last long enough, are when at night, you do it with objects that emit light, like cars or county fair rides, they last because the background is dark, and it takes more time to be exposed.

Still

For many years of advertisements, the still has been the selling point for cameras, even nowadays, in which there are cell phones with very sensitive sensors… Just as in school, the opposite of blur is the still, in which everything that may be in motion will appear frozen in time, that magic moment in which many sport photographers rely on.

Remembering the Juggler and his toys, in this case we want to have everything still, so we are going to go the opposite way in the shutter speed scale, as his toys may be moving in quite a fashionable way, we will try to set it to 1/250, the blink of the shutter may be fast enough to just see the toys just that 0.004 of a second, not letting expose the trajectory.

The next two images are little examples of a blur and a still, it was made with a digital camera, just for didactic proposes.

This image was shot 1/45, you can clearly see how pages overlap above them.

This one was shot with 1/125, maybe it does not see very obvious, but all the pages look like if the were still.

I leave you with the video tutorial in which I show you how shutter speed is controlled by the camera, and how to select it on a semi-automatic camera.