About aperture, exposure time, ISO and co

In this post I want to explain in more detail some concepts of digital photography. I'm no expert and only photograph just for fun. Therefore, I can't tell you certainly everything, but I'll do my best! I hope these lines may help you in understanding your camera a little.

Exposure time

The easiest way to describe the exposure time is with the "release time". It is expressed in seconds, for example, 1/80 sec., or 1 sec. A slash in the first example is to be read as a fraction, e.g. an 80ieth second. To illustrate: An exposure time of 1 sec is super long and without a tripod you can actually get no image without shake. As the highest limit I always take 1/8 sec., but here you have to have a very, very steady hand, so the photo will not be blurry.

At this time, in which the camera is tripping, the sensor receives all of the image information. The longer this period go on, the more light reaches the sensor and the brighter the picture. If the sun is shining, you require a short exposure time, e.g. 1/250 sec. The light is a very important influence in photography. It determines image quality and atmosphere. In addition, with specific used light you can achieve beautiful and interesting effects.

In this example, I used the low sun behind the trees for a light/shadow shot. Some probably already know the photo (see Spring mini flood of pictures), but look at the light here. The viola in the foreground is illuminated of the sun as the only "object". The remaining area, especially the background is darker and is arranged in the shadow. This play of light is totally interesting I think.

My exposure time here amounts to 1/180 sec., so relatively short despite shadow areas.

Aperture

The so-called "aperture" is specified as a number at the SLR. Usually you will find the information in the documents with a F/ in front, e.g. F/8 (= aperture of 8).

Imagine the aperture as a ring, in which the opening of the ring can reduce or enlarge. However, the overall size remains the same. Only the size of the "hole" is changeable. This is set with the numbers. A high value indicates that this ring has a very small opening, a small number causes a large opening.

Common aperture numbers (f-numbers) are: F/1.4 – F/2 – F/2.8 – F/4 – F/5.6 – F/8 – F/11 – F/16 – F/22

The aperture, so the ring is used for this purpose, to allow more or less light through the lens. Do you provide an aperture of f/5.6, then passes a lot of light on your camera's sensor. This has the consequence that you require a lower exposure time. In addition, a small f-number, i.e. an open aperture, allows more depth of field. This means that you can set a small area of the subject sharp and the rest is blurred. If you want to specifically bring in a lot of depth in the image, one should know how the f-number effect on the result. A high f-number, for example F/22, causes a smaller opening of the ring, so it can penetrate only a little light therethrough. In this case, it is necessary to increase the exposure time to achieve the same result as in example with F/5.6. Depth of field is only present very low, almost everything will be sharp forms.

The following example shows to the left a photo with an aperture of F/1.8 and to the right one with an aperture of F/5.6. The difference in numbers is very small, but the difference in the picture is still very noticeable. As you can see, the left image is much softer in the background because of the open aperture. The right, however, is already relatively "hard". If you want to take this image with an aperture of F/22, then you would need quite a tripod to prevent camera shake due to the longer exposure time. In addition, the image gets much harder and there is less depth of field.

If you would like to learn more about the depth of field, I can recommend the post by Dominik on cyanizer.de : Introduction to Photography – Depth of field

ISO

The ISO value defines the film speed on your camera. Translated, this means virtually the light sensitivity. ISO means only that it is the standard of the International Organization for Standardization.

The most common ISO values ​​are: 100 – 200 &hdash; 400 – 800 – 1600 – 3200

The higher the number, the more sensitive your camera reacts to light. That is, you can create with a high ISO value, e.g. Create ISO-1600, with low light pretty sharp images without setting an ultra long exposure time. A smaller number, such as ISO 100, causes for cameras that they are insensitive to light, that is, you need a lot of light to take a well-exposed image.

As a comparison: at an exposure time of 1/100 sec and ISO-1600 an image is well exposed, even almost overexposed. At the same exposure time of 1/100 sec. and a value of ISO 100, the image is dark and underexposed.

Sounds really great, so why not just take a picture with high ISO only? This has a very simple reason. The ISO value can in fact not screw up without loss of quality. The higher the ISO value, the noisier and grainier the image. With a 100% view the photo looks even something slightly out of focus, causing the fine grain. Therefore I can only recommend almost never take pictures with a higher number than ISO-400! The best, sharpest, and cleanest photographs succeed at values ​​of ISO-100 to ISO-200 and of course with enough light. From ISO-400, noise is already recognizable. These settings I would only use if it is absolutely necessary because you do not have a tripod with, but absolutely want to take a picture.

Tip: In low light, intentionally create an underexposed image with a low ISO (100 or 200). Save the image in JPG and RAW on your camera (in any SLR camera, this setting of the storage format in JPG + RAW should be changeable). If you copy the photos on your PC, then open the RAW file in a compatible program, such as Adobe Photoshop. There you can later change the raw data and optimize. An underexposed image can be quite simply "saved", not an overexposed (much white). There are missing valuable image information, while they are present in the underexposed image, but are just too dark. Read more at "RAW".

So you can imagine the "noise" and "grit", I have created two shots, one of which was created with an ISO of 100 and one with a value of ISO-1600. I think that the difference and the great disadvantage at high ISO values ​​is hereby clarified. In my opinion there are few things worse than grainy photos.

RAW

RAW is the raw data format in digital photography. In addition to the JPG format digital SLRs are also possible to store the image in a RAW format. On my Canon you take this setting in the menu item "quality":

RAW is particularly suitable for smaller or larger corrections of the image, especially in color and brightness/contrast. There you can correct an image in a few steps and sliders back to "normal expose" if it was previously underexposed. Also, it is easily possible to convert the photo to grayscale and to ensure it stands out only one color, e.g. red in a grayscale image. In the regular image processing, this is a bit more complicated, when processing the raw data format, however you have just to reduce the saturation of all colors except red (by slider).

In my opinion all professional photographs should store in JPG + RAW or at least only in RAW. This allows the images work much easier and more professional. I prefer JPG + RAW, because I can look at the pictures on my PC in the preview. RAW can be viewed and opened only in special programs, such as Photoshop. And you need sometimes even certain plugins for some RAW formats of the producer. On this site you can download for free the plugins for different cameras for Photoshop (Windows). For my Canon EOS 450D I need the Camera Raw 4.4.1 update. However, the latest versions of Photoshop can read many RAW formats without plugin. Inform you specifically for your equipment.

Depth of field

Many often say also falsely "Definition of the image". The term depth of field depth of focus will be described, i.e. the depth of the sharp appearing space. So the question is: "How deep is the focus?"
The noun "depth of field" formed therefrom consists of the actual word (sharpness) and the corresponding adjective (deep). The property is so used after the word.
An example: To define the thickness of a slice of bread, the question is: "How thick is the slice of bread?" So would the associated noun "slice thickness" (slice + thick) – and not "thick disk". Sounds weird, right?

Imagine now a space before by various objects are placed behind one another. Up front is a cup, a little further back a chair and a large bed in the back. So we have three different levels here. The level with the cup is farthest forward. Now, if one of the three objects is focused, then you take this level the same time. The other two levels are not focused and therefore blurred. It is up to you which level should be focused. You could also put the bed in the back sharply, so that the cup and the chair are totally out of focus. So you can also create specific effects. Basically: The level, which is farthest from the "in-focus point", is most blurred. So the cup would be very out of focus in the last example.

This example shows a champagne bottle front right, center left a champagne glass (both objects are on the same table) and a complete room in the background. The champagne glass is in focus, and the fact that the champagne bottle is only a few inches away from the glass, this is only slightly blurry. The rest of the room, however, is shown completely out of focus. In this case the furniture is removed farthest of the table with glass and bottle.

Bokeh

The Bokeh is the blurred area in a photo. Especially SLRs work with foreground and background and form what was focused sharply and "blurred" the rest. Compact digital cameras can not do this often, and they are nowadays quite well. The bokeh is not about the strength of the blur, but the form. There are bokehs which are restless and have double outlines. A beautiful bokeh is circular, soft and evenly. But beauty is in effect only in the eye of the beholder.

In order to generate the largest possible area of focus, the aperture of the camera should be opened, that is, the f-number should be set to the lowest level. With good lenses this can be an aperture of e.g. F/1.8, with somewhat poorer lenses, the smallest area can be approximately F/3.5. So it is at least in my lenses.

A form-bokeh you can generate by cutting out a template from e.g. a cardboard and then mounted it in front of the lens. The mask should cover the entire lens aperture, except of course, the cut-out shape in the center, such as a heart or a star. This is not the round, soft spots develop in the blurred area, but these take the form of the template. With this knowledge, you can really create some interesting images.

Left is a picture with a regular bokeh and right is a form-bokeh. Admittedly, the difference is in my example not quite so extreme, but on the fly, I can not create a better illustration. But you can see the little heart just a little, or not?

Tip: The bokeh is the "most beautiful" and seen best when you have included various light sources or reflections in the scene. Wenn diese nicht fokussiert werden und als Nebensächlichkeit ruhig verschwimmen dürfen, dann kann man durch das Licht wunderbare weiche "Flecken" erstellen. Am besten fokussiert ihr einen Gegenstand, wobei sich hinter diesem mit in einem großzügigem Abstand verschiedene Lichtquellen (z.B. Laternen oder Kerzen) befinden, welche dann unscharf werden. Vergesst dabei nicht die Blende zu öffnen, damit viel Schärfentiefe entsteht (s.o. "Blende").

Sensor

In my opinion the sensor is next to the lens one of the most important component of your camera. If the sensor is small, the quality of the image can not be much better, and high MP (megapixel) numbers also do not help, which is always advertised in the advertisement. Imagine it like this: A camera with a small sensor can only create a small image with a certain MP number. Because the sensor can only take a limited amount of information. However, if the megapixels are much larger than the sensor can actually handle, then the image is almost stretched. This photo has a large size, but the quality is (very) bad. Imagine the pixels as small dots. The closer they are together, the finer and high resolution the image. Each pixel is a color. And if these pixels are stretched, then the spaces in which actually no pixels are, are calculated (interpolated), that is, it is calculated and represented a midpoint between two adjacent colors. If the left is a white dot and a black dot on the right, then appears a shade of gray between these points. I think, so you can imagine that. Therefore, you can never turn a low-resolution photo into a large one. The other way around, it is of course possible. And the camera sensor can provide only absorb a certain amount of information. If the limit is reached, then you can also bring out nothing more.

The larger your camera sensor, the better therefore your photos can be. The amateur SLR cameras usually have a APS-C sensor (see picture below), at least for the Canon DSLR cameras amateur this is the case. The green marked sensor is a small-size picture format. These were then the standard among the cameras. But that's also very expensive. Only with newer cameras smaller sensors could be installed, which significantly lowered the price, but the quality did not make any noticeable difference for the amateur photographer. Thus, large and high-resolution photos are needed more in advertising and the large poster printing.

If you look at the various camera models, then you will find out that there are really almost SLRs which are far too expensive. These are then usually installed this sensor in small picture format. The cheaper models usually have a smaller chip.

What everything is still influenced by the sensor size, I declare to you the "Crop factor".

Crop factor

Although the crop factor, or also called form factor, in digital photography is still quite important and interesting to know about it rather the least notice, I think.

Let's start from scratch to: At that time the camera sensors had in analogue photography, the small-size picture format (SPF) of 36 χ 24mm. Later in digital photography, it was possible to produce even smaller sensors and incorporate them into the camera, like as with my Canon EOS 450D, which has a sensor with the dimensions of 22.2 χ 14.8 mm (APS-C). This SLRs were much more favorable and therefore of course also sold better. A further consequence was that the lenses were also less expensive and lighter in weight. The reason for this is that it was only possible to the lens because of the smaller sensor, take a smaller image area. The lenses were almost matched the lower power of the smaller chips.

The crop factor is a value here, the results from the quotient of the SPF-sensor height and the camera sensor height. As an example: the SPF format is as I said 36 χ 24mm and my Canon DSLR has a sensor with dimensions of 22.2 χ 14.8 mm. Now the SPF-height must be calculated by my sensor height, i.e. 24mm / 14.8 mm = 1.6 (rounded). So my SLR camera has a crop factor of 1.6. This value I will later pick up again.

By the way: Each camera has a different crop factor. To find out which ship you have installed, you have to either look in the instruction manual or on the internet looking for it. For all Canon cameras: There is a table with the DSLR sensor dimensions and the form factor.

Now you ask yourself sure why you need all the information. Namely, it is important to know how the crop factor affects your photos. Because of the smaller chip area a reduced image area can be accommodated. There are as I said lenses that are designed specifically for smaller chips, these are all Canon EF-S lenses. If you compare a photo of a camera with a 50mm EF lens (without crop factor, SPF-sensor, 36 χ 24mm) with a photo of a camera with a 50mm EF-S lens (with crop factor, ASP-C sensor , 22.2 χ 14.8 mm), then you will note that the photo with crop factor, it looks as if you had zoomed in closer and would have taken with a focal length of 80mm instead of 50mm. However, this may not be possible, because both lenses have a fixed focal length of 50mm. The reason for this apparent focal length, is that the EF-S lens has a smaller image section selected as the lens with SPF-sensor. In the following image you can see what I mean:

Because the camera with the 50mm EF-S lens has a crop factor of 1.6, you simply multiplies the focal length with the crop factor, and then you get this seemingly new and larger focal length: 50mm χ 1.6 = 80mm
The photo looks as if you had taken it with a 80mm lens. In regular everyday life, if you have not this direct comparison, you hardly notice it. You're just used to it that your camera creates only such "closer" shots.

Now it is still important to know what happens when you exchange the lenses. If you connect an EF lens on a camera with a small chip and crop factor, then nothing much happens. This is possible, but you also get a smaller image. Although the major objective being to obtain more, but the sensor does not create. If you connect an EF-S lens on a camera with an SPF sensor, then you get black spots in the corners. The sensor can here make less than the lens. The lens want to scan a larger area than the chip can even handle because it is smaller. And because the lens is round, but the picture rectangular, only the corners are just black and no picture.
But: This is only theory and not practical. Canon has not even made ​​it possible that you can connect EF-S lenses on a Kamrea with SPF-format sensors. This is so technically not feasible. Therefore, only EF lenses can be used on the expensive cameras with SPF format, while on the cheaper amateur cameras EF and EF-S lenses are useful. If you connect an EF-S lens here on the bayonet (the body), then you use the white point for snapping and at EF lenses the red one.

Sources

1. Chriusha (Хрюша) / CC-BY-SA-3.0 / wikipedia.org - Sensorformate_KB.svg
2. Marten2k / CC BY-SA 3.0 (de) / wikipedia.org - Format_Factor.gif
3. timmermann.tv

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