Common sense questions and answers about digital cameras

Common sense questions and answers about digital cameras

Question: What is the focal length of a digital camera lens?

There is a digital camera with five times optical zoom. The nominal focal length range is 35 -175mm. The problem is that when taking pictures with a 175mm focal length, the image distance should be between one and two times the focal length, that is, greater than 175mm, but when the lens is fully extended, the image distance it can provide is only 60mm (measure the thickness of the camera). Could anyone please explain whether 175mm refers to the focal length of the lens?

Answer:

Yes, the nominal 35-175 may be the value multiplied by the conversion factor.

This 35-175 is the focal length equivalent to the 135 film format. Most of the surface areas of the photosensitive elements of today's digital cameras (CCD, COMS) are not as large as a 135 film, and the sizes are not the same, which causes trouble. Because focal length is difficult to define. Due to the size of the photosensitive element, some use the 20mm focal length as the light angle, some use it as the focal length of a standard lens, and some even use it as the focal length of a telephoto lens. Therefore, after the production of digital cameras, the focal length value of the lens is generally converted to the equivalent focal length value of a 135 format camera.

The focal length of the lens is calculated based on 135 traditional film cameras. Now is the digital age, because the size of the image sensor of a digital camera is different from the size of 135 traditional film. So there is a conversion process. The traditional film size is 36*24mm. Its diagonal is approximately 43mm. For non-full-frame sensors.

For example, Canon's sensor (not a full-frame SLR) is 22.2×14.8mm, and its diagonal length is approximately 27mm. So if the lens is mounted on a Canon non-full frame DSLR camera. It needs to be multiplied by a conversion coefficient, which is equal to the ratio of the diagonal of the frame, that is, about 43/27=1.6. Similarly, the conversion factor for Nikon and Pentax is about 1.5. The conversion coefficient of 4/3 systems such as Olympus and Kodak is about 2. If it is a full-frame SLR camera, the conversion coefficient is 1. Therefore, there is no need to convert.

Q: Why should the focal length of the camera be converted to the equivalent focal length of a 135mm camera? How is it converted?

Answer:

First of all, the "135mm camera" in your question is incorrect. It should be "135 camera" or "35mm camera"

To Therefore, the concept of equivalent focal length is often mentioned because traditional 35mm cameras used to be very popular cameras, and everyone knows how many millimeters the lens angle has. There are so many sizes of digital camera sensors now that you only know the actual focal length of the lens but you don’t know how big the shooting range (that is, the angle of view of the lens) is, so you only tell the equivalent focal length or equivalent magnification. For example, a 17mm lens is The viewing range of an APS-C sensor (such as the Canon 400D) is the same as the viewing range of a 27mm lens on traditional 35mm film (24*36mm). Therefore, the 17mm lens of the Canon 400D camera is equivalent to that of a 35mm camera. The focal length is 27mm.

The equivalent focal length coefficient depends on the size of the CCD or CMOS. The smaller the size, the larger the coefficient.

Q: What is the difference between a full-frame camera and an APS-C camera?

Answer:

Full format is true for APS-C format.

In digital cameras, any film size close to the 35mm used in 135 cameras is called full format.

When it comes to APS-C, we have to talk about APS, advanced imaging technology. Advanced Photography System (APS) is a specification for a new generation of photography systems that is different from the 35mm film system launched in 1996 by the five major photographic equipment manufacturers: Kodak, Fujifilm, Canon, Minolta, and Nikon.

The advanced photography system uses 24mm film with a negative area of ??16.7mm x 30.2mm. The film uses a dorp-in cassette, eliminating the need for manual winding. The cassette of the advanced photography system identifies the status of the film, including unexposed, partially exposed, fully exposed, and developed. Supports taking it out in the middle of shooting and putting it back in again. Advanced photography systems support a data exchange system (Information Exchange). In addition to recording image information, the film also records exposure settings, and the processing system can be adjusted based on this information. When shooting, the photographer can set three viewfinder settings: standard (C 2:3), HDTV (H 9:16), and panorama (P 1:3). This setting will also be stored in the film and can be used during development. Automatically develop photos in three different sizes: 4*6, 4*7, and 4*11. After the film is developed, it will be returned to the box to facilitate the storage of the negatives. When printing again, you can tell the developing shop the photo number (the photo number can be obtained from the index sheet, and the photo number is also printed on the back of the photo)

APS It's called Advanced Photo System, a new type of film after 135, but its lifespan was short and it was quickly eliminated due to the emergence of digital cameras.

The full frame size of APS film is 30.3×16.6mm.

The negative size of an ordinary 135 photo is 36×24mm.

APS film comes in three sizes, C, H, and P. The H type is a full frame (30.3×16.6mm). The C type is to block one end of the left and right ends of the full frame, with an aspect ratio of 3:2. The P type is to block a strip of the upper and lower sides of the full frame to make the screen longer. The wide ratio is 3:1 and is called panorama mode. DSLR borrowed this standard and called the C-sized 22.5 x 15.0 mm and 23.6 x 15.8 mm APS-C frames. 28.7 x 19.1 mm, probably called APS-H format.

Q: What is an APS frame machine?

Answer:

Many CCDs of digital SLR cameras are of "APS-C" format. So, what exactly does APS-C mean?

In 1996, the APS (Advance Photo System) film system jointly developed by FujiFilm, Kodak, Canon, Minolta, and Nikon came out. APS developers have made thorough improvements based on the original 135 specifications, including comprehensive innovations in cameras, photosensitive materials, printing equipment and related supporting products. They have greatly reduced the film size, used a new smart cassette design, and integrated contemporary The latest digital technology has become a smart film that can record optical information and digital information.

APS is positioned in the amateur consumer market and has designed three film formats (H, C, P):

H type is full frame (30.3×16.6mm), The aspect ratio is 16:9;

Type C blocks one end of the left and right ends of the full frame, and the aspect ratio is 3:2 (24.9×16.6mm), which is the same ratio as the 135 film; < /p>

The P type is a full frame with one strip removed from the upper and lower sides, so that the aspect ratio of the screen is 3:1 (30.3×10.1mm), which is called panoramic mode.

The biggest difference between APS photosensitive film and traditional photosensitive film is that the film is not only coated with photosensitive emulsion, but also coated with a layer of transparent magnetic media. In addition to having all the functions of traditional film, it also has digital writing capabilities. Ability to use the area of ??the strip guide on the side of the film perforation and the other side to record the relevant data on the film at any time during the shooting process, such as: focal length, aperture, speed, color temperature, and date. Some APS cameras also store more than a dozen languages ??and more than 100 messages, greetings or titles. You can select the desired and photo production requirements through the buttons on the back of the camera, and record the information on the film. This information It can also be modified. A "thumbnail index" catalog photo could also be printed out during development, which was a very novel and advanced design at the time.

In order to facilitate the viewing of APS films, the APS system is also equipped with a "film image player". Put the film into the device and connect it to the TV, you can watch it on the TV, and it can also be equipped with There is music that can be played continuously, the image can be partially enlarged, and the color and brightness of the image can also be adjusted, just like watching a movie, adding to the entertainment of photography.

Since the advent of APS, more than 50 manufacturers have joined. APS cameras of various brands have similar performance. In terms of appearance, they can be divided into two categories: one is cameras produced by film manufacturers, all of which are pocket-sized. This type of APS machine is small in size, fully functional, simple to operate, and easy to carry. For example, FujiFilm's Fotonex1000ix; another type of camera produced by camera manufacturers, including Minolta (VECTISS), Canon, and Nikon. The biggest feature is that all lenses of the original 135 system can be used except for Lens specially designed for APS. Such as Canon's EOS1X, Nikon's PRONEA 600I, etc.

However, APS is sandwiched between the traditional film photography system and today's digital photography system, and is a transitional product between the two. It is not difficult to see that the above advantages, such as recording shooting data, saving archive information, editing digital photo albums, computer projection and playback, etc., can be fully realized in today's digital cameras, and have been greatly expanded. Therefore, under the impact of the rapid development of digital camera technology, the APS system "died before it was launched" before it could be applied, and it had "died" long ago.

Since most of today’s digital SLR cameras use CCD or CMOS photosensitive devices with a size smaller than 135, except for Olympus’ 4/3 system and Canon’s full-frame, almost all existing cameras are The same size as APS-C film: the aspect ratio is 3:2, and the side length is approximately 24.9×16.6mm. For ease of description, people call photosensitive devices of this size "APS-C specifications" .