فن التصوير .. المباديء والمنهاج -٨- انظمة المشاهدة tlrو slr ومحددات النظر

**Ali Abbass** · 04-15-2023, 11:19 PM

art of photography . . Principles and curriculum, lesson eight

TLR and SLR viewing systems and viewfinders

Before taking any picture, you must know the subject that will appear on your film, and this is how you look through the viewfinder within the camera, and move it until you get the exact arrangement that you want, and this is the function of the viewfinder.

However, different cameras use several types of viewfinders, and cameras are classified according to a specific type of viewfinder in each of them, hence some of them - such as Nikon, Pantex Chinon and others - are called single-lens reflex cameras, according to a specific system of viewfinder, while Leica is called (MM), for example, the expression of a field-defined camera, and that also depends on the specific system under consideration.
Let us, then, learn in this lesson the meanings of the following expressions, which, by the way, are the main and common systems of determinants of vision:
1- An optical viewfinder, a normal viewfinder, and a rangefinder.
2 - Single lens reflex (SLR).
3 - Bi-lens reflex (TLR).
4- Grained glass back.

- Focused and field specific

The common and simpler viewfinder system relates to an image that you watch directly through a small viewfinder window. On this window there are signs that give us an approximate idea of the part of the scene that the film will record.

This is the system adopted in many 11000 cameras, and it is also used in small expenditure cameras such as “Minox” and “Rolly 35”.
It's simple and straightforward, but it doesn't allow fine tuning of the image as long as you can't focus by looking through the viewfinder.
This restriction is bypassed by a change to this system - a field-specific system
It is possible to integrate the viewfinder with a device - called a field finder - that makes you able to focus the lens accurately on targets of varying distances. This is the type approved in the Leica M + camera.

And when you focus through the viewfinder looking at the fieldfinder camera. It works to modify what you see until you see it sharp and shiny, but what you see is not what you will necessarily get. It is possible for the real image that reaches the film through the lens to be out of focus if there is a leakage defect between the fieldfinder and the lens, or because the lens cover was left on it, so the image does not reach the film at all, but the image in both cases appears sharp, bright and completely clear by looking More than this, when you aim the camera at a very close target. The area that you see through the viewfinder may differ slightly from the real area that will appear on the film. This is known as a virtual defect.

This, and the single-lens reflex camera, avoids these dilemmas. That is why you find some photographers, then, and they prefer the image that appears bright and clear even in low light conditions. The single-lens reflex camera shows you an image with less luster in low light, and therefore its use is more difficult in such conditions. The viewing system in the single-lens reflex camera is complex, huge, and complex. As for the rangefinder camera, it is usually lighter in weight and smaller in size, and it can withstand more shocks.

Single-lens reflex camera (SLR)

The viewing system in these cameras is the most common today, and you can find it in most 35 mm cameras and most 120-film cameras, such as: “Hasselblad”.
In this system there is an ingenious arrangement of a mirror and a prismatic lens that makes you able to watch through the lens directly so that you see a clear image on the focusing screen once you see through the viewfinder.
The heart of this system is a moving mirror positioned at an angle of 45 degrees facing the film plane when light enters from the lens. The woman reflects it upwards towards the gritted glass. In most SLR cameras. There is a shutter that cuts off the light from the surface of the film, so that this light does not reach the film during viewing.
You may think that this (SLR) is a relatively new system, and the fact that it dates back to
The beginning of this century when the principle of the SLR was used in many large cameras - the most famous of which is the Graflex.
What is new, then, is the miniaturization of this system to accommodate 35 mm film. In the first SLR cameras, you had to hold the camera at waist level and look down at the grained glass directly - as for the image in the grained glass, although it was vertical, it was reflected from left to right to correct this situation. It works from eye level today with a pentahedral prismatic lens standing above the grained glass. Thus, this prismatic lens pushes the image round until it emerges from the lens of the eye at the back, standing in a correct erection and corrected from left to right.

Why does the light that enters the camera not reach the film and present it subtly while you are watching it? ...
The first reason is that the mirror reflects most of the light upwards towards the pentagonal prismatic lens. More importantly, most SLR cameras have a shutter directly in front of the film. Since this shutter is located at the flat film, it is called the flat-focal shutter (*). Thus the shutter is closed while you are watching, so the light does not reach the film.

This is to deliver the light to the film, the woman separates. When you press the shutter-release button, slide up and out of the way, and the shutter opens, allowing light to reach the film. This woman is characterized by an immediate return in most cameras, that is, she twitches back to her position as soon as the shutter is closed again.
However, this necessary behavior of women raises its own dilemmas - and blackout is one of them - as soon as the picture is taken, the viewfinder turns into complete darkness, and this is not a problem
Main with mirrors - return - instant, as long as the blackout period is temporary, but it may cause dilemmas from time to time.

A second dilemma here is the noise caused by the movement of the woman. It is a problem that may become annoying when filming in a silent theater or a courtroom - if that is permitted - or if you want to photograph a person who falls asleep without waking him up.

The third dilemma is the shaking of the entire camera as a result of the mirror moving. This will not have an effect when you shoot at 1/500 of a second, for example, but when you take a precise shot at a slow shutter speed. This shakiness becomes a problem - when you're taking telephoto shots under low light, for example.
Overall, however, the SLR's viewing system is great for most conditions, and since you're viewing directly through the same lens that will take the picture, there's no problem with outward shifting. Likewise, you see for observation, you bring it into focus, what is within the focus and what is outside it. That's because your viewing screen is also your focus screen, as long as you bring the image into focus for capture as well. So what you see with an SLR camera is roughly what you get.
And you can't even forget to take off the lens cap, because if you leave it on, you can't see anything in the viewfinder.

Remember, however, that most SLRs will not show you every SLR that shows 100% of the image that will be recorded on the negative. While some cameras do not have the image in the viewfinder,
In some of them it happens that it deletes a small part of the outer edges of the image. Typically, an SLR camera will show you between 90% and 100% of the entire image area.

This, and there is another ingenious feature in (SLR) lenses. When you focus, you want to get the picture, the brightest, so what happens if the shot you take needs an f / 8 aperture, for example, because the image on your screen, which you see through the lens at f / 8, may be very dim, making it difficult to focus. To solve this problem, you find many SLR cameras that have an automatic diaphragm - remember that the diaphragm is the mechanism that adjusts the aperture of the lens - with an automatic diaphragm. This diaphragm opens until it reaches its maximum aperture - f / 2 for example - while you are watching and focusing Even though the picture is set up to be taken at f/08, you get maximum light on your viewing screen. Then when you press the shutter button, the aperture of the shutter diaphragm automatically narrows to the aperture you chose - f / 8 in this case - and at the moment the photo is taken, the aperture widens again to its fullest and you are ready to watch your next shot.

**Ali Abbass** · 04-15-2023, 11:22 PM

However, despite the presence of an automatic shutter diaphragm, the image in the SLR finder is not as bright as the image in the field finder system, and the SLR camera, as we mentioned earlier, is larger in size and heavier in weight, although the size has been reduced. To a noticeable extent in some SLR cameras, such as the Olympus (OM), Pentax (MX) and Nikon (FM) series.

All in all, the SLR system is a great ingenuity and has revolutionized photography since it was popularized in 35mm builds during the 1950s.
When you look through a camera's optical viewfinder or rangefinder, you see a reasonable-resolution image of your intended subject, but the scale of that image is generally limited by the small dimensions of the viewfinder window. This means that the image you see has nothing to do with the actual scale of the image that will hit the film and produce the negative.

As for the dual-lens reflex camera (TLR), its viewfinder produces an image at the same scale as the image on the film.
In the TLR camera, there are two lenses, as is evident from its name. One is directly above the other. The lower lens transmits the image that will be focused on the film, while the upper lens transmits the image concerned with viewing and focusing only. The image that you see is almost the same as the image that will hit the film.

As shown in the attached drawing. The light passes through the upper lens to hit a mirror placed at an angle of 45 degrees, then it is reflected upwards towards a horizontal viewing screen, made of granulated glass. The scale of the image on the granulated glass is the same as the scale of the image on the film. The upper lens is connected to the lower lens by a system similar to interlocking.
As moving one of the two lenses moves the other automatically by the same amount. The result is that you adjust the upper lens to obtain the most accurate focus that you see in the fine-grained glass.
The lower lens automatically produces the most accurate image on the film.
The TLR system is an ingenious arrangement that was very common during the 1930s and 1940s in cameras as widely used as the Rolliflex. . It is still available in a few cameras, such as the Mamiya (C330).

The TLR camera works with 120 or 220 film negatives of 6 square centimeters - that is, 1/4 of a square inch - and to operate it, you hold this TLR camera at waist level where you look down towards the rolling glass, and the image you see in the rolling glass It is 1/4 2 x 1/4 2 also, correct from top to bottom, but reflected from right to left.

Can you imagine the reason for this reflection... Think of the criteria for what happens to the image as it passes through the lens, and is reflected on the woman and then seen from above through the grained glass. As for the dilemmas of the TLR, it includes the following:

1- The image on the grained glass is not bright compared to that which appears in the optical viewfinder or the field finder.
2- Having to look down at waist level to see the target in front of you is an annoying thing, and it can be corrected in modern (TLR) cameras by adding a link called a borofinder that allows viewing from eye level.

3- As the viewing lens is separate from the photographic lens, the (TLR) camera suffers from the same dilemmas of apparent imbalance when photographing close targets, and we point out again that some modern TLR cameras are characterized by automatic compensation for the apparent change within the viewing system.

4- The two lens system is somewhat large in size by nature. Instead of one lens, you need two. Large size can be seen as a problem with today's fast and large lenses.

E - The ability to exchange lenses is limited. If you want to change the photographic lens, you must change the viewing lens as well. Modern (TLR) cameras come as dual lens units to exchange lenses.

The TLR camera has been a very successful structure in wide use for many decades.
Today it has almost been replaced by the single-lens reflex camera which removes all of the aforementioned dilemmas, and for those who prefer a larger 1/4-inch body, there are larger SLR cameras as well. Hasselblad and Brunica, but why would anyone persist in working with a TLR camera today then...?
The main reason is that these latest cameras are less expensive for the same relative quality.
It is also characterized by light weight, simplicity of installation and strong stability.

- Tempered glass back

There is a fine-grained glass viewing system located on the back of most Pouch-and-Watch system cameras (*), which is a sheet of semi-transparent glass smooth on one side and grained with a satin finish on the other side. As for the image, it passes through the lens and falls directly on the glass. There is no room for film in the camera while you are using the fine-grained glass.

It is worth noting that the image that you see on the fine-grained glass is of the same scale as that which will be produced on the film. It's a picture, what you see.
This is what you get, since you focus on the finely ground glass directly. Whereas, a typical viewing camera uses large format film
Like 4 x 5 or 8 x 10, the image on the granulated glass is large and can be focused accurately. You can also take close-up photos without deviating from the apparent change.

However, the image on the granulated glass comes upside down, and is reversed from left to right. With a little practice you will become accustomed to this if you happen to use a glass-reinforced camera for any extended period of time.
The image on the fine-grained glass is also somewhat upright to reduce wasted scattered light
so that he can view the image.
The photographer usually covers his head and the fine-grained glass with a black cloth (or pasteurizes it). It's the classic format for the photographer of bygone times, and it's still the style most adopted by modern studio photographers today⏹

- Next lesson focus and depth of field

فن التصوير .. المباديء والمنهاج -٨- انظمة المشاهدة tlrو slr ومحددات النظر

فن التصوير .. المباديء والمنهاج -٨- انظمة المشاهدة tlrو slr ومحددات النظر

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