The viewfinder is the part of a camera a photographer uses to see the scene they are going to photograph. Looking through the viewfinder allows you to frame a composition. In a DSLR light enters through the photographic lens lens. It deflects off a flip-up-mirror or reflex mirror, up to a pentaprism lens which re-directs the light through the viewfinder into the viewers eye. Thus, the DSLR viewfinder gives a view through the photographic lens. This system is sometimes called a ‘TTL’ or ‘Through the lens’ viewfinder.
There is a disadvantage to the TTL system. While the shutter is open the DSLR has to flip up the reflex mirror. That will allow the light coming through the lens to fall directly on the digital sensor. But, while the mirror is flipped up, the mirror does not deflect the light into the viewfinder (instead it hits the sensor). Therefore, while the shutter is open, you cannot see through the viewfinder. However, the shutter would normally open for less than a blink. So, a flipped up mirror will usually only be a problem when making a long exposure.
In a DSLR, through the viewfinder you see exactly what is seen by the main lens. This is because the optical light path to the viewfinder passes through the main lens. This use of the main lens means a photographer sees…
- …the scene as the photographic lens frames it.
- …the scene as changed by the type of lens in place (any lens).
- …what is exposed to the digital sensor when the mirror flips up.
These three things are not the same in a viewfinder camera.
A viewfinder camera has a direct optical path through the viewfinder. It is a dedicated, fixed lens to view the scene. The photographer sees the scene through this viewfinder lens, not through the photographic lens as in the DSLR. This means three things…
- …the photographer is not seeing the same scene that is exposed on the digital sensor.
- …what is seen through the viewfinder has the characteristics of the viewfinder lens (not the photographic lens which is different and can change).
- …the photographer is seeing a parallel view of the scene which is captured by the photographic lens. This view is slightly different to the main lens.
Consequently, these three things make the viewfinder camera difficult to use.
First, you have to frame the view through the viewfinder without being able to see what the photographic lens has framed. Of course, camera makers try to match the viewfinder lens to the main lens. For fixed lenses (bridge cameras and compact cameras) that is relatively easy. However, for other types of camera it is a problem. This is especially true with respect to the next point.
All lenses affect how the scene is projects onto the sensor. This means that, looking through a viewfinder, a photog is not viewing the scene as the photographic lens would show it.
The viewfinder has its own lens. However, interchangeable lens cameras can have any type of lens mounted. Thus, anything seen in the viewfinder could be significantly different to the view in the main lens. A photographer could not see the difference either. In addition, the changing focal length of a zoom lens could not be matched by a separate viewfinder lens. This means, a viewfinder camera is not suitable where lenses are changed.
The viewfinder sees a scene slightly offset from light entering the photographic lens. The error is relatively small, but it can make a difference. This offset makes it is easy to cut off the tops of heads in portraits. Shot angles can be different through the two lenses as well. That can affect perspective; it can also affect what is actually visible too . Referred to as parallax error , this problem can significantly affect precise shot set-ups. While the problem is small at a great distance, closer views can mean big differences between the viewfinder and taker lenses.
They do have their place
Viewfinder cameras do have their place. There is no need for a mirror. So, the camera can be much more compact, and lighter, with no mirror technology. As a result, they make great compact cameras, point-and-shoot pocket cameras and fixed lens cameras.
The rangefinder is normally a specialist camera. However, it is possible to fit them as an accessory on a few limited cameras. In general, they are not common in modern photography.
A number of cameras are named ‘Rangefinder’. The reasons for the name varies. So, more information can be found by searching the Internet for the name of the camera.
Usually, an expert would use a rangefinder for specific photography projects. Survey work would be one job example.
With a rangefinder you can find the distance to the subject from the camera. In early rangefinder cameras people looked through a split-image viewfinder. As you bring the two views into focus the camera is able to triangulate and measure the distance. Modern digital versions use electronic means to calculate distance.
You can find out more about rangefinder cameras here .
Photographic Glossary – Definitions, articles and resources…
Photographic lens – a definition
DSLR :: Digital Single Lens Reflex Camera
Flip-up-mirror or reflex mirror (Definition)
Wikipedia article – Pentaprism lens
Optical path of light explained
Wikipedia article :: Parallax error
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Damon is a writer-photographer and editor of this site. He has also run some major websites, a computing department and a digital image library. He started out as a trained teacher and now runs training for digital photogs.
See also: Editors ‘Bio’.
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