What are the Differences between SLR and SLT Cameras ?

Introduction to D-SLR ( Single Lens Reflex ) and SLT ( Single Lens Translucent )

SLT is a type of camera by Sony which is used in its Alpha family of products which replaced D-SLR cameras. To know about the differences between a D-SLR and SLT Camera we must understand the way cameras operate to capture the image.

SLT technology used by Sony in its Alpha family of products has replaced the D-SLR cameras. But why? To answer this, let us first try to understand the operation of both D-SLR and SLT cameras. Guess it’s now time to brush up some concepts of physics!

Let us go with the traditional approach of following the chronology.  So, the D-SLR comes first.

Digital Single Lens Reflexive [ D-SLR ] Camera :

How DSLR Works

In a D-SLR camera light will enter through the lens and passes through a partially transparent mechanical mirror system which is placed at an angle of 45 degrees so that it can reflect most of the light vertically into the pentaprism which will revert back the vertical light as horizontal light so that you can see the actual image you want to capture through the viewfinder. While reflecting most of the light the main mirror allows a small portion of the light to through it which will be received by a secondary mirror for the purpose of phase detection autofocussing.

Whenever a photographer want to capture the image these two mirrors flip out of the way to allow all the light on to the image sensor which will capture the image.

Have you ever wondered how the miniature version of the object that is being captured appears in the view finder? Here is the story.

Light rays that pass through lens hit the translucent mechanical mirror system that is tilted at an angle 45 degrees and get reflected making a right angle. Now, if the view finder is placed here don’t you think the miniature images will be upside down? To avoid this chaos we place a Pentaprism between the tilted mirror and the viewfinder, whose sole objective is to direct horizontal light rays into the viewfinder by reflecting the rays twice to make the image Picture perfect!

But, what happens to the light rays that manage to pass through translucent mirror? This is received by a secondary mirror used mainly for phase detection autofocussing.

How on earth is the crystal clear being image captured when there are two mirrors obstructing the path of light to sensor? This is no magic. Both these mirrors obviously flip out when the capture button is clicked, giving way for the light rays to reach the sensor that captures the image.

Let us now move on to SLT cameras.

Single Lens Translucent [ SLT ] Camera :

How SLT Works

Single Lens Translucent camera does not use a mirror to reflect the light onto viewfinder instead an electronic view finder is used to display the image received by the sensor. It uses single translucent mirror in front of the image sensor for the purpose of phase detection autofocussing.

Unlike the former, the complexity of operation of latter gets hidden under the tag ‘Electronic View Finder’. The story of phase detection autofocussing is also simplified as it uses a single fixed translucent mirror in front of the image sensor to accomplish the mission.

Analyzing the PROS and CONS of SLT Camera

Advantages of SLT:

  • SLT Camera uses single fixed translucent mirror instead of flip out mechanical mirrors, hence camera shake because of moving mirrors can be eliminated. Since there is no need for mechanical movement of mirrors it will have less shutter lag. The result of less shutter lag and no camera shake is the clear image with less possibility of getting blurred.
  • It can significantly take more number of shots continuously than any traditional D-SLR because of less shutter lag which will be an added advantage for capturing images of moving subjects.
  • Since an SLT camera uses a fixed translucent mirror for camera’s phase detection auto focusing, it enables the camera’s phase detection auto focus system to operate continuously on a moving subject or even during a video capture.

Disadvantages of SLT

  • Since there is a translucent mirror in front of image sensor it reflects portion of light to phase detection autofocus (approx. 30 %). As a result less light reaches the camera sensor than like complete light in the case of a D-SLR which would be a little problem if you capture images during low light conditions.
  • View finder is electronic which receives image from the processor because of which it consumes more battery power and hence can capture less number of shots.


The Advantages of SLT over a D-SLR is that its continuous autofocus while capturing at higher frame rates and its ability to continuously auto focus on moving subject during video capture and at the same time keep in mind that you have to compensate the camera performance under low light with other factors.

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