Sony SLT camera

The Sony α33 has a semi-transparent mirror allowing light through to the sensor at all times.

Single-Lens Translucent (SLT) is a Sony brand name for cameras which are positioned in between digital single-lens reflex (DSLR) cameras and mirrorless interchangeable-lens cameras (MILC).^{[citation needed]} While Sony SLTs' aspect recalls DSLRs in gross form and they use the same lenses (having the same flange-back distance), they are fundamentally different and - functionally - Sony SLTs are possibly closer to MILCs rather than to DSLRs, because Sony SLTs have an electronic view-finder whereas the fundamental characteristic of DSLRs is a view-finder which allows the user to directly view the optical image generated by the lens.

Sony SLT cameras have a mirror, but - unlike the one in DSLRs - it does not move, and it is semi-transparent, allowing the majority of the light to pass through to the sensor whilst reflecting a portion of it onto a phase-detection autofocus sensor, this way allowing full time phase detection auto focus.

Like MILCs, Sony SLT cameras have an electronic viewfinder, using the image collected by their sensor. MILCs, though, focus by contrast detection, i.e. the same technology used by compact cameras^{[citation needed]} (and by DSLRs when operating in live view mode and/or to record movies). See Autofocus. Sony SLT cameras - instead - are able to use phase-detection autofocus all the time, including during video recording, which - in general - is faster and more reliable than contrast detection autofocus. Therefore - at focusing - SLT cameras have an advantage^{[citation needed]} both towards MILCs and towards DSLRs.

Fixed semi-transparent mirrors have been used in single-lens reflex cameras from at least the 1960s (see Canon Pellix). Olympus was the first - in the year 2000 and with its Olympus E-10 model - to introduce a similar concept to digital photography. Olympus E10 worked by splitting the light coming in from its lens into two beams: one for feeding the sensor, the other one for feeding in continuum an optical viewfinder, thus doing without a flipping mirror.

The "SLT" brand name has been introduced by Sony with the launch of its Alpha 55 model. Its mirror can be raised for sensor cleaning.

SLT compared to other digital cameras

SLT

Advantages:

• Continuous phase-detection autofocus even during video, live view or continuous shooting mode
• Lack of camera shake due to lack of mirror movement
• Shorter shutter lag due to lack of mirror movement
• Larger viewfinder image (compared to APS-C DSLRs, but not compared to full-frame DSLRs)
• Depth-of-field, exposure value, white balance and other settings can potentially be verified on the electronic viewfinder (and thus tweaked) before taking a picture.^{[citation needed]}

Disadvantages:

• Less light reaching sensor, due to a portion of the light being reflected to phase-detection autofocus array (approximately 1/2 EV or ca. 30% in visible spectrum 400-700nm).
• Slight image quality reduction (compared to no mirror), and possibility of ghosting
• Low dynamic range of view-finder image (compared to optical viewfinder)
• Low resolution of view-finder image (compared to full-frame DSLR optical viewfinder)
• Bad color reproduction of view-finder image (compared to optical viewfinder)
• Refresh rate limited by the time it takes the sensor to form an image; in low light this causes severe stuttering of the viewfinder image when panning (e.g. if it takes 1/4 sec for the sensor to gather enough light to form an image then the EVF updates at 4 frames/second).
• No real-time image in viewfinder due to the time necessary for image processing; there's a short but recognizable and sometimes disturbing delay between the real world action and the continously displayed viewfinder image
• No continous viewfinder update at high shooting rates, the viewfinder shows the last picture taken instead of where the camera is actually pointed; mostly a concern with fast-moving subjects. (Note: Some DSLR's do not update the image at all, as mirror is up when shooting. However, some will give you a glimpse of what is being shot as the mirror and shutter reset for the next shot.)^{[citation needed]}
• Delicate foil construction with unknown durability and long-term spare parts supply
• High power consumption for electronic viewfinder

Pellicle mirror SLT

Advantages

• More resistant mirror^{[citation needed]}
• Bright viewfinder
• More compact body^{[citation needed]}

Disadvantages:

• Lack of optical viewfinder

Mirrorless interchangeable lens camera

Main article: Mirrorless interchangeable lens camera

Compared to mirrorless interchangeable lens camera, SLT's major advantages are:

• Much shorter delay between touching the trigger and shot taken^{[citation needed]}
• Faster autofocus (phase-detection vs contrast-detect)
• Continuous phase-detection autofocus even during exposure^{[citation needed]}
• Phase-detection autofocus in live view, including during video recording.

SLT's disadvantages compared to mirrorless interchangeable lens camera are:

• Increased camera size / weight.^{[citation needed]}
• Higher cost.^{[citation needed]}
• Less light reaching sensor, due to portion of the light being reflected to phase-detection autofocus array (approximately 1/2 EV in current designs).

List of SLT cameras

Sony Alpha 55

• Sony Alpha 33
• Sony Alpha 35
• Sony Alpha 37
• Sony Alpha 55
• Sony Alpha 57
• Sony Alpha 65
• Sony Alpha 77
• Sony Alpha 99

See also

Pellicle mirror Digital single-lens reflex camera Mirrorless interchangeable lens camera Four Thirds System Rangefinder camera

Optics Single-lens reflex camera Twin-lens reflex camera Digital photography