Before I go ranting, I assumed all of you understand how a Single Lens Reflex (SLR) camera work. If you don't, please read it here in Wikipedia.
Cross-section of a SLR camera
1) Front mount lens
2) Reflex mirror, instant return
3) Focal plane shutter
4) Film or digital sensor
5) Focusing screen
6) Fresnel lens
Looking at the construction of the SLR you probably realised why this type of cameras are bulky and heavy :)
A couple of years ago, innovative manufacturers like Panasonic and Olympus launched what is now known as the EVIL (electronic viewfinder interchangeable lens) cameras.
All they did was to take a SLR with a large sensor and "chop-off" it's top!
Cross-section of a EVIL camera
1) Front mount lens
2) Light path straight to sensor
3) Large sensor
4) The "EV", electronic finder; LCD screen
How elegant! How compact the camera became!
Not long ago I used, wrote about and raved about such gem; the Olympus Pen E-P2.
The simplicity of the EVIL design is great EXCEPT (always except!) for it's relatively S-L-O-W auto-focus!
It seems, to achieve fast AF, the AF sensor array MUST see some part of the image! This is not possible with the "light-straight-through" design!
SLR cameras get around this obstacle by placing a small secondary mirror at the back of the reflex mirror. By employing a phase detection method, it achieve extremely fast and accurate AF!
There is a really good article on phase detection here.
Along came Sony, who; scooped everyone by launching their innovative SLT (Single Lens Translucent) cameras!
This is how they did it:
By using a stationary TRANSLUCENT mirror which both reflect AND transmit light, Sony is able to achieve features that never been done in a mid range SLR before!
Go to here to take a look at their innovation!
And why I am so excited about this camera? Well, just go over to the excellent IN DEPTH review of the A55 at dpreview and here, salivate over the scores of NEW features like sweep panorama and how about Continuous Phase Detect AF During 10 fps High-Speed Shooting and Full HD Movie Shooting?
I want one NOW!!
Famous Last Words:
I am disappointed with Canon!
Hello... this Sony Translucent Mirror technology is not new ;) Canon has been using such a mirror in their Canon Pellix camera all the way back in the mid 60's!!
I have been always intrigued and have enormous respect for Sony, I remember when I was young; I was in awe when they launch their ELCASET and their BETAMAX video! But alas I hope their SLT cameras are going to be successful, not like the other two mirages ;)