in T20 canon are showing ad of 100D mostly I think...there ad are soo beautifully made that I tend to neglect the main product itself
[MENTION=17225]Rishi[/MENTION] ...mirrorless is the future...DSLR shape + mirrorless for me ....and a pocket mirrorless with APSC sensor+3x zoom as secondry shadi party holiday camera
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Non-AI is the oldest one and it can not be used directly to modern DSLR ...it had to be converted to AI to be usable
AI - normal manual lenses ...will not confirm AF or meter with any modern DSLR
AIS - It gives AF confirmation when you rotate the AF ring and it will meter ...I think spot metering woks with them
AF - it will autofocus with all DSLR above D80, D90, D7000, D200,D300 etc
AF-D - It have a distance technology which helped flash compensation or you can say that DSLR could calculate how far away you are from the subject and will use flash acordingly (I think this is correct...have to recheck)
AF-S - its the modern lenses which have ultrasonic motor inside ....the cheaper ones or budget ones have a smaller motor soo they focus slow but from Nikon 70-300 VR onwards all lenses have ultrasonic motors