Originally posted by sany Just my little concern is to avoid changing the lens outdoor particularly in a place where I live is dusty
be carefull but don't obsess about that...all the point in a reflex is to be able to swap lenses to get the perspective and angle of view you might want. If you got a rocket blower, handle the lenses with care, blow the dust from them before storage and put the cleaning sensor vibration on for when you power on the camera, it's very unlikely that you'll have troubles with dust (unless of course you are immersed on the fear and loath in las vegas' desert race on a daily basis). Don't obsess about dust and litle scratches. Just enjoy your equipment and handle it with care and all will be fine.
Oh and superzooms have to compromise on a lot of things to cover those insane focal lenghts...i personally prefer moderate zooms as workhorses and primes for specific purposes.
The Pk/A adapter will likely be more expensive than some adaptall lenses
but that will let you use a lot of lenses,with some level of automatization (Av,Tv,Sv modes) that are usually very well priced.
A mirror or catadioptric lens is made with a two circle design...you will see like a doughnut where the glass is, that goes to a mirror that reflects on to another mirror wich is housed on the center of the doughnut wich in it's turn directs the light to the sensor. The design was used to make cheaper and more compact long telephotos (example 500mm). They produce a ring bokeh that some dislike, and that i personally love when used creatively. The tamron adaptall 500mm mirror lens is one of the few that is considered to have good IQ (there are loads of them like the centon or Samyang dirt cheap that have poor IQ).