spot on picture
 

when i changed lens and clicked pictures i saw spot on the pics....can any one tell me reason and how to correct it

Dust on lens or sensor, get a Rocket blower take the lens off hold the camera face down and use the blower [B][U]DO NOT[/U][/B] push the end inside keep it level with the face of the camera. Dont use a brush either, If that doesn't work you will need the sensor cleaning professionally, blow the lens out as well and hold the camera down when changing lens.

Yup, sounds like dust! You might find this post on cleaning your sensor useful: [url]http://www.digitalcameraworld.com/2012/05/25/dont-bide-the-dust-a-perfectly-safe-guide-to-sensor-cleaning/[/url]