Newbie question ? - Multiple suns when rendering images

Hi,

I´m struggling with a problem where I want to render out a series of images where the sun direction is rotating (10° per frame). My problem is that the sun itself appears several times in the rendered images, since it seems to have a “lag” to disappear. So, when it is moved to a new position, the sun disappears very slowly on the previous position, resulting in multiple suns showing in each rendered image.

Is there a way to increase shutter rate or change the fading of the sun to disappear faster ?

Thanks,
Martin