ios - Animation does not origin from where I want it to? Why? -

i'm doing countdown clock game. want numbers animated come middle of screen , fade away in middle. when run code come right bottom of screen instead of specified (160,284). problem be?

} else if (startgameeveryint == 3) {     uiimageview *object = [[uiimageview alloc] initwithframe:cgrectmake(160,284,280 ,280)];     [object setimage:[uiimage imagenamed:@"1.png"]];       [self.view addsubview:object];     [uiview animatewithduration:1                      animations:^{                          object.alpha = 0;                          object.frame = cgrectmake(160, 284, 50, 50);                      }                      completion:^(bool finished){                          startgameeveryint = 0;                          [startgametimer invalidate];                          startgametimer = nil;                          [self startit];                          (uiview *view in self.view.subviews) {                              if (view.tag > 10) {                                  [view removefromsuperview];                              }                          }                      }]; } 

if change cgrect settings before animation-

cgrectmake((self.view.frame.size.width-160)/2, (self.view.frame.size.height-284)/2, 160, 284) 

then changing size of object did before to

cgrectmake((self.view.frame.size.width-50)/2, (self.view.frame.size.height-50)/2, 50, 50) 

this should work in middle of screen. x, y positions of cgrect put top lhs points of object position. why object looked off bottom right.

i hope helps

cheers, jim