pro loadlt,seq,first,last,a

exten='.00'
imno=strtrim(string(first),2)
strput,exten,imno,3-strlen(imno)
fzrd,seq+exten,img,h		;read 1. image
dim=size(img) & a=intarr(dim(1),dim(2),(last-first+1)/2)
a(0,0,0)=img
imno=strtrim(string(first+1),2)
strput,exten,imno,5-strlen(imno)
fzrd,seq+exten,img,h		;read 2. image
a(*,*,0)=a(*,*,0)+img
for i=first+2,last do begin	;loop over image series
  imno=strtrim(string(i),2)
  strput,exten,imno,3-strlen(imno)
  fzrd,seq+exten,img,h	  ;read image 
  ind=(i-first)/2
  a(*,*,ind)=a(*,*,ind)+img
endfor

end