//validação form login
function validaLogSistema(){
	var login = document.form_login_sist.login.value;
	var senha = document.form_login_sist.senha.value;
	if(login.length < 1){
		alert('Informe o Login!');
		form_login_sist.login.focus();		
		return false;
	} else if(senha.length < 1){
		alert('Informe a Senha!');
		form_login_sist.senha.focus();		
		return false;
	} else {
		return true;
	}
}

<!--Início Janela Ver Foto Zoom
function ampliar_imagem(URL, width, height) {
	
   var left = 50;
   var top = 50;

   window.open(URL, '', 'width='+width+', height='+height+', top='+top+', left='+left+', scrollbars=auto, status=no, toolbar=no, location=no, directories=no, menubar=no, resizable=no, fullscreen=no');
}
//-->Termino Janela Ver Foto Zoom

<!-- Pop Equipamantos -->
function abrir_equipamento(URL, width, height) {
	var larguratela = screen.width;
	var alturatela = screen.height;
	var largurajanela = 650;
	var alturajanela = 500;
	
	var iniciolargura = (larguratela - largurajanela) / 2;
	var inicioaltura = (alturatela-alturajanela) / 2;

   window.open(URL, 'equipamentos', 'width='+largurajanela+', height='+alturajanela+', top='+inicioaltura+', left='+iniciolargura+', scrollbars=yes, status=no, toolbar=no, location=no, directories=no, menubar=no, resizable=no, fullscreen=no');
} 
<!-- Pop Equipamantos -->

<!-- Inicio Janela Central -->
function NewWindow(mypage, myname, w, h, scroll) {
var winl = (screen.width - w) / 2;
var wint = (screen.height - h) / 2;
winprops = 'height='+h+',width='+w+',top='+wint+',left='+winl+',scrollbars='+scroll+',resizable=no'
win = window.open(mypage, myname, winprops)
if (parseInt(navigator.appVersion) >= 4) { win.window.focus(); }
}

function MM_openBrWindow(theURL,winName,features) { //v2.0
  window.open(theURL,winName,features);
}
<!-- Fim Janela Central -->