Here you go:
mport arcpy.mapping, os
mxd = arcpy.mapping.MapDocument (r"E:\workspace\Test.mxd")
arcpy.env.workspace = r"E:/workspace/images/"
df = arcpy.mapping.ListDataFrames(mxd)[0]
df.scale = 40000
gridlayer = arcpy.mapping.ListLayers(mxd,'JERGRIDINDEX', df,)[0]
arcpy.SelectLayerByAttribute_management(gridlayer, "NEW_SELECTION")
for row in arcpy.SearchCursor(gridlayer):
df.panToExtent(row.shape.extent)
arcpy.RefreshActiveView()
filename = "E:/workspace/images/" + \
str(row.getValue("PageNumber")).zfill(4) + ".tif"
arcpy.mapping.ExportToTIFF(mxd, filename, df, df_export_width= 65000, df_export_height=30000,geoTIFF_tags=True)
## arcpy.mapping.ExportToTIFF(mxd, filename, df, df_export_width= 1280, \
## df_export_height=440, geoTIFF_tags=True)
print arcpy.GetMessages()