With mphx‘s help，I edited some buttons of both multicam way and bcam way.
Now I can easily shoot and download images.
So I found out a old CRT and downloaded SyncTest011 to make a sync test.（see a.jpg）
I used two canon powershot A1200, set shutter speed to 1/200 sec , ISO 400 (at home night),F2.8.
The CRT is LG 775FT plus( vertical frequency 83Hz, horizontal frequency 66.4KHz, resolution 1024 x 768).
In multicam way, I used “preshoot” command which is better than shot “shoot” command.
In bcam way, I turned on the sync of each camera in the bcamrem script and shot through controlling the switch of central usb hub.
I just took ten shots in each way.
The result of multicam way:
Minimum Mis-Sync (ms): 4.80 Average Mis-Sync (ms): 12.35 (1/81 sec)
Maximum Mis-Sync (ms): 27.86 Average Deviation: 6.51
The result of bcam way:
Minimum Mis-Sync (ms): 0.05 Average Mis-Sync (ms): 0.54 (1/1852 sec)
Maximum Mis-Sync (ms): 2.94 Average Deviation: 0.52
The datasets and reports are as below.https://drive.google.com/folderview?id=0B4hGaTy8v6W1amdxbDNyOHJ4UUE&usp=sharing
multicam way is more convenient.
bcam way is more stable and synchronous.
@mphx：You said the multicam way is enough for building 3D model，do you use faster shutter speed? Thus I think you must use brighter lights.
@ reyalp：Is it possible to improve the Synchronization of the multicam way？
@ waterwingz：Now I use three a1200s，I can shoot just by controlling the switch of the central usb hub to disconnect the USB 5V power without any modification（see b.jpg）. Could I still use this method when using 40+ cameras？