Electronic – arduino – Can 50 Arduinos be daisy chained

TCP/IP on Arduinos isn't exactly the best choice for anything real-time. Ethernet timing isn't deterministic, so regardless of any method that attempts to remove jitter or compensate for latency, it will never be spot on.

You mention "Arduino -> network -> Arduino" as your desired topology, in which case I would throw away the idea of using the (very expensive) Ethernet boards and use something designed for embedded systems, like RS-485. As you have total network control, your master module could send a 'shutter' message for every slave to pick up and act upon after message completion. They would all receive it at the exact same time (+/- 1 ns/foot), so jitter and lag would be negligible for any camera application.

Here's a shield that has RS-485 on it, but it's just a single chip (e.g. MAX485 & friends) that you could breadboard.

Edit:

How far apart are these cameras? If they're only ~10 meters apart and you want a (light?) sensor that goes to each one, just wire up a sensor+shutter+power cable and run them to the same Arduino. It should only be 4-6 wires; buy some good connectors and it should be painless to tear-down and set-up. You might be able to get away with significantly longer cables even, depending on the sensor, etc.

Paraphrased from my comments above

Depending on the flexibility available in designing the sensor modules, a common signaling / sensor approach traditionally used with long cables in industrial applications is the 4-20 mA (or 10-50 mA for longer throws or EMI-intensive environments) current loop signaling standard.

• The cable and sensor module make up a current loop, module regulating current through it
• A current of 4 mA indicates analog minimum, or digital LOW
• 20 mA indicates analog full-scale or digital HIGH
• Open circuit = 0 mA = sensor offline alarm
• Short circuit = Current limit = sensor shorted alarm

Industrial sensor modules are often designed to be powered by the same current loop, thus eliminating the need for local power supplies. This is feasible, of course, only if the sensor module does not require greater than 4 mA drive current.

Various options exist for signaling current regulation, such as using BJTs, MOSFETs or complementary TrenchFET parts.

At the data collection end, voltage generated across a shunt resistor is amplified using an op-amp, for analog sensors. Digital signals can be captured using a suitably trimmed comparator circuit designed with some hysteresis.

Depending on any lightning or other high voltage risks perceived along the transmission cables, isolation amplifiers may be recommended instead of conventional op-amps for amplifying the shunt voltage. This ensures that the data collation devices are protected from potential differences that may creep in through induction, ground potential differences, or other causes.

For example, TI's AMC1100 Fully-Differential Isolation Amplifier is designed specifically for current-shunt sensing with HV isolation.

An added advantage of using a current loop signaling approach is that security breaches to the home security system implied in the question, can be detected if any sensor is either shorted out, or disconnected.