USB - TTL Converter

I'd like to build an USB - TTL converter for my camera. I've seen on FTDI site many options but I don't know which one to use, some of them are USB - SERIAL converters.
I have an ideea to use one of these schematics to build USB - SERIAL converter, then an level shifter with MAX232, then use optocouplers to output safely TTL.
I have also a question: If I build this converter, it is necessary to add the optocouplers? Is there any chance to have the surge problem, spike, lightning and grounding problems if I don't use the optocouplers?
Below is the schematics for the converter SERIAL - TTL, opticaly isolated, which needs power supply. I am trying to get power for this converter from a USB - SERIAL converter.
Can this be done?
THANKS

yes, you can use isolated DC/DC converter (5V in from USB port, two 5V outputs to your circuits Vcc and Vcc2). low power versions should be $10-12 but you can build your own too.

----edit ----

here is what BB Electronics makes (not detailed presentation of the circuit)

https://www.electro-tech-online.com/custompdfs/2006/07/232ottl.pdf

Thanks for posting.
The whole idea is to mount on same board the USB-Serial converter, MAX232 circuitry and optocouplers. MAX232 circuitry will connect as on real serial port, will get power from this port and the optocouplers will get power on one side from serial port's adapter, and the other side from camera.
The new USB - TTL converter will contain:
1. USB-Serial adapter
2. MAX232 circuitry
3. optocouplers.
It is not only to power the adapter from USB port, but to create une virtual COM port, using FTDI chip & driver. On this port suppose to connect rest of circuitry, powered from this newly created serial port.
Can this be done?

why don't you try and let us know? i think i saw some development kits too...

If you're after a USB to TTL why would there be a need for RS232 level conversion?? Try a FX2 wich includes a UART, couple that to the opto and boomshanka

Idea

Thanks for posting. I got the idea with RS232 Level Convertor.
Here is what I found: on FTDI site, datasheet for FT232, includes the RS232 Level Converter. I tried to make a schematic, I don't know if it is correct.

Beside that, I understood that the data cables for mobile phones also create a virtual COM port, come with CD with drivers and I'm thinking to use one cable for mobile phones, cut it, add the optocouplers and connect to camera. What do you think, could the GSM data cable work with the optocouplers?