Sony also provide that. Both, HVL-F20AM and HVL-F58AM flashes are also IR wireless controllers. If you want to prevent the wireless flash controller signals from the flash appearing in the shot, just attach a piece of exposed and developed color negative film to the pop-up flash.
Here are more info:
New HVL-F20AM flash and a DIY (Do-It-Yourself) IR Filter Switch
Juan
The A850 and A900 do not have a pop-up flash.
What I am talking about are devices such as the Canon STE-2 and Nikon SU-800 Commander units which provide sophisticated wireless IR control of multiple TTL flashes or groups of flashes at the camera, as well as different types of close up flash control in the case of the Nikon SU-800 ...
without the need for any flash on the hot shoe ... which is preferable in most off-camera situations I ever do. I prefer to control where the fill is coming from, not just accept it at camera.
IMO, I'd be leery of placing any ND filter over any hot shoe speed-light ... wouldn't that be asking for it to shut down or to fry it in rapid sustained shooting conditions like at a wedding or event?
In addition, both the STE-2 and SU-800 have infrared AF assist lights that keep the AF assist beam where it should be ... at the camera over the lens. Sony's off-camera cord doesn't even have this, where Canon's off-camera cords do. AF assist at the camera is valuable for shooting available low light photography without using flash, where contrast issues can cause a lens to hunt.
I ALWAYS used a STE-2 in the hot shoe even when not using off-camera flash when shooting with the 85/1.2L which significantly improved the AF ability of that lens in low contrast conditions ... and dearly wish there was a Sony version of this to assist with the 85/1.4 and 135/1.8 in low light.
The Sony HVL-F58AM flash in itself is great ... but the flash system is way behind Canon and Nikon ... making it difficult to employ more sophisticated
strobists techniques.
The HVL-F20AM may be a partial answer, and worth getting ... but it doesn't have an AF assist light that I can see.
In truth,
all of these infrared controllers are basically very limited solutions as they depend on line of sight, and the distance performance is humorous at best.
I do also wish Pocket Wizard would include Sony in the covered flashes controlled by their new TTL radio system, but I'm not holding my breath.
-Marc