You may have read or seen these features and and wondered how they work or what they are for. I know of a lot of people who expected to much from HSS (High speed sync) thinking they could shoot every thing at 1/8000th of a second with the perfect exposure from a tiny system flash.
To understand how they work you need to think a bit differently to how you would normally view your exposure. Normally the exposure is made up of our 3 aspects ISO, f/, and shutter speed. This is still the case when using strobes/flashes but things don’t quite work the same. By adding light we are changing the exposure formula, at first it may seem a lot more complicated but once things fall into place it all becomes so much easier. If we forget about the shutter speed for now and replace it in the exposure triangle with the flash. Now the bigger (I will define bigger latter) the flash the lower your f/and or ISO will have to be to not over expose the image. You can now set the shutter speed to match your ambient lighting. The faster the exposure the less ambient light will get in, isolating your flashed subject from any distracting background/foreground (but exposing too quick my cause parts of the photo to be black as the shutter isn’t properly open when the flash fires). The longer your exposure the more ambient light will get in adding background/foreground atmosphere (but exposing to long will over expose your image).
Personally I’m a big fan of slow sync flash work if done properly it can be fantastic. there are also 2 basic settings I can use when doing a slow sync. Normal slow sync or rear sync. The difference is in a slow sync the flash fires at the start of the exposure, and with a rear sync it fires at the end of the exposure. The wont change the photo is the subject is static but if there is movement during the exposure it make a lot of difference.
As far as I know all Alphas have the slow and rear sync feature but not always activated the same way. But the end result is the same. I’m going away this weekend and hope to shoot and example or 2 🙂 (but I hope to write a bit more about slow speed sync and high speed sync before then as well as Big and small light )