Summary: I purchased this unit as a dedicated flash for my Pentax K10D dSLR. The flash is an awesome unit that fully integrates with the K10D camera. It can even be used as a remote flash by using the camera's built in flash as the master. Tilt and swivel head insures control over bounce flash to eliminate harsh flash lighting. The control panel is easy to read and quick to set up. I have read that caution must be used when locking the flash on the camera. An internal pin/cam can break causing the flash to become stuck on the camera body. I personally have not had this experience but I have read forum posts documenting this issue. My experience is that this is a great flash unit and have had no trouble.

Summary: I bought this because of more power and ability to twist horizontally, as well as vertically, compared to 360 model. I have started trying some things out in high speed and other modes. It is definitely a step up from just the pop-up flash on K10D. There is a bit of underexposure by default. But you can set flash compensation. I also took others' advice and got a Sto-Fen omni bounce flash diffuser to provide more flattering light. This flash can use the optional C powered battery pack, but you can get better performance with Li-Ion rechargeable AA's. I see that there is also a port to plug in the flash extention for contrast control using multiple flashes or to connect the camera to the flash for use on a bracket.. cool (not sure when I will get into that, but great to know that I can). If you're looking at a flash for your Pentax DSLR, with an eye toward advanced use, the 540 is excellent choice.

Summary: Having recently bought the Pentax K10D I found myself looking for a good flash unit that would meet my high expectations of build quality, ease of use, and functionality. After going to a local photo store to check out the Sigma 500 Super DG flash, I decided to go with the Pentax 540. The new Sigma 530 is supposed to be very comparable to the Pentax, but since the Pentax isn't much more $, why not spend a little more and get the Pentex OEM quality? Anyway, the flash works as advertised. The wireless operation is awesome, allowing off-camera fills for some great strobe effects. If you have the money to spend on a $250-$350 flash unit, go Pentax. Can be had for $320 shipped on line (got mine from buydig.com) and the Sigma 530 Super is about $260 currently.