[bxf]

The K-3 is set to Wireless/Control, the AF540 is set to Wireless/Slave. Both are set to Channel 2.


When I take a shot, the AF540 goes off, but all photos are severely underexposed.

The AF540 manual says "Press the flash mode button (MODE) to display (P-TTL) if the flash mode was set to modes other than P-TTL auto", but the only modes available while the unit is a Slave are A and M.


If I try to change the channel by simply setting it while the flash is mounted on the body and then pressing shutter release half way, the new channel number is not reflected in the body display (so I set the flash unit to the channel shown by the body). I'm mentioning this in case it is indicative of some related problem.


I just noticed that there are only five pins (plus one hole) at the bottom of my AF540, even though the manual shows six pins. Am I missing one? Note that the flash works properly when mounted on the K-3 body, and it probably wouldn't make much sense to think that a missing pin would be responsible for wireless operation failure.


I am thoroughly confused. Why is everything underexposed?

[Adam]

Is the flash set to deliver 1/1 exposure, and are both the flash and camera set without a flash exposure compensation?


There's a more in-depth walkthrough here, to make sure you have the right settings:
Comprehensive Pentax P-TTL Flash Guide Updated - Articles and Tips | PentaxForums.com

[CarlJF]

As I remember it, with the 360 you had to change a slave setting from the default SL1 value to 2 (or the other way around). By default, these flash were set to work as dump optical unit and not P-TTL, which was new at the time these flashes were launched and thus not supported by most camera. This is why you can only choose A or M mode. And the pictures are underexposed because the 540 is trigerred by the camera preflash, thus not synchronized with the shutter.

[pschlute]

As I remember it, with the 360 you had to change a slave setting from the default SL1 value to 2 (or the other way around). By default, these flash were set to work as dump optical unit and not P-TTL, which was new at the time these flashes were launched and thus not supported by most camera. This is why you can only choose A or M mode. And the pictures are underexposed because the 540 is trigerred by the camera preflash, thus not synchronized with the shutter.

The default setting should be SLave mode 1 which is the P-TTL -wireless compatible mode. The SLave 2 mode is for the dumb flash mode you describe.

To the OP. Is this a version I or II AF 540 ? Make sure your slave mode is in SL 1. Make sure your shutter speed on the camera is below your sync speed ....1/180 or less. What lens are you using ?

Also, make sure the camera is awake (not in stand-by/sleep mode) when you try to select P-TTL on the flash unit. Not entirely sure if this will make a difference !

You say the AF540 fires but you get underexposure. What is your flash to subject distance , including any bounce. What camera exposure mode are you in, and what are your ISO/Shutter speed/Aperture settings.

[bxf]

Is the flash set to deliver 1/1 exposure, and are both the flash and camera set without a flash exposure compensation?

This setting is not available, because I have only A or M modes, no P-TTL. But see below...

As I remember it, with the 360 you had to change a slave setting from the default SL1 value to 2 (or the other way around). By default, these flash were set to work as dump optical unit and not P-TTL, which was new at the time these flashes were launched and thus not supported by most camera. This is why you can only choose A or M mode. And the pictures are underexposed because the 540 is trigerred by the camera preflash, thus not synchronized with the shutter.

In fact, the manual leads me to use SL2, due what I take to be an inconsistent use of the term SLAVE. See below...

The default setting should be SLave mode 1 which is the P-TTL -wireless compatible mode. The SLave 2 mode is for the dumb flash mode you describe.

To the OP. Is this a version I or II AF 540 ? Make sure your slave mode is in SL 1. Make sure your shutter speed on the camera is below your sync speed ....1/180 or less. What lens are you using ?

And now we have the correct solution, which I discovered myself as I was experimenting with various settings

When setting the M/C/S (Master/Controller/Slave) mode, one is instructed to use Slave for wireless use. However, in the Slave Mode Setting instructions it says:

SL 1: When photographing in wireless mode
SL 2: When photographing with slave flash

It appears that the use of the word Slave here is different from its use in the M/C/S setting. Here, as pschlute points out, SLAVE (i.e. SL2) refers to a dumb flash. When set to SL 1, P-TTL mode is available, and the flash works correctly.

By the way, is Auto Zoom supposed to work in wireless mode?

Thanks for all replies.

[pschlute]

By the way, is Auto Zoom supposed to work in wireless mode?

No because there is no communication between camera and flash unit until you press the shutter, and the "optical" communication between them is only concerned with flash power required.

I use Cactus radio transmitter/receiver units for my camera to communicate with the off camera flashes, and this method does allow for the zoom settings to be controlled from the camera either in auto, or by manual control from the transmitter unit on the camera hotshoe.

[bxf]

No because there is no communication between camera and flash unit until you press the shutter, and the "optical" communication between them is only concerned with flash power required.

I use Cactus radio transmitter/receiver units for my camera to communicate with the off camera flashes, and this method does allow for the zoom settings to be controlled from the camera either in auto, or by manual control from the transmitter unit on the camera hotshoe.

Good to know, thanks.