Sunday, February 15, 2009

Pentax Wireless P-TTL (Part 2)

In Part 1 we talked about the camera/flash configuration. In this article we're going to talk about how to use the single flash with the camera.

The camera built in flash acts as the commander that controls the remote flash (slave). The commander sends signals to the slave flash and in P-TTL mode tells the slave flash to fire so it can calculate the exposure according to the camera/flash settings. There is a lot going on here in just a few milliseconds and it all happens in a few exchanges of light between the commander and slave flashes.

So let's get going.

I'll start off with a word of caution!

NEVER fire the flash when the flash head pressed up against an object that blocks the output of the flash head. The flash will fire at full power and a lot of heat is generated that will burn or melt the object against the flash head and may fry your flash bulb. I have done it and left a rectangle shaped scorch mark on a suede shoe. I was lucky that I did not fry the flash bulb but the flash head got so hot that it melted the plastic that supports the fresnel lens and produced a nasty odor of burnt plastic. So be careful where you place the remote flash and pay attention to not let any flammable materials get near the fresnel lens.

You won't need any thing but your camera and your flash but be sure you have set your flash and camera to the same channel as described in the previous post.

1.Turn the on the flash, set flash to wireless and turn the camera on.
2.Make sure the flash is set to slave mode.
- Press the Master/Control/Slave button on the flash until Slave appears in the LCD screen.
3.Make sure the flash is in P-TTL mode.
- Press the MODE button on the flash until P-TTL shows on the LCD screen.
4.Make sure the camera is set to wireless mode.
- Press the Fn button.
- Press the 4 way control button down to select the flash settings.
- Scroll to the wireless setting (W with lightning bolt)
- Press OK twice to exit the Fn menu.
5.Set the camera mode to Program mode (P) for now. We'll get to Av and Tv modes in a future article.
6.Set the built in flash to not fire during exposure.
- Press the menu button.
- Scroll left once time to the Custom Setting menu.
- Scroll up twice to the Flash in Wireless mode.
- Scroll right and select option 2 (Off).

You are now ready to shoot with the remote flash in wireless P-TTL mode. You're going to need a wider angle lens most likely or a close focus macro lens is actually perfect for this type of flash work. I've used this setup to take macro shots of flowers and insects. It's great for that quick catch that won't wait for a complete macro flash setup.

Before we take any real photos we're going to take a look at all the flashes that are happening during the photo taking process.

Lay the remote flash on a table or chair with the flash pointing away from your eyes and the front of the flash pointed up. The front of the flash contains the sensor that picks up the signals from the commander flash on the camera so it has to see what's going on. If you have the sensor pointing down on the table it may not see the signals from the commander flash.

Point the camera up and at an angle away from your eyes so you can see the commander flash from the side but so it will not directly blind you.

Release the shutter (you may have to set the camera to manual focus if it can't focus on the wall or ceiling) and notice the commander flash fires twice. I'm not exactly sure what each flash does, but since the commander flash has been told not to fire during exposure then we know all it is doing is communicating with the slave flash.

The slave flash also fires twice, the first one is the pre flash (the P in P-TTL) and the second is the actual flash used in the exposure.

Now let's take a picture of something.

First frame the subject in the camera before you even hold the flash up in the air. Your arm will get very tired very soon so give it a break.

Once the zoom/focus have been set to frame the subject how you like, hold the flash up and out in your left hand and point it at the subject. The further from the camera the better.

Keeping both eyes open, pre-focus the camera on the subject, hold your breath and gently release the shutter.

A few things you may have noticed, you actually saw the subject lit up with the flash through the view finder and then the viewfinder went black and you saw a repeat flash with your other eye that lit up the subject (or the room if you can't see the subject with your other eye.

The flashes are pretty fast, so if you want close your non viewfinder eye and just notice that you do see a flash through the viewfinder before the shutter released.

Now close the viewfinder eye and you will notice 2 very close flashes.

The first flash is the pre flash which the camera uses to set the exposure of the frame depending on how the camera is set up. In P mode the camera adjusts the shutter speed and aperture to what it thinks best fits the scene and then tells the remote flash what power to fire at.

The second flash fires while the shutter is open and the camera captures the image.

That's all there is as far as the average photographer needs (or wants) to know about P-TTL. The details are more complicated but you don't need to know the details to get the job done.

Stay tuned for the next article due in a couple of weeks. We'll discuss how to properly set up the flash zoom and umbrella shaft distance to produce the optimum flash fill pattern.


Bob Ell said...

Thank you so much for your easy to follow instructions. I've was frustrated trying to get my flash to work in conjunction with my built in flash and with your step by step guide, I was able to do it in a few minutes. Keep up the good work.

I would be interested in suggestions on using the built in flash and wireless flash with a lightbox

Anonymous said...

Great to see Pentax-specific strobist advice!!!

One comment - as they say, a picture is worth a thousand words. If you could find a way to embed pictures illustrating your points, your blog would be much easier for me to digest.

Photography Rulez said...

I will add some photos this weekend then.

Thanks for the feedback.

Anonymous said...

Very useful guide. I followed the steps, however I am unable to set Flash to p-ttl in wireless mode. Once I remove flash from the cam after setup, it only cycles between M and A mode.

Photography Rulez said...

@Anonymous: Make sure your camera is set according to Step 5 in Pentax Wireless P-TTL (Part 1).