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01-18-2013, 09:44 AM   #1
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Will a flash radio trigger allow metering of the AF540FGZ off camera

I don't have much flash experience, but does this work the same as using it with a chord?

Also, can I use a corded shutter release to do exposure bracketing, and where would it plug in?

Sorry for the rookie questions.

01-18-2013, 10:01 AM   #2
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In general no as most triggers are manual only. They provide only a trigger signal no metering. There is a company that said they were going to make a P-TTL radio trigger for this purpose but I cannot remember the name or find them at the moment. Not sure I have ever seen it for sale so it may not be released yet.

Maybe someone else can remember the name.
01-18-2013, 10:35 AM - 1 Like   #3
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There are two "flavors" of radio trigger if you will. manual, and xTTL (replace the x with the nomenclature of the particular brand). Manual radio triggers which are by far the most prevalent, only send a signal to "fire now!", where as TTL triggers work a little differently. When the shutter release is pressed on the camera, the TTL trigger tells the flash to fire a test burst, the camera reads the resulting exposure, calculates how much more or less power is needed and then tells the flash (via the TTL trigger) "fire now @ 1/4 power" or 1/2 or whatever fraction of full power it deems appropriate to make a good exposure.

The only pTTL radio triggering system at the moment is from Aoktec, and it uses light from an on-camera flash, converts it to radio, and sends it to the receiving unit(s).

HOWEVER, you can rejoice. In answer to your original question, yes, it is possible to meter the AF540 off camera thanks to it's built in auto thyristor circuit. The way it works is like this, you set the flash to auto mode, and on the flash set the aperture at which you want to shoot. You can use a simple manual radio trigger for this, like a Pocket Wizard, a Cactus V5, or a YongNuo 602. When the shutter is pressed, the radio trigger sends a signal to "fire now!" and the flash does. Then in real-time, as the exposure is happening, the light sensor in the flash looks at the subject, and decides when the correct amount of light for the programed aperture has been emitted, then quick as lightning, turns off the power. The result is a perfect exposure in theory. There are several factors that play into the equation, such as relative subject size, color, and reflectivity, but in all honesty, it's at least as accurate as pTTL.
01-18-2013, 11:04 AM   #4
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Maxfield is right - his advice for radio trigger is the easiest and least expensive way to go, and will typically yield fine results as long as the flash is positioned to illuminate (bounce or not) where you are aiming the camera lens (can be a bit tricky but that's why we take test shots).

No corded shutter release for the K-01 - wireless is pretty much the standard nowadays. You can get a Pentax wireless trigger, or spend just a few bucks for a generic universal wireless release that includes Pentax; sensor is only in the front of the camera which has triggered (no pun intended) a few complaints but isn't much of an issue in practice. The JJC RM-E3 works fine.

01-18-2013, 03:19 PM   #5
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Thanks all! With regards to the corded shutter release, I thought you couldn't set wireless remote and bracketing at the same time, as they are both on the same menu? I want bracketing without the camera shake of pressing the shutter. I don't think you can do timer and bracketing for the same reason. True or false?
01-19-2013, 07:23 PM   #6
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Bump....anyone...hello?
01-19-2013, 08:21 PM   #7
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Wireless and bracketing

Well, if your goal is bracketing exposure in a series of separate images without returning to the camera to make adjustments, you are out of luck.

If your concern is HDR which is usually the reason for quick-fire exposure bracketing; that is a separate function dedicated on the main dial, and you certainly can use that mode in wireless remote.
01-19-2013, 09:06 PM   #8
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QuoteOriginally posted by ScooterMaxi Jim Quote
Well, if your goal is bracketing exposure in a series of separate images without returning to the camera to make adjustments, you are out of luck.

If your concern is HDR which is usually the reason for quick-fire exposure bracketing; that is a separate function dedicated on the main dial, and you certainly can use that mode in wireless remote.
Yes, my goal is to use some sort of remote, wired or wireless, to to shoot bracketed exposures without returning to the camera in any way, thus moving it. I want to do HDR is post, not on camera.

01-20-2013, 02:14 PM   #9
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Yep, you are out of luck on that. Even if auto HDR was OK - you are stuck with JPG as the output which is less that ideal, obviously. The camera is great for a lot of non-action shooting uses, but it wasn't designed for many specialty uses.
01-21-2013, 08:31 AM   #10
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QuoteOriginally posted by ScooterMaxi Jim Quote
Yep, you are out of luck on that. Even if auto HDR was OK - you are stuck with JPG as the output which is less that ideal, obviously. The camera is great for a lot of non-action shooting uses, but it wasn't designed for many specialty uses.
Yeah, sounds like it. Not thrilled. This would have been easy to implement.
01-25-2013, 07:39 PM   #11
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QuoteOriginally posted by maxfield_photo Quote
There are two "flavors" of radio trigger if you will. manual, and xTTL (replace the x with the nomenclature of the particular brand). Manual radio triggers which are by far the most prevalent, only send a signal to "fire now!", where as TTL triggers work a little differently. When the shutter release is pressed on the camera, the TTL trigger tells the flash to fire a test burst, the camera reads the resulting exposure, calculates how much more or less power is needed and then tells the flash (via the TTL trigger) "fire now @ 1/4 power" or 1/2 or whatever fraction of full power it deems appropriate to make a good exposure.

The only pTTL radio triggering system at the moment is from Aoktec, and it uses light from an on-camera flash, converts it to radio, and sends it to the receiving unit(s).

HOWEVER, you can rejoice. In answer to your original question, yes, it is possible to meter the AF540 off camera thanks to it's built in auto thyristor circuit. The way it works is like this, you set the flash to auto mode, and on the flash set the aperture at which you want to shoot. You can use a simple manual radio trigger for this, like a Pocket Wizard, a Cactus V5, or a YongNuo 602. When the shutter is pressed, the radio trigger sends a signal to "fire now!" and the flash does. Then in real-time, as the exposure is happening, the light sensor in the flash looks at the subject, and decides when the correct amount of light for the programed aperture has been emitted, then quick as lightning, turns off the power. The result is a perfect exposure in theory. There are several factors that play into the equation, such as relative subject size, color, and reflectivity, but in all honesty, it's at least as accurate as pTTL.
Does the AF360 have a built in auto thyristor circuit and work in the same way?
01-25-2013, 08:41 PM   #12
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QuoteOriginally posted by chiane Quote
Does the AF360 have a built in auto thyristor circuit and work in the same way?
Yes, it does. I would assume that the new AF360 mk II will as well. If you look on the front of the flash, you will see a little round hole, that is the photo cell. The thyristor is actually the circuit that controls the power, but in some modern flashes the thyristor has been replaced by a quicker circuit called an IGBT. I'm not really sure which type of circuitry is in the Pentax flashes, so technically it may be a misnomer to call it an "auto thyristor" but I do it anyway.
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