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Old Jan 12, 2008, 2:19 AM   #1
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I've been playing around with the wireless flash function of my k10d and Sigma 530 Super, I'm just trying to get a handle on how this works. I saw a post by Snostorm outlining the setup test to see if its working right.

The first 2 shots are taken with the on camera flash set to controller, the next 2 will be taken with the on camera flash set to master. Exposure settings are the same on the camera and on the flash (flash set to p-ttl wireless)

Questions: what is the difference between the controller and master modes of the on camera flash? Each time the on camera flash fires, so won't that effect the exposure of the image? Can you give me an example of where these modes would be useful?
What is the range of the wireless capabilities of the k10d? do they have to be set up in a certain way? I noticed that the off camera flash has to "see" the cameras flash, so is this really wireless or just optical?
Along the optical lines... what is the difference between wireless and optical modes of the external flash?It seems like the optical sensitivity is much greater than the wireless sensitivity.
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Old Jan 12, 2008, 2:19 AM   #2
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Old Jan 12, 2008, 2:20 AM   #3
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Old Jan 12, 2008, 2:22 AM   #4
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Yeah, I know, these are amazing picutes.... It's 1:20 in the morning and I am waiting for my newborn son to settle down so I was just in the "playing around mode"

:|
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Old Jan 12, 2008, 3:09 AM   #5
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The way I understand wireless P-TTL, which could be totally wrong, is this:

In master mode, the on-board flash will fire, adding light to the photo. Furthermore, it will also trigger its slaves as well, communicating flash info via the pre-flash. This is shown in your 2nd pair of images, where the foreground is lit, as well as the remote flash firing.

In commander mode, the on-board flash will fire the pre-flash to get exposure info, then communicate information to the remote slaves. However, it will not fire the main flash, and therefore should not contribute any additional light to the photo. In reality, the pre-flash may add a tiny hint of light, but it's usually negligible. This is shown in your first pair of images, where only the remote flash is lighting the scene.

Someone correct me on this, but I believe the wireless function can be achieved either optically or through RF. The K10D has an RTF transmitter, so it should be able to communicate with remote units using RF signals. Otherwise, you'll need line-of-sight between the remote unit(s) and the camera to achieve optical wireless.

You would want to use commander mode if you want to do some unique lighting conditions, rather than the on-camera light. Commander mode becomes extremely useful if you want to move the camera around but maintain a fixed light source at an object. If you used master mode and moved around, your on-board flash would light the foreground every time, making it difficult to obtain some unique and dramatic lighting.

If you want some good uses for the remote flash, check out the Strobist blog: http://strobist.blogspot.com/

- Jason
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Old Jan 12, 2008, 10:42 AM   #6
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Thanks for the info Jason, I am familliar with Strobist, I hit that site once or twice a week... very cool stuff there, mostly over my head though.

If it is a true wireless rf signal, why does it need the preflash to send the info? It seems like the external flash has to be able to "see" the pre flash on the camera to fire. true wireless should be able to fire from another room right?
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Old Jan 12, 2008, 12:35 PM   #7
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fisheye4 wrote:
Quote:
Thanks for the info Jason, I am familliar with Strobist, I hit that site once or twice a week... very cool stuff there, mostly over my head though.

If it is a true wireless rf signal, why does it need the preflash to send the info?* It seems like the external flash has to be able to "see" the pre flash on the camera to fire.* true wireless should be able to fire from another room right?
Hi FE4,

Wireless TTL is an optical system. No RF involved. The camera mounted flash preflashes first to alert the remote that it's using wireless mode and to get exposure settings, and the remote fires a preflash to confirm this. Then the camera mounted flash preflashes again to transmit the exposure info to the remote flash, then the shutter is tripped and the exposure is taken. There's another preflash from the camera mounted flash for flash duration only if HSS is being used.

As shown in your shots, with the onboard as controller, as in the first two shots, the remote is the only flash that effects the exposure -- the remote flash unit in the frame is in silhouette (so severely underexposed).

In the two shots with the onboard as master, the flash unit in the frame is exposed reasonably, as well as the far wall or the cushion, so the onboard is contributing to the exposure as well as the remote.

The difference between this and a "dumb" optical slave is that with just an optical slave, there is no exposure metering communication between the camera and remote flash, and the remote flash will fire at whatever power it's set to manually. In TTL wireless flash, the camera body meters the flash (with the first preflash) and communicates the metering information to the remote (with a second preflash) before the shutter trips and an exposure is taken. A "dumb" optical slave will only sense any triggering flash and fire from it. That's why to get an optical slave to work properly with a P-TTL onboard flash, you need to get a "digital" slave which ignores the preflash and only fires on the second, "exposure" flash of the P-TTL onboard. If it's not a "digital" slave, it'll fire off the preflash, and won't contribute to the exposure at all. Also, since the additional output of the slave isn't factored into the metered exposure, you might have to play with the slave's output settings to get it right, then readjust it manually if, for example, subject distance varies.

An RF remote system also will not use the camera's meter to adjust the exposure, so each flash's output must be preset and/or adjusted manually. The RF trigger just fires the system at the time of exposure just like any non-dedicated hotshoe flash (on a signal from the center contact on the hot shoe), without any metering preflash nor any info communicated between the camera and flash(es). That's why RF systems are universal and not mfg specific (except in the case of Minolta/Sony where the hotshoe design is proprietary and physically different from the other mfgs).

The only limitations of wireless TTL are range of the remote (@ 4 meters, which is usually more than sufficient), and potentially the amount of ambient light (it's more iffy outdoors in the sun)

This is really confusing stuff -- took me quite a while to get my brain wrapped around it -- but the metering is the difference -- you just have to set the camera and the flash for wireless, use any synched shutter speed, just about any ISO, and just about any aperture, and the system does the rest of the work -- pretty cool feature. . .

Scott
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Old Jan 12, 2008, 6:31 PM   #8
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Gotcha, Thanks Scott. Makes sense, although a very confusing system overall. I didn't know that the info was transmitted by the flash so I thought it should work around corners, etc. And the funny part was, I was trying to over flash/ expose a scene to create shadows and make sure the flash was working right and no matter what camera exposure settings I used, the picture would always turn out... no wonder since they where "talking" to each other and adjusting the flash output. :?
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Old Jan 13, 2008, 4:24 PM   #9
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I just found that the wireless function is not enabled with a K-mount lens.

The option is greyed out.

Not sure why this should happen.

Any ideas anyone??


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Old Jan 13, 2008, 5:38 PM   #10
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It makes sense - the flash is p-ttl, and requires information about aperture to set the appropriate flash setting. It can't get that when you set the aperture on the lens, so it doesn't allow you the wireless option.
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