Suggestion for off camera light setup

[Mo]

Originally Posted by MyKey

I know a little about eTTL what questions do you have! Even if it is not me, someone here on the forum surely can help you so ask away!

Haha, well basically how it functions. I tried youtubing it, but couldn't really find any concrete answer. So let's say I have a 580 on my camera, and another flash oc, if I have the px system attached, will it automatically talk to the ocf and have it act like true TTL? Also, can I use the 580 on my camera for example, at the same time? Sorry if my questions don't make much sense...I'm trying to wrap my head around all this...

[MyKey]

Lets see if I can make some sense of all this black magic we call TTL Flash Metering :) I took your questions and placed them in bold and tried to answer them individually. Not quite sure on some of the details your asking so please ask away and I will try and help you out anyway I can. Also not trying to sell my DVD or Guide but your problem with no information on TTL is why years ago I wrote the Guide and now our DVD. Its an area which many overlook in our profession.

So hope this all helps I got Nerdy on ya

How TTL Functions
The Official Nerdy Definition - TTL -
Through-the-lens is a photographic term describing a feature of cameras capable of measuring light levels in a scene through their lens. This information can then be used to select a proper exposure, and/or control the amount of light emitted by a flash connected to the camera. Now that is nice but we are talking flash photography here so with the TTL definition in mind now lets talk about TTL-Flash Metering. This is the process of calculating the correct amount of light coming from your flash using “Through the lens” metering takes in several conditions of the environment which the portrait is being taken. This metering is significantly different than the “Through the lens” non-flash method.


First, lets talk about how the camera body, master flash, and slave flash units are able to communicate using Digital TTL-Flash Metering. When your on-camera flash is set to Master mode, as you press the shutter release to capture an image, a sequence of events happens very quickly between the camera and your flash system. This sequence happens all together in a few milliseconds - fast enough that the human eye can’t perceive the individual events happening. It may appear that the flash system activates one time in an instant when in fact there are multiple individual events taking place. This sequence is described below to help you understand exactly how the camera and flash system work together to achieve a proper exposure.

As the shutter button is pressed, before the shutter curtain in the camera actually opens, the master flash (the one on the camera body) sends coded commands to any slave flash units (the wireless flashes) that may be present. These commands are sent by very quickly blinking the flash tube in the master flash (the blinks are sort of a light-based morse code - similar to how your television remote control talks to your TV). Using these coded blinks, the master flash commands any slave flashes present to begin emitting a “pre-flash”. The pre-flash is a known amount of light (about 1/32 power of the slave flash). During the time the slave flash emits the pre-flash, the metering system inside the camera body measures the amount of light produced by the slave flash. Based on this known amount of light, the camera is able to determine that a correct flash exposure for the given conditions of the scene will require a specific amount more or less light compared to the pre-flash. After the pre-flash from each slave flash is measured, the camera does some math and logic and computes the amount of light required of each slave flash to produce the desired exposure including any ratios between slave flashes that may be set. After all of these calculations are performed, the master flash sends firing instructions to each slave flash using a second set of coded blinks of the flash tube - these firing instructions being the correct amount of light required of each slave flash for a correct exposure. Finally the shutter begins to open inside the camera. The master flash sends a third coded command which causes all the slave flashes to fire together - each with the prescribed amount of light (this is the “main flash”) which is the light you see in your captured image.


So a quick review on everything that happens in a split second during the press of the shutter release:

* Photographer presses button half way, the ambient light of the scene is evaluated via through the lens metering.
* Photographer presses the shutter release all the way which begins the communication, pre-flash, and main flash process of capturing the image.
* The Master flash unit sends a wireless signal to all Slave units using a very fast coded light signal which commands each slave flash to issue a low-power “pre-flash”.
* Any slave units which see this command from the Master flash, will fire a “pre-flash” at 1/32 power.
* The pre-flash light is measured through the camera lens by the evaluative metering system inside the camera.
* The camera calculates the correct amount of light that should be emitted from each slave flash during the actual exposure (the “main-flash”) based on the amount of light observed during the pre-flash.
* The camera may adjust the calculated value if the photographer has set any exposure compensation or ratios settings in the master flash.
* The final calculated value is sent to each slave flash using a second coded light signal.
* The camera mirror flips up and the shutter opens (this is the cla-clunk you hear when the picture is taken).
* The Master flash sends a final short command which causes all slave flash units to fire at the same time. This is the “main flash” that illuminates the actual image captured.
* All Slave units fire at whatever level the master unit has commanded them to. (Note: For our (TriCoast) technique all Slave flash units fire at the same power including the Master unless you have the master set to “commander only” mode, described later in this guide).
* The camera flips down the mirror and closes the shutter – completing the image capture process.





I hope this helps explain a little about TTL and the metering system what happens when you click the release button on your camera. There is of course more to this method but understand what TTL is and how it meters is truly the first step in creating images faster, better and much easier in the long run.




So let's say I have a 580 on my camera, and another flash oc, if I have the px system attached, will it automatically talk to the ocf and have it act like true TTL?
YES without any question. The beauty of the RadioPopper PX system is it transfers in a VERY clean radio freq 100% of what your Canon / Nikon flash speedlites can do. So ANYTHING the Canon to Canon or Nikon to Nikon speedlites can do with direct line of sight can be done using the RadioPopper PX System (Transmitter mounted on your master flash and receiver mounted on your wireless flash)

High Speed Sync - YES
Ratios - YES
Flash Compensation - YES
ANYTHING


Also, can I use the 580 on my camera for example, at the same time?
If your meaning can your Master flash send the command signal to the slave(s) flashes for lighting AND fire flash to expose in the same image - YES of course it can. While we (TriCoast) opt out of this method of the time and only have our Master flash as a wireless transmitter (sending the signal to the wireless flashes only) the beauty of this system once you learn it, is the amount of different options you have with it to blend into YOUR style and not my style.

Sorry if my questions don't make much sense...I'm trying to wrap my head around all this...
Its a lot to take in but I promise you once you understand TTL flash metering and how and when to use it in either TTL mode or Manual mode it truly opens up so many doors for you. Much more than just manual methods without High Speed Sync options. If I want to capture an image at 1/200 of a second at f/11 I can or if the same location I want 1/2000 of a second at f/2.8 I can do it. Without High Speed Sync all my images has to have an f/stop of usually f/8 or higher giving me a great depth of field. If I am in an ugly ally way and want to blur it out I cant unless I have High Speed Sync or some sort of Neutral Density Filters (which is one more thing I don't want to carry with me)

Again there are a TON of options, no way is the right way, I applaud you for wanting to better yourself in education and by using that education with your photography. NEVER stop learning, learn your equipment inside and out and by default you will become a better photographer.

[Mo]

Wow, Mike...thank you so much for that! Definitely learned something today, and also narrowed my options down that much more! Now I will use all this info and invest wisely! Thank you sir!! :)

[MyKey]

Originally Posted by Mo

Wow, Mike...thank you so much for that! Definitely learned something today, and also narrowed my options down that much more! Now I will use all this info and invest wisely! Thank you sir!! :)

No problem glad I could help. I am so busy these days I don't get to help like I enjoy doing (and as I did in the past) so it is nice to jump on here again and share knowledge with everyone.

The write up is from our Guide so I can't take credit for writing it all out just for you (sorry bubble burst I know) But I thought this part of the Guide was a perfect section to put here as it answers your questions in pretty good detail.

Again glad it helped and remember don't take my word or anyone else for that matter, research yourself and make the choice for what you need yourself since you will be the one left with the gear once purchased.