I have a question regarding the wireless flash feature on my 7D.
I have the built in flash function setting to the icon that shows the hot shoe flash only. I have my 580 EXII set to slave. I know that it triggers my flash but when I tested it in front of a mirror you clearly see the pop up flash in the exposure.
How do I set this up so that my pop up flash isn't contributing to the exposure?
The little flash from the popup flash is what the 7D is using to communicate with the 580EX II. What you are seeing is how it works. If you want something a little less distracting, you might consider the ST-E2 or one of the other wireless options.
There is a part that you can buy called the Nikon SG3-IR and it will block your flash from contributing to exposure while allowing commander flash. At least it works on Nikon, and no reason why it shouldn't work on Canon too, as there's nothing electronic about it.
The master flash must send a coded "fire main flash" signal to the slaves after the first curtain clears and that is what you are seeing.
The solution is don't aim the camera at mirrors and you probably won't notice it. Worst case is will be providing some fill which isn't a bad idea in most situations if you are just using a single flash off axis.
What does the 7D manual say the specified signaling range is for the built-in flash in Master mode?
Avi B wrote:
There is a part that you can buy called the Nikon SG3-IR and it will block your flash from contributing to exposure while allowing commander flash. At least it works on Nikon, and no reason why it shouldn't work on Canon too, as there's nothing electronic about it.
Wow, this item looks very interesting (if it works on Canon flashes) and it's incredibly inexpensive. Has anyone actually tried to use this with Canon?
It works on the camera body itself. Simply put it in your hotshoe in front of the pop-up flash. So I would expect that it would work with Canon bodies too.
Avi B wrote:
It works on the camera body itself. Simply put it in your hotshoe in front of the pop-up flash. So I would expect that it would work with Canon bodies too.
Well, I can see how it would physically mount but my question was would it interfere with the flash communication? I agree that it seems that it should work but has anyone actually tried it?
well if you mount it in the hot shoe wont that stop the pop up flash from fireing?
I dont know about the 7D bt all othe pop ups I know of from canon wont pop up if the micro switch in the hot shoe is depressed by something in the shoe. Could work I guess if you pop the flash up before inserting the thing if the 7D lets the flash fire with something in the shoe
As I understand it from e-mail exchanges I've had with Chuck Westfall of Canon the slave sensor is sensitive to visible and IR wavelengths. The topic under discussion at the time was how the ST-E2 worked.... Here's what he told me:
"EX Speedlites with master unit capability emit visible light preflashes through their main flashtubes, so IR is not involved for wireless flash communication with those products, The ST-E2 also uses a conventional flashtube and reflector to emit its wireless signals, but the reflector is covered by a translucent red panel. If you're in a darkened room, you can see the preflash from an ST-E2 (as well as the AF Assist beam, but that of course is a separate issue), so for that reason, the wireless signals are not completely in the IR range. However, the peak wavelength for the wireless communication signal from the ST-E2 is 750 nanometers, which is at the low end of the IR spectrum. On the other hand, the AF assist beam for the ST-E2, as well as for all other EX Speedlites, has a peak wavelength of 695 nanometers, which is still within the visible light spectrum. "
So if we put a filter similar to that of the ST-E2 over the pop-up flash in the 7D it would function in a similar way to filter out most of the visible light and only pass the IR. But unlike the ST-E2 which is designed for peak IR transmission the pop-up flash might not be as efficient.
Controlling the flashes via pop-up will likely prove to have the same limitations as the ST-E2 with regard to range and coverage angle. Its a good idea in theory an in terms of geek appeal, but in practice having a 580ex on a bracket over the lens with off camera slave(s) will be still be the more practical and versatile lighting solution.
Exposure 101:
Correct exposure in the technical sense is when the scene range matches the sensor range and there is detail everywhere. When the two end-points are exposed with detail at the same time everything else falls into place correctly perceptually (i.e. a gray scale looks the same in the photo as in person) because the response is engineered to be linear.
The f/stop range of many ambient scenes do not fit the sensor, exceeding it by several stops. The only way to obtain detail everywhere in the scene is to first expose the ambient highlights with detail, then shoot in to the dark shadow side with flash.
Adding flash evenly from the direction of the camera fills everything the camera records, but only to the point where the ambient light hitting the shadow side + flash lifts the DARKEST tones up to where the camera can record detail in them at whatever f/stop, shutter speed and and ISO the photographer selects. Then adding a second flash in the role of "key" light over the top of the fill defines shape with the highlight pattern.
That's the cause and effect underlying the effective use of flash which allows the scene contrast in the foreground the flash hits to be lowered to exactly match the sensor and correctly reproduce the scene content with detail over the entire scale. In most situations doing that requires two flashes capable of equal power output. A light tone 2:1 ratio is 1 part key overlapping 1 part fill in the highlights and 1 part fill in the shadows: 1+1:1 = 2:1. Two lights of equal incident strength at the point they hit the subject.
So if we have a wimpy flash on camera for fill it will limit the over range and effectiveness of the lighting options. Score one more for the marketing department
Thanks Chuck for that very thorough answer...it does imply that at best, the SG-3IR would allow limited capability and at worse, it will completely block the communication signal. Still, I'd like to see if someone can actually try it and report what level (if any) of functinality they are getting.
Okay well the way it works on the Nikons is that you pop-up the camera onboard flash, then you put this thing into the hotshoe. An alternative is to use developed unexposed film (ie dark frame) to cover the flash so that it doesn't contribute to exposure (tape it on) - it will let the IR through. However, it seems that the Canons don't have as much IR being emitted as the Nikons do - so this solution may not work either.
I love this feature on the 7D. I need to get a couple of light stands, a couple of umbrellas and an extra flash and I'll be finally on my way to understanding proper lighting. So far, I've only played with a 420EX Speedlite set up on the side and controlled by the 7D. I think it will come in very handy for me. ;-)
Yeah, I've played with it a bit myself. Quite effective indoors! I set the flash in the other room, around the corner and the 7D still triggered it. I set it behind the camera and it triggered. Really a great option to avoid having to deal with triggers and such when I'm indoors.
I only played with it indoors till now, but am dying to try it with 2 flashes and diffusers on both, outdoors, which is where I take most portraits. It's great for rim-lighting and with fill-flash from the on-board flash. I took some of a small statuette last night and it was fun to get rim-lighting without much effort.
saaketham wrote:
I love this feature on the 7D. I need to get a couple of light stands, a couple of umbrellas and an extra flash and I'll be finally on my way to understanding proper lighting. So far, I've only played with a 420EX Speedlite set up on the side and controlled by the 7D. I think it will come in very handy for me. ;-)
But the visible Master flash signal from the pop-up or a speedlight mounted on the hotshoe is still undesireable...
For example, direct flash is not permitted for volleyball or basketball. Unfortunately, when I point a 550EX to the ceiling as the Master, the Slaves could not see the trigger signal.
Unfortunately, it sounds like the 7D pop-up Flash Control will have the same issue... if it sends out the trigger signal with visible pulses, the officials will stop the play on-court.
RF is sooooo much better. Plus, the range is MUCH farther and there's no line of sight requirement. I like RadioPoppers, but I'd love to have RF built-in to the body and speedlites.
