In this article I will try to explain whether it is possible to work with studio light while using short exposition time. From the moment of appearance of new “Pockets” on the market, on various forums very often appear topics about usage of studio light for short exposition times. Rapturous owners of “Pockets” describe how excellently everything works, but when you ask them to send a few pictures, nobody sends anything. I decided to investigate this. I have the drafts of the article lying around for over half a year already. Now autumn has come, and forced me into the warm house, a good reason to describe the work done. So far there will not be any talk about any working device, but small helpers were still required – Arduino and a Breadboard.
So here is the list of all the myths.
Myth one: “On the synchronizer, the “Pocket” generates a number of short impulses. That way it causes the generator to create a number of short flashes.”
Wow! “Pocket” is great. Sounds almost like a flash system in FP mode. I would like to believe in this. I would be so happy if the developers of Elinchrom would permit a design flaw, and allowed such a possibility. Then I would be one of the first who would make TTL for a studio. However marketers do not allow engineers to implement many of the useful innovations. But this is all just talk. In reality everything is simple. It does not work. But it has to be tested. I began by measuring the duration of the signal on the central contact of the camera. For Nikon it is 7,6 uSec. I connected the generator to Arduino, and while changing the duration and the number of flash signals for the generator, I measured the light for all durations with a flashmeter. No wonder happened. The light always stays the same, and corresponds to the set value on the generator. Lets hope that engineers defeat the marketers, and the firms will supply photographers with advanced technologies, instead of feeding us from a teaspoon. Nowadays I do not see a reason, technically or technologically, to not make X-synch with TTL in a studio.
Myth two: “By controlling the delay between the camera and the flashlight one can use X-synch with system flashlights.”
Sounds tempting. But it does not work. In my camera the minimal exposition time with flashlight is 1/250, and with 1/320 a black line appears on the picture. I connected Arduino to the camera and the generator. By increasing the delay, the black line became only bigger. But therefor I could measure the LAG of the shutter. I set the exposition time to 1/250 and by increasing the delay, I achieved that the picture became completely black. In D700 the LAG of the shutter is approximately 100 uSec.
What does “Pocket” use?
To answer this question I had to go a bit deeper into the protocol of communication between the camera (D700) and the flashlight (SB-900). About the protocol itself I will write another time. Up to this moment the behavior of the camera and the flashlight was predictable and understandable. The shutter is triggered, and when the frame is completely open, the signal is sent to the flashlights. But after connecting a flashlight with an FP mode to the camera, everything changes. It practically works like this: the camera triggers the flash, the flash lights up, the camera triggers the shutter. I assume that the delay time can be changed, and that it depends on the model of the flashlights and other things. Turns out, the camera adjusts the triggering of the shutter to the flashlight. There is no limit to the happiness. What use does this knowledge have to us? Very simple. By attaching SB-900 to the camera in the “M-FP mode 1/128” and by attaching the generator to the camera via PC port, one can photograph with short exposition times without a “Pocket”. This solution has a problem though. Depending on the exposition time, a gradient appears on the pictures. “Pocket” has the same problem, by the way. But it can be dealt with too. For that, one has to program Arduino a bit. The program is very simple. The signal comes, a little delay, signal goes. My Arduino is connected to an LCD display of a mobile phone, and an encoder to change the values for the delay. This circuit is put into the cable between the camera and the generator.
With what light does it all work?
I repeated the work on three different blocks, and two generators. With an additional delay circuit with Arduino, everything works with a precision of up to 1/8000. With such an initiation of blocks, a dependency can be observed: the worse the block, the better the light. The gradient is less noticeable. The cheaper block's duration of the light impulse is longer, and it is easier to choose a delay with which the gradient on the picture is minimal. With the fastest head Quadra A Head Action, one can easily make pictures with up to 1/1000. The delays on Arduino turned out as following.
shutter speed delay uS
320 3000
400 2900
500 2540
1000 1440
I connected to the PC port a radio trigger RF-602 and EL-Skyport Transmitter SPEED. Everything works without complications. If you do not need TTL, why should you buy “Pocket”?
Conclusions and perspectives?
Knowing the specifics about how the camera works in the FP mode, one can make pictures with any studio light and with short exposition times. The light can be synchronized via cable or via radio. With inexpensive light, pictures can be made with even shorter exposition times.
What I plan.
I intend to thoroughly learn the Nikon protocol between the camera and the flashlight. Then I intend to put the SB-900 emulator and the delay circuit inside of RF-602. And afterward I want to make a hot shoe with the delay for comfortable work with EL-Skyport Transmitter SPEED.
Successful shots to you.
P.S.:
I would not call this approach ideal, but it can be used.
© Andrew Buckin.
Shutterstock 
Dreamstime
Fotostream http://www.flickr.com
Keine Kommentare:
Kommentar veröffentlichen