In concert photography, where light is at a minimum, the capturing of images is tough. But sometimes, bright lights flood the stage in often seemingly random intervals and for brief periods of time. I’m not talking strobes, but spot lights that come on and then go off again in matter of 1 second. Enough time for me (the photog) to realize there’s lots of light, but by the time I push the shutter, the light is gone.
Yes I realize that training the photographer is simpler and cheaper, but I’m a geek that like to build shit.
Build some sort of device that triggers the camera to take a photo which when turned on will focus and snap a photo based on light levels passing a certain threshold. The light sensitive are should be directional. I don’t want it going off just because buddy’s flash went off 3 feet from me.
In the search for a focus solution, I am going to abandon the laser pointer light source in favor of an AF assist light from a proper flash unit.
Doing some research here and looked at a whole bunch of flashes, and some of the flash manuals have a range in which the AF illuminator/assist light is effective. The listed number is the max range listed in the official user manual (in meters and feet). Continue reading
To layout the expectations for the next AF assist tool. The last AF assist tool v2.0 had it’s weaknesses, and I will try to address some/all of those with the next tool.
Some of the changes from v2.0 to v3.0:
– Explore the use of other AF lights. Try lights with grids from existing flashes, near IR leds, (others) to achieve a pattern/light that is both not distracting to anyone and not very visible yet enables a DSLR to quickly focus.
– Follow and recreate some of the efforts out there to reverse engineer the ETTL protocol and use it to keep the tool on ONLY while the camera is focusing. The two sources for the reversed-engineered protocol are on Kzar.net and Bill Grundmann’s Blog. I’ve wanted a project for an Arduino, and this may be the one.
Some more efforts to create an AF assist light:
I recently attended a 5 day music festival (Kinetik Festival) in montreal, Canada where I was asked to photograph the 35 bands playing. A month before the festival I had a chance to try out my first AF Assist tool. After seeing the results I knew I wanted to take such a helpful tool with me to the music festival to help in the making of images. This is the second incarnation of my AF Assist tool. Continue reading
Continuation of AF Assist v2 post.
The change o the op-amp did not do the trick as expected. In fact even though the NE5532 has a much quicker slew time, I didn’t make a difference. In fact I think it made things worse. Continue reading
Continuation from this post. Build and experimentation log continues.
I built the unit and tested it last week. The laser seemed lower power then the first one I built (which was just the laser pointer hooked up to a set of 3 AAA batteries along with a pushbutton).
Last night I had time to take a multimeter to it. The laser LED is seeing a total of 3.4V from the output of the LM358 OpAmp. The rail voltage was 4.6V (3 AAA bateries) yet the maximum I could coax the output to put out was 3.3V – 3.4V. This explains why the laser beam seemed weaker at first try.
I’m really going blind here using an OpAmp. Did lots of googling, but found nothing to explain this behavior. I tried several LM358, and they all worked the same way. It must be how they work.
So after an hour of dead end attempts and research, I decided to add a 4th AAA battery (for a total of 4 AAA) to give the op-amp 6V, and that did the trick. Now the laser LED sees 4.3-4.4V, and the brightness is back to what I remembered. Continue reading
I built a controller for the laser pointer (so it would be controlled by the camera’s hot show) as per the directions given on this post on fred miranda forums. The OpAmp I used was two LM741. However as I found out after I built the setup, the LM741 needs over 10V to power it, which is why I was having no success with that build.
My power source is 3AAA batteries (4.5V).
After some searching , I bought some LM358 op-amps, which will run on any voltaqge between 3-30V which should run just fine on 4.5V. Also, there are two op-amps in each 8pin chip, so I can make the board smaller.
I also bought a few NE5523 op-amps (which have the same pinout as the LM358) just so I have another option.
Below is a schematic of what I will be building later today:
The new version of the AF Assist tool will use a similar laser pointer but have the function of it be controlled by the camera and not the push button.
I know there is a pin on the hotshoe that gets energized by the 1/2 push of the camera shutter button. This is the AE-Lock feature of the camera. I know this because my wireless trigger has an LED on it which goes green at the half press of the shutter button. The LED goes red with a full shutter button press.
What I want to do is trigger the AF assist light to come on when the AE-Lock (1/2 press of shutter) button is pushed, and turn off the AF Assist light when not pushed.
The other thing I need is for the AF light to momentary go off when the flash is triggered so not to record the AF light into the image.
UPDATE : See this post for the first builds
Last september (2010) I wrote a blog entry about hooking up a laser pointer as an Auto Focus assist light for a camera. The need came up because I wanted AF assist in AI Servo focusing mode of my DSLR. Currently to my knowledge all Nikon and Canon DSLRs will only put out the flash AF assist beam until focus is achieved. After that if the (if the camera is in AI-Servo focus mode) if the subject moves and the focus changes, you’re out of luck in dark situations because the AF assist beam will not continually come on to keep assisting the focus.
The previous look at using a laser pointer as an AF assist tool, I had very little success with that projects. Last week I came across the laser pointer again and new thoughts/ideas came to mind.
So I rigged a laser pointer to a bunch of batteries and a push button to act as an Auto Focus assist to my Canon 40D. The results are spectacular.
I’ve already started working/thinking about the next version of this. Updates on the AS Assist Tool V2.x will be here.
This is what I did, and how it worked.
The need to control an off camera flash came about a while back. I purchases an hotshoe extension cable (YONGNUO FC-681) which allowed me to handhold and aim the flash by hand. In itself the cable worked great, however I needed the AF assist feature that the flash provides and aligning the AF assist beam of the flash by hand is next to impossible while looking through the camera’s viewfinder.
So I bought a YONGNUO ST-E2 wireless controller for its AF assist light and in itself works great, but doesn’t control my flash very well in E-TTL mode. Further to that, since the ST-E2 control is done by optical communication, I am afraid that even if a new flash will be able to be controlled by the ST-E2, outside or otherwise dark environments with black walls there may not be much/enough light reflected to be able to trigger and communicate with flashes that are placed behind the camera.
So I decided to combine the E-TTL hotshoe extension cable with the ST-E2 controller. With this setup I get the AF assist beam of the ST-E2 and am able to E-TTL command the flash where ever it may be pointing.
Brief description of the project: I chopped off the hotshoe connector cable at one and, and soldered the wires into the ST-E2 right as they come off the hotshoe.