Tag Archives: AF assist

AF Assist tool v3.0 – more testing

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I tried out the 540ez lens with both the LED that came with the assembly as well as the LED I bought from digikey. The digikey LED was brighter then the led that came with the 540ez lens. Brightness was judged with the LED installed in the housing, and the projected pattern was the object of judgment.

However, when it came to what the camera saw, it was a different story. At 40ft (the length of my basement; can’t go any longer indoors) the camera was pointed at a blank wall, and all the lights were turned off. The LED that came with the 540ez lens assembly was able to get a focus confirmation out of my 40D whereas installing the Digikey LED in the same lens assembly, did not provide AF confirmation. This was very interesting because the same contrast producing pattern was projected, and even though to the human eye (my eye) the digikey LED seemed brighter, the camera saw something else. At 40ft, I was could not visually  see the pattern projected by the 540ez led (yet focus was confirmed by the camera). With the Digikey LED, I could see the projected pattern (just barely) but the camera was not able to use that information to focus.

The Digikey LED is of 66onm wavelength. I can only guess that the led that came with the 540ez flash is higher then that (nearer to infrared).

I also tested a few other flashes to see if I could achieve AF confirmation on the same blank wall in total darkness, 40ft away.

Canon 420ex – AF confirmation achieved (pattern just visible 40ft away)
Nissin Di622 mark II – AF confirmation achieved (pattern not visible 40ft away)
Younguo ST-E2 – AF confirmation achieved (pattern clearly visible 40ft away)

Looking at the flash quoted AF assist distance I compiled for a few flashes seems to be understated?

The Plan:

Near-infrared is starts at 780nm and goes up from there. So I’ll have to find some LEDs that are between high 600nm and 800nm
OR
Find some brighter deep red LEDs.

UPDATE:

For the next version of the autofocus tool I’m currently working on I need to test several wavelengths of IR light .
3 x IR LED 770nm (p/n: 15P2280)
3 x IR LED 830nm (p/n: 93K0966)
3 x IR LED 850nm (p/n: 97M1058)

AF assist tool v3.0 – testing

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So I got some parts from DigiKey today; enough to  do some more testing. Took out the ebay purchase I’ve had for a few weeks, and got to work.
I picked up this AF assist lens from a Canon 540EZ flash, complete with LEDs.

CANON AF LED UNIT SPEEDLITE 540EZ FLASH NEW

I hooked up an LED to the 540EZ AF lens along with a resistor (200 ohm) and a 9v battery.

This is what I got in terms of a pattern. Shot on the left was from 7.5ft, then 15ft, then 30ft. At 30ft, I could barely, just barely make out the pattern on the flat white door onto which I was projecting the pattern.

The camera exposure was:  ISO:3200, aparture: f1.4, exposure: 1/40

Again I must stress, there was VERY little light on that door from 30ft away, however the AF sensor on the camera locked in an instant. Maybe took a fraction of a second longer then from the 15ft distance, but it was hard to say.

I can hardly believe that such little amount of light can produce such a focus lock on a flat color (white) door in total darkness.

I took out my 420EX flash and fired the AF assist light (was not able to capture it since the flash was on the camera, and the light goes off once AF is achieved) and the light is much brighter. Maybe 1-2 stops brighter from 30ft. Maybe I need to use a lower value resistor to get more power out of the LED that came with the 540ez lens, or just replace it with a brighter LED.

Either way, it looks like adding contrast is MUCH more effective then just adding light to help the AF sensor focus and the idea of using a flash AF assist lens is looking much more promising then the laser pointer idea.

The 540ez lens module is kind of bulky. I would prefer it to be a little slimmer. The AF assist lights in my 420ex is made of 2 side by side lenses which are a better size. Will need to scope out some of those lenses.

AS assist v3 project update: The light source

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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 →

AF Assist tool v3.0

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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:

http://www.flickr.com/groups/strobist/discuss/72157625363074208/
asa

http://www.youtube.com/watch?v=IhiHNzx0tMA&feature=related

AF Assist tool v2.0 log

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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 →

AF assist v2

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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:

AF Assist tool – Version 2.x

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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