Electronics project (focus assist lamp)

Shay Stephens

I have a problem. When I shoot weddings, there are times when the venue turns the lights down so low I can no longer focus. They "claim" it's to create "mood", but I think it is their way of torturing photographers ;-)

So I have been looking here and there for a focus assist lamp that I could add to my camera. Ideally, it would be small and light weight, as well as being able to last at least 3 to 4 hours on battery power.

I would like to use AAA batteries, and I was thinking of pulsing the light (555 to the rescue) so as to get a brighter output without burning the LED's up.

I have not been able to find anything commercially available, so my thought is to make it myself. I have some electronics experience and have built circuits before, so I can do the assembling, but the problem is in the design phase. I only have rudimentary skill in design.

So I thought I would post the project to see if there is any feedback out there from other who have either done this before, or can steer me in the right direction at least.

In the next week I will post a a circuit design to see if there is any feedback on it. My goals again are small and light weight (AAA powered), 3 to 4 hours, and allows the camera to focus from 10 feet away...we'll see how close I can get that :-)

MrBook2

My two cents
I like the idea, but my gut reaction is to not build it from scratch. Go buy the cheapest white LED headlamp that you can find (that runs on AAA batteries). Make sure that it is an LED rather than a bulb or your battery life will be terrible. Disassemble it and replace the sliding switch with a button switch. Attach it to a small metal plate and screw that into your camera's tripod mount with a short 1/4 - 20 bolt. That should hold it securely to the bottom of the camera so that you can trigger it with your right thumb (if you put it on the right side) when you need it. It should be bright enough and should have great battery life. All told it should cost less than $25 including the button switch from Radio Shack.

The one problem you might have is exposure. If the camera meters when you half press to focus (with the light on) it may screw up the exposure for the picture (I don't know how your camera operates).

Hope this doesn't sound too crazy. I am really tired right now so I can't promise that I am making any sense.

--Aaron

blackwaterstudio

Shay, maybe I missed read your post but is this something that your looking for?

Focus Assist

BigAl

jdsphotography wrote:

Shay, maybe I missed read your post but is this something that your looking for?

Focus Assist

This looks like a good option. I was going to suggest starting with a speedlite with autofocus-assist and modding that. Using this gadget will give the option to trigger remote flashes (which may be to Shay's advantage).

I've just read this thread on FM, which says that the Canon D60 has a CF which allows the autofocus-assist on a speedlite to work, yet doesn't trigger the flash. Not sure how common this function is.

regards
alan

Shay Stephens

Small Update
MrBook2:
The headlamp idea is a good one, and it is where I will be kicking off the project. I have a 3 AAA headlamp from Garrity that I picked up. It is very light and the batteries last a long time with the 2 white LEDS it has. More on this later.

jdsphotography:
I probably should have added in my first post that a pocketwizard transmitter is going to be sitting in the hotshoe of the camera. Your suggestion could be made to work, and it remains an option. It would certainly be lighter than using a Canon flash with a focus assist lamp.

BigAl:
As I mentioned above, a speedlight is bigger and heavier than I want to consider at this early stage. If I get desperate though, it is on the table :-)

---

Ok, the update. I took apart the case of the headlamp I have. Didn't do too much damage, the case was glued shut, and the only thing that is really damaged is the clear lens. It has a crack, but I suspect this will only be cosmetic damage in nature.

The light has two white LED's, which right now I am assuming has a voltage of 3.6v each. The IR LED's from Radio Shack have a voltage of 1.5v at 100ma. So my thinking is to replace a white LED with two IR LEDs wired in series and a 6 ohm resistor (a 10 ohm and a 15 ohm in parallel as I can't find any 6 ohms around anywhere).

If this works, it will be a real bonus, not only in time and expense, but also in matching all my goals in one fell swoop!

More later as it develops...

Shay Stephens

Oh, one other thing...
I picked up the Sunpak CA-1AF module as I thought this would be the perfect solution...

Turns out the TTL capability does not extend to the Canon 20D and I could not get the IR lamp to light at all. The unit just sits there doing nothing on the 20D.

This baby is for film cameras only it would seem. So off to ebay it goes

ziggy53

A little more light, please?
Shay,

I suggest you use a "Maxa Beam Searchlight" for those sessions in low light. Weddings, Receptions and the occasional Briss, all take on a special significance when you add six-million candlepower of light. Direct or bounce, you get the light you know you need. With a range of one-and-a-half miles, I think it'll reach your subjects. The Xenon lamp puts out 5600K daylight color temperature, so you're color balanced as well.

You can get the "Maxa Beam Searchlight Security Kit" which adds a covert infrared filter, but where's the fun in that? (Just for focus assist, I guess.)

Six-million candlepower of light is sure to set the right kind of mood with all those party-goers. Think of the fun you can have with neighbors and parking teenagers when you sneek up on them and click on "the Bad Boy"!

Price? Well, if you have to ask...?

http://www.peakbeam.com/index.htm

ziggy53

Higgmeister

Just an idea,
Hi Shay,
I did a quick google search and didn't find anything on 20D, IR and AF together. I'm not sure how sensitive the AF is to IR, but this might be something to look into. The headlamps can have their LED's replaced with IR ones. With the hotmirror on the 20d, it shouldn't change the exposure on the sensor, but might be enough for the AF to lock onto. It would also be pretty much invisible the the participants.

Just an idea,
Chris

Shay Stephens

Failure...
Ziggy, I think you're on to something. The mood, oh man, the mood!!!! hehehe

Chris, I just finished modding a head lamp. After measuring the voltage, I altered the plan to a 10 ohm resistor and two IR LED's from radio shack. I pulled one white LED and left the other in. I put the two IR LED's in with a 10 ohm resistor and turned the unit on. All three light turn on. So far so good, but the camera won't focus with just the IR LEDs. It's as if they are not even on. So I am thinking that the IR is too far from visible for the camera to pick up.

Radio Shack says the wavelength is 940nm. I tried taking a picture of the LED's and there is nothing from them. Now this has me very confused. What kind of IR lights are they using on the speedlights?!?!

I am going to try and research to see what wavelength the speedlight IR system uses. If anyone has a resource on this, please let me know.

Nikolai

Big Brother is watching you!
I'm a bit late for the start, but I'm very untested in the results!
Shay, I hope you are taking pictures as you go and eventually post a great DYI AF assist device how-to:-)

Nikolai

IR LEDs online
I froogled for "ir led" and found a whole bunch of them all in $.50..$1.50 ballpark.
E.g. http://www.hobbyengineering.com/SectionLD.html#CatLDIR
There are separate LEDs and the whole assemblies (46 in one, $15)

HTH

USAIR

Shay
How about this light or maybe a couple of these
Be nice if Canon took a lesson from Sony on this
My 717 and 828 AF worked great in the dark no problem
Can't wait to see what you come up with

Fred

ziggy53

Shay Stephens wrote:

...Radio Shack says the wavelength is 940nm...

Shay,

For focussing, 940nm is way far from the visible spectrum and focus will be off from visible light focus. (Some lenses have focussing marks just for IR spectrum and they are different than the marks for visible light.)

You need to be around 715nm or so which is slightly visible as a deep red. Hot lamps and filters are more viable at this frequency than are LEDs.

ziggy53

Shay Stephens

You're right
Just found this histogram of the frequency response of the 350D:


http://www.astrosurf.org/buil/350d/350d.htm

Those IR LED's I have are useless. So now I will try to find a source for LED's that will get closer to the sensitivity of the sensor.

Trying to find info on what the Canon specs are on the focus assist light seems impossible right now!

Fred:
I like the Camera Bright, it looks like it would work. If I could replace the LED's with something a little less noticeable that would be great. I think I will order one to experiment with.

Nikolai:
Thank you for the LED link.

ziggy53 wrote:

Shay,

For focussing, 940nm is way far from the visible spectrum and focus will be off from visible light focus. (Some lenses have focussing marks just for IR spectrum and they are different than the marks for visible light.)
ziggy53

Shay Stephens

Inside the Sunpak module
To try and get closer to my goal I decided to take the Sunpak CA-1AF module apart and take a look at the focus assist lamp:



Below is the focus assist module taken apart. I was rather surprised at two things in particular:


The first thing was the color and size of the LED. It is not an IR led but just a regular red LED. The second thing was the thin film with lines on it:


I tested it to see if it was a polarizer of some sort, but it is not that. Here it is mounted:


So I put the unit back together to power it up and see it in action:


It wasn't until I turned the light that I figured out what the film was meant to do:


The film is at the focus of the lens and the unit acts as a projector. The film provides sharp vertical patterns that help aid the focus when looking at something that has no contrast.

So now I have my answer. The focus assist module is not IR but visible red light. So now I need to think a bit and figure out what direction I want to go next. I do think the projected pattern idea is a good one.

ziggy53

Shay,


I think the Sunpak CA-1AF is almost exactly what I would recommend for the job. If you could figure a way to make it work with the half-depressed shutter button or at least add a momentary contact switch which could be depressed before the shutter, you'd have what you need. (... and you'd have what many others need as well.)

Good stuff this is.

ziggy53

KD5NRH

Shay Stephens wrote:

The film is at the focus of the lens and the unit acts as a projector. The film provides sharp vertical patterns that help aid the focus when looking at something that has no contrast.

I know it's a zombie thread, but if anyone's still working on this, what about the cheap laser pointers with interchangeable projection lenses? I had one that did a single thin line that, IIRC, was about $3. Find a way to align it so that the line always crosses your center AF point, and it should be a lot more subtle, or at least more professional looking than a bright red dot.

ziggy53

KD5NRH wrote:

I know it's a zombie thread, but if anyone's still working on this, what about the cheap laser pointers with interchangeable projection lenses? I had one that did a single thin line that, IIRC, was about $3. Find a way to align it so that the line always crosses your center AF point, and it should be a lot more subtle, or at least more professional looking than a bright red dot.

I've done just that (manually) but it is dangerous and illegal to shine a laser LED at humans because of the danger to retinas. Even the lower powered lasers are (potentially) dangerous.

The way that most commercial products work is to collimate a red LED light output and then project that through a grid reticle mask, or they put a mask over a LED diffused cover and project that image. Either way it is safe and effective at short distances.

The bigger problem for this project is how to interface the electronics with the focus sequence of the camera so that the beam stays on during focus and shuts off for the image capture.

The manufacturer flashes with a focus assist can do it as can the 3rd party flashes with assist. I just haven't seen a schematic which describes how to interface the different dedicated hot shoe pins to external appliances.