How does Speedlite AF-assist beam work? DIY solution possible??

Hi,

 

I'm happy with my EOS D30 except for one thing:

The AF really sucks in low-light conditions, and the built-in AF-

assist lamp is so close to the lens mount that it's almost completely

hidden behind the hood of my Sigma EX 20mm/1.8.

(No wait - that was TWO things... ;)

 

Anyway, the "pro" way of getting a good (and almost infrared!) AF-

assist beam is to buy the $200 speedlite transmitter called ST-E2,

which can act as the AF-assist beam in its flash sisters.

This solution is far too expensive, and I'll never use it for

its "real" purpose (triggering remote flashes wirelessly) anyway, so

I'm wondering how hard it could be to make my own AF-assist device to

be mounted in the flash shoe.

 

- How does the flash shoe contacts and communication work? I have

looked all around the web but never found any specification.

 

- Can the camera body drive the AF-assist beam in the flash shoe, or

is the flash battery always used? (Since the body can drive its own

assist light, I guess it should be able to drive an external one as

well)

 

- Are there any known Do-It-Yourself solutions or suggestions on this

matter? I guess I'm not the first one to think in these directions,

but still I haven't found any info on the web.

 

Please help me to shed some light! :-)

 

best wishes

Mattias Rickardsson, Gothenburg, Sweden

Simple. Get the flash off of the camera. How you do that is up to you, but I'd suggest combining a Canon Off Camera Shoe Cord 2 with a Stroboframe bracket. The additional height on the flash will not only allow you some clearance for the AF-assist beam, but will improve your flash photography as well by moving the flash.

Mattias-<p>Brett's response assumes you already have a shoe mount Canon flash, which I assume is incorrect, as a shoe mounted speedlite would probably clear your lens hood.<p>I haven't seen any specs for the hotshoe contacts, and wouldn't recommend spending any time or money trying what you are suggesting. Your best bet is to buy a 420EX, which has AF assist to cover all 3 of the D30 AF points.<p>Even third party flashes with AF assist don't cover all points (such as the Sigma EF 500 Super, which only covers the center AF point), so I don't think you could economically build one yourself. I <i>believe</i> that AF assist is not just near infrared light, it actually projects a pattern for the AF to lock onto.<p>BTW, the body does not power anything in the hotshoe.

I JUST acquired a 220ex to use on my D60. it's AF assist only works on center spot, but that's what we use to focus anyway. Tried it out last night, and so far not convinced that it makes much differencr...

Good call by Maureen M... I'd assumed (how's that bit go again?) you were already using an accessory flash. Heck, if you're not, then the 420EX on its own may well clear the lens hood, though if you're going to be shooting with flash you can improve your results further still with a stroboframe and OCSC2 as I initially said.

 

I wouldn't invest any time in trying to build up a wireless AF-assist solution - just pick up an accessory flash to do it for you. Be aware that if you *do* pick up the 420EX, and subsequently decide to use it for flash photography with your Sigma 20mm that it only offers coverage down to 24mm focal lengths.

Hi Mattias - finally someone who wants to play with soldering iron!<br><br>

1.I dont know anything about the specification of signals betweeen camera body and the flash<br>

2.The AF assist beam always uses the power from flash batteries.<br>

3.As far as I know there is nothing like that on the entire internet<br><br>

Anyway: <b>I would recommend</b> you to buy some CHEAP (maybe second-hand?) third party flash with the AF assist light. Only the center AF point will work - but it is still better than MF or buying an expensive 420EX. Then you might use the flash (but only in M mode based on the Guide Number) or disassemble it (maybe remove flashbulb and condensator? to eliminate battery eating) and use it only as AF assist device (but be careful not to mis-align the IR diode axis, as it would not illuminate the AF point).<br><br>

If you want to read about some <b>"inventions"</b> of another DIY maniac, please visit my website here: <a href="http://spyderman.ekodapo.sk/?s=t"><b>Spydermans homepage</b></a><br><br>

PS: yes, the AF assist light projects VERTICAL LINES on the subject to make it easier for the AF to achieve focus.

The 380EX can be found quite cheaply in the used market and will cover all 3 AF points.

 

Happy shooting ,

Yakim.

Ok, this is something that hadn't occured to me since I exclusively use available light. Could I put on a flash to assist the low light AF that wouldn't turn me into a beacon screaming, "Hey, I'm about to take your picture! Act natural!"

I'm with Chris on this. I *think* the original poster wants a way to do AF assist that doesn't necessarily involve setting off a flash.

 

As a recent purchaser of a 300D (digital rebel) I immediately found it's 'flash, flash, flash' methodology of AF assist from the built-in flash not only distracting, but downright rude in situations were flash is frowned on, but the light is otherwise insufficient to get AF to work reliably to do available-dark photography.

 

The solution I hit on, after doing some web-surfing, was to get a 550EX (I know, it's an *expensive* solution, but was helped a bit by ordering the IMPORT version from B&H for about half of what the local retail emporiums wanted for it), and set its custom function to 'TTL'.

 

Since the 300D does not support TTL (only E-TTL), the interesting side effect is that the near-infrared gridded-lines 550EX AF assist is used by the 300D during focusing, but the flash doesn't fire.

 

I admit that it's an expensive solution if you never intend to take flash shots with the 550EX, but the 550EX is a nice bounce flash in its own right, and also adds back some of the missing functionality of the 300D, namely, 2nd curtain and high-speed sync.

 

And it *still* cost me less than a 10D, by a long shot.

 

I don't know if any of this will help you, Mattias, with your D30 problem, but maybe something will come to light. 8-) I'm also aware that their is an article floating around that shows how to design a plastic shim (from an old credit card, I believe) that blocks one of the hot shoe contacts. This would allow you to mount a completely 'auto' flash like the 420EX, but again, the camera would use only the 420EX's AF assist, and not trigger the flash.

 

Good luck, Let us know what you come up with.

Brett, not to keep picking on you today ;-) but the 420EX would still give full coverage with a 20mm if the lens is mounted on Mattias's Canon D30, or a D60, 10D, or 300D. Don't forget that on those cameras, you will only see a 32mm's field of view when using a 20mm lens. But the flash doesn't know this, so it is still illuminating an area equivalent to a 24mm lens on a full frame camera. I successfully use the 420EX on a 10D with a 17-40 at 17mm. Plenty of leeway.<p>Dave, interesting, albeit expensive solution! The only "problem" with using a 550EX on your 300D is that the AF assist only covers the five horizontally lined up AF points. The 550EX AF assist doesn't cover the top and bottom AF points, but like you said, using TTL mode does give you the option of using AF assist without actually triggering the flash during exposure.

<cite>The 380EX can be found quite cheaply in the used market and will cover all 3 AF points.</cite>

 

<p>You sure of that? It only covers the center AF point on the Elan II, which is the 3-point AF body for which the 380EX was designed in the first place (stupid move on Canon's part).</p>

Well, on the 300D, you may have to buy a 550EX and set it to TTL.

 

BUT on a 10D, there is a custom function that can force the flash not to fire while still using the AF assist. Does the D30 have a similar CF?

How about using an older E or EZ series flash? They are TTL only, so wouldn't fire on Canon DSLRs, but the AF assist light should still work. You can get a 300EZ for dirt cheap these days. Nobody wants them, but they are fairly small. A 160E or 200E might even be better. They're downright tiny.

 

I've got an old 300EZ thats missing the diffuser on the front, but otherwise works. I'd let that go very cheap, but shipping to Sweden would bring the price up to more than it's worth.

I've used a small LED flashlight straped to my head for AF assist. It works really well up to about 20 feet. A good one is $40-50. However, you really look like a geek when you use it!

I've been able to use a laser pointer that projects a line. I just paint the subject with a vertical line and focus on the line.

 

Most laser pointers are eye safe, but I would still be careful with people subjects.

The external light sources (LED flashlight, laser pointer) have me intrigued. Does anyone know if true-IR (near red, but invisible to us humans) will work with any of the digital EOS AF systems?

 

I'd still like the ability to focus well in near-dark, without alerting (or annoying) the subject(s). Think taking photos of critters at a night feeding station, or some such, either by remote, or from a blind.

 

Or, the one that challenged me years ago, was taking pictures without flash in the national archives, of original documents (Constititution, etc), without tripod, and being required to stay at least 'x' feet away (I forget the 'x', but it was at least six or more at the time, probably more these days). I managed to snag a really nice one of the Declaration of Independence with my aperature-preferred, manual focus OM-10, with a 135mm/f2.8 prime lens. Pure luck, now that I look back on it.

 

And it was really dark in there. There is a lot of concern for light fading of these old treasured documents. You could imagine how folks would react to the 300D's 'flash, flash, flash' system of autofocus, and they might be even not very comfortable with a near-IR system that 'paints' red lines on the subject, like the AF assist lamps do.

 

I remember being told, for instance, in no uncertain terms, that I couldn't lean on the benches that were at the base of the Washington Monument, so I could take a picture of the dedication plaque, that was mostly obscured by one of the benches. I guess the benches are not there to be used. Even though the line wound around the base of the monument, next to the benches, we were all forbidden to sit on them. I guess I never thought of a park bench as a national treasure, before...