a flash without the flash part?

Dear Lazyweb,

I shoot with a Canon EOS 5D. I shoot in the dark a lot. It's a great camera, but it doesn't auto-focus very well in low light, so I usually have a flash attached (Speedlite 580EX) and have the flash set to "emit, no fire". This means that when the camera tries to get a focus lock, the flash unit flashes a dim red light, but when I take the picture, the flash itself doesn't fire. (I don't understand how the on-camera, flashless autofocus works, but it doesn't involve emitting visible light.)

This works reasonably well. But, the flash is bulky and heavy.

Can I get a device that is, like, just the bottom inch of the flash unit? The "focus-light" part, but not the "flash" part? (Will an ST-E2 do this?)

Alternately, what's the smallest/lowest-profile flash I can use for this instead? I'd like something I can just leave attached to the camera without making it be twice as big.

Update: I guessed right, the correct answer is "ST-E2".

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34 Responses:

  1. drreagan says:

    Yes - the focus-assist light on the camera and the flash units uses infra-red (or close to it)

    The ST-E2 will also serve this function, as well as acting as a remote-trigger unit for off-camera flashes, if you were to use such things.

    • jwz says:
        Yes - the focus-assist light on the camera and the flash units uses infra-red (or close to it)

      Like I said, when the camera itself focuses, it does so invisibly. When the flash focuses, it uses a very visible red light. They use different mechanisms.

      • drreagan says:

        The "dim red light" you mentioned is what you're seeing in the lower end of the visible spectrum - its also emitting fairly brightly in the infra-red.

        • drmandrake says:

          Yeah he's right - the on camera AF uses whatever light is available to focus, so when it looks dark through the viewfinder, chances are it's going to struggle. But it's definitely using the very red end of the spectrum because it still manages to autofocus when using a Hoya R72 infrared filter, which blocks nearly everything with a wavelength shorter than 720nm, and which appears basically black to the naked eye.
          So theoretically I suppose any bright source of near-infrared would help you focus...

        • drreagan says:

          Actually, I've gone and double-checked the specs on the 5D - its one of the ones not using an IR emitter for this, unlikely the EOS 5(non-D) which I was thinking of. So I guess it is just using whatever ambient light is around.

  2. netik says:

    Yes, the ST-E2 will do that and it also has a another nice feature -- It'll remotely trigger that 580EX you have, which allows you to play with off-camera flash, the first step in getting good soft light photos.

    If you purchase the ST-E2 and add on a clamp, tripod, and umbrella (<$65) you've got a nice kit for doing portraits.

  3. wisedonkey says:

    If you'll notice, the speedlight not only gives off light, but vertical and horizontal bands of light. That helps to give contrasty areas that just happen to line up with the autofocus sensors in the camera. If there's enough light or at least enough contrast no AF-assist, be it infrared or visible, is needed. For the most part, the autofocus mechanism works practically the same as the split prism on all-manual bodies.

    My suggestion is to learn to live without autofocus. It's surprisingly easy to do with just a little practice. Somehow I manage to churn out sufficiently in-focus shots in less-than-ideal light with an all-manual film camera. Pick a focal length, settle on average exposure, get X feet away from your subjects, focus once, and you're good to go for the entire night.

    • jwz says:

      I'm usually shooting moving targets who are ten feet away when my depth of field is less than a foot. Manual focus is not an option.

      Also, film cameras are easier to focus manually than digital because digitals don't have a focus-prism in the viewfinder.

  4. bitwise says:

    Can I ask how well your existing technique works, compared to using the onboard AF sensor? I've had similar problems using autofocus in low light, and have been wondering if using an external flash would help.

    Also: is the "emit, no fire" setting on the flash, or is that a camera setting?

  5. otterley says:

    Have you tried calling B&H? Given the sheer volume of their photography catalog that arrives in my mailbox, their salespeople probably have some idea as to what you need. I've received great service from them in the past.

  6. injector says:

    I have a 30D, a 580EX and the ST-E2. I'll add one more "yes" to the collection you are getting here.

    The ST-E2 works very well for low-light AF assist. It actually makes the AF faster and more accurate in almost every situation, so I just usually leave it on my camera.

    Since you have the 580EX you can also make use of the designed feature of the ST-E2 and use it to trigger the flash remotely. This is also very nice. Gets the flash off the camera and allows for much more creative lighting. (You can add two more remote flashes to the mix, if you are a flash type of guy.)

    Even with the ST-E2 alone; it seems that "emit, no fire" custom setting is a benefit. I think the camera still tries to tell the (non-existent) slave flashes to do the pre-fire E-TTL flash to get an idea what how much light the flash will use during the exposure. Since the IR communication system is one way (camera talks to slaves, they don't answer) it can't tell what you have or don't have out there. The camera can just say, "fire", the intensity and "quench". So with the ST-E2 trying to do E-TTL and not getting any boost in lighting doesn't really change anything, but it does make the shot take a bit longer.

  7. cryllius says:

    Like everyone else said, the ST-E2 is exactly what you want. I've been using it with my Digital Rebel forever. With no autofocus assist light on the camera whatsoever an ST-E2 saves the day. (At least whenever you can afford to shoot an orange flash light at the subject - rarely a problem in night clubs!)

    Incidentally, have you tried custom function 4 to move the autofocus off the shutter half-press and onto the * button on the back? That's one of my favorite tools, especially for low light shooting (on cameras that have it anyway). Press * to get a good focus (with assist from ST-E2) and then you can fire off a number of shots before either you or the subject moves out of position without having to worry about AF screwing you up.

    I like it so much that I end up flicking the AF/MF switch on the lens constantly on the d.rebel since it has CF4 removed from its firmware.

    It's probably one of those things everybody loves or hates but being able to focus when you need to, and not have to focus when you don't need to, I find really improves my ability to concentrate on getting the shots I want.

    • jwz says:

      Yeah, I have focus on the star button too. Much easier...

    • da_zhuang says:

      Holy crap! That's brilliant! Thanks for the tip!

    • violentbloom says:

      I haven't tried it, but I was under the impression you could hack the rebel so that you got the full feature set.

      • cryllius says:

        I just did a very quick check to see if anything obvious has changed since the last time I was keeping an eye on the 'alternative' firmwares out there - don't see it.

        All the ones I've seen only support a few parts of the full feature set, definitely not all of it, and specifically not CF4. Which sure is the one I'd pick. It's probably just as well because I never did particularly like the way they grafted so many extra controls on to the camera's poor little buttons anyway.

        Shame they were charging about $400 for CF4 and a thumb wheel 3.5 years ago. I really wanted them but I kept the money to spend on glass instead! That camera was such a bargain, I can't even manage to hold it against Canon for screwing with the firmware any more.

  8. babbage says:

    If it's for use in DNA Lounge, why not just put a big-ass wide-angle continuous IR source up there with the rest of the lighting, and use nothing at all on the camera? I mean, the worst you can do is bake the performers, right?

  9. lrc says:

    My trick for focusing in dim light with my FZ20 is to put it on "manual focus". I then click the autofocus button, so that it will set the focus on my current target. At that point the focus is set, and fine and dandy until I or my subject move.

    If you mean the autofocus that is used in bright light, it uses the visible light to maximize the sharp edges in the picture. I don't know the details, but I bet it moves the lens to maximize an edge detection algorithm.

    You could try attaching a solid state laser to your camera and see if that helps it focus in a dim room. If so, make a mount with a thumb switch so that when you're going to take a picture, turn on the solid state laser (cat toy), and let the camera focus on that dot.

    You might also be able to probe the hot shoe contacts with a DMM and see which ones have a voltage or resistance change when you press the shutter enough to autofocus.

    I don't suppose you've tried the low tech method of setting the camera to manual focus, and setting the distance based on the number on the focusing ring?

    • injector says:

      Canon's auto-focus system actually works quite a bit like a split-prism viewfinder, but in miniature. It's AF sensors split the light into two paths. It then compares the phase of each half of the area covered by the sensor. It can use that phase information to know which way the focus needs to be moved. (So a single point of a laser probably won't help much.)

      It is an algorithm that seeks to increase contrast, but with a little more smarts to know which way it should go. Unfortunately when it gets it guess about the phase wrong it'll just run until it bangs off the end of the range.

      Also when the multi-point AF is active the system seeks focus with point that covers an object closest to the camera. So phase is compared between points too.

      There are also two types of AF sensors. The normal split-type, and then a cross-type. The split-type are normally oriented for a left-right split and thus need horizontal contrast to help find focus. That is why the pattern emitted by the ST-E2 is a series of vertical lines. Canon has started rotating the left and right AF points to be up-down split now. So when the camera is held in portrait position they become left-right (the world has more things with vertical strips than horizontal).

      The cross-type sensor is a 4-way split so it is sensitive to contrast in either direction. Canon usually reserves these for the center AF point, but the "pro" models may have more than one these days. I usually just select this center point and use the focus and recompose method--unless I'm doing portraits then I set it to the right-most (which becomes the top when I turn the camera). This avoids the system I mentioned above of picking the closest point which generally just screws with me.

  10. agentcooper says:

    You don't mention which lens(es) you're shooting with. Obviously faster than f/4 will help a lot.

    The on-camera focus simply looks for contrast at the focus point. It's 100% passive. If it won't focus, try moving the focus point from a solid area to an edge or pattern (eye brow, jaw bone, ear, shoulder). Focus should just *snap*.

    The emitted light merely provides edges so you can focus on otherwise featureless regions, like blank walls or foreheads.

    As others have said, if looking for edges doesn't work the ST-E2 is exactly what you want.

    • cetan says:

      Took a few comments to get there, but that was my thought as well. On the 5D using a lens with an aperture larger than or equal to f/2.8 will get you better autofocus results without external sources (as you have access to higher-precision AF)

      But I too would recommend the ST-E2 for lower light situations.

  11. ninjarat says:

    Something of a tangent but what are you using for lenses and are you locking the aperture to the widest settings? A good 50mm f/1.4 locked at maximum aperture may be enough to offset the low light autofocus problems without needing a speedlight or AF assister.