Focusing with dim modeling light

[myshkin]

<p>I'm new to studio lighting and find it extremely difficult to focus precisely when doing low-key portraits with strobe lights. The modeling lights are so dim that the autofocus hunts. And manual focusing is almost impossible under these conditionss. Any advice?</p>

[frank_scheitrowsky1]

Measure camera/subject distance and use the focus scale on the lens. This only works for static subjects.

[Matt Laur]

<p>Hate to say it, but brighter modeling lights. Or, depending on how you're equipped, you can put a flash unit (with focus assist features) in the camera's hot shoe, and set the flash/camera to <em>not fire the flash</em>. That's easier to do with some systems than it is with others. I've used my Nikon speedlights in that manner before - the red grid they project works very tightly with the camera, and can render accurate focus in otherwise next-to-dark situations.<br /><br />I've also seen some people use something like a small flashlight mounted on a stand behind the camera. It's completely overpowered by the strobes when the time comes, but it has the benefit of throwing just a bit more light onto the subject's face if you position it correctly. Some like the fact that it also tends to contract the subject's pupils a bit more than would otherwise happen. If the scene (with modeling lights) is so dark that you're having trouble focusing, then the subject's pupils are probably a mile wide, too.<br /><br />Also: what lens(es) are you using? Even if you're shooting at f/11, one of the nice things about a fast prime lens is that when you're composing/focusing, that big aperture lets a lot more light into your viewfinder, and gives the camera's AF system more to chew on.<br /><br />On the modeling light issue: check your hardware. Some let you set the modeling lights to different modes. I'll sometimes use the power tracking features to help me estimate key/fill ratios by eye, but then set the modeling lights to a higher power (independent of the strobe power) once the scene is set. Specifically to help with the problem you address.</p>

[john_a5]

<p>Are you keeping your modeling lights set to track the power of the flash? Most units can be set to full power or tracking. Just set it to full power and that should solve your issue. My experience has been with a good fast shutter speed, the modeling lights are negligible, especially when they go off when the flash does and don't come on until the unit recycles. But even if they don't, they are often weak in comparison to the f-stop/shutter speed used for the shot itself.</p>

[craig_shearman1]

<p>What kind of strobes are you using? Some of the very low-cost units come with 60-watt modeling lights, which are useless. My Novatrons came with 100-watt modeling lights, which I replaced with 150-watt quartz bulbs (the sockets were standard household light-bulb sockets so they were easy to swap.) Some strobes can take 250-watt modeling lights, which are even better. I would put in brighter bulbs if that is possible on your units, and make sure they are turned up to full power as John suggets. If that's not enough, turn on the room lights so you have enough light to focus, and keep the shutter speed high enough (use your camera's highest sync speed, probably 1/250) so that the room light doesn't affect exposure. The room lights will wash out the modeling lights so you won't get the benefits of seeing what your ligthts are doing, but it sounds like the modeling lights aren't doing their job anyhow. You can always checks the results on the LCD on the back of your camera after you do a test shot or two (assuming you're shooting digital).</p>

[Charles_Webster]

<p>The 4-5 sec recycle time at full power on those strobes would be a deal killer for me also. But Craig's suggestion of raising the ambient light level can help if you are committed to buying those strobes.</p>

[markonestudios]

<p>In a pinch (usually on location, before I got my strobes), I have been known to have the subject hold up a cell phone facing the camera; I lock focus on its lit screen, then they put the phone away and I have my shot all set :D</p>

<p>In your case, I'd agree with the general consensus: get modelling lamps with more juice or, if not possible, use the flash AF assist function if your external flash has it. If your flash doesn't have the no-fire custom function, maybe set it to the very lowest power setting so that the strobe lights overpower it anyway.</p>

[myshkin]

<p>Thanks for this valuable advice. I used 3 Profoto Acute heads. Modeling light is on full power. The lens is a Canon 85 F1.2. The Autofocus problem occurs only at very close distances (head filling frame)</p>

[bob_bill]

<p>If it only occurs on tight head shots, I wonder if you dont have your focusing spot on an area of contrast, like eye to eye lid or cheek but on even skin. Putting it on even skin because there is so much of it may be not giving enough contrast for the camera to acquire focus. </p>

[michael_s10]

<p>Are you closer than the minimum focusing distance of 3.1 ft for that lens?</p>