low-light action photos w/ D70

One of my hobbies is swing dancing, and I like to take pictures at the

evening dances. In many ways, this is the worst possible case for

photography, because you've got low light (indoors, at night, with the

house lights low) and fast action. I'm typically chasing after my

subjects with the lens zoomed wide open. There's no time to carefully

select an AF point and reframe for the shot. Instead, I put the

camera in AF-C mode with nearest-subject focus and hope for luck. My

resulting hit rate is less than 3%. Almost everything else comes out

back-focused. To compound the problem, the back-focus makes the flash

put out more light, washing out the foreground.

 

My gear: Nikon D70, kit lens (18-70mm zoom), SB-800 flash

 

In broad daylight, the camera has no trouble focusing spot-on

perfectly, so I suspect it's a low-light issue rather than some kind

of calibration problem. My question for people here is what sorts of

solutions I might pursue. One possibility would be to shell out the

painful big bucks on a Nikkor 28mm f/1.4D. With two and a half extra

stops, I imagine the autofocus system would do a better job, but it's

a steep price to pay. Also, the lens is longer than I'd like.

Another intriguing possibility is the Sigma 20mm f/1.8, which is

significantly cheaper, and the wider-angle is closer to the wide end

of my kit lens, where I do most of my dance photography. Still, I've

read complaints that the Sigma is not terribly fast at focusing.

 

On the flip side, maybe it's not a lens problem but a body problem.

For barely more than the cost of the 28mm f/1.4D, I could get a Nikon

D2H with its much more sophisticated autofocus system. How much would

that improve the low-light situation? In general, A D2H would be

overkill for me. I don't really need 8 frames per second, and I'd

rather have the higher resolution of my D70, but I could potentially

get a lot of value out of the D2H's autofocus sensor, assuming it

really works in lower light. (Nikon's web site says both cameras can

autofocus down to "EV -1", although I suspect the D2H, having more

sensors, is more likely to luck into some of its sensors getting

useful data in a low-light setting.)

 

Flash question: Right now, I've got the SB-800 in normal, TTL-BL mode.

I suppose I could try AA instead. That would presumably make the flash

watch the exposure and ignore the AF point, perhaps dealing with the

highlight burnout issues. Thoughts?

 

Final question: In various forums in the past, I've read about f/2.8

being a magic number for "cross-type" sensors. Is that extra half-stop

over my kit lens enough to make a noticable difference in autofocus

accuracy? Would the D70 be able to take advantage of the extra

brightness of a more exotic lens like the 28mm f/1.4D?

You seem to be in a major metro area, maybe try a rental? I'm still a newbie with my D70, so I can't help much with the details. I find the 85/1.8 AFD does OK with AF in the ISO 1600 / f2 / 160 regime, particularly if you stick to the center AF point. I also gave my 20/2.8 AFD a shot, and it tracked OK (I was doing ping-pong photos).

 

A less expensive possible alternative is the 35/2 AFD. I was bummed to find that my particular one has a broken (EE, min aperture) tab that renders it nearly useless on the D70 (but it works fine on everything else I own).

depth of field at the wide end should allow for quick manual focusing. if you're not

adverse the idea.

to the idea

The D70 uses the Multi-CAM 900 AF module. My D100 uses exactly the same module and I have trouble locking focus on moving subject at broad daylight with AF-S lenses. In a dark room, IMO it is a pretty hopeless situation.

 

The D2H uses the latest Multi-CAM 2000. That is the best Nikon has at this point. I do not yet own any camera with that module. I am sure you'll see a drastic improvement with the D2H. But you might need to borrow/rent one to try it out. I cannot tell you whether the D2H will be sufficient in your particular situation.

Some background info:

 

In AF-C mode the SB-800's auto focus assist lamp does not light. That means the camera's autofocus system has only the contrast present in the subject as lit by the ambient light. In many cases that's not enough, especially for the four line type sensors in the peripheral AF zones.

 

Also, see this document about the positioning and orientation of the D70's AF sensors: http://md.co.za/d70/focus21.pdf

 

A possible few solutions, some better than others:

 

Use faster glass to increase the amount of light reaching the AF sensors.

 

Since you're already using flash, stop down a whole bunch and use manual focus to keep most of the stage in focus at all times. If the SB-800 isn't enough to light the scene at the required aperture and shooting distance, move the SB-800 closer and use the D70's commander mode. If that's still not enough, add more CLS compatible flashes until you've got enough.

 

Adjust your composition so you can get away with using only the center AF sensor. Depending on the distance and aperture, focusing on the head vs. the body may not make a huge difference and there will be less risk of accidentally focusing on the background. Also, the center AF sensor is a cross type and deals better with low light / low contrast than the peripheral sensors.

 

The AF system in the D2H has more cross type sensors, and so will do a better job in low light / low contrast situations. The internal AF motor on that family of cameras also has a bit more oomph than the one in the D70, which means screwdriver AF lenses will focus faster.

 

Hack up some sort of AF illuminator suitable for use in AF-C mode. Remember, it needs to be inconspicuous in photos or shut off before the shutter opens. If you dig through this forum, you'll find talk about laser pointers, IR lamps, and other interesting AF assist light sources.

"I was bummed to find that my particular one has a broken (EE, min aperture) tab that renders it nearly useless on the D70 (but it works fine on everything else I own)."

 

try jamming the tab sensor switch open with a piece of matchstick, if you don't want to get it repaired.

An f/2.8 AF-S lens should make a difference, the wider aperture will give more light for the AF system to work with, and the SWM will respond more quickly, so you're less likely to find yourself focussed where your target was a second ago. Alternatively try picking up a used D1h which has a MultiCAM 1300 AF module, same as the F5. But low-light photography of moving subjects is hard (I do some gig shooting myself) and a low yield is just something you have to accept. 3% does seem a little too low tho'; I get around 15% correctly focussed and exposed with my gear (F5, 50mm f/1.4 and 105mm f/2 lenses).

"try jamming the tab sensor switch open with a piece of matchstick, if you don't want to get it repaired."

 

soething i would never recomend, what if it falls off and ends up in the camera body and scratches the sensor? it's cheaper in that case just to get it fixed right? also that switch is whaty controls tha tapture from the body to isin't it?

One fast-and-cheap thing to try is this: buy (or borrow) the Nikon 50mm f/1.8. It's a great lens and it'll give you a lot more speed. I shoot live theatre for my wife, and the 50mm and 85mm f/1.8's are GREAT on the D70!

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"try jamming the tab sensor switch open with a piece of matchstick"

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That would work. When I discovered the problem, I found I could make it work by jamming the little fingernail of my left hand into the switch while shooting, but of course that's a little awkward.

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The switch in question does not communicate aperture value per se, it just communicates to the camera that the lens is at minimum aperture. It's an 'on-off' switch.

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I have been reluctanct to stick a foreign piece in there, and I need to see about getting the lens repaired.

Heh, reminds me of a trick you could do with the <i>other</i> kind of SLR¹, with a matchstick, to make it fully automatic...

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¹Self Loading Rifle, the British Army's standard-issue weapon before the SA-80. Semi-automatic only, usually!

I think you may be a victim of all of your technology. You said you follow your subjects all around the room. Have you tried just trying to step with them at a fixed distance, say 8 ft. or so, that yeilds a nice composition? Leave the camera on MF, focus the lens to that distance, and leave it put. With a little practice, I have a feeling you'll get more shots that way than with AF-C.

 

If that doesn't work, have you given AF-S much of a try? That gets you the benefit of the excellent AF lights on the SB 800. I was playing with my d70 + sb800 last night, and it will focus on objects in a pitch dark room pretty much instantly. It also did the same outside at night on trees where the nearest object was 30 or so ft off. Those red leds shoot off forever and seem to be a little less distracting as well. On the other hand, I believe the d70 manual mentions that, with moving subjects, AF-S mode will try to wait for them to stop before locking. That wouldn't work.

 

One more thing; I think changing your flash from TTL-BL to TTL might properly expose the foreground at the expense of the background. You might give that a try, along with the diffuser, ceiling-bouncing, etc.

Thanks everybody for all the suggestions. I'll have to try shooting another dance to see if I can get any more traction with the different modes. I also like the idea of renting some pricier gear to see whether that helps or not.