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Old May 7, 2006, 11:45 AM   #1
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Using my D70, SB600 and 70-300 Quantaray LDO Zoom, I was experiencing under-exposure on many shots during a Tae Kwondo competition in a school gym. Shooting in S-mode down to 1/100 gave blur and higher speeds made situation even worse. I did not up my ISO from 200, which I probably should have done. Subjects at 25' or more and focusing was also a problem. Does anyone have recommendations on what could be done better to get acceptable exposure in low-light action situations? Saving grace is that Photoshop cures the problem; maybe that's the answer and I'm asking too much of the D70.

Thanks, Dan
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Old May 7, 2006, 11:53 AM   #2
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Sorry about the mis-post, Steve. Should I repost in the Nikon Digital SLR section?


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Old May 7, 2006, 12:29 PM   #3
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I moved it for you.


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Old May 7, 2006, 12:47 PM   #4
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Use a Wider apperature and Up the ISO are basically your only 2 options there then.

since photoshop can correct a lot of noise and gain up pictures by adjusting the levels, You don't have to worry too much about a little bit of underexposure, So using Shutter priority in that situation might be your best bet. (since you were getting blur at 1/100 1/200 probably would work)

For focusing its tricky though, You could raise the Fstop # and manually focus on the ground underneath them (so that everything is in focus) That would almost guaruntee you would need an ISO of 800+ though. Otherwise you would just have to rely on your camera's autofocus. From what Ive heard the 70-300 is quite slow at focusing so it might be your only option there, If you zoom out slightly so the fighters aren't full frame your DOF will also slightly increase, so for manual focus that could also be an option.
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Old May 7, 2006, 1:00 PM   #5
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Thanks, Lexiticus, that's what I thought. I'll try uppingthe ISO next time and maybe looking into a faster zoom ($$$?)...

Thanks to JimC for moving the post... Sorry :crazy:
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Old May 7, 2006, 1:21 PM   #6
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No problem.

I was actually typing a long winded response. ;-)

Looking at the specs for the SB600, it's got a Guide Number of 98 feet at ISO 100. Your lens is a relatively dim one on it's long end (dropping off to a largest available aperture of f/5.6).

So, that means the maximum flash range would be around 25 feet at ISO 200 with it on the long end of your lens.

To determine flash range, you need to divide the GN (98 )by the aperture (largest available is f/5.6 if you're on the long end of your lens)at ISO 100.

For example, 98 / 5.6 = 17.5 feet at ISO 100

Then, each time you double the ISO speed, flash range increases by about 1.4x

So, 1.4 x 17.5 = 24.5 feet for ISO 200, shooting on the long end of your lens at f/5.6.

If you're using a diffuser or bouncing the flash, range will decrease. So, chances are, you were just trying to use the flash outside of it's rated range causing the underexposure.

As for Autofocus, as you zoom in, you lose light reaching the AF sensors, too. Your lens is about twice as bright on it's wide end versus it's long end (f/4 is exactly twice as bright as f/5.6). So, a camera can't "see" to focus well indoors using a lens this dim at longer focal lengths.

My suggestion for future shoots with your existing lens would probably be to up your ISO speed to increase your flash range, and bump up your shutter speeds to around 1/300 second or so to reducemotion blur (just in case you get enough ambient light to contribute to the exposure), not to mention that camera shake can be a problem at longer focal lengths if ambient light contributes too much.

If light is too low for proper exposure, the camera should automatically use the largest available aperture (f/4 on thewide end of your lens, dropping off to f/5.6 on it's long end) if you shoot in Tv Mode. If not, just use Manual Exposure instead, setting to the smallest f/stop number.

In some condtions, I'd do the opposite (keep ISO speeds set lower, keep shutter speeds at a reasonable value around 1/100 second, and let the flash burst freeze the action. As long as your subject is not exposed enough by ambient light, the flash itself can stop motion (since the flash burst is very short).

But, since you appear to have a flash range problem and will probably need to increase ISO speed to solve it, I'd also increase shutter speed to make sure you don't get blur if ambient light contributes too much at higher ISO speeds. You can increase it up to 1/500 second with your camera without needing FP mode on your flash.

If you don't want the flash to be the main light source, I'd suggest a different lens.

Depending on how close you can get, a 50mm f/1.8 or 85mm f/1.8 may make good choices if you set ISO speeds high enough, depending on how bright the light is.

If a zoom is absolutely needed for flexbility, I'd look at something like a Sigma 70-200mm f/2.8. This lens is twice as bright as your existing lens on it's wide end (f/2.8 is twice as bright as f/4) and 4 times as bright as your existing lens on it's long end (f/2.8 is 4 times as bright as f/5.6). But, it may be "borderline" insome gym environments, even at higher ISO speeds, formoving subjects without a flash.
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Old May 7, 2006, 6:32 PM   #7
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JimC

Thanks, I'll remember to take your suggestions at the next opportunity, especically upping the ISO.

I was looking for a potential zoom and I will look into your recommendation an I borrowed the one I have and I need to get it back.


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