lens and exposure settings for moving subjects in low light

[t_g12]

<p>I recently picked up a d90, and an nikon 85mm f/1.4 lens for taking portraits- especially for our first child that's on the way :) I thought the shallow depth of field would help create an intimate feel. But I also read that the lens is very good for low light situations, and while I've had a little luck with that (VERY new to photography), I'm still working on understanding how to control exposure, and I'm wondering how/if I can take sharp pictures of moving subjects in low light with this setup.<br>

I should be clear- it seems when some people say 'low light' they just mean indoors without natural light or something. In my case, I 'm talking about outside, at night, mostly just street lighting around. The example I was thinking of, was being able to photograph my dog playing outside in very low night. Like dusk-full night with minimal overhead lighting like street lamps, parking lot lighting etc.<br>

The things I know so far about shooting a moving subject, and shooting in low light seem to almost contradict eachother (such as- slow shutter speed for low light, but high shutter speed for moving subject. Would I want a high shutter speed and large aperture? Would the lens I have be up to the task, or would I need some different equipment (oh, and I do have a tripod)<br>

<br /> Thanks!</p>

[andrewg_ny]

<p>Not sure exactly what sort of results you're hoping for but flash might help you freeze subject motion even if you can't manage a very high shutter speed. A problem with using super-fast glass (and that 85/1.4 qualifies) is that effective focusing on a moving subject with such little depth of field is tough.<br>

Glass doesn't come much faster and your camera has pretty good high ISO capabilities--try raising ISO high like 3200 and see what you can get.</p>

[jim_momary]

<p>'Photo ... graph' = 'light ... picture''.<br>

A large aperture like your 85mm 1.4 (wide open) lets in 'lots' of light. So, shutter speeds can stay 'high'. Now, what's 'lots'? To Bill Gates it's not worth bending over to pick up a stack of hundreds. I'd put on my running shoes to get there 'cuz that is 'lots'. Likewise 'high' is relative.</p>

<p>Low light photography either needs you too add light (flash or other source of light) or do 'something' to make up the deficit. You can open up the lens to maximum aperture, then if you need more light, you can drop the shutter speed to slower values. Still need more, then raise the ISO of the sensor on the camera. (Not necessarily in that order.)</p>

<p>Like most things, capturing an image is a set of 'options' or also also could be called 'trade-offs'. Open the lens to max and you have razor thin depth of field, so focusing becomes touchy if not critical. Slow the shutter speed down and both blur from hand holding the camera or subject motion gets recorded as a smear. Raise the ISO 'too much' and digital noise begins to rear its head.</p>

<p>No doubt about it, low light photo taking takes skill and practice. So, add light or 'deal with it', i.e. select the options that give the best photo. Modern digital cameras are really splendid with the ISO pumped up.</p>

<p>There is a great book, <strong><em>Understanding Exposure</em></strong> by Bryan Peterson. Makes a head scratching thing into a learned lesson rather well. Any book about photography works too, as digital is nothing more than taking a photo with a new kind of 'film', per se.</p>

<p>The neat thing about digital, is the 'film' is free. You can try a whole bunch of things with instant feedback on the LCD or your computer and note what works for you as your skill builds. In math, that's successive approximations. The learning curve with digital crushes that which film provided.</p>

<p>It takes time, but never give up.</p>

<p>jim</p>

[devon_mccarroll]

<p>You are correct that if using a high shutter speed, you will need a large aperture to let in more light. Obviously your lens has plenty of room to open up, since 1.4 is very wide open--remember that the smaller the number, the wider open the lens is. The higher the number, like f16, the more stopped (closed) down the lens is, and it will let in less light. That's a nice lens you have! I wish I had that one!<br>

If you want to take sharp photos of a moving subject in very low light, then you'll need to add a flash to the mix to stop the action of the subject. A tripod is great to use in any situation if you can, but it's not going to help freeze the action.<br>

If you don't want to use a flash at all, then your moving dog will likely be blurry, but you could use that to your advantage for some fun creative shots, like slowing down your shutter and getting a long "trail" of your dog's image going by, kind of like the shots people take of taillights on a freeway that look like a long line of red.</p>

[asafrye]

<p>The conditions you'd like to shoot under can be challenging depending on what kind of results you'd like to achieve. What you'll come to learn as a photographer is the less you're willing to compromise, the more expensive your solution becomes. And there's a limit even to that. Having said that, I agree with Andrew's comments. I'm not familiar with the D90 (I shoot with the D70, also often under "low light" conditions) so I don't know how it performs under various low light situations. I suspect it may be a step up from the D70, but doesn't perform quite as well as the D700 or D3 (i.e, the expensive solutions). I shoot moving subjects almost exclusively with the speedlight except in daylight. Reason is simple: the focus assist capability of the speedlight is indispensable in low light. Now for exposure, I think you have that problem solved with the 85/1.4. If you use a flash, your shutter speed won't matter and you can choose your ISO/aperture settings to optimize image quality (higher ISO will give you more noise) or control depth of field (DOF). For a given ISO, since you want to capture your (fast?) moving dog, you might choose to work in shutter priority and let the flash/camera choose the right aperture based on the dogs distance to the camera at the instant of exposure. On the other hand, if you'd prefer to capture images under the existing light only, you'll need faster shutter speeds if you want to "freeze" your dog in flight. You may need to go higher in ISO (and accept the noise level, whatever that is) for decent exposure. With the wider aperture, and thus shallow DOF, focusing will become more of a challenge. I find the auto focus lamp completely inadequate under low light with moving subjects.</p>

[t_g12]

<p>Thanks for the helpful responses! After reading this and looking around, it seems like that kind of situation is a challenge even for more experienced photographers, so it sounds like I should expect it to be more of a journey than just a 'correct answer'. Allong those lines- one thing I've heard a few times now in my beginning questions is how the good thing about the digital format is free experimentation with instant results. So I guess you're right, this is the perfect time to just get out and experiment. It's good to get some knowledge as a point of reference to start out though, and the responses have been very helpful in that regard.</p>

<p>Thanks!</p>