Orquid "Phoenix"

Orquid "Phoenix"

by ceinmart

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I am trying to get DOF portraits of my daughter with my Nikon d7000, as per my previous post.

I have zoomed in to 100mm or so and tried to get a large aperture but as I zoom, the camera decreases f# to about 6.

I have also tried in aperture priority mode and still have the same problem lowering the f#.

What am I doing wrong?

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3  
This is pretty well covered in your previous questions! –  mattdm Dec 24 '10 at 16:58
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Also, it's nothing Nikon-specific. –  mattdm Dec 24 '10 at 16:59
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And third, the effect you are looking for is low DOF. –  mattdm Dec 24 '10 at 17:02
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But it's important to understand that this is very fundamental, and that Nikon isn't some weird special universe — the general advise is right for Nikon and for everything else. The specific models of lenses are different but the properties of those lenses follow the same rules. –  mattdm Dec 24 '10 at 17:33
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As you pointed out, the lens is f/5.6 when zoomed in, the only way to change that is buy a different lens. –  Alex Black Dec 24 '10 at 22:11
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5 Answers

up vote 14 down vote accepted

You can't zoom to f/3.5 at 100mm on your lens, your lens will do at best f/5.6 at 105mm.

You can however get a shallow DOF effect quite easily, for example by shooting at f/5.6 at 105mm, with your subject quite close (say 6ft) and you background say 10ft behind the subject.

See this set of photos I took with a Nikon D70 (much older predecessor to the D7000!)

You can see the shot at f/2.8 has a shallower depth of field than at f/5.6, but at f/5.6 you can clearly see the subject in focus and the background blurred, you can even see that at f/8. (They aren't all sharp, I was on a tripod, long exposures, and caused the camera to move when I released the shutter, i used a 5s timer after that..!)

At f/5.6 at 200mm the effect is even more pronounced.

I'm sure at f/5.6 at 105mm you could do even better than I did, getting closer to the subject, and having the background further away.

DSC_9335
f/2.8, 105mm

DSC_9336
f/5.6, 105mm

DSC_9337
f/8, 105mm

DSC_9341
f/5.6, 200mm

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Great examples! –  rfusca Dec 25 '10 at 0:23
    
thanks for the example, this is getting all clear for me, but one issue remains. physics... how large is your room in these examples? cause with the subject 6 feet from me and the background 10 feet back thats a total of 16 feet required to get a nice shot. the million dollar question is how do i get shots like this in a 10 foot long room? –  kacalapy Dec 27 '10 at 18:41
    
In a small room, if you're taking pictures of a person, you probably need a different lens to get this effect, perhaps the Nikon 50mm f/1.8. –  Alex Black Dec 29 '10 at 4:09
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The aperture range on your lens indicates the maximum aperture at the shortest end to the maximum aperture at the longest end. So, at 18mm you can have f/3.5 but at 105mm you can only have f/5.6. That's pretty typical for a kit lens, the much more expensive zooms will offer a constant aperture across the entire range.

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so then how can i get a dof effect with my d7000 kit? –  kacalapy Dec 24 '10 at 16:29
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f/5.6 is wide open for the lens at that focal length, so the DoF will be more shallow than if you stopped it down to say f/8, but it won't be as shallow as it would with a faster lens or a bigger sensor. Kit lenses are designed for general consumer shooting, e.g. friends, family, tourist attractions, and the like. –  John Cavan Dec 24 '10 at 16:38
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The way to get a DOF with this lens is to shoot at 105mm, f/5.6, have your subject be maybe 6ft from you, and have nothing close behind them. If you take a photo like that, and it doesn't exhibit shallow DOF, please post it so we can help! –  Alex Black Dec 24 '10 at 22:14
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It all depends on the lens, not so much the camera. My suggestion, buy a better lens, there's several that'll do the trick for only a small amount of cash. Take a look at Nikon's Lens, and here's a few specific ones that might catch your attention. Sorry, I'm a bit more familiar with Canon's line-up, but they seem to be adequate.

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can you point me to these lenses? –  kacalapy Dec 24 '10 at 17:09
    
Sure, I added more to my topic. I guess small is a relative term, Nikon lenses are more expensive then Canon's, which I'm more familiar with... Still, you should be able to find something that'll catch your eye on the Nikon site, just pay attention to lenses with 2 F/#'s listed. –  PearsonArtPhoto Dec 24 '10 at 17:22
    
Also the cheap 50mm f/1.8 which people suggested in previous questions. And the 35mm f/1.8 (Which gives a more-generally-useful "normal" field-of-view.) –  mattdm Dec 24 '10 at 17:37
    
Sure, I've got them added as well. –  PearsonArtPhoto Dec 24 '10 at 17:50
    
checking them out now, thanks. @personartphoto –  kacalapy Dec 27 '10 at 18:44
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Frankly, I don't care if this gets downvoted (and it seems I'm headed in that general direction with this topic), but how difficult would it be to zoom out to 50-60mm and get twice as close? Just to run an empirical experiment, you understand. Yes, getting faster glass will help (a lot), and there's no way you'll get nearly as shallow a depth of field with you current lens as you'd get with an f/2 or faster lens, but give it a shot. The only thing you can possibly lose is a bit of time. (It cost me a lot of money in film to learn what I've learned.)

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That might not result in smaller DOF. See the earlier posts. –  mattdm Dec 24 '10 at 21:23
    
I have seen the earlier posts. And I've taken several tens of thousands of photographs over the years (including a stint as a professional) -- enough to have learned what really affects DoF. It boils down to distance, aperture and the final magnification factor (the final size of the image). Lens length only applies as it relates to the magnification factor. –  user2719 Dec 24 '10 at 21:28
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Whether you're better off zooming in depends on the subject size, if you're anywhere near the hyperfocal distance zooming out will massively increase the depth of field. For most subjects (people included) teles tend to work out better (that's the result of my experience after hundreds of thousands of exposures). At the end of the day, the 18-100mm kit lens is not good for doing shallow depth of field portraits. –  Matt Grum Dec 27 '10 at 21:10
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Depth of field for a portrait (which will be at a medium distance) depends basically on two things: the aperture and the size of the subject on the sensor. Therefore, to minimize the depth of field you want to (a) get as close to the subject as possible without being so close that her features are distorted so that (b) you can get the widest possible aperture obtainable with this variable-aperture lens.

There's still going to be a fairly wide depth of field with this lens. For example, if you have to be zoomed out to 105 mm then your maximum aperture is f5.6. Suppose the subject's near eye is 4.00 meters from the camera. If you focus on that eye, the calculated depth of field (using, for reference, a circle of confusion of 0.03 mm diameter) will lie at distances between 3.77 m to 4.26 m. This will put her entire face and head in focus, with the near eye and the plane of the cheek the sharpest. To make this depth of field shallower, just focus a little closer. (You will need to focus manually to do this.) If you were to focus at 3.85 m, say, then the depth of field would range from 3.64 to 4.09 m. If you have a clear line of sight to your daughter, everything from 3.64 to just under 4.00 m will be air, so this part of your DoF range is irrelevant. The parts of your daughter in focus (back to 4.09 m) will include her face and any hair framing it, but everything behind that will be (relatively) out of focus.

The price you pay for this workaround, besides having to make the simple manual adjustment to the focus, is that no point on the subject's face will be perfectly sharp. However, you will be able to visually isolate her face from the background better than before. If the resulting image still does not meet your needs, you need to find a lens that offers a better combination of longish focal length and large maximum aperture (small f-stop). In the Nikon (and Canon) lines the least expensive options are the 50 mm f/1.8 and 85 mm f/1.8 primes. The former is quite cheap while the latter will attain half the minimum depth of field and is an excellent focal length for portraits.

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