How well does vibration reduction on Nikon lenses work?

▼ I couldn't help myself and bought yet another lens a couple of weeks ago. It's the Nikon 55-200 mm VR II. It's a small and cheap tele lens for Nikon DX digital SLRs, and I'll be talking about it some more soon. What I want to do today is look at how good the vibration reduction works.

Modern camera systems use vibration reduction (VR), optical stabilization, vibration control or image stabilization to let you take sharp photos even if you can't hold the camera completely still. Each camera/lens company has its own name for it, but it's all the same thing. If the camera moves while the shutter is open, your photo will be blurry. Unless either an element in the lens or the sensor moves to compensate.

With Nikon SLRs, VR is built into the lens (if the lens supports VR). As a result, the image in the viewfinder is also stabilized when the system is active, which is quite noticeable with tele lenses. The rule of thumb is that you need a shutter speed of one divided by the focal length (or faster) to make sure you don't get any camera shake. That would be 1/200 on the 55-200 zoomed to 200 mm. Of course a lot also depends on your technique.

I tested the vibration reduction on the 55 - 200 mm lens at 200 mm by shooting ten test shots at shutter speeds starting at 1/500, turning off autofocus before each set so the focus would be the same for all ten shots. Without VR, 1/500 and 1/250 resulted in 10/10 perfect shots as far as camera shake is concerned. Without VR, at 1/125 about half the shots were perfect and half pretty good, but not quite perfect. At 1/60, 60% were pretty good and 40% worse, but still somewhat usable. At 1/30 and 1/15 I got one or two shots out of ten that were still usable, all the others were useless.

So bottom line for no VR at 200 mm: use 1/250 or faster to make sure camera shake is not an issue, 1/125 is still workable and 1/60 will do in a pinch.

With VR enabled, the results were pretty much identical for 1/500, 1/250 and 1/125. The 1/500 and 1/250 shots were all perfect, at 1/125 it was about 50/50. At 1/60, 1/30 and 1/30, the best shots weren't quite perfect, but pretty close. Interestingly, at 1/60 I got 80% very good shots, at 1/30 60% (with the remaining ones merely "good") and at 1/15 all ten shots were very good. At 1/15 nine were merely "good" and one still usable. At 1/4 there were no good shots, but they were all still usable in a pinch. At 1/2 I again got 40% good shots, 40% usable and 20% unusable. At one second, only one was usable and the other nine were unusable.

Bottom line for VR on the 55 - 200 lens at 200 mm: for perfect sharpness you don't want to depend on VR, so stick to 1/250 or faster. VR doesn't seem to help at 1/125, but it produces very good results at 1/60 to 1/15 and you can still get usable shots at shutter speeds as long as 1/2.

So the four stop improvement claim holds up. But the limitations are that VR doesn't give you perfect results and it also doesn't seem to be helpful at 1/125.

These are some of the test shots at 1:1 zoom. This is 1/250, which is nice and sharp but also too dark because it's underexposed and grainy because the sensitivity was very high at ISO 3200.

This is a representative sample of the 1/60 set: not super sharp.

And then strangely the 1/15 ones are better:

This is a good sample at 1/2. Note that the background is much smoother because the sensitivity is now at ISO 200.

But not all the 1/2 shots are good. This is an example of a bad one:

Permalink - posted 2015-11-23

Back button focus

▼ If you've used a camera in the past decade or two, you know the drill: half-press the shutter button and the camera focuses, then press the shutter all the way to take the photo. Should you find yourself second guessing the autofocus system, then you can flip a switch or go into a menu to turn off autofocus (AF) and manually focus (MF) using the lens' focus ring instead. With a single lens reflex camera you'll have a dot in the viewfinder that tells you AF or MF has been achieved successfully. If not, the Nikon D7100 has a couple of extra indicators next to the focus confirmation dot that tell you in which direction you need to turn the focus ring to achieve focus.

For some types of photography, such as close-up / macro or astrophotography, you may find yourself switching to autofocus and manual focus quite often. I'm here to tell you there is a better way: back button focus.

First, let me explain the traditional way that back button focus (BBF) has been used. I'll get back to switching between autofocus and manual focus after that.

Professional cameras often have an "AF-ON" button. When you press this button, the camera autofocuses. On a midrange camera like the D7100, there is no separate AF-ON button, but you can assign the AF-ON function to the depth of field preview button on the front of the camera (menu option f3) or the AE-L / AF-L button on the back of the camera, i.e., the infamous "back button" (menu option f4). An interesting side effect to assigning AF-ON to either of these buttons is that (half) pressing the shutter then no longer makes the camera autofocus.

So with BBF enabled, the camera will only autofocus when you press the button programmed with the AF-ON function. If you forget to do that and simply press the shutter, the camera will happily take blurry photos.

There are two additional AF settings you'll want to use together with BBF: AF-C and 3D tracking. Out of the box, the D7100 uses AF-A and AF "auto" mode. AF-S (single) means that the camera focuses once and is done, while AF-C (continuous) means that the camera keeps adjusting focus the whole time that the shutter is half-pressed or AF-ON is engaged. AF-A automatically switches between AF-S and AF-C as needed. With BBF, you'll want to use AF-C, which will give you both the AF-S and AF-C behaviors: AF-S by pressing the button and AF-C by keeping it pressed.

Having the camera automatically choose the AF sensors to be used ("auto" AF mode) is not ideal here; I prefer 3D instead. In 3D mode, you'll see one active focus point. You can select which one using the cursor pad on the back of the camera, or use "ok" to select the middle AF sensor. Usually, I prefer to use the middle one by pointing the camera to what I want to focus on and pressing the AF-ON button quickly. Then I reframe my shot and press the shutter. But if you want to track a moving subject, keep the AF-ON button pressed as you recompose your shot and the camera will try to track the subject using any of the focus points.

BBF has a number of advantages: you can take a bunch of shots in a row without the AF system possibly messing up focus and/or having to wait for autofocus to happen. You can easily focus and recompose beforehand. You get both AF-S and AF-C without having to change settings or having to rely on the camera to correctly detect what's needed.

But the most important advantage is that you get to mix autofocus and manual focus very easily with most Nikon lenses. There are basically three types of autofocus lenses:

• The older screw-type AF lenses. You need to switch the camera between AF and MF using the switch on the camera before you can turn the focus ring, because in AF mode, the focus ring is mechanically connected to the AF motor in the camera.
• AF-S lenses with an A / M or AF / MF switch. These lenses have their own focus motor, but in AF mode, the focus motor is again mechanically connected to the focus ring. So in order to focus manually, you need to set the switch to M or MF. Nikon only has a few lenses like this, such as the 18-55 and 55-200 lenses. Most (all?) lenses from other makers are also this type.
• AF-S lenses with an M/A - M switch, also known as M / A or A / M modes. With these lenses, it's ok to manually adjust focus at any time by turning the focus ring without the need to set the camera or lens to manual focus mode first.

With an M/A - M lens in BBF mode, you simply turn the focus ring to focus manually or press the AF-ON button to autofocus. If you half-press the shutter, the focus dot in the viewfinder will still tell you whether the image under the selected focus sensor is in focus or not. (Unless you use AF "auto" mode.)

Note that with these lenses, you can also adjust focus manually when not using BBF, but then you need to make sure you keep the shutter half-pressed because the AF system will reactivate if you release and then re-engage the shutter.

A lot of people swear by back button focus. I've tried it for a bit, but I kept forgetting to press the button too often, resulting in photos that weren't completely sharp. An added complication with enabling BBF is that now most people won't be able to take photos with your camera—BBF persists even in AUTO mode where pretty much all settings are automatic. So rather than keep my camera in BBF mode at all times, I set my D7100 to aperture priority and enabled BBF and then saved those settings to the U1 profile. Then, I turned BBF off again. So when I'm in AUTO, P, A, S or M mode, I'm using regular autofocus using the shutter button. But if I need to, I can easily turn on BBF by rotating the mode dial to U1,

Permalink - posted 2015-11-08

Comparing depth of field: iPhone 6 vs camera

▼ In my post about the iPhone 6 as a camera, I talked about how phone cameras have extensive depth of field (objects near and far are both in focus) compared to regular cameras because their sensors are so small. This is even more pronounced in the iPhone 6 because it has a wide angle lens.

So I thought I'd do some comparisons. This is a photo taken with the iPhone 6. The camera is focussed at a distance of maybe 30 centimeters, so the parliament buildings in the distance are out of focus.

This is the same image taken with a Canon SX280 compact camera with a 20x zoom lens. At this wide angle, the minimum aperture of the zoom lens is f/3.5, which lets in only half of the light that the iPhone's f/2.2 lens lets in. The focal length of the lens is just under 6 mm, while that of the iPhone is just over 4 mm. So the sensor of the Canon camera is 1.4 times larger than that of the iPhone. The depth of field looks a bit larger than that of the iPhone.

Last but not least, the same image taken with a Nikon D7100 with an 18-55 mm lens at 18 mm, resulting in an image that's a bit wider than that of the iPhone and the SX280. The aperture is also f/3.5. The sensor of the Nikon is about 4.5 times larger than that of the iPhone, so even though the lens is a bit wider and the aperture a stop smaller, the depth of field is a lot smaller.

Here's two 100% zooms of the middle of the image. Click on the links to load the specified version of the image: iPhone 6, Canon SX280 or Nikon D7100. The ones with the ∞ symbol are focussed at infinity and should provide a sharp image, the others are focussed at 30 cm and should be more or less blurry. I've also included Nikon versions at f/8 and f/22, so you can see the effect of a smaller aperture on depth of field. Select two images of your choice to compare them.

If you compare the f/22 ∞ version to the f/3.5 ∞ or f/8 ∞ version, you'll see that the sharpness actually goes down at very small aperture sizes. Also, the f/8 ∞ is somewhat sharper than the f/3.5 ∞ version—f/8 is usually the sharpest aperture for most DSLR lenses. However, the SX280 already starts to suffer from the diffraction effect at f/8, so the f/8 ∞ version isn't quite as sharp as the f/3.5 ∞ version, and f/8 is the smallest aperture.

Permalink - posted 2015-01-10