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A Simple Rule to Guarantee Sharp Photos

Guarantee Sharp Photos - example of photo with fast shutter speed

Shot at 1/500 second; Aperture of f/8; ISO 400; using focal length of 17 mm.

If you want to guarantee sharp photos, I propose that you always make sure your hand-held photos are shot with a shutter speed that is double your focal length.

Let me explain.

Most sharpness problems with your photos are not because your lens isn’t good enough. It usually isn’t because of a bad focus or aperture setting (although those certainly happen). Rather, it is because your shutter speed is too slow.  You moved the camera slightly during the shot.

This problem gets exacerbated as you zoom in.  The more you zoom in, the more tiny movements matter. Therefore, as you zoom in (or increase your focal length) you need to use a faster shutter speed.

As you can see, the shutter speed needed to ensure a sharp picture changes depending on your focal length. To provide guidance to those trying to make sure they were using a fast enough shutter speed to get a sharp picture, the photography world developed a rule  of thumb called “the Reciprocal Rule.” This rule says that your minimum shutter speed should be the reciprocal of your focal length (I have written about it previously here). In other words, if you are using a 50 mm lens, your minimum shutter speed should be 1/50th of a second. If you are shooting at 300 mm, your minimum shutter speed should be 1/300th of a second. And so on.

Problems With Reciprocal Rule

Nevertheless, I keep seeing pictures that comply with that rule but are still blurry or at least not as sharp as they should be. Sometimes they are my own pictures, and sometimes the pictures of others. There are 3 reasons for this that I see:

1. The Reciprocal Rule Fails to Account for Modern (Smaller) Digital Sensors

The Reciprocal Rule was invented in the days of 35mm film before APS-C and Micro 4/3 sensors became common. When you use a camera with an APS-C sensor, it has a crop factor that causes effective focal lengths to increase by 40%. If you are using a 50 mm lens, all of a sudden it behaves like an 70 mm lens, so now a shutter speed of 1/50th of a second isn’t good enough.

The crop factor is even greater for Micro Four-Thirds cameras, since their sensors are even smaller. They have a 100% crop factor such that effective focal lengths are double what is shown on the lens. If you are using a 50 mm lens on a micro 4/3 camera, your minimum shutter speed should be 1/100 second.

The Reciprocal Rule assumes a 35 mm (or full frame) image. You could make an adjustment to compensate for a smaller image sensor, but you don’t want to be out in the world taking pictures and trying to figure out what is the reciprocal of 1.4 times your focal length. Well, most of us don’t anyway.  Doubling your focal length makes it easier.  It avoids tricky math.

2. Higher Resolution Increases the Standard

The resolution of cameras continues to escalate. Nikon has had cameras shooting at 36 megapixels for some time. Canon just introduced two new cameras that shoot at over 50 megapixels. Sony just increased the A7r line from 36 megapixels to 42 megapixels. Increased resolution means more detail, and that detail needs to be sharp.

This increased resolution means that even the smallest of movements during exposure will show up in your pictures. In fact, many photographers urge that you always shoot these high-resolution cameras from a tripod. That way you can ensure that the resolution offered by these cameras results in sharp details.

Of course, you are going to want to take pictures while hand-holding these high-resolution cameras at least some of the time. To make sure that the details are sharp, you will need to use a fast shutter speed. These high-resolution cameras are all full-frame, so you don’t have the problem mentioned above, but still you are going to need to shoot with a faster shutter speed than the Reciprocal Rule calls for.

In other words, the Reciprocal Rule does not take the need for increased sharpness into account. If you used a shutter speed that is double the reciprocal of the focal length, it would.

3. It Is A Minimum for Sharp Photos

In any case, keep in mind that the Reciprocal Rule is a minimum.  It is designed to get you pictures that are acceptably sharp.  If you are reading this, you are probably not the sort of person that just wants acceptably sharp pictures.  You want super-sharp pictures. You need to go well beyond the minimum.

Sure there are times where acceptably sharp will do. Sometimes sharpness is the foremost thing on your mind when you are shooting, and sometimes it is not. But for those times when sharpness is paramount, it will not do to flirt with the minimum.

Decreasing “Cost” of Faster Shutter Speeds

At the same time that you have these changes going on that have created a need for faster shutter speeds, the cost of an increased shutter speed continues to decrease.  What is the “cost” of increasing the shutter speed? Light.

As you shorten the shutter speed, you let less light into the camera. Unless you make an offsetting move, the picture will be underexposed. There are only two ways you can offset the shorter shutter speed and let more light into the camera:

  1. you can increase the size of the opening in the lens that allows light into the camera (i.e., increasing the aperture), or
  2. you can make the camera’s digital sensor more sensitive to the light it receives (i.e., increasing the ISO).

If you increase the aperture, you decrease the depth of field of the picture. If you increase the ISO, you increase digital noise.  So neither of these options is always an attractive option.

Times have changed though. Now camera manufacturers make cameras with outrageously good low light performance. That means the cost of increasing the ISO isn’t that high.  It used to be that everybody shot at ISO 100 whenever possible and only went above ISO 400 in dire circumstances. Any higher ISO than that and you were sure to have a noisy picture.

Now, it is fine to use ISO 200 as a default and most photographers think nothing of cranking up the ISO to 800. In fact, many photographers routinely go much higher with their ISO settings. I think it is fair to say that the low light performance of modern cameras is at least 1 stop better than cameras of 5-10 years ago. (Remember that a stop is a doubling of light). You can easily double your ISOs and thereby give you room to double your shutter speeds.

Using Increased Low-Light Performance to Increase Shutter Speeds

Let me give you a quick example to make this concrete. Let’s say you are outside shooting a scene and you look at your exposure settings and they are:

  • Shutter Speed: 1/80 second
  • Aperture: f/8
  • ISO 200

Your focal length is 80 mm (with no crop factor).

You technically comply with the Reciprocal Rule, but let’s say you want to use a faster shutter speed to ensure a sharp picture. You could easily double your ISO from 200 to 400. There will be no negative consequence to this in modern cameras, since significant noise will not kick in until higher ISO levels.

Having increased your ISO by 1 stop (by doubling it), you are now 1 stop overexposed. You shorten your shutter speed by 1 stop to correct that and get a proper exposure. Doing so shortens your shutter speed from 1/80 second to 1/160 second. You now have a proper exposure and a pretty fast shutter speed.

What’s more, you have a shutter speed that is double the focal length you are using. You have done this by using one of the prime advantages of modern cameras – improved low-light performance – to increase your shutter speed and guarantee a sharp photo.

Making Sure You Get Sharp Photos

From now on, if you want to ensure a sharp picture when you are hand holding your camera, try to use a shutter speed is at least double the reciprocal of your focal length. It will take into account the crop factor and higher resolution.

Do you need to do this all the time? NO WAY!!! I don’t. In fact, I violate it all the time. There are times when you have other priorities, and having a shutter speed that fast just isn’t realistic. Plus I haven’t even mentioned Image Stabilization in this article, but that may give you a stop or two (or more) to work with.

This is just something to use when you want to make sure that your picture is sharp. Perhaps the number one reason most images are not sharp is that the shutter speed is too slow. You still have to focus, use the right aperture, and all that stuff. But this will fix sharpness problems related to shutter speed – guaranteed.

Related Articles

Here are a few related articles on taking sharp pictures:

 

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