How Do You Get It Sharp?

Posted by ciaran on February 12, 2011 in Blog, Technique | 4 comments

It’s pretty nice to be asked to show your work to other photographers and recently I was invited along to Palmerstown Camera Club to show some images and talk through my thought process; how I plan a shot, execute it and process it afterwards. One of the questions I was asked, was about how I get my images so sharp. To be honest, I am a sharpness freak Ensuring my shots are critically sharp is an obsession of mine and this blog is a little insight into the process I use to ensure I get the sharpness I want in my shots.

The Grip

It might seem pretty straight forward, but it starts out with the grip and how I hold my camera. How you hold your camera and lens can be a huge factor in how sharp your images are, or more to the point, how soft they are. Every day, I see photographers hold their camera’s incorrectly. This seems quite prevalent in photographers that have moved from digital compacts up to SLR’s. They are used to holding the camera away from their face, extending their arms away from their body. If they’re not doing this, they’re often cupping the lens incorrectly, resting the lens in their thumb rather than in the palm of their hand. This just isn’t stable and can lead to the camera being shaken (even imperceptibly).

The camera should be as secure as possible. I cup the lens in the palm of my hand, keeping my elbow pressed firmly into my body and the camera pressed firmly against my eye. My legs are often bent and apart, keeping my weight (no smart jokes please ) centered over my legs – not leaning forward or back. My finger rests over the shutter release and when I do take a shot, I tend to roll my finger across the release rather than snatching at it or pressing it. Basically taking care to keep the camera as steady as possible.

What is a must see, is the video of “Da Grip” from Joe McNally… an excellent illustration of camera holding technique.

Camera Shake, Focal Length, Shutter Speed & Vibration Reduction

If you look through a wide angle lens, zoomed all the way out, any slight movement of the camera is not really noticeable in the viewfinder. However, using a telephoto lens, zoomed in to it’s maximum; that same slight movement now appears to have a huge effect when looking through the viewfinder. So the longer the focal length, the more acute an effect camera shake will have on the image. We can try and counteract this effect by using a faster shutter speed. The faster the shutter speed, the less time the sensor is exposed during that movement. The longer the exposure, more of the camera shake movement is captured.

A good rule of thumb to avoid camera shake in your images, is to use a shutter speed that is 1/focal length. So if I was using a 70~300mm lens at 300mm, I would need to ensure that the shutter speed is at least 1/300 (1/320). But this is just a rule of thumb Things can get complicated when you start to consider factors like real focal length versus effective focal length due to sensor crop factor. How you hold the camera (see above) also comes into play, as does age. The older we get, the less stable we can hold a camera. So err on the side of safety. Use MUCH faster shutter speeds than this rule, if you want to eliminate camera shake.

Modern lenses, indeed some cameras, often offer a feature which is called Vibration Reduction (Nikon speak) or Image Stabilisation (Canon speak) which helps us enormously with camera shake. But this should be seen as something that can assist us rather than it being relied on as a crutch. It should not replace good camera holding technique and should never compensate for making a good choice for shutter speed. Obviously if we roam into the area where we can not hold the camera as steady as we would like, or are using super long telephoto lenses, or need to use longer shutter speeds, then this feature comes into play more and more. Does it work? Amazingly so. It’s a super aid and really comes into it’s own on longer lenses. But expect to pay for it (monetary terms)

Subject Movement

Even if we were able to hold the camera incredibly still, it still won’t guarantee we have a sharp image… because the subject can also move This poses two problems. First is what shutter speed to use? If we want to freeze motion, we need to use faster shutter speeds. The faster the subject moves, the faster the shutter speed that is needed to freeze this motion (flash can help here… but let’s not complicate things). One of the issues with this is that with a faster shutter speed, less light is available for the exposure. An obvious solution is to open up our aperture, but this reduces our depth of field. This in itself is not a bad thing, but the shallower our DOF becomes, the more likely we are too mis-focus (see below). Another solution is to increase our ISO, which also increases the noise in an image. The more noise… the less sharp an image becomes So it’s a trade off and one that only the photographer can make. It’s worth noting, that VR/IS does not help us with blur due to subject movement.

The second problem is focusing. If we have a moving subject, our camera/lens has to track that movement. Modern cameras have fantastic auto-focus features, but unfortunately they are often fantastically complicated to use as well. It really isn’t a case of just pointing and clicking. If you want consistently sharp images, it is worth investing the time to understand the auto-focus system in your camera. How it behaves, what it’s strengths and weakness are and what the different modes are for… all too much to discuss for this blog.

The Lens

Even the most mediocre camera is capable of taking critically sharp images. However, unfortunately most mediocre lenses are the weak link in the chain. It is unfortunate, but for really sharp images, we really do need really good lenses, which can cost a premium. A good tip for buying any lens, is looking at the “zoom factor”. Take the lenses maximum zoom and divide it by the minimum zoom. The larger the result, the poorer that lens will be optically. For instance a prime lens, which has only one focal length would have a zoom factor of 1, e.g. and 85mm lens would be 85/85=1. As you move into zoom lenses, this factor moves away from 1, leading to a reduced optical quality. I would generally never go for a lens with a zoom factor of 3 or above.

Common zooms like the 70-300 (300/70=4.285) or the super zoom 18-200mm (11.11 ) just don’t offer the same optical quality of the more pro end lenses. Obviously they are far cheaper, but you do lose on quality. In my bag I have the 14-24mm (1.71), the 28-70mm (2.5), 50mm (1), 85mm (1), 70-200mm (2.85) and a 300mm (1).

Aperture: Depth of Field & Diffraction

Most photographers are pretty comfortable with the concept of Depth of Field. If we shoot wide open, everything just before and just after the point of focus, is thrown out of focus. As we stop down the lens, this range or depth of focus/depth of field increases. So most landscape photographers will typically shoot with very narrow apertures to ensure everything in the image is sharp and most portrait photographers will shoot at wider apertures to isolate the subject.

This concept can be used to help mis-focusing. In that if we use a small enough aperture, we don’t have to be very precise with our focusing, as the object we are focusing on will most likely be within our depth of field. So by stopping down the lens, theoretically, we would never really need to concern ourselves about focus? Right?

Wrong As we stop down the lens, particularly beyond a certain point, we enter the world of diffraction. Diffraction is related to your lens in that it’s related to the aperture you have your lens at and the quality of the optics that the light passes through. As light passes through the lens, it’s squeezed through your aperture diaghragm. Normally light travels in straight lines, but during this squeezing it’s deflected/disperses (which is called diffraction). The smaller the hole it gets squeezed through, the greater the degree of diffraction. So at smaller apertures, we have a greater amount of diffraction.

As the light diffracts, rather than getting parallel light waves hitting your sensor directly and at the same time, they diverge. So some have to travel different distances before hitting the sensor. One’s that have diverged will interfere with parallel rays of light, sometimes adding to and other times subtracting from them, with CA and softness in the picture being the result.

Sharpening For Output

Assuming the image taken is sharp, assuming it was shot as a RAW file, then the next step in the flow, is sharpening the image for output. I generally use “Unsharp Masking” in Photoshop to sharpen my images. Every single shot is different in terms of how much it needs to be sharpened. But more than that, I will also sharpen files differently depending on what their output is. For instance, images which are sized for being displayed on the web, will be sharpened differently than those due for printing. In addition to this, I will apply differing amounts/degrees of sharpening depending on the size of the print being produced and the type of paper being used.

There are various different ways to sharpen an image and an image can be sharpened to different degrees. Common mistakes are people over sharpening an image, but more often than not, is that people try to compensate for soft/out of focus images by sharpening them. You can only sharpen an in-focus image. If the detail is not in the image to begin with, it can’t be sharpened.

And That’s It

So that’s it. Hold the camera correctly,watch your shutter speed/focal length, use VR/IS to assist us, pay attention to your subject movement, understand your auto-focus system, and sharpen for output in post production. Or at least, that’s how I do it. Simple