When we speak of the sharpness of a lens, what we are actually referring to is the capability of that lens to resolve fine detail. When a lens that is in focus is able to reproduce a greater number of distinct details in an image, we refer to that lens as being sharp. The sharpness of a lens is not always the same; it shifts depending on the aperture, the focal length (if it's a zoom lens), and the distance between the subject and the lens.
There is a difference between the resolution and the resolved detail. An image that was taken with a modern DSLR but was not in focus will have a very high resolution but will not have any resolved details.
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Sharpness is typically measured in line pairs per millimetre (lppmm), which is an abbreviation for lines per millimetre, or by the size of the blur on the sensor, which is measured in microns. Know that there is a scientific and well-understood method for determining sharpness that involves a little more than just eyeballing it! The exact specifics of these measurements are not important for this tutorial; just be aware that there is such a method!
How to Choose the Sharpest Aperture
The situation is difficult for photographers. A small aperture is required for use at all times if you want your photographs to have the greatest possible depth of field, which encompasses the entire scene from the foreground to infinity. On the other hand, a small aperture will cause your photograph to suffer from diffraction, which will result in a loss of sharpness. Where exactly is the optimal point? In this piece, we will discuss how to select the aperture setting that will produce the sharpest photograph possible while still being practical for use in the field.
However, before we get into that, it is important to point out that this article is only relevant to you if you want your photographs to be sharp all the way from the foreground to the horizon (or infinity). This is not the right article for you to read if all you want to know is which aperture on your lens produces the sharpest image; instead, take a look at our reviews of lenses, which each include assessments of image sharpness. In a perfect world, you would always be able to use the aperture setting on your lens that produces the sharpest image. If you need more depth of field, however, you will find that in practise you will need to stop down to smaller aperture values, which are more prone to diffraction.
An old rule of thumb among photographers states that the aperture that produces the sharpest image on any given lens can be found approximately three stops away from its widest opening. This indicates that the aperture that produces the sharpest image on a lens with a maximum aperture of 2.8 will most likely be somewhere around 8.0. In practise, it varies depending on the lens that you're using, but it's almost always in the middle of the frame. If all other factors remain the same, the apertures in the area of /8 or /11 are going to produce a sharper image than the apertures at the ends of the dial, and this applies to both wide open (whether that's /2 or /4) and stopped down (like /22 or /32) shooting situations. Therefore, if you do not have any particular requirements regarding the depth of field, you would be well served to simply set your lens to an aperture of f/8 and go from there, knowing that you are going to produce an image in which the sharpest areas are extremely sharp.
But what if you want to know the exact aperture at which each of your lenses produces the sharpest image? You can do a simple test to determine for yourself, for instance, that your wide-angle is sharpest at f/5.6 and that your normal prime and telephoto zooms may be sharpest at f/11. This will allow you to determine which aperture setting is optimal for your particular lens. The only things you'll need for the test are a newspaper, a tripod, and any kind of light.
To begin, place your camera on a tripod and ensure that it is level and centred before aiming it at the wall from a distance of approximately five feet. Move in closer for a wide-angle lens or move back as far as you need for a telephoto lens, and then tack or tape a page from the newspaper to the wall. If you want to read something with a lot of small type, go with the financial report. This is the fine detail that you will compare between different shots taken at different apertures in order to determine which one has the sharpest image. (You could purchase a resolution chart for the test; however, newsprint will accomplish almost the same thing while costing a fraction of what the chart would.)
When you have the newspaper hung up on the wall and the camera is focused on the type on it, you should use a mirror lockup and/or a cable release to ensure that there is no camera shake, which could cause the test to be clouded with blur. Make sure the aperture setting on your lens is set to "wide open."
Your light source should be positioned in such a way that it does not cause lens flare or glare in the area being shot. As was the case with traditional copy work, minimising the risk of glare can be accomplished by positioning the light source at an angle of more than 45 degrees to the side and maintaining an appropriate distance from the newspaper. You have the option of using an aperture or a continuous light source; the only thing that will change is the way that you adjust your exposures.
Take a reading with the metre fully open using a source of continuous light, and then adjust the exposure so that it is appropriate. Let's say that at ISO 100, the appropriate shutter speed to use with an aperture of 2.8 is 1/250 of a second. Take a picture using this setting on the camera, and then change the aperture to the next stop down, which is /4. Take another picture after adjusting the shutter speed to maintain the appropriate exposure (in this case, to 1/125th) in order to achieve it. Repeat the process with a shutter speed of 1/60 and an aperture of 5.6, and then proceed to the lowest possible aperture and the slowest possible shutter speed. It is especially important that there is no camera shake in this particular instance; therefore, you should make use of any technical means available to ensure that you eliminate all traces of shake. Are you interested in wedding photography in Melbourne? No need to look any further! You are in good hands with Wild Romantic Photography.
If you are using an aperture, make sure that it is set to manual power and that its output is at its lowest possible setting. It should be positioned (and possibly modified with a scrim) in such a way that the correct exposure is achieved at a value of 2.8. Moving the dial to /4, /5.6, and further to /32 will require the output of the aperture to be adjusted. This is due to the fact that the shutter speed will not affect the exposure caused by the aperture. Because you began with the flash output turned all the way down and the aperture wide open, it is likely that you will need to increase the flash output by one full stop for each adjustment you make to the aperture. For example, you would continue your progression by going from /2.8 and 1/128th power to /4 and 1/64th, then /5.6 and 1/32nd, and so on. If you find that you have achieved maximum power but not the smallest aperture, you will need to begin increasing the ISO in order to keep the exposure settings accurate.
In each scenario, the final product will be a series of photographs of newsprint, all of which will give the impression of having the same amount of exposure. However, as soon as you open these images on the computer and view them all side by side at one hundred percent, you will begin to recognise not-so-subtle differences in the degree to which the newsprint has been sharpened. In the middle of the range, between /8 and /11, the print may be so sharp that you can see the tiny inconsistencies in the way the ink was laid down on the paper. On the other hand, the text may be unintelligible when viewed at /2.8 and /32. It is possible that these two values will produce a blurry appearance. (You also might notice issues such as edge distortion and vignetting, particularly at the wide-open aperture; this can be seen in the examples here as what appears to be a slightly darker exposure wide open.) The difference between the sharpest and the blurriest apertures should be easy to pinpoint. In some instances, the difference will be subtle, but when you look closely, you can see that there is a difference.
An estimate of the aperture that produces the sharpest image is sufficient for many people as the only piece of information they require. However, if you want to be one hundred percent certain, you will need to switch back and forth between the exposures that seem to have the most clarity. If this is not made simple by the file browser you are using, you can create a two-layer image in Photoshop and then drag and drop one file onto one layer and another file onto the other layer. (Because it is easy to get confused about which layer was which, you might want to give each of the layers a name that corresponds with the aperture that it uses.)
You always have the option to perform the test once more if you require the results to be extremely precise. After determining, for example, that f/8 is the most sharp of the apertures you tested, you could repeat the process and adjust the aperture in third-stop increments from f/5.6 and a third to f/8 and two-thirds (which would be f/6.3 and f/10, respectively). This would allow you to find the aperture that produces the sharpest image. It's possible that you'll find that the lens in question has an aperture of 7.1, which results in the sharpest image. After that, you can make this your standard aperture setting for all of your shots. Work with the apertures that produce the sharpest images on your lens unless you have a specific need for a greater or lesser depth of field. This will ensure that your camera produces the sharpest images possible.
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The method described above is by no means the only way to determine which aperture will produce the sharpest image for a given scene. Although it is mathematically accurate, it takes quite a bit of time to process each photo, and there are other methods that are much simpler.
You might, for instance, try to focus stack in order to photograph a challenging landscape. This is not a particularly quick method, but it yields photographs that are exceptionally clear and crisp. After you have your lens set to its aperture that produces the sharpest image, take a series of photos with the focus set at varying distances. (Once more, I strongly suggest downloading the FocusStacker app.) You can combine the resulting images in a programme such as Photoshop or Zerene Stacker, which produces a single photograph that combines the sharpest parts of each individual shot into a single image. Regardless of the method that you employ, this approach will provide you with more information than a single photograph ever could. Unfortunately, it usually only works well if your subject is completely still throughout the entire process.
If you are unable to focus stack, another method is to focus at the hyperfocal distance and then estimate the aperture that will give you the best results based on the experience you have gained in the past. For instance, if you are photographing a scene that has an incredible amount of depth, you might decide to shoot at f/16 simply because you have enough experience doing so. Although this method is extremely fast, it does not always produce the sharpest aperture possible; even experienced photographers may find this to be the case.
Reviewing the LCD:
You might simply choose to review the image on the LCD screen of your camera if the sharpness of a photo is something that is particularly important to you. You are able to make adjustments from that point on, including setting the aperture to its widest possible setting while maintaining the required level of depth of field. However, despite the fact that this method can be quite helpful, evaluating the critical sharpness of a large photograph with a three-inch LCD is by no means the most effective method.
Each of these approaches may be useful, but many photographers find that achieving a "mathematically perfect" aperture is unnecessary complexity. This is especially important to keep in mind if you plan to create smaller prints or if the primary location where your images will be displayed is online. It is entirely dependent upon the circumstances at hand.
You now possess the most potent tool available for achieving the sharpest possible technical image. In your capacity as an artist, what are you planning to do with it?
This method enhances the sharpness at both the beginning and the end of the range of interest. It just so happens that the optical sharpness in the middle of your range is exactly twice as high as it is at the ends of your range, but due to the limited resolution of the film and the printing process, this will not be visible. This will be especially true if the scale tells you that apertures like f/11 and f/16 are required, at which point the definition throughout the image is very high.
If you are photographing a subject that is very far away and your scales instruct you to use extremely small apertures, such as f/64, then the optical image will not be particularly sharp anywhere but will still be the best it is possible to get. Keep in mind that even if the image is perfectly focused, the diffraction that occurs at smaller apertures will limit the image's sharpness. When working with small apertures such as f/64, you may begin to notice that the image in the middle of the range is twice as sharp as the image at the endpoints of the range. This effect is most pronounced when working with longer focal lengths. This is because the best possible sharpness is already low enough at f/64 for there to be a possibility of it being visibly degraded, which in turn enables you to see variations in sharpness throughout the image. If you are photographing an image that is flat enough to permit f-stops in the range of f/16, then everything will be so sharp that you will not notice the delineation between the different areas.
If you would like the middle of the distances in your photo to be rendered with a bit more sharpness as opposed to the far and near points, then you may want to open up a stop on your camera. If you do this, the sharpness at the far and near points will decrease, while the sharpness in the middle will increase slightly. This is probably a difficult concept to understand and visualise, but for the photographer who is proficient in technical aspects, this is a tool that can be used to fine-tune the distribution of critical sharpness.
If one's setup requires a small aperture, one might want to sacrifice overall optimal sharpness in the scene in favour of a wider aperture. This will enable the main subject, if there is one, to be rendered with greater sharpness in the portion of the image that contains the main subject. In order to achieve the look you want, you will need to return to the creative process of experimenting.
Keep in mind that you won't be able to see these effects until after you've compared how sharp the sharp parts of your images are at apertures like f/16 to the diffraction-limited ones made at f/64. Until then, you won't be able to tell the difference.
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Why You Shouldn’t Worry About Sharpness
Before we get started, there is one more thing we need to cover, and that is the reason why attaining maximum sharpness doesn't usually matter all that much. In every scenario, there will be a combination of aperture and focus point that yields the sharpest possible image; however, there will also be an infinite number of other combinations that will produce results that are satisfactory. When compared to an image that is sharp enough, the sharpest possible image can only be distinguished from an image that is sharp enough by zooming in extremely close and engaging in a practise known as "pixel peeping."
Making sure that an image is sharp is only one aspect of producing a high-quality photograph; there are many other considerations involved. An image can be technically perfect without having any artistic merit at all—like all of those extremely sharp, extremely dull pictures of test charts—while an image that is astonishingly creative might be barely sharp at all. The subject, the tones, and everything else that contributes to the wonderful subjectivity of photography play a much more important role than they used to.
There are some circumstances in which having focus, which is, in many respects, an alternative to having sharpness, is important. When taking portraits, for instance, you want the subject's eyes to be the point of focus and, as a result, the sharpest point in the image. However, as long as the image is sharp enough, other things become a great deal more important than the portrait's sharpness alone.
As you continue to read through this tutorial, keep all of this information in mind. Photographers, particularly those who specialise in landscape or architectural photography, can benefit from knowing how to calculate the ideal aperture and focus for producing an image with the highest possible resolution; however, this is just one of the many factors that go into the creation of an image. If you follow the general guidelines that I'm going to go over in this post, you should be able to get an image that is sufficiently, or even extremely, sharp, even if it's not the sharpest image that's technically possible.
The Sharpness Balancing Act
The degree to which a lens is able to resolve details is primarily determined by two factors: defocus blur and diffraction blur. When the aperture is wide open, defocus blur is most prevalent, whereas diffraction blur is most prevalent when the aperture is narrow. It is by striking a balance between these two competing factors, in addition to the required apparent depth of field, that one arrives at the aperture that is best suited to a particular scene. At Wild Romantic, we have the best wedding photographer in Mornington Peninsula to capture every single moment on your wedding day.
Sharpness in the Real World
In the real world, sharpness is not the only thing you need to worry about. When shooting a landscape, rather than a test chart, depth of field is one of the most important considerations. The nearest point of focus is moved from 45 metres to 15 metres when the aperture of the 50 mm lens is stopped down from f/1.8 to f/5.6, which is roughly its sweet spot. Although this is an improvement, it still doesn't give much of a foreground. If you stopped the lens down even further, everything would be within your depth of field; however, if you stopped it down too far, diffraction would reduce the sharpness of the image.
This entire article can be summed up in a single question: what aperture setting should you use when you want your photos to have a shallow depth of field? There is absolutely no issue at all if you choose to keep the aperture set on the camera to f/11, for example, regardless of the subject that you are photographing. Your resulting photographs might not be quite as sharp as they could be, but in most cases, they will be satisfactory. However, if you want to spend some time making sure that your aperture has the best possible ratio of the depth of field to diffraction, the suggestions that are covered in this article are the most accurate methods that are currently available.
Photographers often strive for artistic and technical brilliance. It is wonderful to push ourselves to create the best photographs we are capable of; if nothing else, it demonstrates that we care about the work that we are doing. On the other hand, mathematical perfection is not always required, and there are times when it is not even sought after. If we do not take into consideration the inherent aesthetic qualities of a photograph, none of these technical settings will be able to make it successful.
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If you do decide to use the aperture charts or formulas, you should have a purpose in mind for doing so. Sharpness that is "perfect" is not an end in and of itself; rather, it is a tool that can assist in the communication of your photographic message. If you are planning to make large prints of a dramatic landscape, it is highly likely that you will find these techniques worthwhile. If, on the other hand, you are only interested in photography as a hobby, there is no reason for you to give up the techniques that you already find satisfying.