Novices to experienced photographers may be surprised to know that there are many different factors that influence your overall image sharpness. Here is a brief summary of each area that can potentially affect your image clarity.
I. Shutter speed - Shutter speed is probably the first thing most of us think about when shooting tack-sharp images. Our first lessons in SLR photography are how camera shake and movement can ruin a picture if your shutter speed is too low. For more information on shutter speed and what your minimum shutter speed should be, check out our article Shutter Speed Guideline – The Reciprocal Rule.
II. ISO - The second thing that may come to your mind is your ISO setting. While ISO speeds up the process in which your film/sensor absorbs light, it also adds grain to your image. This grain destroys detail/sharpness in the image. The higher your ISO setting, the more detail is destroyed. New professional DSLR cameras such as the Nikon D700 and the Canon 5D Mark II (and higher models) can shoot at much higher ISO settings while retaining much of the image detail. However, with the proper lighting, it is usually best practice to shoot at the lowest ISO setting possible.
III. Lens quality - The quality of the “glass” (lens) contributes to image sharpness, contrast and saturation. For the most part, professional series Nikon and Canon lenses produce sharper images than cheaper lens models or third party lens manufacturers. However, this generalization does not apply to all lenses, and some tests for select lenses have claimed better overall sharpness from third party manufacturers than their Nikon or Canon counterparts. Does this mean you should buy third party glass? Usage and budget are important factors; but keep in mind that cheap glass, in general, will already put you at a disadvantage when trying to create tack-sharp images.
IV. Image area - In composing your shots, keep in mind that different areas of the image will be softer (less sharp) than others. The center of your frame will always be your sharpest point, while the image will only get softer as you continue to the edge of the frame. While shooting your subject off-center for composition purposes is often necessary, it isn’t in your best interest to compose shots carelessly because you are relying on cropping the image down in post production. In general, areas away from the center will be less sharp relative to the center at wider apertures (F1.4, F2.8, etc), while areas away from the center will have similar sharpness as the center at smaller apertures (F8, F11, etc).
V. Aperture setting - Aperture is probably the last thing you would think of when it comes to obtaining tack-sharp images. However, it is one of the largest determining factors of shooting tack-sharp images. We all know that aperture controls your depth of field. However, did you know that shooting the exact same shot with the exact same focal point will yield different levels of sharpness on your focal point at different apertures? For example, if I focus on the nose of a face at F1.4 and with the exact same exposure value and composition, shoot the same face at F4.0, the nose will actually be sharper in the image shot at F4.0. This is simply because each lens has a “sweet spot.”
Shooting at your lenses sweet spot will improve sharpness, contrast and saturation. Now you may be thinking, “well how do I find the sweet spot on my lens?” There are several rules of thumb, but the most prevalent is that your sweet spot is around 2 full stops above your lens’ minimum (widest) aperture. Depending on the lens, this will be in the range of F4-F11 or so. Keep in mind though, raising your aperture too high (small) will result in aperture diffraction, another phenomenon that will reduce overall clarity. For more information on diffraction, read our article Avoiding Aperture Diffraction.
One last thing, before you go shooting all of your images at your “optimal aperture” setting. Keep in mind that composition always rules! If blurring the background to make the subject “pop” is part of your look and composition, then shoot the lowest aperture possible! A well exposed composition shot at F1.4 will still be plenty sharp for any purpose, it just may not be considered “perfectly tack-sharp.” However, we should always think of composition first, and when appropriate keep your aperture within its sweet spot.
Last but not least, Digital Photography Review has an amazing widget that allows you to check out the sweet spot on pretty much any lens.
Article written by:
Lead Photographer | Partner
Lin and Jirsa Wedding Photography