How Sweet it is? or Isn't?

I liked this topic from an earlier post that I'd thought it'd make a great article to interact on and for all to share their thoughts--the sweet spot of a lens--but to take it one step forward on how you can use it to your advantage

Back to the ranch--Every professional photographer understands that all lens, with a few exceptions like Leica, have a "sweet spot" or an optimum aperture that provides the sharpest image over the entire range of that lens' particular aperture range (range of F/stops). There are many myths or perceptions as to what a lens' sweet-spot is or isn't, but in reality, if you check the manufacture's specifications of every lens or have an accurate bench-test method with scientific eqiupment you'll learn that the sweet spot varies from lens to lens and from manufacturer to manufacturer.

First, let's look at the legend and a fact--Leica. Leica invented the 35mm format, not Kodak. Kodak invented film. According to Leica, most Leica lenses have a sweet-spot throughout the entire aperture range. Leica even makes an F/1.0 lens--they have the best glass and people in the photo industry acknowledge this, they also are appropriately priced. The old adage, you pay for what you get applies here, though there are many other brand name lenses that are expensive too, and the price doens't necessarily make a lens have a broad sharpness range throughout all it's apertures. With that said, the entire range of F/stops (apertures) on a Leica are sweet and there are also other manufactures with sweeter lenses too, though many fall behind.

Now let's look at the myths or perceptions--

1. Many say that the sweet-spot on a lens is two to three stops up from the widest aperture of the lens. While this could be, it's not scientifically proven, only a perception.

2. Many say the sweet-spot on a lens is F/8 to F/11, again, this is not scientifically proven, only a perception which is further instilled by the world-wide photojournalist's motto, "F/8 and be there!".

3. Many say it's the middle F/stop of the lens, again, this is not scientifically proven, only myth.

4. Zooom lenses have a better sweet spot at the middle focal-length, middle aperture, i.e., a 70-200mm zoom has the best sweet spot at 140mm at the middle aperture, again, this is not scientifically proven, only myth.

Now, with all the four most common myths outlined, let's look at a lens with the maximum aperture of F/2.8 and a minimum aperture of F/22, focal length of 70-200mm (non-Leica). If we apply myth #1, then the sweet-spot will be between F/5.6 to F/8. If we apply myth #2, the sweet-spot will be F/8 to F/11. If we apply myth #3, the sweet-spot is F/8. If we apply myth #4, the sweet spot for the lens is at F/8 at 140mm.

What all three myths have in common is F/8. Remember, "F/8 and be there?" Nope, that's not why, so don't go there, that has more to do with exposure and the Sunny Sixteen rule and the old days of Tri-X pan film--another article to come!

The whole concept of the sweet-spot is the characteristics and physics of the lens as all lenses have a sharper center with the edges becoming softer and because of this, their sharpest point is not wide-open, and at smaller apertures the lenses suffer from diffraction. When shooting glamour, this can come in handy, especially when you have an older subject or someone with not so porcelain skin. Why make imperfections sharper? You can use the knowledge of the sweet spot to avoid it, thus adding another layer of make-up without the powder.

There are so many variables that determine the sweet-spot, focal length (magnification), zoom vs prime, glass quality, resolving power, contrast of the lens glass, longitudinal and lateral chromatic aberration, refractive index, low-dispersion glass, volume of fluorite in a lens, diffraction and accutance. Lens manufactures have to comprise based on costs and economies of scale--with the latter they often make compromises to deliver a competively priced product. You can use this compromise, or the fact that most lenses have a super-sharp and not so sharp spot in your favor. If you're shooting a product or some type of macro/micro shot, obviously you go for the sharpest part, but as outlined before, not necessarily for glamour, or for that matter people portraits.

If you're shooting a male subject and you want the distinct masculine character, shooting at the sweet spot is the way to go, but if you have a female subject, keep it more soft, smooth and feminine. You can do this many ways, and they all help each other. First, shoot with a softer quality of light, second, great make-up, third, a great model, and fourth, stay away from the sweet spot, shoot with a wider aperture and with longer lenses you have a naturally reduced depth of field (DOF), thus if you focus on the eyes, they'll be sharp while the cheeks fall off softer.

While it's important to know your equipment, it's also important to focus on your photography and not get too wrapped up in scientific data--unless you're a forensic photographer.

You won't go wrong estimating the sweet-spot at F/8 on most lenses. In the end, the manufacturer's data sheets provide a more specific "optimum aperture" for their specific lens--or the compromise between chromatic abberation and lens diffraction. Trust me, it's in their engineering notes and probably filed with their patents. But your focus should be what to keep in focus. Before you even start a shoot, you should've already taken the sweet spot, out of habit, into consideration and use it to your advantage whether it be to shoot at the optimum aperture or to stay away from it.

As with all camera adjustments, one change affects other elements, such as dept of field, more or less light, blurred images, sharp images, etc., and the aperture is a major role in those considerations, more so than, "Am I at the sweet spot?" Keep shooting, rg sends!