Ever wondered why your cameras sharpness seems to vary from shot to shot. One shot would be tack sharp, another shot just didn't have the same sharpness and would be a little murky . While there are many factors that affect an image sharpness, you can increase your chances of a tack sharp shot by knowing your lens' sweet spot.
That's right, every lens has a sweet spot. The sweet spot refers to the aperture setting of a given lens that yields the best overall sharpness. The fact is, that lenses are not uniformly sharp at every aperture, nor at every focusing distance.
So how does one go about identifying a lens' sweet spot?
Here's what you'll need:
1. DSLR Camera w/ a self timer
2. A Tripod
3. Newspaper or sheet of paper with printed text on it.
Now, tape the newspaper to a wall making sure that it's as flat to the wall as possible. If the light is required then set it up and shine it on the newspaper. Next, set up your tripod with the camera on it at a distance that will allow you to fill the frame with the newspaper. Set your camera on aperture priority mode. Set your aperture to the maximum that the lens will allow. Depending on the lens that you are working with, the minimum and maximum aperture values will be different.
For the purpose of this article I will be using the Canon EF 50mm f1.8 II.The maximum aperture of this lens is f1.8 and the minimum aperture is f22. Next, focus the lens on the newspaper. For each shot we will us the cameras built-in 2 second self timer function to prevent any vibration caused from pressing the shutter . Next we want to take a series of images carefully adjusting the aperture down by one stop at a time (example – f1.8, f2.8, f4.0, f5.6, f8.0, f11, f16, f22). Once we have completed each of the exposures it’s time to download the images to our computer and have a look!
The above image shows 100% crop examples taken from the top left corner of each of the images.
F1.8 is downright fussy & soft.
F2.8 is better, but still soft.
F4.0 is much better.
F5.6 better still!
F8.0 Now that's sharp as a tack.
F11 softening a bit.
F16 still softer.
F22 softer still.
Well based on results from the above examples, this particular lens offers the best overall sharpness at F8.0.
For the Canon 50mm f1.8 - The SWEET SPOT is F8!
Now go ahead and test all of your lenses, and identify the "sweet spot", the results may surprise you!