Image Sharpness

Image Sharpness

By William Lulow

We all want sharp images because when we are looking at photographs, we want to be able to see what the camera was seeing. It is sort of like listening to music. We want the instruments to be rendering notes that are true and in tune. That’s why there are musical keys and notes that sound good together. In the same way, camera manufacturers and lens makers strive to produce materials that can render sharp representations.

Now I am allowing for blurry images if they make a point (as in showing speed) or music that is cacophonous to make that point. But generally speaking, photographers want sharp images. Most of us try to make our images as sharp as possible. We use sophisticated cameras and lenses made of high quality glass. We use tripods and extra light to make sure our techniques can produce sharp, easily viewed pictures.

However, there may be times when there is not enough light to allow us to use techniques such as fast shutter speeds, small lens apertures and camera sensitivity settings designed for optimum sharpness. What about those times when photographers need to make images under less than normal lighting conditions? There has always been a term called “sharpness in grain” that referred to a sharp image, but one with more of the film medium showing than would normally be acceptable in a sharp image. GRAIN refers to the minute particles of a light-sensitive emulsion from a piece of film that can show up in a print, even though the print is technically sharp. If there wasn’t sufficient light to allow for normal exposure and development techniques, the film was often developed for a longer time or in a special developer that allowed for an exposure to be made in very low light conditions. Under these situations, a film emulsion like the old Kodak Tri-X, which had a rating of ISO (ASA) 400 could be exposed AS IF it were twice as “fast”, or ISO800! The consequent underexposure could be compensated for by using a special developer called a “fine-grain developer.” Sometimes, this film could be exposed using an ISO of 1600 and processed in an even finer grain developer. Anything to gain a couple of extra “stops” of light sensitivity.

In the digital photography age, camera manufacturers have been able to produce sensors that are capable of recording light waves much dimmer than normal. These sensors are much more sensitive than any film was, so now it is possible to make an image with an ISO setting of 12,500 or greater. I have made many images with an ISO (sensitivity setting) of 2500 or even 4000 and the images are pretty sharp, even amazingly so. But when you trade lower ISO settings for higher ones, you will always lose a bit of sharpness along the way. The question is: How much loss of total sharpness is acceptable to produce an image that is still considered a “good” one?

Here are some examples of images shot with high ISO numbers:

Shot with my Canon 90D, 135mm f/2 lens, f/4.5 @ 1/800th of a second with and ISO of 4000!

Shot inside a circus performance Canon 90D, 135mm f/2 lens, f/5.6 @ 1/250th of a second, ISO 2500.

Do you think these ISO numbers are producing sharp enough images?

This one was made with the Canon 135mm f/2 lens, f/9 @ 1/400th of a second, ISO 1000.

I have enlarged each of these to several sizes: 8×10″, 11×14″ and one to 16×20″. The largest one shows some “grain” (called “digital noise” as a way of indicating that it really doesn’t resemble a continuous tone image). But digital noise is not quite the same thing as grain in continuous tone images. It appears to be more tolerable.

This is a framed 32×44″ image of Jerry Garcia shot with my old Nikon F, my old 50mm f/1.4 lens, on Tri-X film rated at 400 ISO. It is a huge blow up from a single frame of 35mm film and it shows some grain, but certainly not enough to degrade the image.

When I shoot in the studio, by contrast, my settings are ISO 100, f/11 @ 1/125th of a second, Canon 85mm f/1.8 lens. Here is an example:

Everything is tack sharp and so is an 11×14″ enlargement. My Canon 90D digital camera has a 32MP sensor which renders details extremely sharp. I have compared some of the images I get with what I used to achieve with film and they are every bit as good. Here is an image from a frame of Kodak Tmax film rated at ISO100 (shot with my old Hasselblad, medium format camera with a 150mm Zeiss Sonnar, f/4 lens in the studio):

Here, every single pore on the model’s face is sharp. This is the kind of sharpness I expect from my digital equipment today, and with studio settings, it is always possible. (The lenses for Hasselblad’s medium format 2 1/4″ square film were the normal 80mm Planar, the 150mm Sonnar, and the 250mm Sonnar.)

Remember, the lens focal length has something to do with sharpness as well. Wider angle lenses of course, render scenes sharper than telephotos. But a good telephoto lens used correctly (stopped down a few stops and supported with a tripod or monopod) will yield much sharper images. You often don’t want to use a long telephoto for portraits because, depending on aperture settings, you might not get the entire face, head and shoulders in perfect focus due to the shallower depth-of-field of these lenses. That’s why I almost always use the 85mm (medium telephoto) lens for my studio portrait sessions and it is almost always mounted on a tripod.