f-stop understanding

October 25, 2015  •  Leave a Comment

Nope, it’s NOT a ‘dirty word’ and is something everyone behind a camera should learn. They are one of the most commonly questioned, and misunderstood… and misused, parts of photography. Basically, the f-stop is simply THE SIZE OF THE OPENING INSIDE THE LENS, and the amount of light that lens is capable of allowing through. On still cameras, it's usually referred to as 'aperture,' whereas on video cameras the same thing is called an 'iris.' It all boils down to the SIZE of the hole that allows the light in. The bigger the size, the smaller the number... which is logically opposite of what most people think, but it's been that way since the beginning of cameras and photography.

Again, opposite of common sense and normal logic, the smaller the f-stop number, the wider the opening, the less light is needed for a shot… the faster your shutter speed can be, or the lower your ISO, for the same amount of light. The larger the number, the smaller the hole… the less light is allowed through… the higher your ISO or slower your shutter will need to be, to get the same image. But the f-stop is vital in professional photography, and PURPOSEFUL BLUR of the foreground or background.

If you understand the ‘exposure triangle’ – then you know that you have to PICK THE ANCHOR POINT: if you’re shooting moving objects you don’t want blurred, then shutter speed should be your 'anchor point.' The most important factor of your shots at that time, for that subject, for that day, regardless of the amount of light available... if you are attempting to stop motion, your shutter speed is the key, with very few exceptions, unless you want blurred movement. If it’s still objects, then shutter speed is only important if you’re shooting freehand (or while moving), and aperture is your anchor point. ISO is almost always the variable, adjusted based on the goals (and needs) of the other two points. The aperture is a key part of photography, and ultimately one of the most powerful tools to master.

There are plenty of ‘visual’ examples on the internet about what ‘size’ comparisons of different f-stops are. For sake of argument, f/1.4 is wide open… say the size of a silver dollar… depending on the width of your lens (circumference) it will vary from lens to lens, which directly varies based on focal length (mm length of the lens) AND aperture, it might be even bigger in reality.  Whereas f/22 is about the size of the lead in a pencil, and f/36 about the size of a sewing needle. In general, the wider the aperture, the smaller the number (f/1 being the smallest and most expensive, and rarest).  The average person is stuck using f/3.5 or greater, with some ‘professional’ lenses still in the 4.5 – 6.3 range for their minimum aperture size because of their focal length (at costs under $20,000 for a single lens).

The circumference of the lens, and the aperture setting options, help determine a lens’ ‘drop off’ – not just ‘DOF’ (depth of field)… but also, just how FAR that ‘blurred’ (or Bokeh) area really can be. That all gets into some wild math, and often times requires either years of experience and repeated testing & practice… or a DOF Calculator… to really ‘plan’ a shot with.  For the sake of example, and the primary purpose of this post, is to get a person thinking… and hopefully wanting even more information. When in doubt, USE A DOF CALCULATOR (really, there are free apps available for all 'smart phones.'

When you see those amazing big blurred circles of lights behind a subject, the person behind the camera likely DID THE MATH (or has the experience) to create the Bokeh. It is real rare with 'stock' lens (glass), and requires a great deal of practice to consistently recreate it, if your widest aperture is 3.5… but very easy if it’s 1.2 (and nearly impossible to avoid it).

Each indoor location and activity is slightly different, but in general… to get the subject in focus, and blow out (blur) the crowd in the background:

  • f-stop: 1.2 to 4 is usually preferred (though few people can afford lenses below 2.8 or 3.5)
  • Shutter Speed: 250 to 400 preferred, for action (like basketball or football, faster for hockey & volleyball)… tough to go below 1/60th if there is movement, unless you want to blurr it (like I regularly do with a drummer’s sticks… depending on the speed of THEIR HEAD movement, I’ll usually shoot them at 1/8th, 1/10th, or 1/15th, seldom over 1/30th... regardless of the focal length of the lens I'm using).
  • ISO: 100 to 3200 preferred, without strobes (flashes) or just awesome lighting, it’s rare most people can get below 1600 ISO in low light situations without a flash… and some are up past 6400. (I've lit up audiences in low light with ISO speeds of 25600, but the images weren't as sharp as I would get at 3200 or less and a defused flash.)
  • Focus – spot, AI or Servo when possible with constant refocusing on moving objects, and learn to pan WITH the moving subject. (Personally, I shoot with both eyes open at most sporting events & concerts, and usually SPOT FOCUS, though if they are really moving fast & often I'll switch to AI... and usually only use 'servo' when using the dSLR for video)

Most concerts, basket ball games, and assorted other sporting events don’t want the participants blinded by a flash, thus not allowing a flash to be used. Believe me, you don't want some athlete, their parents, team, or coach blaming YOU for their player missing a vital shot because your flash blinded him (or her). Therefore, learning how to shoot without a flash (and still get the shot) is vital in many indoor environments. Some performers have literally STOPPED THEIR SHOW, and had someone popping flashes talked to (or kicked out)… because they don’t want to fall off the stage because they blinded by the flashing.

I’ve also been in museums (Bitmore Estates, being one) that will NOT allow any flash photography, at all… PERIOD… inside, as repeated bright flashes can degrade the colors in the paintings, etc. So, again, learning to shoot without a flash enables you to make captures when most people are told to put away their cameras. It helps distinguish between a beginner and experienced photographer.

Having the ability to control the settings of your camera is vital… having the practice and knowledge of what those settings do is even more important.

The cool part about digital… you can practice to your hearts content… and delete the failed attempts. Make a note of what works in which settings, and how those things effect the shot. You’ll pick it up pretty quickly… IF you pay attention.

“F8 And Be There!” For years, this was the cry of the photojournalist. It meant that a great photo was being prepared, in the right place at the right time, with a focal length set to F8 for the sharpest image (most reasonable DOF)... and 90% of the time those film photographers would 'get the shot.' True, it was simplistic, but in the Age of Photoshop, this maxim is too often forgotten… and proves that most of the outdoor photography doesn’t necessarily require a massively expensive hunk of glass. No matter how much you play with the bits and bytes, the best images always start out with a great vision, clearly and cleanly seen.

Be in the right place at the right time… prior planning, practice, and placement are key to most all action photography. Set your camera to “Program” (or MANUAL MODE, once you have enough experience)… adjust the exposure triangle, and GET THE SHOT. Back in the days of film, the right film (ISO) had to be loaded before anything else, not so with digitals. Also, contrary to what some pros claim (jokingly or seriously), the “P”, which stands for ‘Program,’ doesn’t stand for “Pro Mode.” Being ready and where you need is far more important than fretting over your camera’s settings (past ‘to flash’ or ‘not to flash’ – and how do you accomplish that). Though the 'A' mode is still pretty much the 'AMMATURE' mode, because other than where to point it... and when to click that shutter... the camera is doing all the thinking for you; even when it thinks a flash is necessary. You might get some good to great images, but you'll never learn to get them consistently... or how to shoot where a flash isn't allowed... or how to deal with motion, purposeful blurs, or shooting through obstructions.

Learning to play with the manual settings really helps change the photo. Aperture & Shutter Speed are the most important… ISO, WB (white balance), EC (exposure control), and focus points (and type: one spot, AI Focus, AI Servo) are also important, and will drastically alter the end results… as is shooting RAW (rather than JPG)… all of it adds up to something that will effect what can be accomplished in post processing.

Happy Shooting… and Best Wishes.

If this helps you, PLEASE SHARE with your photography friends. And check out my photography pages on facebook (likes on my website home page).

Terry Mercer
~ More than Just a Camera Guy


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If you have any questions about photography, please feel free to ask. I might not know the answer off the top of my head, but odds are I can either help you find the answer or know someone that knows the answer. After nearly 45 years of playing with hundreds of different cameras, both film and digital, I probably don't know specific 'make and model' info... but I UNDERSTAND PHOTOGRAPHY, and the PRINCIPLES & CONCEPTS of capturing and creating good to great images.
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