Photo Tech Talk-Basic Concepts in Photography, Part 1

 

911 Museum

If you can’t explain it simply, you don’t understand it well enough.” -Albert Einstein

Why is it a “stop”, leading to ƒ-stop? Stop down?
   Aperture rings on older lenses would click and the iris stops at the aperture you want. All 3 functions of the Exposure Triangle, Aperture, Shutter Speed, and ISO, their changes are all described as “stops. 1/50 of a second to 1/100 of a second is one stop, f/2.8 to f/4.0, ISO 200 to 100, all are one stop changes, and all are equal in that these examples I just gave, all reduce the brightness by exactly 50%. Stop down means reduce the amount of light.

Confusing part for beginners: aperture is a fraction! (¼ is a larger number than ⅛, so the aperture is wider at ƒ/4 than ƒ/8).
    You instinctively know that ¼ is a bigger number than ⅛ so of course f/4 is brighter than f/8, and wider. Tech alert: the stops are each multiplied by 1.4, the square root of 2, to get the next stop (with some rounding off). 1.4X1.4 is 1.96, but we round up to 2!

Even experienced photographers, though, can miscommunicate. Some say “Use a high aperture, use a low aperture”. What they might mean is “high aperture number”, like f/22. 22 is a higher number than 2.8 but only if you don’t think of it as a fraction. Better to say “use a wider aperture”, and let them figure it out! “Stop it down” always means close the aperture down (or shutter speed or ISO) to allow less light
    The ƒ/stop scale: ƒ/1.2, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45.

“Normal” lens? Why is it called that?
    50mm is the same angle of view as your eyes see, so it's called "normal".

What’s a “fast lens”. What’s fast about it? It does fast autofocus?
        A wider aperture allows you to use a faster shutter speed (to stop the action/get a sharper image).

What’s “Full Frame”? Yes and No!
    35mm sensor size (actually 36x24mm), same as a 35mm piece of film. That's not the whole story, but good enough for government work!

Crop Factors, APS-C Sensor: 1.5 (Sony/Nikon), 1.6 (Canon)
    You take a 50mm lens and put it on an APS-C sensor camera, what is your actually focal length? 75 for Sony/Nikon or 80 for Canon. On a Micro 4/3rds camera? Micro 4/3rds is a 2X Crop (a 50mm lens would actually be an actual 100mm).

Medium Format (Film): 6x4.5cm, 6x7cm, 6x9cm
    For digital it depends on sensor size, but for medium format film cameras it would be “Half + 10%”. So for a 50mm lens it's 25 + 2.5=27.5mm! If you have a 90mm lens it's 45 + 4.5=49.5mm.

ETTR exposure compensation
    It means "Expose to the Right". If you look at your histogram, 80% of your photo file size is in the brightest 20% of your histogram. So a bright photo will have more information, and be megabytes larger, than a dark photo, allowing you to make larger adjustments-bringing up shadows more, recovering the highlights more, without introducing more noise, and your image will look better as a result. BUT, and it’s a big but, comedy happens, it’s nobody’s fault - only as long as your highlights are not completely clipped, when highlight recovery becomes impossible. You have to try it on your camera, one shot at 0, one at .5, one at 1, one at 1.5, then look at them in your editor and see what works best. Maybe 2 always clips the highlights for you, so bring it down.

ETTL exposure compensation
    "Expose to the Left". You can also override your auto exposure settings and ETTL, expose to the left, when you’re shooting, say, a black horse at night. That should be a dark exposure, for the horse to look black, but your camera doesn’t know that you want that, it’s trying to make everything 18% grey again. You still have to push the exposure in the correct direction manually in these extreme situations.

Holy Trinity
    Three zoom lenses that cover most shooting circumstances, so you are ready for any situation. They are 16-24mm, 24-70mm, 70-200mm.

Three factors that determine Depth Of Field.
    The aperture, the distance from the camera to the subject (macro is tiny), and the focal length of lens (wide is bigger dof, telephoto is less). Rule of Thumb: depth of field, the area in focus is ⅓ in front of your subject, and ⅔ behind, but as your focal length increases it gets closer to 50/50 in front and behind.

Sunny 16 Rule
    On a sunny day, at 100 ISO, F/16, your shutter speed should be 1/100 second for a correct exposure.

Hyperfocal Distance-Simple DOF Calculator app

    How far away your subject has to be, at a given aperture, so that from your focus point to infinity everything will be in focus. Very useful for landscape photography, so you know whether the distant objects are in focus, or not in focus (if that’s what you want). Quite useful for DSLR owners, whereas a mirrorless camera can show you exactly what’s in focus in the viewfinder!

In Part 2 we'll go into Flash Sync Speed, ISO, ISO Invariance, and other topics!