"Understanding Exposure - Seeing the Creatively Correct Exposure"

[Amnesia180]

Hi there...

Firstly, I'm not sure wether this should have gone under the Critique Corner section.... so if it was supposed to be there - Could a mod please move it

I've been following the "Understanding Exposure" book by Bryan Peterson, and I've got to the Exercise labelled "Exercise: Seeing the Creatively Correct Exposure".

I've taken photos of my little sister as a Portrait, Jumping and photos of running water.

The water is a write off - because I only have a built in flash, and the room was so dark - they aren't worth viewing.
I understand the concept that the widest aperature (smallest number) makes the water look like it has stopped still, because everything is in focus and the shutter speed was fast enough to capture it all. And the smallest aperature (larger number) makes the water look like it is flowing...

The photos of my sister jumping - Haven't really come out very well. There was too much background, and they all look very much the same!

However, the ones I am looking for comment on are of the Portrait photos.
I understand I didn't use a flash.. and the light isn't shining properly - It's getting late here and sun is so low that it's not reflecting off anything with enough background... so I've tried my best.

I've started with the lowest f-stop that my lens will allow - which is 3.5. I've then gone up one stop each time, adjusting the shutter speed as necesary. (All is done in Manual [M] mode).

Photo 1 - f/3.5 ... 1600
Photo 2 - f/4 ... 1250
Photo 3 - f/5.6 ... 640
Photo 4 - f/8 ... 320
Photo 5 - f/11 ... 160
Photo 6 - f/16 ... 80

Thanks in advance...
Amnesia

p.s: I'll re-edit this post tomorrow. I have an artificial flower/bush thing which I'm going to put in the same location as my sister is sat, but I'll do it straight from work - the light will still be out then (or in my lunch hour)...

[evandavies]

Hey Dan,

I think you will learn very fast as you are going through step by step to learn the basics properly unlike some who just snap away hoping to get a good shot.

You have understood the need for longer exposures at higher f/stops and you can clearly see the background getting sharper as the f/ goes up (aperture gets smaller)

It will be harder to get nice blurred bg (Bokeh) with a minimum f/3.5
Maybe try and get a bit closer and get the backround as far as possible.
Is the lens as wide as possible?

Good going...

[Amnesia180]

Hi Evan,

Thanks for the reply...
Yes, the Lens is as wide as possible. I am fully zoomed out (to 18mm... it's an 18-55mm lens) and it only goes down to f/3.5

One thing I don't understand - How come when the f-stop goes up (number gets bigger, aperature gets smaller)... the picture becomes clearer?

I think that is explained in the next chapter "Depth of Field".... maybe I'm just jumping the gun

[evandavies]

I'm sure your book will explain it better but in brief...

In the early 19th century lenses were the length of the focal length. ie. a 100mm lens was 100mm long. This was obviously inconvenient so by adding more elements they could shorten the lens but this increased the amount of light travelling through so a diaphram was introduced to control the light.

The f/stop is a fractional representation of aperture times focal length.
Thats why f/stop is written as f/2.8 It actually means 1/2.8
Or to put it in a more practical sense f/2.8 means that the Aperture is 1/2.8 times smaller than the focal length.

Example: lets say we have this lens:
Focal length = 50mm
f/stop = f/2.8

To find the aperture:
Focal length / f/stop = aperture
50 / 2.8 = 17.857mm aperture

To find f/stop:
Focal length / Aperture = f/stop
50 / 17.857 = 2.8

Finally to find Focal length:
f/stop x Aperture = Focal length
2.8 x 17.857 = 49.9996mm = 50mm (slight inaccuracy due to rounding down f/stop value above)

An interesting thing to note is that these calculations assume the diaphram is at the front of the lens. As this is not how lenses are made and the diaphram is usually near the back of the lens, the actual diameter of the aperture will be smaller than the calculation.

[AdamLM]

Originally Posted by evandavies

It will be harder to get nice blurred bg (Bokeh) with a minimum f/3.5

In this case, I think it's a function of the wide angle lens not f/3.5...
(evandavies, I'm sure you knew that but that might confuse Amnesia180 who seems pretty new to the concept.)

Originally Posted by evandavies

Maybe try and get a bit closer and get the backround as far as possible.

...but this is the way to throw the background farther out of focus and keep the same focal length.

[mavericksupersonic]

Amnesia,

You might want to consider picking up a 50 f/1.8 lens. They are very cheap and will allow you to learn about DOF and bokeh much better than the kit lens.

For the now, i would suggest that you zoom all the way out to 55mm and get as close to your sister as possible. Even though you will have your aperture set to 5.6, you should get better bokeh. Also, the more distance you can put between your sister and the background will help improve the bokeh.


Also, for your waterfall comments, even though you are correct about what is going on with the aperture, it is really the shutter speed that is changing the motion/non-motion of the water. The longer you expose, the more flowing your water will look. The shorter you expose, the more still it will appear. Chaning the the aperture is automatically changing the shutter speed to give you proper exposure and this creating the motion/non-motion of the water. The correct way to think about this though is that you need to change your shutter speed to convey motion.

[form]

Shutter speed is the duration that the sensor is exposed to the light.
In that manner, it is an opposing factor relative to the aperture; but, unlike the aperture, it has no influence on DoF.
It affects how bright a scene is, and how motion is captured.

Focal length is the multiplication factor of the lens. It affects DoF and how close objects appear.
The longer the focal length, the shorter the DoF.
Focal length also affects perspective, which influences how proportion and angles are interpreted relative to the distance of an object from the lens. The shorter the focal length (AND the closer the object), the greater the effects of perspective distortion are.
Focal length has no effect whatsoever on amount of light gathered, or how motion is captured.

The aperture limits the rate at which light is allowed to pass through the lens.
The wider the aperture, the shorter the DoF.
The aperture has no direct effect on stopping motion, but smaller apertures force slower shutter speeds in order to capture the same amount of light.

As far as I understand it, the goal is to make the face or person the primary point of interest by making backgrounds less distinct and, consequently, less distracting. The face also must not be affected by perspective distortion, which could make a nose or other protrusive feature that is closer to the lens appear larger and "less flattering."
Ideal portrait lenses are usually rather long (85mm or greater, according to what I've read) and have large apertures. This combination allows for narrow DoF and negligible perspective distortion.

[Meaty0]

Well getting back to your photos Amnesia. I'm not sure if they are loading correctly, but it looks like I'm only getting the top half of your sister. Portraits (mostly) look best taken in portrait orientation, rather than landscape. (Well D'uhh )

I like the one taken at f/3.5 best because it does have a slightly blurred background to throw emphasis onto the subject. It's hard when your subject is so close to the background. You really need to shoot about f/2.0 to get the effect you need. (A 50mm f/1.8 Lens isn't too expensive you know )

Now I have a question for you. How did you get your sister to pose so patiently?

Paul

[Amnesia180]

I will read through all the replies later.. I'm at work at the moment and a bit pressed for time! I Really need to absorb the information...

However, in answer to Meaty0... I do prefer the one taken at f/3.5 aswell - but that was mainly an exercise to see the different effects by putting the aperture down a stop each time.

I don't know how I got my sister to stay so patient... I had the camera on my tripod, and knew which aperture I was changing to - so I tried to do things as quickly as possible.... However, she did get up from the seat once!