aperture

I think trying to teach a new photographer about exposure by telling them about diffraction and collimating while engaging a lot of hand-waving about depth-of-field and "bokeh" isn't helpful.

Here are the basics:

Aperture means "opening" or "hole".

Your camera has an opening that allows light to enter when the shutter is open.

Bigger hole - more light.
Smaller hole - less light.

Aperture is expressed in terms of f-numbers.

Bigger number - more light.
Smaller number - less light.

A common series of f-numbers is: ... f/1.4 f/2 f/2.8 f/4 f/5.6 f/8 f/11 f/16 ...

Numbers are larger at the beginning of the series and smaller towards the end.

f/4 is greater than f/8 in the same way that 1/4 is greater than 1/8 or 93 is greater than 50.

Each number represents an opening that lets in half as much light as the greater number to its left and twice as much light as the lesser number to its right.

This change of double or half as much light is called a "stop".

Each number in the f-number series above represents a change of 1 stop: the difference between f/4 and f/5.6 is one stop; the difference between f/8 and f/16 is two stops; the difference between f/2 and f/5.6 is three stops.

The shutter speed of your camera is the amount of time the shutter stays open and admitting light when you're taking a photograph.

Long time - more light.
Small time - less light.

By expressing shutter speeds as fractions of a second that form a series in which each speed is half as long as the one before it and twice as long as the one following it we can express shutter speed in terms of stops also.

That means if we take a shutter speed and aperture value and change them so that the shutter speed lets in twice as much light as before and the aperture lets in half as much light as before, the same total amount of light enters the camera.

If we want to change the amount of light entering the camera, we can change the shutter speed, or the aperture, or both.

Finally, ISO is a measure of how sensitive your sensor (or film) is to light.

Higher ISO - more sensitive.
Lower ISO - less sensitive.

ISO is also expressed it stops so you can think of ISO in the same terms as you'd think of your f-number of shutter speed.

A camera set at a constant f-number and shutter speed will produce a brighter photograph when set to ISO 400 than it would when set to ISO 200, and it will produce a darker photograph when set to ISO 100 than it would when set to ISO 200.

Aperture, shutter speed, and ISO are the 3 primary ways of controlling exposure. They are all expressed in stops allowing you to balance them to get your desired photograph.

The secondary effects of these 3 things are (simplistically):

1: A change of aperture results in a change in the size of depth-of-field. Larger apertures result in smaller depths-of-field.

2: A change in shutter speed results in a change in the amount of motion blur due to the movement of the subject or the camera. Higher shutter speeds result in less apparent blur due to motion.

3: A change in ISO results in a change in the amount of "noise" in the image. Higher ISOs result in "noisier" images.

These secondary effects are greatly simplified and should not be considered true in all cases, but they are sufficient for someone to begin learning about exposure.

Promac wrote: »

The thread is specifically about aperture. Not exposure nor shutter speeds nor ISO settings. If anyone's confusing the matter it's you and as Chorcai rightly pointed out, bringing up shutter speeds or any other part of the process will only make thing worse. You've added nothing on topic that hasn't already been said and then went off on a big essay about things that no-one asked about after insulting most of the people who posted in the thread before you.

There is no practical purpose to talking about aperture in isolation when someone is trying to learn about exposure.

The thread also wasn't about depth-of-field, but that didn't stop people posting various diagrams and descriptions attempting to illustrate that concept.

Frankly, it was the suggestion of ignoring shutter speed that prompted me to write that "big essay" that will be of far more use to anyone trying to learn about aperture for the purposes of a basic understanding of exposure and while I realise the thread was started by someone wanting answers to questions specifically about aperture (which many people repeatedly answered with minor variations on a similar theme) they didn't need to know about lasers, and bullets, and "bokeh"; they needed to know about exposure. The "big essay" I wrote answers the OP's specific questions and places aperture in context of exposure and if you feel what I wrote was personally insulting I think you need to read this.

There's no better way to air a group of people's misunderstandings about something this simple than asking a basic question about it.

You know what - forget it. Narked out of another thread by charybdis.

Promac wrote: »

Again, the OP didn't say or imply anything about exposure - just aperture. And a logical extension of a thread about aperture is why you would use it in most circumstances - i.e. to produce a nice bokeh effect by way of a shallow depth of field.

Then you come along, declare everyone to be wrong and that discussing the effects of various aperture values isn't helpful and decide that what the OP actually wanted to know about was exposure. Did you read the first post?

I did read the first post, and I answered every question the OP asked therein.

A logical extension of a thread about aperture is how it affects (or effects) exposure.

That's not what "bokeh" means.

Again, I didn't give the OP just what they wanted, I gave them what they needed.

Promac wrote: »

You know what - forget it. Narked out of another thread by charybdis.

You can keep acting like a victim whenever you take issue with something I've said and I respond, but I don't think it'll help your argument and any rational person should be able to see I'm being perfectly reasonable in what I'm saying.

Promac wrote: »

It's nothing to do with being a victim - I'm a big boy, I can take a slaggin off. It's about you coming in with an attitude problem, insulting people who are only trying to have a discussion and mouthing off about "You're all wrong, I'm right and even the person who asked the question is wrong cause they should've asked the question that I answered anyway".

You're an odd mix of troll and know-it-all and I really should know better than to let you get a response from me.

I'm not trying to insult you. There is a difference between criticism of something that has been done and ad hominem attacks. My suggestion that a lot of what had been said so far in this thread probably isn't helpful to someone trying to learn about aperture would be an example of criticising something that has been done; calling someone a "troll" and "know-it-all" in circumstances such as these would be an example of an ad hominem attack.

Promac wrote: »

We're not having a debate here - I've no need for any kind of ad hominem tactics to win any arguments. Who's playing the victim now?

I don't know, but then again, I wasn't aware we weren't having a debate.