aperture

youllneverknow

iv a few questions about it.
1. what is it?
2. is it an f that stands for aperture?
3. is it a higher value gives a wide view and the lower it is the narrower
4. when would you use thisaperture?
5. did i spell aperture right?

vectra

Bit of a description here that may help you >>>Aperture

youllneverknow

thanks alot

Thecageyone

youllneverknow wrote: »

iv a few questions about it.
1. what is it?
2. is it an f that stands for aperture?
3. is it a higher value gives a wide view and the lower it is the narrower
4. when would you use thisaperture?
5. did i spell aperture right?

1. It's basically how wide the lens opens to let in light. Think of your hand making the "OK" sign, the wider the circle between thumb and forefinger, the wider the aperture, but lower the number.
2. Yup, f/2.8 is a wide aperture. For example.
3. The higher number, the narrower the aperture. f/8 has a much smaller opening than f/2. just think opposite.
4. Indoors, fast lenses that can maintain wide apertures like f/1.8 - f/2.8 are useful. Outdoors in strong sunlight you'd be more likely to use f/8 or narrower. Depending on the depth of field you want/shutter speed/ISO ... there' s many factors.
5. Yes.

vectra

youllneverknow wrote: »

thanks alot

you are welcome

I'm horribly terribly bad at explaining things, but I'll try here.



1. what is it?

A series of 'blades' inside a lens that open/close as you alter the aperture.






(I'm being pretty broad/general here)


2. is it an f that stands for aperture?

Aperture is measured in F-Stops, so yes. If you see f/1.8 - it's referencing aperture.



3. is it a higher value gives a wide view and the lower it is the narrower

A higher F number means the series of 'blades' inside the lens are closed (bigger number = smaller hole) and the lower the F number, the more the hole is open (lower number = bigger hole).


Pretend the camera sends a laser out to scan the room, and that's how a photo is taken. Also pretend you have a person standing in front of the camera and a wall of shelves behind them.

If you have a low F stop (big hole) then you are letting more light into the camera which means you'll be able to use a faster shutter speed, because the shutter will open/close so fast, this pretend laser doesn't have enough time to scan the entire room. Therefore, it only 'scans' the person you focused on and doesn't have enough time to do the background. Because of this, you get a clear person, but a blurry background.


If you use a High F stop (small hole) there is less light getting into the camera and your shutter needs to stay open longer. This means that the pretend laser gets a longer time to 'scan' the scene, and can record the detail not only in your person, but also the detail in the shelves behind him. Everything is in focus.


To be honest, I really struggled with Aperture and it was only when I spoke to Chorcai (a member here) in person that he explained it pretty well to me. The book Understanding Exposure also helped cement it. That said, I always find it difficult to explain things, so the above may make no sense, as it's full of hypotheticals, but it's the best I can come up with off hand.


4. when would you use thisaperture?

With a Low F stop (smaller number; f/1.8, f/4.5, etc) you can use it to make a background look blurred out;



(Using my "laser scans the scene" bollocks above; the laser would be given time to see the insect, but wouldn't have had enough time to travel back enough to catch the background in focus)


Whereas if you use a smaller hole (F/22, etc) then you can get everything from front to back in focus;




So essentially, if you're using a small F number, then you're only going to get in focus, whatever you're focusing on. If you're using a large F number (22, for example) then you should get everything in focus.

5. did i spell aperture right?


Yep



(That whole laser thing was me making it up as i went along, it's not real and i'm sure I was probably fairly inaccurate with a lot of what i said, so hopefully others will correct me and help you out. The pictures/gif were stolen from google.)

magicbastarder

the f-stop is the ratio of the length of the lens to the width the lens opens. so f2 on a 50mm means the aperture is open 25mm, f4 means it's open 12.5mm, etc.

and here's the clever part - the difference in the physical size of the same f-stop on different lenses (e.g. f4 on a 50mm, vs. f4 on a 150mm) is nicely counterbalanced by the fact that the lenses gather different amounts of light, so it means the same amount of light reaches the sensor/film in the end (for the same f-stop selected).

youllneverknow

i understand it now i was thinking it had something to do with the width of the shot

the laser crap was easy to understand thanks.:D:D:D:D:D:D

the_monkey

Deleted User wrote: »

Whereas if you use a smaller hole (F/22, etc) then you can get everything from front to back in focus;

But isn't there a minimum distance from the lens ?

cos i have taken pics of stuff at f/22 but close to the "main object"
and the background has been blurred , not as much as f/2.8 obviously but
still bokeh there.


Is there a formula with focal length and f value the minimum distance
you need to be from the foreground object to also have the background in focus.


cheers

Thecageyone

The magazines always state "back to front sharpness" rather than front to back. They usually recomend f/8 - f/11 for sweet spots

DaireQuinlan

the_monkey wrote: »

Is there a formula with focal length and f value the minimum distance
you need to be from the foreground object to also have the background in focus.

http://www.dofmaster.com/dofjs.html

is a handy reference. you want to find what is called the 'hyperfocal distance' for your lens at a particular aperture. Then everything from a particular point to infinity will be in focus at that aperture.

On a pedantic note, its a common misconception that 'the smaller the aperture the larger the hole'. The aperture is expressed as a ratio, ie f/2.8 or f/22. So its actually the case that the smaller the aperture the smaller the hole, not opposites at all.

Thecageyone

That is pedantic alright. As I just meant, think opposite number-wise. Small number/large hole .. being opposite.

Ghost Train

It's the hole in the front of the camera that the light goes through

DaireQuinlan

Thecageyone wrote: »

That is pedantic alright. As I just meant, think opposite number-wise. Small number/large hole .. being opposite.

Maths obviously isn't your strong suit, is it ? But yeah, it's probably back to front. Or front to back. Or something. I forget already.

Thecageyone

DaireQuinlan wrote: »

Maths obviously isn't your strong suit, is it ? But yeah, it's probably back to front. Or front to back. Or something. I forget already.

Humour isn't yours is it?

I said the thing about opposites earlier, the front to back thing was nothing to do with that. Keep up :P And far as I know, Big and small are opposites, and not much to do with math.

Again ... Small number - Big Hole ... opposite, where's the math?

DaireQuinlan

Thecageyone wrote: »

And far as I know, Big and small are opposites, and not much to do with math.

Ok, thats a good start, now go look up 'ratios' and get back to me. I'm sure wikipedia has a page.

AnCatDubh

keep to the topic at hand folks or step away from the thread.

I won't be asking twice.

Thank you.

Thecageyone

we're talking about apertures ... and how best to explain them to someone who asked. That is on topic is it not? This place does confuse ...

Thecageyone

DaireQuinlan wrote: »

Ok, thats a good start, now go look up 'ratios' and get back to me. I'm sure wikipedia has a page.

That's what I've been saying all along Opposite. Small number, big hole. It's how I 'got' it in the beginning. Hadn't a clue what aperture was just over a year ago.

Thecageyone

Thecageyone wrote: »

That's what I've been saying all along Opposite. Small number, big hole. It's how I 'got' it in the beginning. Hadn't a clue what aperture was just over a year ago.

I'm the same. Hadn't got the faintest Idea what it was in January! It was Chorcai and Understanding Exposure that explained it to me.


Aperture is something That I just couldn't work out in my head. Had no idea what it did or how it affected pictures. Now that I'm aware of it, though, I can't figure out how I didn't understand it at the start. It seems so simple when you've got your head around it.

I do think that visual aids help though. When people take a mathematical approach to a beginner, you just unnecessarily add confusion and make it more difficult (though, that said, I've never been good with numbers).

youllneverknow

mention maths and i get confused lol

i seem to understand it the bigger the f/value there less light let in. and you can use faster shutter speeds.
the lower the f/value the bigger the hole and more light is let in because of the bigger hole allowing the camera to capture every thing in the picture.
to big will give you over exposer and to little will give you under exposer

the_monkey

Far as i know the f/2.8 is f (focal length) divided by 2.8.

so the smaller the divisor the bigger the hole.

why 400mm at f/8 , gives similar bokeh then 50mm at f/1.4 .

magicbastarder

bokeh is not necessarily related to depth of field - it's actually how aesthetically pleasing the lens 'renders' the out of focus sections, not the *extent* to which they are out of focus.

the_monkey

the_monkey wrote: »

Far as i know the f/2.8 is f (focal length) divided by 2.8.

so the smaller the divisor the bigger the hole.

why 400mm at f/8 , gives similar bokeh then 50mm at f/1.4 .

Also not sure if this is true, correct me if i am wrong,
but i have noticed the depth of field decreasing as the focal length increases..
even with f/8+ ...

charybdis

the_monkey wrote: »

Also not sure if this is true, correct me if i am wrong,
but i have noticed the depth of field decreasing as the focal length increases..
even with f/8+ ...

Bokeh and depth-of-field are separate things.

Depth-of-field is dependent on focal length, aperture, focus distance, and what you consider to be acceptably sharp. Arguably, of these factors, changes of aperture have the least effect on depth-of-field.

Also, 400/8 == 50 and 50/1.4 == 35.7.

5uspect

youllneverknow wrote: »

mention maths and i get confused lol

i seem to understand it the bigger the f/value there less light let in. and you can use faster shutter speeds.
the lower the f/value the bigger the hole and more light is let in because of the bigger hole allowing the camera to capture every thing in the picture.
to big will give you over exposer and to little will give you under exposer

Think of the aperture as being much like the iris of your eye.
The iris opens and closes to let in less or more light.
In the dark it opens up to let in more light and in bright day light it makes the hole smaller. This also has the effect of determining what is in focus.
You may notice that your vision isn't very sharp in a dark pub. (Well mine isn't!)
Also if you get your eye's tested they may ask you to look through a pin hole.
This improves the sharpness.

Also if you squint your vision also appears sharper. This is because your "stopping down" the light entering your eye.

Now on a camera this can be used to our advantage to help us control the depth of field. Make the camera squint and things get sharper. But since the optics of the lens are very well designed what object is at the camera's focal length will be pretty sharp. All other objects will be blurry.
By squinting things in front of and behind this object also come into focus.

Now lenses have all kinds of f numbers..
In order to get that very narrow depth of field effect we all love the optics need to be very good. This is because a bit of squint always helps a poor lens be sharp. If you make the lens well it will be sharp without squint. Also the lens needs to be large to allow for the wider hole.
This makes lenses with f numbers less than 2.8 more expensive.
You usually get a minimum of f5.6.

You can then squint pretty much any of these lenses to f 22 or 32.

zerohamster

In terms of physics f=focal length so f/2.8 for example is the focal length of the lens divided by 2.8 which gives you the diameter of the hole.

as the aperature get smaller (in size) DOF gets wider because defocus blur decreases but diffraction blur increases as the hole gets smaller and as such there is a "sweet" spot which both the defocus blur and diffraction blur are at the optimum level resulting in the sharpest image quality.

I have heard and read this is usually between f/8-11 depending on the lens.

youllneverknow

youllneverknow wrote: »

i seem to understand it the bigger the f/value there less light let in. and you can use faster shutter speeds.

Other way around, actually. The bigger the f value (f/16, f/22, f/36, etc.) the smaller the hole, and because the hole is smaller, you're letting less light into the camera. Less light means a slower shutter speed.


The smaller the f setting (f/1.8, f/2.8, f/3.5, etc.) the bigger the hole and because the hole is bigger, you let more light in, meaning a faster shutter speed.


The faster your shutter speed, the less time the camera has to "take it all in" and so, with a big hole (f/1.8) your shutter speed is so fast that it doesn't have time to scan everything, and you're left with a lot of stuff out of focus.


Try this; Set your camera to aperture priority and put it sitting on something (desk, table, whatever). Put an object five feet in front of the camera and put another object five feet behind that. Focus on the closer object. Take two photos, one with your lowest f/value and one with your highest.

When you're using a low f/value, you'll get less in focus. If you use a higher f/value, you get more in focus.


Your results should be something like this:










(You'll need more space between the items to get a more noticeable effect. Also, the above photos aren't realistic representations of what f/1.8 and f/22 will do, i'm just using extremes to help you get your head around it)

to big will give you over exposer and to little will give you under exposer

Changing the aperture will only affect your exposure if you're in manual mode. If you're in aperture priority on your camera, then the camera will adjust the shutter speed accordingly.

upaho

I'd actually forgotten about diffraction blur, memories of Davison's friday night lectures in the DIT (Kevin's St Tech with aspirations at the time).

But the best way to demonstrate the effect of aperture (apart from taking a few photos) you need 2 people, a laser pointer, a line drawing (as a subject), a large sheet of black paper with an aperture punched in the center and a large sheet of paper for the image formation and a marker.

Line up the drawing, the aperture and the image sheet, plane parallel. Using the back of the laser pointer trace around the line drawing shining the laser through the aperture onto the image sheet. The 2nd party places a dot with the marker where the laser beam illuminates the image formation sheet.

As the image builds up it's actually fun to see how little image information you need to recognise the original.

The effect of a larger aperture can be imagined at any image point. Originating from one point on the original the laser can illuminate a single dot on the image with a small aperture. As the aperture gets larger the size of the area illuminated on the image gets exponentially larger.

Give it a try and have fun

Promac

You guys should check out the wiki page for Aperture - it's extremely enlightening.

As someone pointed out - f/1.8 is a larger number than f/22 and understanding why will help you understand the difference between a small and large depth of field.

Consider this - The "f/" is part of the number in the same way that 1/2 is a number (0.5, 1 half, etc). In this case the F should be replaced by your focal length - for example, with a 50mm lens at an aperture setting of f/1.8 the size of the actual hole is 50/1.8 which is 27.8mm. At f/22 the hole is 2.27mm - almost a pinhole in comparison and 10 times smaller.

Here's a handy diagram, courtesy of wikipedia:


The reason this is important for understanding aperture and focus is because of the idea of "Collimated Light". Instead of light, think for a second of firing bullets at a target. If you have an air-rifle and you fire 50 pellets from the same position into one target, always aiming for the same spot, then you'll end up with a small hole in your target, not a lot larger than 1 pellet. If you use a shotgun to fire once but firing 50 pellets at the same time, you'll end up with a big circle of dots. If you imagine that shotgun pattern of dots then think of your bokeh circles you should hopefully see a link there. The bokeh circle is the shotgun pattern of light hitting your camera's sensor.

The reason the smaller aperture setting of f/22 will give you a more focused overall picture is that, for any given spot on the sensor, light is restricted in how many different directions it can make it through the aperture and be recorded by the sensor - most of it just hits the aperture blades and bounces off. So only light travelling in relatively straight lines gets to be part of the final image. With a larger aperture setting of f/1.8 the hole is wide open, so light can come at the sensor from loads of different angles which means that what should be a clear line ends up being a big fuzzy one, or a small dot of light becomes a big blurry circle.

With the smaller aperture, the light is more orderly. With a larger aperture, the light is more disorderly. Order = focus. Disorder = blur.

Chorcai

Better not say anything about shutter speeds relating to F stops... heads will burst.:D:D:p

Promac

Chorcai wrote: »

Better not say anything about shutter speeds relating to F stops... heads will burst.:D:D:p

I didn't want to chance it!

charybdis

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

charybdis wrote: »

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.

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.

charybdis

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.

Promac

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?

Promac

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

Chorcai

Both of ye are right.

In most cases I asume people use Av and let the camera auto manage the shutter speed.

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

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.

charybdis

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

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?

charybdis

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.

youllneverknow

stop the b***ingn seen as im the op think i should say something.
Charybdis did put thing in that i didnt ask about but what he said was very helpfull. it cleared up aperture. the same with the shotgun description and the diagrams and all the other input.

magicbastarder

jaysus lads, starting a fight about apertures?
this thread is fast disappearing up its own aperture.

Morrisseeee

Small aperture = big f(in) number = small hole = tight arse
or...
Small = Big = :eek: