Do I have this right? (questions about aperture)

[lepierce3]

Ok, so I've been doing a lot of reading and experimenting trying to get a better understanding of settings. It's all very confusing for some reason, but I thiiiink I finally get aperture, but I just want to make sure I dont have it backwards!

So from my understanding:

-A higher number = more of the image in focus
-A lower number (like f2.8 or something) = less of the image in focus and you get effects like bokah (sp?)
-A lower number is called having a wide or large aperture?
-A higher number is called having a smaller aperture? (doesn't this seem backwards? Lol)


-If you have a wide aperture (small f-stop number) you need a smaller shutter speed and ISO too because otherwise too much light will get in?


I don't know why I'm having so much trouble with this, but it's probably just because I am terrible with understanding numbers lol. If someone could please let me know if I am actually understanding this right, or if not, what's wrong and why, that would be amazing! Thank you!

 

[fjrabon]

THink of the f/stop number as a fraction, as that is what it is (though in reality it's complicated fraction, the basic idea holds). The higher the number, means a greater denominator, which means smaller number in reality. One way to think about it, which isn't actually accurate, but can help understand it is this: think of the F more or less like a 1. So f/2 would be 1/2. f/8 would be 1/8.

This isn't actually accurate, because the real number involves square roots and multiplying by pi and the like, but it gives you the basic idea of how it works, which is practically all you need.

Another thing to know is that lower f/stops let in more light, meaning that you'll have to adjust ISO and/or shutter speed. This is why a lens with a very low f/stop capability is often called a 'fast lens' even though aperture itself doesn't have anything to do with shutter speed. Having the ability to have a wide open aperture (low f stop) means that your camera can quickly gather more light, allowing the shutter to stay open for a shorter amount of time.

 

[jwbryson1]

Ok, so I've been doing a lot of reading and experimenting trying to get a better understanding of settings. It's all very confusing for some reason, but I thiiiink I finally get aperture, but I just want to make sure I dont have it backwards!

So from my understanding:

-A higher number = more of the image in focus
-A lower number (like f2.8 or something) = less of the image in focus and you get effects like bokah (sp?)
-A lower number is called having a wide or large aperture?
-A higher number is called having a smaller aperture? (doesn't this seem backwards? Lol)


-If you have a wide aperture (small f-stop number) you need a smaller shutter speed and ISO too because otherwise too much light will get in?


I don't know why I'm having so much trouble with this, but it's probably just because I am terrible with understanding numbers lol. If someone could please let me know if I am actually understanding this right, or if not, what's wrong and why, that would be amazing! Thank you!

You got it about right. A higher number (e.g., f/16 versus f/4.5) will create a longer depth of field (DOF) which will make more of the photo in focus. A smaller number (f/2.8) is a much wider opening which lets more light pour in and onto the sensor. Result? Less DOF which causes the background of the image to be out of focus (the "bokeh").

A small f-stop number (2.8) is a wide aperture (more light) and a big number (11, 16, etc.) is a small aperture (less light).

If you have a wide aperture, you will need a shorter shutter speed (SS) (e.g. 1/500, 1/1000) and a lower ISO (100, 200) because you don't need as much "help" getting light onto the sensor. If you have a small aperture (11, 16, etc.) you may need a higher ISO (400, 800), and a longer shutter speed (1/10, 1/60) because you need MORE help (or more time) getting light onto the sensor.

 

[Heitz]

No, it can be confusing. A lot of photography seems to be inverted. With f-numbers, think of it as a ratio. It is the ratio of the focal length of the lens and the size of aperture letting in the light. if you had f/1.0, then the aperture would be as wide as the focal length, letting in the most light. As you decrease the aperture size, that ratio changes and proportionally less light is allowed to pass to the sensor. At the same time, larger apertures (lower f numbers) shorten the depth of field (DOF). So smaller apertures (higher f numbers) will leave more of the image in focus. because the size of the aperture directly controls the amount of light entering the lens, something must compensate to maintain accurate exposure. as you open the aperture, you (or the camera) will increase the shutter speed to offset the amount of light coming in (this too is usually expressed as a fraction of a second, so it appears inverted too. 2000 = 1/2000 of a second which is shorter than 200 (1/200) or 20 (1/20) ). The same thing can be done with ISO, to some point, and your camera will do this for you if you leave ISO to auto. Many of us do not do this, though; we set ISO manually and allow shutter speed to vary (shooting in Aperture Priority Mode), because higher ISO can lead to image noise, or grain. We like to maintain control of this.
Oh and it's 'bokeh' (boe - kah) though some people pronounce it 'bouquet', apparently.
Hope that helps.

 

[Bob in GV]

So from my understanding:

-A higher number = more of the image in focus
-A lower number (like f2.8 or something) = less of the image in focus and you get effects like bokah (sp?)
-A lower number is called having a wide or large aperture?
-A higher number is called having a smaller aperture? (doesn't this seem backwards? Lol)


-If you have a wide aperture (small f-stop number) you need a smaller shutter speed and ISO too because otherwise too much light will get in?

First, I feel it's mandatory for me to suggest you find a copy of The Amateur Photographers Handbook by Aaron Sussman. It's out of print (I think) but can usually be found on Amazon. Ansel Adams' 3 book series The Camera, The Negative, and The Print can still be purchased. I saw them in a camera shop in Sacramento in the last couple of months. If you're not sure about the second book then substitute Sensor for Negative. Now it's a modern book.

Now, the first two items you've mentioned refer to "Depth of Focus" and generally speaking you seem to have the concept that the smaller opening will give greater DOF while the smaller opening gives a shorter DOF. As with anything, there is big HOWEVER. These also depend on the focal length of the lens. Shorter focal lengths tend to have greater DOF than longer lengths using the same f: number.

Regarding questions 3 and 4, the number f:2.8 or f:16 is actually a ratio of the focal length to the aperture size. So understanding that, given a fixed focal length of 50mm with an effective lens aperture of 25mm will result in a f/2 factor. The same 50mm lens with an effective aperture of 12.5mm will result in a f/4 factor.
So, the smaller the f/ number the less light admitted so to achieve the same actual exposure, you'd need 2x more exposure time for the larger number.
ISO is a measure of the sensitivity of the sensor/film to light, so it adds a third element to the equation.

Beyond reading Sussman, I suggest you set your ISO on a digital camera or purchase several rolls of the same film and go out and experiment with different combination of aperture and shutter speed so you can see the relationship and the effect of each.

I hope this helps. There's a lot more to it, and I'm not very good at explaining but I think you can get the idea. It's now up to you to do some research outside internet forums.

 

[o hey tyler]

Ok, so I've been doing a lot of reading and experimenting trying to get a better understanding of settings. It's all very confusing for some reason, but I thiiiink I finally get aperture, but I just want to make sure I dont have it backwards!

So from my understanding:

-A higher number = more of the image in focus
-A lower number (like f2.8 or something) = less of the image in focus and you get effects like bokah (sp?)
-A lower number is called having a wide or large aperture?
-A higher number is called having a smaller aperture? (doesn't this seem backwards? Lol)


-If you have a wide aperture (small f-stop number) you need a smaller shutter speed and ISO too because otherwise too much light will get in?


I don't know why I'm having so much trouble with this, but it's probably just because I am terrible with understanding numbers lol. If someone could please let me know if I am actually understanding this right, or if not, what's wrong and why, that would be amazing! Thank you!

You got it about right. A higher number (e.g., f/16 versus f/4.5) will create a longer depth of field (DOF) which will make more of the photo in focus. A smaller number (f/2.8) is a much wider opening which lets more light pour in and onto the sensor. Result? Less DOF which causes the background of the image to be out of focus (the "bokeh").

A small f-stop number (2.8) is a wide aperture (more light) and a big number (11, 16, etc.) is a small aperture (less light).

If you have a wide aperture, you will need a shorter shutter speed (SS) (e.g. 1/500, 1/1000) and a lower ISO (100, 200) because you don't need as much "help" getting light onto the sensor. If you have a small aperture (11, 16, etc.) you may need a higher ISO (400, 800), and a longer shutter speed (1/10, 1/60) because you need MORE help (or more time) getting light onto the sensor.

BTW f/16 is a smaller number than f/4.5.

f/2.8 is not a small number.

 

[fjrabon]

BTW f/16 is a smaller number than f/4.5.

f/2.8 is not a small number.

I think part of the confusion is even though f/2.8 is not a small number, you commonly hear it called a 'low f stop'. The problem being that even those within the photography world are kind of inconsistent in how they use them.

 

[KmH]

Yep.

To many people didn't pay attention in math class, because that was the 'cool' thing to do. :lmao:

 

[jwbryson1]

[/QUOTE]

BTW f/16 is a smaller number than f/4.5.

f/2.8 is not a small number.[/QUOTE]


Read it however you'd like to read it but my post is 100% accurate.

 

[o hey tyler]

BTW f/16 is a smaller number than f/4.5.

f/2.8 is not a small number.

Read it however you'd like to read it but my post is 100% accurate.

Read what however I like? There's only one way to read it, and it's incorrect.

f/numbers are not whole numbers. They're fractions. Your post is maybe 50% accurate.

If you have learned about fractions, you'd know your post is not 100% correct.

Lets do some math, shall we? f/numbers have a relationship with the focal length of the lens, hence what 'f/' stands for. You have a 100mm lens, at f/2, the aperture diaphragm is open to 50mm in diameter. You stop the same 100mm lens down to f/4, and it is now an opening of 25mm, therefore 100/2 is larger than 100/4.

 

[fjrabon]

BTW f/16 is a smaller number than f/4.5. f/2.8 is not a small number.

Read it however you'd like to read it but my post is 100% accurate.

Read what however I like? There's only one way to read it, and it's incorrect. f/numbers are not whole numbers. They're fractions. Your post is maybe 50% accurate.If you have learned about fractions, you'd know your post is not 100% correct. Lets do some math, shall we? f/numbers have a relationship with the focal length of the lens, hence what 'f/' stands for. You have a 100mm lens, at f/2, the aperture diaphragm is open to 50mm in diameter. You stop the same 100mm lens down to f/4, and it is now an opening of 25mm, therefore 100/2 is larger than 100/4.

Yeah, but in your own signature you call it a low f/stop. Would you call 50 a low number compared to 100?

 

[Helen B]

At an aperture of f/2.8 the f-number is 2.8. At an aperture of f/16 the f-number is 16. 2.8 is lower than 16, so the f-number at f/2.8 is lower than the f-number at f/16. The f-number is the focal length divided by the entrance pupil diameter (eg 50/25 = 2 for a 50 mm lens with a 25 mm entrance pupil), it is not f/2 (ie 50/2) for example.

So from my understanding:

-A higher number = more of the image in focus
-A lower number (like f2.8 or something) = less of the image in focus and you get effects like bokah (sp?)
-A lower number is called having a wide or large aperture?
-A higher number is called having a smaller aperture? (doesn't this seem backwards? Lol)


-If you have a wide aperture (small f-stop number) you need a smaller shutter speed and ISO too because otherwise too much light will get in?

...

Now, the first two items you've mentioned refer to "Depth of Focus" ...

By the way, 'Depth of Focus' and 'Depth of Field are not synonymous. Depth of Field refers to what appears to be in focus in front of the lens. Depth of Focus refers to how much you can change the image-lens distance and still keep the object that is being focused on in apparent focus.

Also by the way, lenses can have an aperture greater than f/1 - you can have lenses that let in more light than an f/1 lens (ignoring light loss through the lens which is another issue). f/0.5 is theoretically possible, but f/0.7 is about the practical limit for a camera lens. There are quite a few lenses of f/0.9 and f/0.95.

 

[jwbryson1]

BTW f/16 is a smaller number than f/4.5.

f/2.8 is not a small number.

Read it however you'd like to read it but my post is 100% accurate.

Read what however I like? There's only one way to read it, and it's incorrect.

f/numbers are not whole numbers. They're fractions. Your post is maybe 50% accurate.

If you have learned about fractions, you'd know your post is not 100% correct.

Lets do some math, shall we? f/numbers have a relationship with the focal length of the lens, hence what 'f/' stands for. You have a 100mm lens, at f/2, the aperture diaphragm is open to 50mm in diameter. You stop the same 100mm lens down to f/4, and it is now an opening of 25mm, therefore 100/2 is larger than 100/4.

Good grief, do we really have to do this? This is silly. We are both here trying to be helpful to this person so let's not split hairs.

To be clear, yes, I understand how the f-stop is calculated and yes, I understand what you are saying when you say that f/4.5 is a "larger" number than f/16. Having said that, it was my perception that the OP had limited experience based on his/her question, so my response was written in a manner that was intended to be easily understood by a layperson. In my attempt to be as simple as possible, I thought it made sense to avoid any unnecessary confusion about calculations, ratios, etc. When I refer to "f/16" being larger than "f/4.5" -- TO BE CLEAR -- I am referring to the number 16 being larger than the number 4.5. That is a true statement. I was trying to give the OP an easy way to quickly look at the f/stop and understand what it meant. Comprende amigo?

 

[Helen B]

When I refer to "f/16" being larger than "f/4.5" -- TO BE CLEAR -- I am referring to the number 16 being larger than the number 4.5.

Just to clarify the correct terminology: f/16 and f/4.5 are apertures. f/16 is a smaller aperture than f/4.5. 16 and 4.5 are f-numbers. 16 is a larger f-number than 4.5. The smaller the aperture, the higher the f-number.

 

[jwbryson1]

When I refer to "f/16" being larger than "f/4.5" -- TO BE CLEAR -- I am referring to the number 16 being larger than the number 4.5.

Just to clarify the correct terminology: f/16 and f/4.5 are apertures. f/16 is a smaller aperture than f/4.5. 16 and 4.5 are f-numbers. 16 is a larger f-number than 4.5. The smaller the aperture, the higher the f-number.

Exactly. I think we all understand this. Some of us just want to be argumentative it seems.