1 Correct answer
aperture is the F stop ( indicated by an F number)
Oddly, the higher the number, the smaller the aperture.
You can think of the aperture as a certain size hole that lets light into the lens, which is adjustable via changing the F stop setting.
F2 is very big hole
F 22 is very small hole.
The F stop is determined in part by some match formula type stuff that has to do with the size of the lens ( focal length). That gets complicated. But generally, if you have a light meter and it tells you that the li
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aperture is the F stop ( indicated by an F number)
Oddly, the higher the number, the smaller the aperture.
You can think of the aperture as a certain size hole that lets light into the lens, which is adjustable via changing the F stop setting.
F2 is very big hole
F 22 is very small hole.
The F stop is determined in part by some match formula type stuff that has to do with the size of the lens ( focal length). That gets complicated. But generally, if you have a light meter and it tells you that the light requires a certain shutter speed and F stop combination then that works for all lenses, no matter the size of lens. This is also related to ISO speed. One F stop is worth 1 traditional shutter speed.
For example, if your light meter says " shoot this at ISO 400 with a shutter speed of 1/60th of a second, and F 8... then you can change the ISO to 800 (twice as fast ), and HALF the F stop ( F 4.5 )
You can also relate the shutter speed to the F stop the same way. At 1/60th of a second shutter speed ( as light meter told you to do) with F 8, you can reduce the shutter speed by half ( 1/30th of a second ) and close the F stop one stop... from F 8 to F 5.6.
It's kinda easy once you get the hang of it.
The depth of field ( amount of stuff in front of and behind the subject you are focused on, INCREASES the smaller the aperture ( once again this means ( odd as it seems ) a HIGHER F stop number.
More stuff is in focus in front of, and behind, your subject focused on, the higher the F stop NUMBER.
The speed of light is a constant, and has nothing to do with this. It is a matter of the AMOUNT of light (F stop), and time exposed (shutter speed), and SPEED OF FILM ( ISO).
One reason this is so fresh in my mind is because I was fooling around in the ppro forum yesterday and mentioned I had a few beers and shot some guy in my apt. building and he was out of focus. I'm using a new camera I'm not familiar with (someone sent me, no manual). It's a bmpcc.
It shoots raw, which I like.
Cinema DNG codec, which is working OK on my computers.
Problems:
1) hard to see focus in little LCD screen
2) drunk
3) low light and very small aperture ( like F 2.8 or something ) which means no depth of field to speak of.
Shooting at 24FPS with 180 degree shutter gives me 1/48th of a second shutter speed.
TODAY I re-shot the guy. I also went online and discovered there are some tricky things I can do to help me focus.
To be on the safe side I backed off a ways from subject, cranked up ISO to the max ( so I could use a higher F stop number and get more depth of field ).
If he ended up blurry again I was going to kill myself.
Now that I have some measure of self assurance, I can get closer next time, open up the F stop a little to get some out of focus stuff in background and foreground ( lower the ISO ), and have a prettier picture !
hehe, Nancy... I know... and the F stops and shutter speeds are like now divided into different degrees of change.. no longer 2, 2.8, 4, 5.6, 8, 11, 16, whatever...gets confusing.
Even responding to this question I screwed up a couple things …. I'm a dope.
I am a bit late to the party but perhaps this will help.
One of the first things you will notice when you see the f/stop notations on the lens barrel is that, as the aperture decreases in size, the number assigned to it becomes larger.
It seems to defy logic until you are reminded that the instance when a larger number designates a smaller measure is when it is the denominator of a fraction. Note as we go from ½ to ¼ to 1/8, the denominator grows as the size diminishes. The fraction referred to here refers to the aperture in relation to the lens focal length. An aperture of f/8 has a diameter one-eighth the lens focal length. (Not exactly, and I will get to that in a moment.)
The beauty of this is that as the focal length increases (meaning the lens is further from the chip or film and the light diminishes within the camera), the aperture gets physically larger but, the amount of light gathered on the chip remains the same.
If this system of fraction-of-focal-length was not used as a reference, you would need a separate meter for each focal length of lens you used.
The lens is marked in increments that allow one half the light of its neighbor’s setting (or twice its neighbor) without you having to do the math to adjust the aperture. If you would like to calculate the system of halving the aperture and you have an iPhone, try this:
Choose the Calculator and turn the iPhone horizontally.
Enter: 1 x 2 then strike the square root key that is marked below, then hit the = key
Each click of the = key will step off the calculation for you as shown here,
Note that f/5.6 is really 5.7, f/22 is really 23. I never found any logic for this inconsistency but I'm too old to argue.
Now, don’t whip out a ruler and check the diameter of the aperture. It will be smaller than you might think. The reason is that the shutter on your camera is positioned between lens elements so that some of the light bending occurs before it reaches the shutter. The aperture is actually an effective aperture.
In addition, you cannot arrive at the precise lens focal length by measuring the distance from the lens to the chip when the camera is set at infinity. The distance must be measured from the emergent nodal point of the lens – the point within the lens where the light stops coming in and begins exiting the lens. So, trust the accuracy of the specs offered by the manufacturer.
There us much more to learn about lenses. As I suggested earlier, hit the books.
Yeah, I was waiting for you to correct that, I knew you knew better
Of course, some specialist cameras do have a leaf/central shutter inside the lens, but you can live a long and happy life as a photographer without ever encountering one of these. In theory you could build a combined shutter/aperture diaphragm, but since nobody has ever done that I assume it's not practical. Hard to get enough precision.
rodney, crop factor usually refers to full frame 35mm (FX). Focal length is just focal length - it doesn't have any particular viewing angle until you project it on a fixed rectangle of a certain size. That rectangle ("sensor") has a viewing angle that depends on its size - the bigger it is, the wider the view.
Assuming the lens projection has enough coverage of course. But coverage is as such independent from focal length. Tilt-shift lenses, for instance, need to have much wider projection coverage than a fixed lens of the same focal length.
hehe, Norman, traditionally you got 5.6 then 8 then 11...you kinda skipped the 8 ?
good explanation. Thanks.
Thank goodness there are other areas of very creative and smart people who make stuff for me to enjoy. Other than 'flat art' or 'photography' or 'sculpture' ( dance, music, etc.).
I can just go read a decent book (if I can find one).
Don't look on TV for anything... it's a wasteland. ( Rat's feet over broken glass ).
Norman…. yep, I owe you a beer ! hehe...
Now I get it... the other F stops are on the right side in whole numbers....duh... didn't even see that before.
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