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FORUMS Photography Talk by Genre General Photography Talk
Thread started 30 Mar 2006 (Thursday) 13:04
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a very newbie question about "stopping down one f-stop"

 
ClickClick
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Mar 30, 2006 13:04 |  #1

Ok, I am rather embarrassed to ask this because it seems so common sense, that I am not sure why I have missed it.

What exactly is meant by "stopping down one f-stop" in photography?

ok, I know what F-stop is... but when you stop down, do you use the auto focus, look at what F-stop the camera is automatically setting on for the image and then go to AV mode and set the F-stop down to the next level?

For instance, if I use the AF mode (green box symbol) on my camera and the camera reads an Fstop of 3.5 once I press the shutter button half way down, I then just reset the camera's f-stop down to 4.0?

or am I completely wrong and just more stupid here?


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Curtis ­ N
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Mar 30, 2006 13:14 |  #2

"Stopping down" means reducing the size of the aperture, adjusting the aperture to a higher f/ number.

One "stop" is an amount that will either double or halve the amount of light that hits the film/sensor.

The traditional f/ stop numbers are 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32.
It's basically a progression of multiples of the square root of 2. Modern cameras can also be set in between these values, in 1/2 or 1/3 stop increments.

Stopping down one f/ stop would mean, for example, going from f/4 to f/5.6, or from f/11 to f/16.

Generally you need to use Av or M modes to maintain control over the aperture. You can also use the program shift in P mode to change the setting that the camera will use.


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Bruce ­ Hamilton
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Mar 30, 2006 13:44 as a reply to Curtis N's post |  #3

Curtis N wrote:
One "stop" is an amount that will either double or halve the amount of light that hits the film/sensor ... Stopping down one f/ stop would mean, for example, going from f/4 to f/5.6, or from f/11 to f/16.

If one stop down halves the light to the sensor, then wouldn't one stop from f/4 be f/8, with f/5.6 being a half stop?


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ClickClick
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Mar 30, 2006 13:48 as a reply to Bruce Hamilton's post |  #4

so basically what people refer to is getting a reading from the camera in Auto mode and then stopping down one stop in AV or M mode (or P mode)?

actually can't this be achieved the same with the auto bracketing feature? It takes the auto fstop and then also brackets it up one f stop and down f stop so you really get three pictures with one take.


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Curtis ­ N
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Mar 30, 2006 14:23 as a reply to Bruce Hamilton's post |  #5

Bruce Hamilton wrote:
If one stop down halves the light to the sensor, then wouldn't one stop from f/4 be f/8, with f/5.6 being a half stop?

Bruce, the f/ number represents the DIAMETER of the aperture as a fraction of the focal length. So going from f/4 to f/8 reduces the diameter by half. Since the amount of light passing through the aperture varies according to the AREA, cutting the aperture diameter in half would allow only 1/4 as much light in.

Remember high school geometry? Area of a circle is PI times the radius squared. Calculate the area of a 2 inch diameter circle and a 4 inch diameter circle. The area of the 4 inch circle will be 4 times the area of a 2 inch circle. So if you want to double or halve the area of a circle, you need to multiply or divide the diameter by the square root of 2.

The term "stop" in camera lingo refers to the fact that years ago, the aperture was adjusted via a lever on the lens. There were detents in the mechanism to "stop" the lever at various points.

Clickclick, I think you understand the concept. "Stopping down" is a fairly general term. It simply means reducing the aperture diameter.

Bracketing is one method. Keep in mind that if you set one stop auto exposure bracketing in Av mode, the camera will use the aperture you select and different shutter speeds for the three shots. If you want to bracket different apertures, you need to use Tv mode, setting the shutter speed and allowing the camera to set the apertures.


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Inspired ­ Photography
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Mar 30, 2006 14:27 as a reply to Bruce Hamilton's post |  #6

Bruce Hamilton wrote:
If one stop down halves the light to the sensor, then wouldn't one stop from f/4 be f/8, with f/5.6 being a half stop?

No. Just like f2 to f2.8, or f2.8 to f4. There is a halving of light to the sensor on each of those moves. f4.5 would be a 1/2 or 1/3 stop (too early in the morning) down from f4.

The actual f-stop number has a mathematical relationship to the amount of light being let in, as explained by Curtis.
You can't look at f2 and f4 and think that there is half the light coming through. That would actually be 1/4 of the light (or 2 fstops).


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Wilt
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Mar 30, 2006 16:51 |  #7

Three principles...

1. 'Stopping down one aperture' is merely having the lens use a smaller diaphram position. Period. (anything more is simply the application of 'stopping down'!)

2. You might 'stop down' with no offsetting adjustment of shutter speed. For example, if your meter says f/11 at the beach, you 'stop down' to f/16 to compensate for the bright scene that fools the meter, with no adjustment to shutter speed.

3. You might 'stop down' and also make an offsetting adjustment in shutter speed at the same time. For example, you 'stop down' to increase the depth of field in the shot, but you also make an offsetting adjustment of slower shutter speed selection (e.g. change from 500 to 250) so that the overall exposure is unchanged.


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ClickClick
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Mar 30, 2006 19:26 as a reply to Wilt's post |  #8

Wilt wrote:
Three principles...

1. 'Stopping down one aperture' is merely having the lens use a smaller diaphram position. Period. (anything more is simply the application of 'stopping down'!)

2. You might 'stop down' with no offsetting adjustment of shutter speed. For example, if your meter says f/11 at the beach, you 'stop down' to f/16 to compensate for the bright scene that fools the meter, with no adjustment to shutter speed.

3. You might 'stop down' and also make an offsetting adjustment in shutter speed at the same time. For example, you 'stop down' to increase the depth of field in the shot, but you also make an offsetting adjustment of slower shutter speed selection (e.g. change from 500 to 250) so that the overall exposure is unchanged.

thank you so much for these examples.

but would I get the same using autobracketing that the camera offers?


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Wilt
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Mar 30, 2006 19:51 |  #9

>>but would I get the same using autobracketing that the camera offers?<<

Autobracketing does #2 only (decreasing exposure) as well as increasing exposure, but it is not #3 (exposure the same with different f/stop being used).


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Curtis ­ N
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Mar 30, 2006 20:50 |  #10

Clickclick,

Bracketing is a technique often used in difficult metering situations, taking three pictures at different exposures instead of just one. It's a way of improving your chances of getting a good shot, at the expense of CF card space, and the time required to sort through the extra images.

Stopping down, without a compensating adjustment in shutterspeed or ISO (#2 in Wilt's post), is a way of reducing exposure, or brightness of the image.

But it's important to understand that reducing the aperture is often done for other reasons. It will increase depth-of-field, and in some cases optimize the sharpness of the image (most lenses are a bit sharper when stopped down one or two stops than at their max. aperture). When using fill flash in the sun, it's necessary to stop down in order to attain flash sync shutter speed. These are the some of the reasons for stopping down while compensating for the exposure loss by changing the shutter speed or ISO setting (#3 in Wilt's post).


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lostdoggy
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Mar 30, 2006 21:21 |  #11

ClickClick this might sound harsh but its time to get a good book and read. From what your original question it appears that that you need to get a better grasp of the actual functions of the camera. for example the green box you mention means full auto. AF means Auto Focus. When you we talk about aperature and shutter speed we are talking about Exposure. Exposure and AF should not be confuse even at time they will corrolate, such as when we talk about Depth of View. Get grasp of photography by shooting 1st in full auto and then study the photos and ask yourself what is wrong with the shots and then graudate to Av mode and study too. and then try your hand at look at a scene and try to determine what type of exposure you would need in manual mode. See if you can determine what has change over time and photo. Keep reading here to get more info there some great advice here to be learned.




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MiG82
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Apr 03, 2006 23:02 |  #12

Green box and stopping down do not go together. To stop down you need to leave the safety of the green box.


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jackies35
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Jun 04, 2010 10:33 |  #13

I know.... This is an old thread but it means so much too me!

Why is photography so cunfusing?!?
Thanks Curtis for your comment on this topic.
"Stopping down" means reducing the size of the aperture, adjusting the aperture to a higher f/number"

Now, first I must say, if I increase the size of anything, the number will go up. If I increase the size of my waist, the number of my pants size will increase.

Here, in photography, when you increase the size of the aperture (down up to a higher number), you are MAKING the hold smaller.

This is so difficult to grasp (well, at first for me).

"Stopping down one f/stop would mean, for ex: going from f/4 to f/5.6, or from f/11 to f/16."

Again, this is confusing and it doesn't make sense. Of course, I understand now but for a beginner, its really hard to grasp!

Thank you all for commenting on this topic 4 years ago. I must have read this 3 times and didn't apply it completely in my photography! Reading is so important!


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Wilt
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Jun 04, 2010 12:17 |  #14

jackies35 wrote in post #10301776external link
I know.... This is an old thread but it means so much too me!

Why is photography so cunfusing?!?
Thanks Curtis for your comment on this topic.
"Stopping down" means reducing the size of the aperture, adjusting the aperture to a higher f/number"

Now, first I must say, if I increase the size of anything, the number will go up. If I increase the size of my waist, the number of my pants size will increase.

Here, in photography, when you increase the size of the aperture (down up to a higher number), you are MAKING the hold smaller.

This is so difficult to grasp (well, at first for me).

"Stopping down one f/stop would mean, for ex: going from f/4 to f/5.6, or from f/11 to f/16."

Again, this is confusing and it doesn't make sense. Of course, I understand now but for a beginner, its really hard to grasp!

Thank you all for commenting on this topic 4 years ago. I must have read this 3 times and didn't apply it completely in my photography! Reading is so important!

Because the f/number is the result of a RATIO, FN = FL/D, where FN is f/number, FL is focal length, and D is aperture size

So 50mm lens and 25mm effective aperture diameter...
= 50:25 = 2:1 or f/2 or [aperture is 1/2 of FL]

and the smaller opening aperture is a smaller fraction of the FL and using example of 50mm lens and 4.5mm aperture...
=50:4.5 = 11:1 = f/11 or [aperture is 1/11 of FL]


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Jun 04, 2010 17:15 |  #15

try thinking about some of the standards in other industries that are also counterintuitive. firearms, especially shotgun bores are all backwards too. an eight gage is HUGE compared to a twenty gage, cause the gage number used to represent the number of round lead balls you could mold from a pound of lead that would fit the bore.
a 'Z' drill is bigger than an 'A' drill, but a #60 drill is tiny in comparison to a #1, cause they were originally based on a wire diameter number that was based on feet of wire drawn from a pound of metal.
it's everywhere, I guess the more you see stuff like this, the easier it is to just live with it and pretty soon it is no longer counterintuitive.


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