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Photography Question 
Kelly 
 

How to Properly Adjust Aperture/Shutter Speed


Hey everybody! I too am a rookie looking for some GOOD advice. I'm currently taking a class in which we use slide film & our cameras in manual mode. I don't have much experience with manual settings, so my problem is adjusting aperture to correlate with the shutter Speed and vice versa. My teacher just breezed thru reciprocity & I just can't seem to grasp which direction you adjust to get the same exposures. My camera shows either "+" or "-" and I have a very difficult time finding balance or the correct exposure. I need someone to just say "If you don't have enough light, ie you have "-" on display you need to move this many stops, and this number of seconds on your shutter speed..." Can anyone break this down for me in a simple way? I have even been reading some on this, but I just don't get it. Seems so simple and yet it ELUDES me :) Please help me. I will be so grateful.


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2/7/2003 5:19:30 PM

 
Jeff S. Kennedy   Probably the most important thing to understand are your apertures (since the shutter speeds are pretty self explanatory). The larger the number of your f-stop the smaller the opening in your lens. Therefore, when you shoot at a high numbered aperture (like f22) you will let less light in and consequently have to use a slower (longer) shutter speed.

It's like filling up a bucket with water. If you don't turn the water on very high and it's just trickling (f22) then you have to leave it on longer (slower shutter speed) to fill up your bucket (your correct exposure). If you crank up the water (large aperture like f2.8) then you don't leave the water on as long (fast shutter speed) to fill up your bucket (correct exposure).

Now, notice that each shutter speed is half (or twice depending on which direction you're going) of the next shutter speed. This means that 1/30 will let in in twice as much light as 1/60. Now, your f-stops work the same way. Each stop is half (or twice depending on which way you're going) of the next one. So f4 lets in twice as much light as f5.6. So if you take a reading of 1/60 @ f4 and want to use a smaller aperture for more depth of field you can go to f5.6. But now that you've closed the aperture down one stop you have eliminated half the light. So to fill up the bucket (correct exposure) you have to let it shine on the film for twice as long. So you have to use a shutter speed of 1/30. So your new exposure is 1/30 @ f5.6.

Hope that helps.


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2/7/2003 6:56:13 PM

 
Bill McFadden   I know the feeling about a teacher who just barely covers the basics. Anyway, one thing I did realize helped is the explanation using the water bucket example shown above. One other thing is a scale of f-stops and shutter speeds. The scale of F-stops is normally:
1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11.0, 16.0, 22.0 and 32.0. As covered before, the lower the number, the more light it lets in.
Shutter speeds are usually 1/4000, 1/2000, 1/1000, 1/500, 1/250 1/125, 1/60, 1/30, 1/16, 1/8, 1/4, 1/2, and so on. The lower the number, the slower the longer the shutter stays open. There are other shutter speeds at both ends of the scale but the ones above are used on most mdern cameras.

Many films have a scale of aperature and shutter speeds. Most films have the sunny 16 rule and settings shown on the inside of the box.

Reciprocity effects occurr at shutter speeds of one second or longer. The settings to use to avoid this problem vary slightly from film to film. The best way to judge the correct settings may be to check the websites for Kodak and Fuji. Also, John Shaw covers a little of the settings in his book.


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2/9/2003 7:24:10 AM

 
Kelly    Thank you Jeff & Bill for the wonderful responses!!! I just shot this week's assigment for class keeping your explanation in mind. I think the bucket reference is just great. It makes perfect sense to me. I'm really glad I decided to ask for help. Thanks again :) I'm sure I will be staying in touch.


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2/9/2003 3:40:30 PM

 
George E. Givens Jr   Kelly,
Reciprocity is an entire different issue then setting correct exposure. What you need to try to understand is that for every correct f/stop and shutter speed there are several other combinations that will give you the same exposure. The simple answer is this; once your in-camera meter says you have correct exposure, if you change one setting you have to change the other one in the opposite direction the same number of stops. For example, if I focus on a supject and my f/stop or shutter speed is set at f/16 and 1/250s and the camera's meter reads 0 (meaning it is neither plus or minus), if I want to adjust for a narrower dof I will move my f/stop to a smaller number, lets say f/8. At this point the camera's meter will tell me I am over exposed +2 (2 stops, meaning I'm letting in too much light). In order to bring the exposure back to a 0 reading and keep the same dof, I will need to change my shutter in the opposite direction 2 stops to 1/1000s which is 2 stops faster than 1/250s. The hard thing for most begginners to grasp is the fact that as the aperture number gets smaller more light is let in and as the shutter speed number gets larger less light is let in. Depending on what you are trying to achieve determines which setting you want to adjust first and then move the other setting in the opposite direction to bring the exposure back to 0. If you are trying to control dof then you will want to adjust your aperture. If you are trying control blur of your subject, you will want to adjust your shutter speed. A really good site to go to get a better understanding of the relationship between aperture and shutter speed is http://www.kodak.com/global/en/consumer/pictureTaking/index.shtml. I hope this helps. Let us know how things come out.

Reciprocity is about the fact that film begins to break down at shutter speeds longer than 1 second. So, if you are trying to do time lapse photography or record a still subject in very dark light requiring long exposure times you need to adjust your exposure for the films reciprocity threshold.


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2/11/2003 10:29:02 PM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  A couple of points to elaborate on some things already posted:

(1) "Reciprocity" is the ability to trade aperture f-stops for shutter speed stops and have the same exposure on film. "Reciprocity Failure" is the breakdown of this relationship. George is quite correct that it's not an issue with long shutter speeds until you get to about one second exposures and longer. However, the specific shutter speed at which reciprocity failure occurs, the effect it has, and how to compensate for it is different for each specific film. If you're contemplating long exposures, read the film data sheet. It's not that difficult with B/W films. The compensation required simply makes the exposure time a little longer. It can be quite difficult with color films as failure kicks in at different exposure times for each emulsion layer resulting in color shift. In addition to adjusting exposure time, there are often color correction filter requirements too. In addition, reciprocity failure also occurs with very fast shutter speeds. This isn't as much to worry about now as it was about 30-40 years ago. All the data sheets I've read for current films (and it's quite a few) show 1/10,000th second at the short end. This is much higher than it was for some films when thyristor controlled auto-flash units were introduced in the 1960's. Look at the spec sheet(s) for your flash unit(s). There should be a minimum and maximum flash duration listed (duration is how the flash adjusts how much light it puts out when under "auto" control; not brightness of the tube). It can also be a problem if you're doing special high-speed photography with a rapid firing strobes.

(2) The lens aperture f-number system provides a common system applicable to all focal lengths. The f-number is the focal length of the lens divided by the effective aperture diameter. If you have a 50mm lens set to f/4, the effective aperture diameter inside the lens is 12.5mm. The amount of light allowed through a lens is directly proportional to the area of the aperture opening. This means it's directly proportional to the square root of its diameter. Thus, the f-numbers, which are based on aperture diameter, change with a factor of the square root of two (~1.414). The common f-numbers are rounded-off approximations. That's why changing from f/8 to f/5.6 lets in twice as much light (divide 8 by 1.414). Changing from f/8 to f/4 lets in four times as much light; twice the diameter is four times the area.

-- John


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2/12/2003 5:05:32 PM

 
Alisha May Furbish
BetterPhoto Member Since: 1/5/2003
  This is far from a technical answer! A tip I learned in a class was to think of the aperture as your eye- When you squint(small f-stop) you focus on what your trying to see and other objects in your field of vision aren't as sharp. When you open your eyes wide(large f-stop) you see everything inclusively. Very simple concept, but it helped me! Then you correspond shutter speed - the more you "squint" your lens, the slower shutter speed you use to compensate for loss of light reaching the film.


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2/22/2003 7:33:29 PM

 
George E. Givens Jr   [quote]This is far from a technical answer! A tip I learned in a class was to think of the aperture as your eye- When you squint(small f-stop) you focus on what your trying to see and other objects in your field of vision aren't as sharp. When you open your eyes wide(large f-stop) you see everything inclusively. Very simple concept, but it helped me! Then you correspond shutter speed - the more you "squint" your lens, the slower shutter speed you use to compensate for loss of light reaching the film.[/quote]
Alisha - good ananlogy except what about depth of field? In your analogy, the depth of field of a large aperture would most closely resemble squinted eyes.


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2/23/2003 3:34:21 PM

 
Sheryl M. Kirksey   GeorgeThanks for the isight on Aperture and shutter. :)


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4/24/2006 9:02:57 AM

 
Christopher A. Walrath
BetterPhoto Member Since: 4/25/2006
  Man, John. His head's gotta be spinning by now. I bet his prof doesn't even know that. (Besides the fact that we do, eh?)


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4/25/2006 2:56:52 AM

 
George E. Givens Jr   Sherylk
You are entirely welcome however after looking at your photo gallery you certainly don't need my advice. Your photos are stunning.

One thing I always felt was left out in my explanation is that just because a camera meter reads 0 doesn't mean the exposure is correct. Camera meters can be fooled. However, I have found that almost all modern day camera meters are so good at detecting backlit situation and determing whether the scene is high (mostly light) or low (mostly dark) key that using the manual exposure mode is a waste of my time. I will typically leave my camera in P mode and adjust the aperature or shutter speed to achieve the results I am after. Most pro level and prosumer level cameras have what is known as a Pa/Ps metering mode which means that when the camera is set to P mode the camera determines the correct exposure (as judged by the camera) then moving the control dials to adjust the aperature or shutter speed automatically adjust the other setting to maintain the proper exposure as seen by the camera's meter. The only other thing I would add is that when you are in doubt as to whether the camera's meter is correct to bracket your exposures either .3 or .5 and choose the exposure you like best. By doing this you will determine if your camera over or under exposes for specific situations base on YOUR specific taste. Thanks for the opportunity to finish my response.
Good Shooting,
George


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4/27/2006 8:47:48 PM

 
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