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11/13/2004 11:49:12 AM · #1 |
I need a little help here. I am taking some advance photo classes for 35 mm slr, and the other night the instructor took things to far in his explaination. From calling two of the other students and saying HELP I found out that I wasn't alone in the confusion.
We were discusing DOF issues and now here I am trying to study without having developed my photos for this weeks class yet and I ran into an issue that I am still not clear on. I know soon as I see my prints it will all be clear but rather than be confused for another day or two til I develop my photos I thought I would ask for some help.
For the assignment I am using a Minolta Maxxum 5 with a Minolta AF Zoom 28 to 80 lens. The lens is to be set at 50mm then I will shoot my photo at the smallest f stop then at f 8 and finally at the biggest f stop the camera will let me. The shutter speed is to be set around 1/60th.
The basic set up is to be something close up something in the middle then something off in a distance. The problem I am having here is a very simple question which f stop will create the best overall focus of the entire photo, which will create the closest object to be in focus with the backround blurred. Which will create the background to be in focus with the closest object blurred.
Somewhere along the line the instructor appears to have went into to much detail and lost everyone with to much information being thrown at us. If I just confused you welcome to the club if not can someone explain dof in a way that anyone can understand it. LOL I know how to get the effect when the camera is in my hands I just don't know the theory behind it.
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11/13/2004 11:59:39 AM · #2 |
Ignoring focal length and subject distance for a second.
The bigger the opening at the front of the camera, the less if the image will be in focus.
That is, the bigger the aperture, the smaller the DoF
Now, aperture numbers are actually fractions - so the lower the number,
the bigger the hole. (i.e. a half (1/2) is a lot bigger than an sixteenth 1/16)
So f2.8 (really 1/2.8)) is a lot bigger than f8 or (1/8)
So the smaller the aperture number, the more of the scene will be in focus.
If you want to selectively focus - i.e., have the object in the front or the back in focus while the other is out of focus, you want a shallow DoF. Shallow DoF means big aperture - which means small aperture number - so the smallest f-stop you have (f2.8 or so)
to get the object in front in focus, with the one in the back out of focus, use a big aperture (small number) and focus on the object in front.
to get the object in back in focus, with the one in the front out of focus, use a big aperture (small number) and focus on the object in back.
To get the whole scene in focus, use f8 or the largest aperture number you have (Smallest opening - think of it like squinting) then focus on the thing in the middle. |
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11/13/2004 12:06:54 PM · #3 |
OK,
Either you're confused about the problem or your teacher isn't giving you a very good exercise. The problem here is that you're describing a situation where both variable focal points and aperture are to be used. I don't understand the 1/60th of a second for the shutter speed, because (assuming it's the same scene under the same conditions) your shutter speed will have to be variable if you're changing the aperture but using the same film speed.
Obviously you're going to want the smallest f-stop possible (like f/22 or something) if you want everything in focus. The largest f-stop (f/3.5 or something on that lens) will give you a shallow depth of focus and is what I'd use if I were wanting to render the background OR foreground as blurry as possible. In that case I'd just focus on either the front or back object with a wide-open aperture.
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11/13/2004 12:13:11 PM · #4 |
The smaller number (F2 for example) will have the largest aperature and therefore a shallow DOF. This can be used to blur the foregound or the background, depending on your focal point.
Largest number, smallest aperature, deep DOF, and "the best overall focus of the entire photo".
The theory is- the large aperature is a "fast" exposure. Since the aperature is wider, light enters quickly. With a smaller aperature the shutter must remain open longer for a properly developed image.
Many people feel that this is the most important thing in photography and therefore shot primarily in Aperature priority mode.
Shallow DOF
Deep DOF
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11/13/2004 12:22:40 PM · #5 |
Originally posted by OneSweetSin:
The lens is to be set at 50mm then I will shoot my photo at the smallest f stop then at f 8 and finally at the biggest f stop the camera will let me. The shutter speed is to be set around 1/60th. |
You'll have to change the shutter speed as you change the f-stop. As you tighten the aperture (higher f-stops), you'll have to lower the shutter speed to prevent underexposure, because less light will reach the film/sensor. For instance if f/8 @ 1/60 is a good exposure, then f/11 @ 1/30 or f/16 @ 1/15 will give you the same exposure, but a different DOF. |
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11/13/2004 12:23:15 PM · #6 |
It sounds like the instructor wants you to learn from experience how fluid the depth of field is.
Here is what I think I got from your explanation.
You're supposed to shoot a closeup (maybe a macro) but its supposed to be at the smallest aperture.
Originally posted by OneSweetSin:
. . . I will shoot my photo at the smallest f stop then at f 8 and finally at the biggest f stop . . . . |
You are then supposed to move to an intermediate range subject and shoot at f/8 (which is a decent f-stop for guaranteeing yourself that humans standing side-by-side should all be in focus as long as one of them is in focus and they are all facing you). Finally you are to shoot something "off in a distance" but with the largest f-stop your lens has (if you were using a digicam instead of an SLR it would be the largest f-stop that the camera allows instead of what the lens allows since the lens and camera are all one piece in digicams).
I think the goal of this is to see that even a small f-stop (large aperture - say something like f/2.8 or f/1.8 or whatever) will give you a moderately large DoF as you move the point of focus away from yourself; hence the "off in a distance" subject. At f/2.8 if you are about 10 feet (3 meters) away from a subject you may find that focusing on his/her eyes (in a portrait) can yield out of focus noses or surrounding objects. If, however, you move the subject farther away from yourself to say around 20 feet (or 6-7 meters) you should find that most of the subject is in focus even though you didn't do anything else to the camera settings. This is an object lesson in variable depth of field due to distance. Obviously since your lens is set on 50mm your composition will be affected by moving the subject back but I think you see that the point is to show how depth of field is adjustable by varying the distance to the subject.
Conversely, with the closeup or macro shots I'm guessing that the instructor might have thought that if 10 people in a class all tried shooting a closeup at f/2.8 or f/1.8 or f/3.5 or whatever then suppose just half the class missed the focus by a smidgen and one or two others had a back-focusing or front-focusing lens error. Now most of the class will have a blurry and semi-useless shot (for instruction purposes anyway). I would think that the instructor would be attempting to show that as you move closer to your subject you need a smaller aperture (larger f-stop number) to give yourself more leeway in getting all the pretinent points of interest into focus.
Now I don't know what the instructor was thinking but this has been my best guess as to what you would actually demonstrate by doing what you wrote.
Hope the class goes well and that you get some good experiences behind the camera.
Kev
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11/13/2004 12:24:26 PM · #7 |
| The amount of focus you get will also be based on your focus distance. An f8 at 1 foot out is going to give you a lot less dof than f8 at 10ft and f8 at 10ft is not going to give you as much as f8 at 50ft. At one foot distance you will have fractions of an inch in focus, at 50 ft will will have yards(the measurement) in focus at the same f stop. |
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11/13/2004 12:24:27 PM · #8 |
Ok I think you all got me straightened out now....
A bigger f stop such as f 2.8 would mean more dof.
A smaller f stop such as f 22 would mean a shallow dof.
So putting it into what I already know and understand...a larger f stop will allow more of the scene to be in focus and the smaller f stop would mean only a small portion of the scene will be in focus.
Do I have it now?
Trust me he confused the entire class the other night, and everyone said oh well we will figure it out once we see our photos.
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11/13/2004 12:25:40 PM · #9 |
| small numbers,ex 2.8=less in focus |
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11/13/2004 12:27:19 PM · #10 |
Other way!
Large aperture NUMBER = Small Aperture SIZE = Deep DOF
Small number = Large opening = shallow DOF |
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11/13/2004 12:29:13 PM · #11 |
the best example of shallow DOF I've seen recently is this:
Edit:
while this one shows nice deep DOF
Message edited by author 2004-11-13 12:31:09.
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11/13/2004 12:30:00 PM · #12 |
Originally posted by KevinRiggs:
It sounds like the instructor wants you to learn from experience how fluid the depth of field is.
Here is what I think I got from your explanation.
You're supposed to shoot a closeup (maybe a macro) but its supposed to be at the smallest aperture.
Originally posted by OneSweetSin:
. . . I will shoot my photo at the smallest f stop then at f 8 and finally at the biggest f stop . . . . |
You are then supposed to move to an intermediate range subject and shoot at f/8 (which is a decent f-stop for guaranteeing yourself that humans standing side-by-side should all be in focus as long as one of them is in focus and they are all facing you). Finally you are to shoot something "off in a distance" but with the largest f-stop your lens has (if you were using a digicam instead of an SLR it would be the largest f-stop that the camera allows instead of what the lens allows since the lens and camera are all one piece in digicams).
I think the goal of this is to see that even a small f-stop (large aperture - say something like f/2.8 or f/1.8 or whatever) will give you a moderately large DoF as you move the point of focus away from yourself; hence the "off in a distance" subject. At f/2.8 if you are about 10 feet (3 meters) away from a subject you may find that focusing on his/her eyes (in a portrait) can yield out of focus noses or surrounding objects. If, however, you move the subject farther away from yourself to say around 20 feet (or 6-7 meters) you should find that most of the subject is in focus even though you didn't do anything else to the camera settings. This is an object lesson in variable depth of field due to distance. Obviously since your lens is set on 50mm your composition will be affected by moving the subject back but I think you see that the point is to show how depth of field is adjustable by varying the distance to the subject.
Conversely, with the closeup or macro shots I'm guessing that the instructor might have thought that if 10 people in a class all tried shooting a closeup at f/2.8 or f/1.8 or f/3.5 or whatever then suppose just half the class missed the focus by a smidgen and one or two others had a back-focusing or front-focusing lens error. Now most of the class will have a blurry and semi-useless shot (for instruction purposes anyway). I would think that the instructor would be attempting to show that as you move closer to your subject you need a smaller aperture (larger f-stop number) to give yourself more leeway in getting all the pretinent points of interest into focus.
Now I don't know what the instructor was thinking but this has been my best guess as to what you would actually demonstrate by doing what you wrote.
Hope the class goes well and that you get some good experiences behind the camera.
Kev |
Actually what he wants us to do is photograph the same scene 3 times to more understand hyperfocal distance but what he did in his eleboration of it was add a lot of confusion to where I wasn't sure which was which anymore.
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11/13/2004 12:35:59 PM · #13 |
Originally posted by GeneralE:
Other way!
Large aperture NUMBER = Small Aperture SIZE = Deep DOF
Small number = Large opening = shallow DOF |
Thank you Paul thats where the clearification issues developed in class the other night...I know the larger the number the smaller the aperture and the smaller number the larger the aperture but when putting it with getting the most and least I was confused along with everyone else cause there were a few students who just kept going over and over on that...so after about 20 minutes of larger and smaller bigger and littler I was CONFUSED...
So based on Paul's correction...
F 2.8 which would be wide open aperture that would mean a smaller dof
F 22 would be the smallest aperture but a larger dof.
Now do I have it?
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11/13/2004 12:40:09 PM · #14 |
Originally posted by skylen:
Originally posted by OneSweetSin:
The lens is to be set at 50mm then I will shoot my photo at the smallest f stop then at f 8 and finally at the biggest f stop the camera will let me. The shutter speed is to be set around 1/60th. |
You'll have to change the shutter speed as you change the f-stop. As you tighten the aperture (higher f-stops), you'll have to lower the shutter speed to prevent underexposure, because less light will reach the film/sensor. For instance if f/8 @ 1/60 is a good exposure, then f/11 @ 1/30 or f/16 @ 1/15 will give you the same exposure, but a different DOF. |
Oops I just reread my notes on he assignment, we aren't to let the shutter speed go below a 1/60th
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11/13/2004 12:48:52 PM · #15 |
You stepped into a circle of confusion!
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11/13/2004 12:51:02 PM · #16 |
Hmm,
Her is a link with some links to DOF articles.
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11/13/2004 01:35:30 PM · #17 |
| The best way to learn this is to experiment with it. I had to convince my husband that "small number = small DOF", so I sat at the dining table and took a photo of a cereal-box, with the kitchen in the background. I took one photo at the smallest possible fstop, one at the largest. Thanks to the EXIF info on digital cameras, it was very easy to see the difference in a very concrete way. |
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11/13/2004 02:30:56 PM · #18 |
| The way I used to remember this when starting out was that when there's plenty of light about, it's easier to get more dof. When the light is low, you need a tripod for lots of dof. This is why most landscape photographers use tripods. When the light is low, you need to let more light into the camera by using a wider aperture (F2.8 for example). This is no good for deep dof, so you need to use a tripod so that you can use a really long shutter speed (several seconds) and close down your aperture to F16 for example for more dof. Hope this helps! |
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