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question about f-stops

pontifex

pontifex

Lifer
so i read Understanding Exposure: How to Shoot Great Photographs with a Film or Digital Camera and wanted to try out some things or just practice some things i learned.

one thing was about f-stop and depth of field. the author says if you use a low f-stop you get less depth of field, which is good for portraits where you want the subject in focus and the background out of focus.

well, i can't get my camera to do this. it wants to get everything in focus. what am i doing wrong?

i was using a 18-55mm lens, at f4 i believe. now i was using the manual setting but with the autofcus turned on. do i have to manually focus to get what i want or what do i need to do?
 
No you don't have to manually focus. Manually focusing is the same as autofocus, but you're doing it.
 
IIRC, if you want a more specific part of a picture in focus, you want a lower depth of field, but you have to make sure the subject is the part in focus. Try taking a pic with manual focus, it's easier to control for taking a stationary pic. However, it depends on how much space there is between the subject and the background.
 
Originally posted by: Aflac
IIRC, if you want a more specific part of a picture in focus, you want a lower depth of field, but you have to make sure the subject is the part in focus. Try taking a pic with manual focus, it's easier to control for taking a stationary pic. However, it depends on how much space there is between the subject and the background.
Click to expand...

one of the examples the author used was this middle eastern man as a close up portrait shot but in the background (about 8-10 ft away i would guess) is another man in front of a wall. main subject was in focus but the wall and other man were out of focus.


i'm trying to learn this stuff so i can take better pics but i'm getting frustrated because my stuff isn't turning out the way it should from what i learned.
 
Just mess around. Try doing lower f-stops (if your lens lets you) or manual focusing to see if you can get what you want. Personally, I think it's best to learn something through trial & error and experience.
 
Try shooting at an even lower f-stop. Also manually focus. What mugs said is true, but how does the camera know what you want in focus and what you dont? They aren't very smart when it comes to DOF shooting. And like Aflac said, it depends on the distance your subject is from the background. The closer the background is the more in focus it will be compared to the subject. Also it depends on how close you are to the subject. The closer you are (within reason), the greater depth of field you will get.
 
Originally posted by: fuzzybabybunny
Switch camera to Aperture Priority, and stop up the lens to its maximum aperture.
Click to expand...

i think i tried that and got the same result, because after he talked about Aperture priority and shutter priority, i thought that was pretty handy.
 
Originally posted by: pontifex
Originally posted by: Aflac
IIRC, if you want a more specific part of a picture in focus, you want a lower depth of field, but you have to make sure the subject is the part in focus. Try taking a pic with manual focus, it's easier to control for taking a stationary pic. However, it depends on how much space there is between the subject and the background.
Click to expand...

one of the examples the author used was this middle eastern man as a close up portrait shot but in the background (about 8-10 ft away i would guess) is another man in front of a wall. main subject was in focus but the wall and other man were out of focus.
Click to expand...

Just FYI, when you really want to get that background out of focus effect, you need a pretty large apertures like f/1.8, f/2.2, and f/2.5.
 
Originally posted by: InverseOfNeo
Try shooting at an even lower f-stop. Also manually focus. What mugs said is true, but how does the camera know what you want in focus and what you dont? They aren't very smart when it comes to DOF shooting. And like Aflac said, it depends on the distance your subject is from the background. The closer the background is the more in focus it will be compared to the subject. Also it depends on how close you are to the subject. The closer you are (within reason), the greater depth of field you will get.
Click to expand...

i think this lens only goes to f4 or maybe f3.5
 
Originally posted by: fuzzybabybunny
Originally posted by: pontifex
Originally posted by: Aflac
IIRC, if you want a more specific part of a picture in focus, you want a lower depth of field, but you have to make sure the subject is the part in focus. Try taking a pic with manual focus, it's easier to control for taking a stationary pic. However, it depends on how much space there is between the subject and the background.
Click to expand...

one of the examples the author used was this middle eastern man as a close up portrait shot but in the background (about 8-10 ft away i would guess) is another man in front of a wall. main subject was in focus but the wall and other man were out of focus.
Click to expand...

Just FYI, when you really want to get that background out of focus effect, you need a pretty large apertures like f/1.8, f/2.2, and f/2.5.
Click to expand...

well, the author said he was using f4 for the example pic i was referring to, unless that was a typo.
 
Also, try moving your self back, and zooming in all the way. A lower f-stop means more light comes in, so you want alot of light to get a a higher f-stop, and then close the iris.
 
Originally posted by: BroeBo
Can you show us an example of yours? With EXIF please.
Click to expand...

can't right now because i'm at work. i may even have deleted them because they didn't turn otu the way i wanted. i could take some more again though.
 
if you don't get it before I get home, I'll take out my S3 and try a few things. The S3 isn't the best camera to make example pics, but it should work...
 
Originally posted by: Quasmo
Also, try moving your self back, and zooming in all the way. A lower f-stop means more light comes in, so you want alot of light to get a a higher f-stop, and then close the iris.
Click to expand...

maybe i should use a differnt lens? like a 70-300 or a 28-80?

the thing is, when i zoom in, the fstop changes to a higher number too.
 
Originally posted by: pontifex
Originally posted by: fuzzybabybunny
Originally posted by: pontifex
Originally posted by: Aflac
IIRC, if you want a more specific part of a picture in focus, you want a lower depth of field, but you have to make sure the subject is the part in focus. Try taking a pic with manual focus, it's easier to control for taking a stationary pic. However, it depends on how much space there is between the subject and the background.
Click to expand...

one of the examples the author used was this middle eastern man as a close up portrait shot but in the background (about 8-10 ft away i would guess) is another man in front of a wall. main subject was in focus but the wall and other man were out of focus.
Click to expand...

Just FYI, when you really want to get that background out of focus effect, you need a pretty large apertures like f/1.8, f/2.2, and f/2.5.
Click to expand...

well, the author said he was using f4 for the example pic i was referring to, unless that was a typo.
Click to expand...

I thought you needed a smaller aperature, hence an f-stop of 4 and up.
 
Originally posted by: pontifex
Originally posted by: Quasmo
Also, try moving your self back, and zooming in all the way. A lower f-stop means more light comes in, so you want alot of light to get a a higher f-stop, and then close the iris.
Click to expand...

maybe i should use a differnt lens? like a 70-300 or a 28-80?

the thing is, when i zoom in, the fstop changes to a higher number too.
Click to expand...

that shouldn't happen.

EDIT: Apparently it should, I'm a cinematographer, the lenses I use are $8k I didn't know about the cheaper ones 🙁, just trying to help out with technique.
 
Originally posted by: Aflac
if you don't get it before I get home, I'll take out my S3 and try a few things. The S3 isn't the best camera to make example pics, but it should work...
Click to expand...

SLRs are the only ones that can create this affect to a degree where it is very noticeable.
 
Have you tried tests at f/3.5 - f/4? Make sure your lens is at this aperture, then focus on something and take the picture. The background is now blurred. Stop the lens down to f/16 and focus on the same subject and take the same picture. Now the background is less blurred.
 
Originally posted by: Quasmo
Originally posted by: pontifex
Originally posted by: Quasmo
Also, try moving your self back, and zooming in all the way. A lower f-stop means more light comes in, so you want alot of light to get a a higher f-stop, and then close the iris.
Click to expand...

maybe i should use a differnt lens? like a 70-300 or a 28-80?

the thing is, when i zoom in, the fstop changes to a higher number too.
Click to expand...

that shouldn't happen.
Click to expand...

Sure about that? My camera changes from a maximum aperture of f-2.7 at the widest setting, but it changes to f-3.5 at the maximum zoom setting (432mm, 35mm equivalent).
 
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