aperture question

[swmocity]

and yes i have looked it up already...ive seen some full body picture where the background is completely out of focus...to get the background out of focus u would have to use 2.8...2.2...i understand that...but what i dont understand is how is it possible to use a low fstop but still manage to get the full body in focus and the background blurred...dosent a low fstop decrease the DOF?

 

[Bitter Jeweler]

DOF changes with your distance from the focused subject.

 

[Markw]

DOF changes with your distance from the focused subject.

Care to elaborate?

Mark

 

[Sachphotography]

Well. Um...hmmm.. I am confused. Why would you want to use a low f stop but have a wide DOF they slightly contradict each other. What are you trying to do? The only way to use a lens at a low F stop would be to position you self further away from the object in which you are taking a picture. Does that help? If you are not further away, your DOF will be shallow

 

[swmocity]

Well. Um...hmmm.. I am confused. Why would you want to use a low f stop but have a wide DOF they slightly contradict each other. What are you trying to do? The only way to use a lens at a low F stop would be to position you self further away from the object in which you are taking a picture. Does that help? If you are not further away, your DOF will be shallow

i just happeen to look at the picture on the net and it kind of confused me...it was a full body picture of two people, like a downtown street location...but the background was all the way out of focus but the people werent...to get the background completely wouldnt u have to use a low fstop? which decreases the DOF...but somehow the subjects entire body was still in focus

 

[swmocity]

or maybe it was the distance between the subject and the background and not so much of the fstop...i cant find the link to the picture

 

[Markw]

That sounds like it could be it. The low F-stop does give you a shallow DOF, but that DOF is still wherever you focus, so if the photographer focused on the people, they would be in focus, but anything behind them and infront of them would be out of focus. The further in the foreground and further in the background you go, the more out of focus the image will become with any F-stop. The severity of the blurred back and foreground is just dramatically increased with a low F-stop.

Hope that makes sense.
Mark

 

[Dao]

Aperture is one of the factor when calculating DoF. There are other factors controlling the DoF.


Go here
Online Depth of Field Calculator

While you are there, choose the camera and play with the settings.

Now, set the Focal Length, F-stop and the subject distance.
Change one settings at a time. i.e., if you want to know the effect of aperture on DoF, just change the Aperture.

Pay attention to the Depth of Field - Near limit and Far limit.

Anything within the range of Near limit and Far limit are going to be in focus. As you will see, you can make it so that the distance between Near limit and Far limit (DoF) is couple feet long (even if the Aperture is wide). In that case, both person should be in focus.

 

[Sachphotography]

Im lost.... sorry. I don't know what you are asking. Only thing I can think of would be the distance between the background and the people
but that was already said.

 

[Markw]

That link was extremely informative (sp?). Helped alot with my understanding. Thanks.

Mark

 

[swmocity]

That sounds like it could be it. The low F-stop does give you a shallow DOF, but that DOF is still wherever you focus, so if the photographer focused on the people, they would be in focus, but anything behind them and infront of them would be out of focus. The further in the foreground and further in the background you go, the more out of focus the image will become with any F-stop. The severity of the blurred back and foreground is just dramatically increased with a low F-stop.

Hope that makes sense.
Mark

yes one more question...so basically its like a "focus circle" i guess?...does the DOF start out in the middle then expands out in a circular pattern...hopes that make since...its kind of hard to explain lol

 

[swmocity]

Aperture is one of the factor when calculating DoF. There are other factors controlling the DoF.


Go here
Online Depth of Field Calculator

While you are there, choose the camera and play with the settings.

Now, set the Focal Length, F-stop and the subject distance.
Change one settings at a time. i.e., if you want to know the effect of aperture on DoF, just change the Aperture.

Pay attention to the Depth of Field - Near limit and Far limit.

Anything within the range of Near limit and Far limit are going to be in focus. As you will see, you can make it so that the distance between Near limit and Far limit (DoF) is couple feet long (even if the Aperture is wide). In that case, both person should be in focus.

thank you...this explains it all

 

[Markw]

Im lost.... sorry. I don't know what you are asking. Only thing I can think of would be the distance between the background and the people
but that was already said.

Ill show you an example. At 50mm, F/1.8 and the subject in focus at 10 feet from the lens, the total distance in focus (infront of to behind the subject, including the subject) is .86 feet or 10-11inches.

If you take the distance of the subject down to 10 inches as if you were taking macro photography, but otherwise keep the F/1.8 and 50mm, the total distance in focus would be only .06". The aperture was kept the same, the focal length was kept the same, but the distance between camera and subject was decreased. That was the only thing that changed and yet the DOF was decreased dramatically because of this.

Mark

 

[Markw]

That sounds like it could be it. The low F-stop does give you a shallow DOF, but that DOF is still wherever you focus, so if the photographer focused on the people, they would be in focus, but anything behind them and infront of them would be out of focus. The further in the foreground and further in the background you go, the more out of focus the image will become with any F-stop. The severity of the blurred back and foreground is just dramatically increased with a low F-stop.

Hope that makes sense.
Mark

yes one more question...so basically its like a "focus circle" i guess?...does the DOF start out in the middle then expands out in a circular pattern...hopes that make since...its kind of hard to explain lol

I wouldnt call it a circle, more of a plane I think. If you were to look at a pool table from standing position and focus on the middle at F/8, you would only get about a quarter of the table in focus, but the floor and ceiling to the left, right, top, and bottom, of the plane would be in focus too, just not outside of that plane.

If you were to take the same pool table, but look at it from above straight down with an aperture of F/8, since the pool table top is flat, the whole 8' (or as much of it that can be in frame) would be in focus, but the ground under the table wouldnt be because its not in the verticle plane of focus.

The plane is always straight up and down, left and right. The only thing that changes is the thickness and that is with a change in the aperture (F-stop). Larger numbers, the thicker the plane. Smaller numbers, the thinner the plane. So its nore like a verticle square than a horizontal circle, if that makes sense.

Mark

 

[Markw]

Take this photo for example, the DOF holds to the left and right of the bug, but is super thin, its not a circle around the bug, but continues forever in both directions (it would up and down too, but theres nothing there to focus on)

Also take into consideration the distance between the camera and the fly was about 2", so the aperture took full effect and made the DOF super thin and the rate at which the back and foreground got blurry much, much quicker than usual. The bug was only about 1/4" long.

Mark