Depth of Field discussion.

[EIngerson]

Many people have the "F-stop" thought process when it comes to depth of field. We see hundreds of posts from people playing with depth of field where they only change the focal point or bump the F-stop around a little. Yes, you get a change in depth of field changing from F2.8 to F11, but that's just one element of depth of field. I am posting this to add a little inormation to that and also draw some information from some that have more knowledge. I hope this helps a few and I ask that some of the more experienced photographers please share some knowledge to make a little more sense of DOF.

In the 2 photos I'm sharing, I left all the settings the same and simply used different focal lengths and distance to subject. Same focal point and I attempted the same framing. (All the exif should be visible in Flickr) The shutter speed changed simply because I shot this in AV.

This first one was at 24mm, F2.8, Subject distance .41 meters from the subject.

DOF 2 by Ingerson"PCD", on Flickr

The second one was at 70mm, F2.8, Subject distance .89 meters from the subject.

DOF 1 by Ingerson"PCD", on Flickr

Thanks for looking.

 

[Robin Usagani]

Im not sure what you are trying to show. Basically what you did, the blurriness is similar, but the field of view is different. Also with the 70mm, your subject isnt as distorted.. you can tell the difference.

 

[Rephargotohp]

Actually what you showed disproved what you wanted to say, Since you framed your subject similarly (And you Moved) the DOF in the two images is actually the same. It appears different in the 70mm one because of Perspective Compression (Bringing the background in closer in appearance)

What you actually proved is, When framing is the same (same magnification) the only thing that will affects TRUE DOF is Aperture

 

[EIngerson]

Im not sure what you are trying to show. Basically what you did, the blurriness is similar, but the field of view is different. Also with the 70mm, your subject isnt as distorted.. you can tell the difference.

Yes, that's what I was showing. Apperantly I suck at trying to say it.

Actually what you showed disproved what you wanted to say, Since you framed your subject similarly (And you Moved) the DOF in the two images is actually the same. It appears different in the 70mm one because of Perspective Compression (Bringing the background in closer in appearance)

What you actually proved is, When framing is the same (same magnification) the only thing that will affects TRUE DOF is Aperture

Thanks for the reply. I have to disagree though. (I'm not trying to come across with attitude, so please don't take it that way)

You are correct in your statement "When framing is the same (same magnification) the only thing that will affects TRUE DOF is Aperture." I did change the magnification while framing the subject the same.Which, in turn, effectively changed the depth of field. The background dolls appear further away in one than the other. Essentially the same as changing the F-stop. Except, instead if changing the size of the aperature, I changed it's relationship to the subject.

edit: If I'm not witnessing a change in depth of field, what is it called? Am I simply confusing field of view with depth of field?

 

[djacobox372]

"When framing is the same (same magnification) the only thing that will affects TRUE DOF is Aperture."

This is only true when u change the subject distance to make up for framing. If u change the sensor size instead of the distance, the dof of the longer focal length will be more shallow.

dof is affected by three things: aperture, focal length, and subject distance.

My shallowest dof setup is a f2.5 178mm lens, but thats only because it covers 4x5" film which means im shooting at the same distances that u would shoot a 35mm lens on aps--its the long focal length and short subject distance combined with the relatively wide focal length that makes for an f0.75 equivalent dof.

 

[EIngerson]

"When framing is the same (same magnification) the only thing that will affects TRUE DOF is Aperture."

This is only true when u change the subject distance to make up for framing. If u change the sensor size instead of the distance, the dof of the longer focal length will be more shallow.

dof is affected by three things: aperture, focal length, and subject distance.

Thanks, I just wanted verification that I wasn't losing my marbles.