The park

[Evertking]

6d
17-40
Ad600

[Shadowman]

Nice atmospheric shot, the focal length chosen has created a bit of distortion in the model's body though.

[rpcrowe]

Using a short focal length can be problematic when photographing people (animals too but, we seem to be more conscious of peoples bodies being distorted).

In this case, shooting with short focal length places more emphasis on Cheyenne's lower trunk, legs and even feet making them appear unnaturally large. Camera placement and angle can solve this to a small degree but, IMO, the better solution is to use a longer focal length lens and shoot from a further distance...

Another added bonus, of using a longer focal length lens, in most cases is the separation it can impart to your subject from the background, especially when shooting at a relatively wide aperture...

[DanK]

Another added bonus, of using a longer focal length lens, in most cases is the separation it can impart to your subject from the background, especially when shooting at a relatively wide aperture..

Unrelated to DOF, longer focal lengths provide more background blur. That is, out of focus areas will be more blurred. This is simply a function of the narrower angle of view, which results in a smaller amount of stuff at a given distance being spread across the frame.

Except when I have a specific reason to get close--e.g., being in a small room--I never use a short lens for shooting people, and I don't think I have ever used my 17-40 for that. On a FF like yours, the classic focal length for portraits to get a flattering perspective is 85-105 mm or so, although going substantially longer has only modest effects. So in close quarters, I use my 24-105 (never going as wide as 24), and when I have more room, I often use a 70-200.

[rpcrowe]

Along with Dan's comment... I really like a 28-70mm lens on a crop format camera for shooting people. The 28mm on a crop format equates to about 42mm on a full frame camera, when shooting with a 1.5x crop sensor and 44.8mm when shooting with a 1.6x sensor. This is wide enough to get a little extra in the frame, yet is close enough to a normal 50mm focal length that the perspective distortion when shooting people is not that serious.

OTOH: the 70mm gives me an equivalent 105mm (1.5x sensor) or 112mm (1.6x sensor); either of which is a very decent portrait focal length...

I have a Tokina 28-70mm f/2.8 ATX for my Canon and a kit 28-70mm Sony for my A6500... I don't feel constrained by either lens...

You could, of course shoot with a zoom with a wider focal length (such as 24mm) just making sure that you are not shooting at the widest end of the zoom.

[george013]

Unrelated to DOF, longer focal lengths provide more background blur. That is, out of focus areas will be more blurred. This is simply a function of the narrower angle of view, which results in a smaller amount of stuff at a given distance being spread across the frame.

Except when I have a specific reason to get close--e.g., being in a small room--I never use a short lens for shooting people, and I don't think I have ever used my 17-40 for that. On a FF like yours, the classic focal length for portraits to get a flattering perspective is 85-105 mm or so, although going substantially longer has only modest effects. So in close quarters, I use my 24-105 (never going as wide as 24), and when I have more room, I often use a 70-200.

What is the difference between out of focus and blurred? Both are the result a coc that's out of the range of dof. I think what you're referring to is the flattening of an image when using a tele lens and a longer subject distance.

George

[DanK]

No, I am not referring to the flattening of the image. Unfortunately, a web page that explained this well, including photographs, has been taken down. Here's a quick verbal explanation. Suppose you take a photo of an object 1 m away from the camera. The background, 25 m distant, is a row of trees parallel to the sensor. Take this twice, once with a short focal length and once with a long focal length, using f/2.8 in both cases to throw the trees out of focus. Now think of the geometry. The longer focal length with have a narrower AOV. therefore, the background will have fewer out-of-focus trees spread across the frame. That additional blurring is what is called background blur, at least in English. this difference occurs despite the fact that the DOF for the two images will be nearly identical.

[george013]

No, I am not referring to the flattening of the image. Unfortunately, a web page that explained this well, including photographs, has been taken down. Here's a quick verbal explanation. Suppose you take a photo of an object 1 m away from the camera. The background, 25 m distant, is a row of trees parallel to the sensor. Take this twice, once with a short focal length and once with a long focal length, using f/2.8 in both cases to throw the trees out of focus. Now think of the geometry. The longer focal length with have a narrower AOV. therefore, the background will have fewer out-of-focus trees spread across the frame. That additional blurring is what is called background blur, at least in English. this difference occurs despite the fact that the DOF for the two images will be nearly identical.

Background blur is called bokeh in Japanese. It's a characteristic of the used lens, not the focal length. It's something in a range of in-focus,out-focus,bokeh. In that last one the characteristics due to lens design are becoming stronger.

You'll get a different picture if you start with let's say 10m

George

[DanK]

No, George, you are wrong on both counts. That isn't usually what bokeh is used to mean, and background blur as I described is is a simple function of geometry (or, I suppose, trigonometry) and has nothing to do with any characteristic of the lens other than focal length. I thought my explanation was clear, but regardless, I won't argue it with you about this. If you don't understand, try it yourself. The concrete examples might help you understand.

bokeh is typically used to describe the overall quality of blur resulting from all factors: DOF, focal length, and other aspects of lens design (hence the term, for example, "onion bokeh")

[xpatUSA]

... this difference occurs despite the fact that the DOF for the two images will be nearly identical.

For some reason the CiC calculator disagrees, Dan. At a shooting distance of 1m, the DOFs for say a 28mm and a 105mm are considerably different.

What am I missing?

[Stagecoach]

What am I missing?

The bit that would or could mention "when the subject is framed the same"

[george013]

For some reason the CiC calculator disagrees, Dan. At a shooting distance of 1m, the DOFs for say a 28mm and a 105mm are considerably different.

What am I missing?

Plus that a shooting distance of 1 meter is not realistic in this situation. Figures are changing with longer distances.
And it's good habit to compare the use of different focal lengths with an equal framing of the main subject.
Plus that using a bigger focal length might half the background and double the magnification: double unsharp.

George

[DanK]

The bit that would or could mention "when the subject is framed the same"

Exactly. My error. The distance from the subject needs to be different in order to frame it similarly.

The page I was looking for is not yet reposted, but the photos at this page:
https://digital-photography-school.c...-in-portraits/ illustrate the phenomenon I described.

[george013]

Exactly. My error. The distance from the subject needs to be different in order to frame it similarly.

The page I was looking for is not yet reposted, but the photos at this page:
https://digital-photography-school.c...-in-portraits/ illustrate the phenomenon I described.

I'll ask again:

What is the difference between out of focus and blurred? Both are the result of a coc that's out of the range of dof.

George

[DanK]

I'll ask again:
What is the difference between out of focus and blurred? Both are the result of a coc that's out of the range of dof.
George

No, George. The phenomenon I described is not a result of the circle of confusion. It is a result of angle of view. I have explained this verbally and provided photos that clearly illustrate the phenomenon.

Sorry that I am unable to explain this to you.

I'm out.

[george013]

No, George. The phenomenon I described is not a result of the circle of confusion. It is a result of angle of view. I have explained this verbally and provided photos that clearly illustrate the phenomenon.

Sorry that I am unable to explain this to you.

I'm out.

What you call angle of view I would call magnification. If your framing on the same distance is half of the framing with another focal length, then the magnification is twice as big. So your coc will be magnified twice as much.
I'm not sure if coc is the right word. It's the diameter of the topped off light cone belonging to that distance. Or in this situation the extension of that light cone.

George

[xpatUSA]

What you call angle of view I would call magnification. If your framing on the same distance is half of the framing with another focal length, then the magnification is twice as big. So your coc will be magnified twice as much.
I'm not sure if coc is the right word. It's the diameter of the topped off light cone belonging to that distance. Or in this situation the extension of that light cone.
George

I have a spreadsheet based on magnification input instead of shooting distance. It agrees with you, George.

For 1000mm appearing on the sensor as 13mm (1:77):

28mm FL lens: calculated shooting distance 2.21m, DOF 566mm.

105mm FL lens: calculated shooting distance 8.29m, DOF 557mm.

And, as you say, the Cone of Confusion varies with Focal Length ...

The Calculator is useful for close-up/ macro work.

[DanK]

Ted, I don't understand your post. At issue was a background that is at a constant distance from the sensor.

However, I think I was wrong: I now think that George and I, while arguing, were actually saying the same thing. For a given distance, magnification of the background with respect to the frame is a simple trigonometric function of angle of view. So when I wrote about AOV and George wrote about magnification, I don't think we were disagreeing.

Similarly, I think noting a larger CoC is simply a more precise way of describing what I was referring to ambiguously as a stretching of content. It isn't the content per se; it's the data in the content. A painter might paint the smaller background area that appears with a longer focal length while not introducing blur. Doing that would require adding more data for an element of a given (real) size than is necessary to maintain the same level of apparent sharpness if the element were pained smaller. We can't do that with a photograph.

Be that as it may, I think the starting point is still this: longer focal lengths will blur the background more than shorter focal lengths, if the subject is placed the appropriate distance to maintain the same size relative to the frame, and this is not DOF. Another way to put this is that once an area is no longer sharp enough to be considered within DOF, sharpness falls off more quickly with distance if you use a longer focal length. This is one reason why some macro photographers prefer longer focal lengths.

[xpatUSA]

Ted, I don't understand your post. ...

Sorry, Dan, which line of the post was not understood?

I was agreeing with George and providing some numbers; I based my magnification on the subject's projection guessing at a tree 1000mm wide. The calculator is not designed for backgrounds. By "framing" I had reasonably assumed that George meant the foreground in-focus subject.