Focal length, focus distance, and depth of field

[Gaerek]

Actually, my experiment was regarding depth of field, not background blur, which is a different matter (as already discussed in this thread). Please take your sarcasm elsewhere. Here, it is not appreciated.

So, your experiment (hard to call it an experiment, as there were still far too many variables in it, but I'll give it to you anyway) proved that in a very specific circumstance, the apparent DoF doesn't change with focal length, given the same framing.

Whether background blur is another issue is completely irrelavent, because for all practical purposes, in most circumstances, it's the blurry background people are looking for, not a shallower DoF. DoF is just another way to control the apparent blurriness of the background. Personally, I think it'd be great if there were a control that would allow me to control background blur independently of DoF. Oh wait, there is, it's called zooming in and stepping back. Why do you think most portraits are taken in the 80-100mm range?

The old adage of, "If you want that nice blurry background, bring out the telephoto." is still very relavant, which is what everyone has been trying to tell you. Your experiment really proves very little practical, as a telephoto will give you a more blurred background, given the same framing as a wider lens. Same DoF? Fine, but what does that prove, in most practical circumstances? You will still get a more blurred background using a telephoto.

So, since you're obviously wanting this, you're right! You're completely right! Focal length doesn't affect DoF given the same framing! There, I've admitted you were right. You weren't here to learn, you were here to prove others wrong. This was glaringly obvious from the start, especially the part where you ignored the person that was trying to explain what I explained above. So much for trying to learn from others here.

I hope I'm not on ignore since I was being sarcastic. God forbid I might have something to teach.

 

[inTempus]

Sweet, progress. Nate, you're a good guy for bringing forth the evidence necessary to set things right in this thread.

 

[robertwsimpson]

Actually, my experiment was regarding depth of field, not background blur, which is a different matter (as already discussed in this thread). Please take your sarcasm elsewhere. Here, it is not appreciated.

So, your experiment (hard to call it an experiment, as there were still far too many variables in it, but I'll give it to you anyway) proved that in a very specific circumstance, the apparent DoF doesn't change with focal length, given the same framing.

Whether background blur is another issue is completely irrelavent, because for all practical purposes, in most circumstances, it's the blurry background people are looking for, not a shallower DoF. DoF is just another way to control the apparent blurriness of the background. Personally, I think it'd be great if there were a control that would allow me to control background blur independently of DoF. Oh wait, there is, it's called zooming in and stepping back. Why do you think most portraits are taken in the 80-100mm range?

The old adage of, "If you want that nice blurry background, bring out the telephoto." is still very relavant, which is what everyone has been trying to tell you. Your experiment really proves very little practical, as a telephoto will give you a more blurred background, given the same framing as a wider lens. Same DoF? Fine, but what does that prove, in most practical circumstances? You will still get a more blurred background using a telephoto.

So, since you're obviously wanting this, you're right! You're completely right! Focal length doesn't affect DoF given the same framing! There, I've admitted you were right. You weren't here to learn, you were here to prove others wrong. This was glaringly obvious from the start, especially the part where you ignored the person that was trying to explain what I explained above. So much for trying to learn from others here.

I hope I'm not on ignore since I was being sarcastic. God forbid I might have something to teach.

First, let me address the now infamous placing of darrel on the ignore list. This is not the first time that I have wanted to ignore him. He trolls the forum making stupid comments to new people and seldom attempts to help anyone. I don't really care to read sarcastic or rude comments in this thread or anywhere else. Problem solved.

Second, I was indeed testing DoF. I'm not sure why you think this is useless, because people claim that DoF becomes smaller when using a telephoto lens. That is incorrect. What I didn't know is that people (in the know) consider background blur and DoF two different things. I'd imagine I'm not the only one too. Now I know, and I can more intelligently speak on the topic. That was the whole point of this thread. Now I can see why people say "bring out the old telephoto." It's not because the DoF becomes smaller, but rather, the background blur is more pleasing. Lesson learned.

Stop being rude, sarcastic or anything else that you think is funny or will get a rise out of people and talk about the task at hand. It will keep things on topic and everyone will get more out of discussion.

 

[robertwsimpson]

Sweet, progress. Nate, you're a good guy for bringing forth the evidence necessary to set things right in this thread.

Indeed, this forum needs more Nates.

 

[inTempus]

Sweet, progress. Nate, you're a good guy for bringing forth the evidence necessary to set things right in this thread.

Indeed, this forum needs more Nates.

And not more inTempus's?

I'm crushed.

At least we agree on Derrel's "contributions" to the forum. :thumbup:

 

[NateWagner]

One other thing to remember is before the telephoto is truly useful with regards to background blur, vs. say a 50mm 1.4 the background has to be a ways away. I.E. if the background is close to the subject a 50 1.4 will actually create a more blurred background than say a 135 at 2.8. However, as the background approaches infinity distance that swings the other way.

In other words, if you're able to separate the subject from the background the fast telephoto is typically your best bet.

 

[Dao]

No, I think that when you view something in a larger print, it looks blurrier because it is larger. Nothing about the photo has changed, you're just able to inspect it at a closer level, because it is larger.

Also, I have read a little about the circle of confusion. I could definitely stand to read more, but on a basic level, I get what is happening. It's the overlap in the circles that causes the shallow DoF and the background blur. Larger aperture opening means larger circles means more overlap.

What is the meaning of DoF? I believe it is the range of distance that appear to be sharp.

Take a look at this
Image quoted from Understanding Depth of Field in Photography

When you look closer, I will say the Depth Of Field is only 3 dots. When you look it at a distance, it seems to be 5 dots.

 

[Gaerek]

No, I think that when you view something in a larger print, it looks blurrier because it is larger. Nothing about the photo has changed, you're just able to inspect it at a closer level, because it is larger.

Also, I have read a little about the circle of confusion. I could definitely stand to read more, but on a basic level, I get what is happening. It's the overlap in the circles that causes the shallow DoF and the background blur. Larger aperture opening means larger circles means more overlap.

What is the meaning of DoF? I believe it is the range of distance that appear to be sharp.

Take a look at this
Image quoted from Understanding Depth of Field in Photography


When you look closer, I will say the Depth Of Field is only 3 dots. When you look it at a distance, it seems to be 5 dots.

That's a very neat illustration. And it makes perfect sense. When I look close, only 3 dots are in sharp focus. When I step back from my screen, 5 look to be sharp. I think this is a perfect example of CoC, DoF, and how they relate to each other and with all types of blur in general.

 

[robertwsimpson]

Sweet, progress. Nate, you're a good guy for bringing forth the evidence necessary to set things right in this thread.

Indeed, this forum needs more Nates.

And not more inTempus's?

I'm crushed.

At least we agree on Derrel's "contributions" to the forum. :thumbup:

lol

One other thing to remember is before the telephoto is truly useful with regards to background blur, vs. say a 50mm 1.4 the background has to be a ways away. I.E. if the background is close to the subject a 50 1.4 will actually create a more blurred background than say a 135 at 2.8. However, as the background approaches infinity distance that swings the other way.

In other words, if you're able to separate the subject from the background the fast telephoto is typically your best bet.

That's why I was trying to use a constant f-number. Interesting things to think about though.

No, I think that when you view something in a larger print, it looks blurrier because it is larger. Nothing about the photo has changed, you're just able to inspect it at a closer level, because it is larger.

Also, I have read a little about the circle of confusion. I could definitely stand to read more, but on a basic level, I get what is happening. It's the overlap in the circles that causes the shallow DoF and the background blur. Larger aperture opening means larger circles means more overlap.

What is the meaning of DoF? I believe it is the range of distance that appear to be sharp.

Take a look at this
Image quoted from Understanding Depth of Field in Photography

When you look closer, I will say the Depth Of Field is only 3 dots. When you look it at a distance, it seems to be 5 dots.

direct quote from the first paragraph of that article:

The depth of field varies depending on camera type, aperture and focusing distance, although print size and viewing distance can influence our perception of it.

No, I think that when you view something in a larger print, it looks blurrier because it is larger. Nothing about the photo has changed, you're just able to inspect it at a closer level, because it is larger.

Also, I have read a little about the circle of confusion. I could definitely stand to read more, but on a basic level, I get what is happening. It's the overlap in the circles that causes the shallow DoF and the background blur. Larger aperture opening means larger circles means more overlap.

What is the meaning of DoF? I believe it is the range of distance that appear to be sharp.

Take a look at this
Image quoted from Understanding Depth of Field in Photography


When you look closer, I will say the Depth Of Field is only 3 dots. When you look it at a distance, it seems to be 5 dots.

That's a very neat illustration. And it makes perfect sense. When I look close, only 3 dots are in sharp focus. When I step back from my screen, 5 look to be sharp. I think this is a perfect example of CoC, DoF, and how they relate to each other and with all types of blur in general.

stepping back does not change the DoF of the photo. It changes your perception of it. Same thing with small prints vs large prints.

Think of it this way:

When you take a 800x600 resolution photo and print it out on a 8'x6' canvas and look at it close up, it will appear pixelated. Step back far enough, and you won't see the individual pixels any more, making it appear clearer. Is this because stepping back increases the resolution of the print? No, it's because your eye can not perceive the fine detail of the print anymore.

 

[robertwsimpson]

It is definitely an interesting thing to think about, though. IE, if you're planning to use a specific DoF, it will appear deeper in small prints and shallower in large prints. Something to keep in mind!

 

[Dao]

Remember one important point here, the meaning of DoF.

"Range of distance that appear to be sharp" And it is human perception as in Circle of Confusion.



From Wikipedia

"In photography, the circle of confusion (“CoC&#8221 is used to determine the depth of field, the part of an image that is acceptably sharp. A standard value of CoC is often associated with each image formathttp://en.wikipedia.org/wiki/Film_format, but the most appropriate value depends on visual acuity, viewing conditions, and the amount of enlargement. Properly, this is the maximum permissible circle of confusion, but it is commonly referred to simply as the circle of confusion"