Focal length, focus distance, and depth of field

[inTempus]

You should probably just put me on your ignore list

Nah, I enjoy reading threads where folks impale themselves.

I'll let ya have your thread back. I'll keep checking in to see how things progress... hopefully they do progress.

 

[Derrel]

By the way, comments and questions are very welcome. We're all here to learn. If you think I've gotten something wrong here, please let me know. Just be respectful.

Hmmm, that's interesting that you would say that.

"You got some things wrong."

 

[robertwsimpson]

I wish you lot would learn to debate rather than just keep sniping at each other. It gets very wearing reading though threads where its only sniping at each other rather than a proper healthy debate (as such its taking me a while to get through this thread)

A quick observation though is could you repeat the test where this time you shoot a subject away from the minimum focusing distance of the lens and keep the camera to subject distance and the aperture but vary the focal length.

I know what will happen when I do that, because I have zoom lenses. When you zoom in on an object without moving yourself or that object, your DoF becomes smaller. That's not what I'm debating. The fact that people keep trying to debate this fact is the thing that is getting annoying in this thread.

 

[robertwsimpson]

A little humility goes a l-o-n-g way

so does making a contribution to a debate instead of dropping by to say something that doesn't have to do with anything being talked about.

 

[robertwsimpson]

You should probably just put me on your ignore list

Nah, I enjoy reading threads where folks impale themselves.

I'll let ya have your thread back. I'll keep checking in to see how things progress... hopefully they do progress.

given the last 3 "contributions," not likely.

 

[SoonerBJJ]

A little humility goes a l-o-n-g way

so does making a contribution to a debate instead of dropping by to say something that doesn't have to do with anything being talked about.

I think the debate ended awhile ago. You're the only one who hasn't caught on.

"Impaling" is a good descriptor. I was thinking it was like watching a trainwreck in slow motion but I like impaling better.

:thumbup:

 

[kundalini]

so does making a contribution to a debate instead of dropping by to say something that doesn't have to do with anything being talked about.

WOW, I thought I was on your ignore list.

My contribution was a concern for cooler heads to prevail before this got really nasty (again) for no good reason. The fact that I haven't contributed to this point doesn't represent this was my first glance at this thread. The fact that I'm pretty comfortable with my gear to obtain the background blur that I desire doesn't mean that I can't still learn more. Stosh and Derrel (yes, there's an e in his name) made some very good comments on the technical side. It became quite boring with your unbending stance.... and lack of humility. The fact that someone else may know more about a subject than you is life. How you deal with it shows character. You did a good thing to start this off for newbies, but this is a far cry from a debate.

Now, if you care to retort with another smartass comment, fire away.

 

[NateWagner]

Robert, check out this site, it pretty much agrees with exactly what Stosh and Derrel have been saying.

http://www.bobatkins.com/photography/technical/bokeh.html
Bokeh and Background Blur Calculator- Bob Atkins Photography

(the image was taken from the site linked, it is not mine. If this is against specific rules I will pull it down, but I thought it was a good example to show those interested).

As you can see, although they were taken from different distances in order to achieve the same FOV, the blurriness of the background is different. The primary reason for this is the physical size of the aperture.

 

[Gaerek]

Robert, check out this site, it pretty much agrees with exactly what Stosh and Derrel have been saying.

Bokeh and Background Blur - Bob Atkins Photography
Bokeh and Background Blur Calculator- Bob Atkins Photography

(the image was taken from the site linked, it is not mine. If this is against specific rules I will pull it down, but I thought it was a good example to show those interested).


As you can see, although they were taken from different distances in order to achieve the same FOV, the blurriness of the background is different. The primary reason for this is the physical size of the aperture.

So Robert's experiment had been tried before...they did a better job of it, in a MUCH more controlled environment, and got the results that everyone BUT Robert have been saying he should have gotten? Absolutely amazing...

 

[robertwsimpson]

Robert, check out this site, it pretty much agrees with exactly what Stosh and Derrel have been saying.

Bokeh and Background Blur - Bob Atkins Photography
Bokeh and Background Blur Calculator- Bob Atkins Photography

(the image was taken from the site linked, it is not mine. If this is against specific rules I will pull it down, but I thought it was a good example to show those interested).

As you can see, although they were taken from different distances in order to achieve the same FOV, the blurriness of the background is different. The primary reason for this is the physical size of the aperture.

Thank you for actually presenting data with your post. It's refreshing!

I saw the same thing in my photos at 18mm and 55mm... I guess the way that I saw it was that the background becomes apparently larger with longer focal lengths, which in my mind didn't mean that they were necessarily more blurry, just that they were larger. In this version with the trees, they do look more blurry though. Interesting.

 

[robertwsimpson]

Robert, check out this site, it pretty much agrees with exactly what Stosh and Derrel have been saying.

Bokeh and Background Blur - Bob Atkins Photography
Bokeh and Background Blur Calculator- Bob Atkins Photography

(the image was taken from the site linked, it is not mine. If this is against specific rules I will pull it down, but I thought it was a good example to show those interested).


As you can see, although they were taken from different distances in order to achieve the same FOV, the blurriness of the background is different. The primary reason for this is the physical size of the aperture.

So Robert's experiment had been tried before...they did a better job of it, in a MUCH more controlled environment, and got the results that everyone BUT Robert have been saying he should have gotten? Absolutely amazing...

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.

 

[Dao]

Robert, check out this site, it pretty much agrees with exactly what Stosh and Derrel have been saying.

Bokeh and Background Blur - Bob Atkins Photography
Bokeh and Background Blur Calculator- Bob Atkins Photography

(the image was taken from the site linked, it is not mine. If this is against specific rules I will pull it down, but I thought it was a good example to show those interested).

As you can see, although they were taken from different distances in order to achieve the same FOV, the blurriness of the background is different. The primary reason for this is the physical size of the aperture.

Thank you for actually presenting data with your post. It's refreshing!

I saw the same thing in my photos at 18mm and 55mm... I guess the way that I saw it was that the background becomes apparently larger with longer focal lengths, which in my mind didn't mean that they were necessarily more blurry, just that they were larger. In this version with the trees, they do look more blurry though. Interesting.

In real life, there is a definition of sharpness. Read up on Circle of Confusion (CoC). If you talks about DoF, you may want to know about CoC first.

If there are 2 dots in the background, with the 18mm lens, the 2 dots may appear as 1 dot. However, when you use a telephoto lens, the 2 dots may appear to be 2 blurry dots. But of course, when you print that photo out and look at it at a distance, it may appear as one dot again.


In your example. the effect may not be too huge. However, if you compare a 24mm photo with a 300mm photo, you may see a bigger difference. When an out of focus object was enlarged, it may appear to have more blur especially when the background is further away from the subject.

You can do another experiment. Subject in the foreground. And an big object such as road sign (in a distance) in the background. Take a photo with 24mm, then take another one with 200mm or 250mm with the framing and with aperture set as F/5.6. You may notice that the road sign may appear pretty sharp (of course, it depends on the distance between the subject and the camera). And the road sign in the one you take with the 250mm may appear to have more blur.

But I believe once you enlarge the road sign in the 24mm photo so that the size of the road sign is about the same as the one in 250mm, both sign may look about the same.

I think what that means is the DoF maybe the same, however, the one with the telephoto will have a better blur background and that is what people always want to suggest to other to use a telephoto lens when someone want to have a nice bokeh. (of course, there are other options as well such as aperture size, medium format, subject to camera and subject to background distance)


Of course, this is just my theory, I could be wrong. I hope HelenB is here to explain in details!

 

[robertwsimpson]

Robert, check out this site, it pretty much agrees with exactly what Stosh and Derrel have been saying.

Bokeh and Background Blur - Bob Atkins Photography
Bokeh and Background Blur Calculator- Bob Atkins Photography

(the image was taken from the site linked, it is not mine. If this is against specific rules I will pull it down, but I thought it was a good example to show those interested).

As you can see, although they were taken from different distances in order to achieve the same FOV, the blurriness of the background is different. The primary reason for this is the physical size of the aperture.

Thank you for actually presenting data with your post. It's refreshing!

I saw the same thing in my photos at 18mm and 55mm... I guess the way that I saw it was that the background becomes apparently larger with longer focal lengths, which in my mind didn't mean that they were necessarily more blurry, just that they were larger. In this version with the trees, they do look more blurry though. Interesting.

In real life, there is a definition of sharpness. Read up on Circle of Confusion (CoC). If you talks about DoF, you may want to know about CoC first.

If there are 2 dots in the background, with the 18mm lens, the 2 dots may appear as 1 dot. However, when you use a telephoto lens, the 2 dots may appear to be 2 blurry dots. But of course, when you print that photo out and look at it at a distance, it may appear as one dot again.


In your example. the effect may not be too huge. However, if you compare a 24mm photo with a 300mm photo, you may see a bigger difference. When an out of focus object was enlarged, it may appear to have more blur especially when the background is further away from the subject.

You can do another experiment. Subject in the foreground. And an big object such as road sign (in a distance) in the background. Take a photo with 24mm, then take another one with 200mm or 250mm with the framing and with aperture set as F/5.6. You may notice that the road sign may appear pretty sharp (of course, it depends on the distance between the subject and the camera). And the road sign in the one you take with the 250mm may appear to have more blur.

But I believe once you enlarge the road sign in the 24mm photo so that the size of the road sign is about the same as the one in 250mm, both sign may look about the same.

I think what that means is the DoF maybe the same, however, the one with the telephoto will have a better blur background and that is what people always want to suggest to other to use a telephoto lens when someone want to have a nice bokeh. (of course, there are other options as well such as aperture size, medium format, subject to camera and subject to background distance)


Of course, this is just my theory, I could be wrong. I hope HelenB is here to explain in details!

That's what I am thinking actually. It's very hard to judge background blurriness when there is such a giant size difference in the photo with different focal lengths... That's why I was mainly concentrating on Depth of Field.

When an object is larger in a photo, but the same amount of blur is present, it definitely appears "more" blurry, so maybe that is why people go for longer focal lengths.

 

[Dao]

When you read up on Circle of Confusion, you will see the Depth Of Field is related to it closely. Let's take another example, you take a photo and print it on a 4x6 and view it at the normal hand held distance. Now print the same photo on a poster size and view it at the same distance.

You may notice some object in the background now appear to be out of focus in the poster because the object is blur. However, same object in the other photo is in focus since it is decently sharp. Do you think the Depth of field had changed?

 

[robertwsimpson]

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.