Understanding DOF with different lenses

Hey guys, I am hoping you can help me understand how this would work.

I really love the SUUUUUPER shallow depth of field look where everything is just completely mixed and buttery in the back, much like Meg Bitton's work. http://www.megbitton.c​om/blog/?p=731

I know she really loves to use her 135mm and 200mm

My question is can you get the same depth of field with a 50mm or 85mm by just being closer? I know actually being closer does decrease your DOF, but often when I get the background as blurry as I like then the in focus part is only like an inch or so. I'm wondering if I had a 200 if I could have that blur with more room to be in focus, more like 6 inches or something. Is DOF directly related to the amount of blurriness?

yes, you can get the same DOF with a different focal length by adjusting distance to subject. Play with this: http://www.dofmaster.c​om/dofjs.html

Depends on the aperture of the wider lens. But you will not get the same look though, as telephotos compress the image. To match the look of a 135mm or 200mm, you need that focal length and aperture.

For example... Even though you can use a 50mm f/1.4, it will not look anything like the 200mm f/2 will, ever. They have a very different way of rendering images. Telephotos compress everything and will blow out the subjects not in that plane of focus with the right distances. Wider lenses even much faster aperture wise will never match that.

Tele lens gives you more dof on your subject, compression and creamy background all at the same time.

No shorter lens can achieve the same look, as you either struggle with dof if you shoot with wide aperture, or you lose the creamy oof area if you stop down to get more in focus like you described.

Invertalon wrote in post #14928289
Depends on the aperture of the wider lens. But you will not get the same look though, as telephotos compress the image. To match the look of a 135mm or 200mm, you need that focal length and aperture.

For example... Even though you can use a 50mm f/1.4, it will not look anything like the 200mm f/2 will, ever. They have a very different way of rendering images. Telephotos compress everything and will blow out the subjects not in that plane of focus with the right distances. Wider lenses even much faster aperture wise will never match that.

Focal length, by itself, does nothing to change perspective (relative sizes of elements of the scene that are at different distances from the camera). Thus, telephoto lenses do not compress images. It's the chosen distance that affects perspective. Focal length choice merely frames the subject the way you want it to.

Please read our "sticky" (found in the General Photography Talk forum) tutorial titled Perspective Control in Images - Focal Length or Distance?.

I agree.

Its possible to duplicate the DOF with a shorter lens. But you cant duplicate the FEEL the image has with another length lent.

The DOF is only part of the look. The most obvious, sure. But you will see by trying it the over-all look the image will have will not even be close. The distortion of the subject will be different as well as the compression of the background. She chose the lens she uses because of this look. Im sure it was not a random chance.

First, the DOF on the subject is a function of the framing and the aperture. So if you use a 200mm lens at 10 feet or a 400mm lens at 20 feet, you will get the same framing and thus the same DOF on the subject (assuming same aperture).

Second, DOF is related to background blur but it is not the same thing. For any given framing and focal lenght, the thinner the DOF, the greater the background blur. I know that is sort of obvious.

What is not obvious is that you can get greater background blur at the same DOF by using a longer focal length. Go back to my first example with the 200mm and 400mm lenses. If I shoot these two equal framing scenarios at the same aperture and same DOF, the 400mm lens will give a noticeably more blurred background.

So if you really like that blurry background look and have the space to do it, gravitate to longer focal lengths rather than super fast apertures. As an added bonus, using a longer focal length lens to get the blur you want instead of using a super fast aperture will give you more DOF, which is a good thing. Nothing looks crisper than a subject that is completely in focus before a very blurred background.

SkipD wrote in post #14928375
Focal length, by itself, does nothing to change perspective (relative sizes of elements of the scene that are at different distances from the camera). Thus, telephoto lenses do not compress images. It's the chosen distance that affects perspective. Focal length choice merely frames the subject the way you want it to.

Please read our "sticky" (found in the General Photography Talk forum) tutorial titled Perspective Control in Images - Focal Length or Distance?.

I clicked on the thread with the intention of linking your tutorial. Really nice work there.

Laramie wrote in post #14928671
I clicked on the thread with the intention of linking your tutorial. Really nice work there.

Indeed, kudos to you and Wilt. I think I've read that twice a year since being a member here. It's a great refresher since I often confuse the terminology in my head, even though the concepts remain.

SkipD wrote in post #14928375
Focal length, by itself, does nothing to change perspective (relative sizes of elements of the scene that are at different distances from the camera). Thus, telephoto lenses do not compress images. It's the chosen distance that affects perspective. Focal length choice merely frames the subject the way you want it to.

Please read our "sticky" (found in the General Photography Talk forum) tutorial titled Perspective Control in Images - Focal Length or Distance?.

Thanks for the link!

DOF is closely related to the size of the object within the frame, so that if you make the object identically sized with different FL and different camera position, the DOF will be close to identical. What does vary is the amount of far field blur...greater blur with longer FL.

JeffreyG wrote in post #14928663
First, the DOF on the subject is a function of the framing and the aperture. So if you use a 200mm lens at 10 feet or a 400mm lens at 20 feet, you will get the same framing and thus the same DOF on the subject (assuming same aperture).

Second, DOF is related to background blur but it is not the same thing. For any given framing and focal lenght, the thinner the DOF, the greater the background blur. I know that is sort of obvious.

What is not obvious is that you can get greater background blur at the same DOF by using a longer focal length. Go back to my first example with the 200mm and 400mm lenses. If I shoot these two equal framing scenarios at the same aperture and same DOF, the 400mm lens will give a noticeably more blurred background.

So if you really like that blurry background look and have the space to do it, gravitate to longer focal lengths rather than super fast apertures. As an added bonus, using a longer focal length lens to get the blur you want instead of using a super fast aperture will give you more DOF, which is a good thing. Nothing looks crisper than a subject that is completely in focus before a very blurred background.

pretty much sums it up

The existing DOF calculators only do one aspect of out-of-focus blur, they simply tell you was isn't "totally sharp".

What they miss is what happens to the background that is not close to focus. As mentioned using longer focal lengths "nukes" such background considerably more but I am not aware of an online resource to calculate how much.

That is why a 28mm f/1.8 full open still gives a reasonably sharp total picture of a room or a meal but a 135L at f/2.0 completely shreds the background.

Buy a full-frame body and some fast primes.

uOpt wrote in post #14937824
The existing DOF calculators only do one aspect of out-of-focus blur, they simply tell you was isn't "totally sharp".

What they miss is what happens to the background that is not close to focus. As mentioned using longer focal lengths "nukes" such background considerably more but I am not aware of an online resource to calculate how much.

That is why a 28mm f/1.8 full open still gives a reasonably sharp total picture of a room or a meal but a 135L at f/2.0 completely shreds the background.

Unfortunately not compatible with all versions of Windows...

http://www.bobatkins.c​om …okeh_background​_blur.html