Question regarding DOF

[EllaElla]

I have been trying some different photos and learning about Depth of field. I am trying to focus on a point about 8' away, while making the foreground and the background out of focus.

For example; I was shooting my friend. He was sitting at a desk with his feet up on the corner. I was shooting from where his feet were. I wanted to focus on his face, leaving his feet out of focus and the stuff behind him out of focus.

From this same shot, I also tried shooting a wide aperture, with a high ISO about 1600 because the space isn't very well lit. So I have a great shot of his shoes, leaving his face out of focus. But how do I do the opposite?

 

[enzodm]

First, put examples, so that is easier to see than verbal descriptions.
Then, if you focus on the face, you should have the face in focus. If not, you did not focus on the face: if you see his shoes on focus, this means that you focused on the shoes. Maybe are you using auto focus point selection, so that you are not choosing where to focus?

And: the overall level of blurring depends on your lens.

 

[Overread]

It would also help to give us an idea of the camera that you were using at the time. It sounds like what has happened is that the auto focus in the camera locked onto his feet (AF generally works by finding the closest possible point it can focus upon) and thus you got the in focus feet; which when combined with the wide aperture resulted in his face being out of the depth of field and thus blurry.

Manual focusing or changing the AF focus point selection option can be ways to help solve this problem - though how much you can adjust these will depend on the type of camera that you have.

 

[KmH]

And: the overall level of blurring depends on your lens.

Actually, the overall distribution of blur in the image is controlled by a number of things.

Focus point distance from the image sensor, relative to the lens focal length, and lens aperture is a major factor.

Focus point distance from the background is also a factor.

In summary, focus point distance generally has the biggest impact on depth-of-field (DoF).

DoF is a plane of acceptable focus parallel to the image sensor. How deep that plane is (it's foreground to backgrond distribution in the final image) is what the photographer wants to control.

DoF seems to be the most important technical aspect of photography, because it so closely relates to focus, that people have difficulty understanding.

On can plug various numbers into a DoF calculator to gain a better understanding of how the various factors the photographer can control affect the depth and where within a scene that zone of acceptably sharp focus will be.

I prefer the display this online calculator generates - http://www.tawbaware.com/maxlyons/calc.htm

But many link to this one - http://dofmaster.com/dofjs.html

 

[EllaElla]

I'm sorry. I live on a ship. We have limited web browsing hours and we can't upload anything onto the government computers. I have to use a laptop and burn them to a CD first. I will upload some shots as soon as I can.

Anyhow, I am shooting with a Nikon D3100, the kit lens that came with it...18-55mm f/3.5-5.6. I had the AF off. I was using manual focus for these shots, f/4-8, ISO 1600. I was shooting in aperture priority mode.

KmH: From reading your response, it seems I just have to find the right aperture. I havent used a calculator yet. Thank you for the input.

 

[enzodm]

Anyhow, I am shooting with a Nikon D3100, the kit lens that came with it...18-55mm f/3.5-5.6. I had the AF off. I was using manual focus for these shots, f/4-8, ISO 1600. I was shooting in aperture priority mode.

KmH: From reading your response, it seems I just have to find the right aperture. I havent used a calculator yet. Thank you for the input.

At f/4-8, it is unlikely you had very shallow depth of field (depending on focal length too). Most likely you wrongly focused. It is difficult to manual focus with a small viewfinder like the one in entry level cameras, unless using live view on a tripod. Try with AF, using only the central focus point (and eventually recomposing).

 

[Dubaiian]

And: the overall level of blurring depends on your lens.

Actually, the overall distribution of blur in the image is controlled by a number of things.

Focus point distance from the image sensor, relative to the lens focal length, and lens aperture is a major factor.

Focus point distance from the background is also a factor.

In summary, focus point distance generally has the biggest impact on depth-of-field (DoF).

DoF is a plane of acceptable focus parallel to the image sensor. How deep that plane is (it's foreground to backgrond distribution in the final image) is what the photographer wants to control.

DoF seems to be the most important technical aspect of photography, because it so closely relates to focus, that people have difficulty understanding.

On can plug various numbers into a DoF calculator to gain a better understanding of how the various factors the photographer can control affect the depth and where within a scene that zone of acceptably sharp focus will be.

I prefer the display this online calculator generates - http://www.tawbaware.com/maxlyons/calc.htm

But many link to this one - Online Depth of Field Calculator

For those with iPhones, iTouch or iPad, I found a useful calculator on the app store called SimpleDoF. Its free and seems to do the job adequately.

 

[DiskoJoe]

Anyhow, I am shooting with a Nikon D3100, the kit lens that came with it...18-55mm f/3.5-5.6. I had the AF off. I was using manual focus for these shots, f/4-8, ISO 1600. I was shooting in aperture priority mode.

KmH: From reading your response, it seems I just have to find the right aperture. I havent used a calculator yet. Thank you for the input.

At f/4-8, it is unlikely you had very shallow depth of field (depending on focal length too). Most likely you wrongly focused. It is difficult to manual focus with a small viewfinder like the one in entry level cameras, unless using live view on a tripod. Try with AF, using only the central focus point (and eventually recomposing).

Your lens will not give you the effect you want. You need a prime lens with a larger aperture that can give you a more shallow depth of field. Get a Nikkor 50mm f1.8 or a f1.4 and you should be able to do what you want.

 

[Designer]

First; read the tutorials about DOF, especially that of your particular lens. Plan your shot accordingly.

Secondly, does your camera have a focus lock? If so, focus on your subject's eyes, lock it, and move the camera down to include his feet in the frame, without moving forward or back.

The wider the aperture, the more narrow is the depth of field, so at wide apertures, you may only get his face in focus. A more narrow opening increases the DOF, but you will probably still will have his feet out of focus.

 

[EllaElla]

Anyhow, I am shooting with a Nikon D3100, the kit lens that came with it...18-55mm f/3.5-5.6. I had the AF off. I was using manual focus for these shots, f/4-8, ISO 1600. I was shooting in aperture priority mode.

KmH: From reading your response, it seems I just have to find the right aperture. I havent used a calculator yet. Thank you for the input.

At f/4-8, it is unlikely you had very shallow depth of field (depending on focal length too). Most likely you wrongly focused. It is difficult to manual focus with a small viewfinder like the one in entry level cameras, unless using live view on a tripod. Try with AF, using only the central focus point (and eventually recomposing).

Your lens will not give you the effect you want. You need a prime lens with a larger aperture that can give you a more shallow depth of field. Get a Nikkor 50mm f1.8 or a f1.4 and you should be able to do what you want.

Looking at the 50mm...is there that much a difference between the f/1.4 and f/1.8??? I ask because they're about $260 price difference between them.

 

[MTVision]

Looking at the 50mm...is there that much a difference between the f/1.4 and f/1.8??? I ask because they're about $260 price difference between them.

Normally the 1.4 would be better build quality and performance but from the reviews the 50 1.8g is actually the better of the 2 and cheaper!

 

[enzodm]

Looking at the 50mm...is there that much a difference between the f/1.4 and f/1.8??? I ask because they're about $260 price difference between them.

don't let you be diverted by G.A.S. (Gear Acquisition Syndrome): your initial problem was related to the place you focused, not on the more or less blurred background. If you are not focusing correctly now, buying a different lens will not help you. Posts are slightly going OT... in the easiest direction: "buy something better".

 

[KmH]

Your lens will give you the effect you want, if you use the lens you have properly.

Many new to photography get a fast prime lens like a Nikon 50mm f/1.8D AF Nikkor Lens for Nikon Digital SLR Cameras but then have a lot of difficulty with focus because the DoF can get so very shallow with close focus point distances, normal focal lengths, and wide lens apertures.

An 18-55 mm kit lens zoomed to 50 mm and set to f/5.6, that is focused on a point 8 feet away, delivers a total DoF that is 1.75 feet deep. The near focus limit would be 9.4 inches in front of the point of focus, and the far limit would be 11.6 inches behind the point of focus. That is a distribution of 45% in front of, and 55% behind the point of focus.

A 50 mm prime lens also focused on a point 8 feet away, but set to a f 1/8 lens aperture, delivers a total DoF that is only 6.6 inches deep. The near limit would be 3.1 inches if front of the point of focus, and the far limit would be 3.4 inches behind the point of focus. That is a distribution of 48% in front of, and 52% behind the point of focus.

Not only is shallow DoF difficult to work with, note how the DoF distribution also changes.

 

[EllaElla]

Got it! Also started using a DoF calculator...definitely a BIG help! I shot a ton of photos yesterday around the ship. Will try to upload some in the gallery next week.

Also, I am still interested in a prime lens. Reason is because I don't shoot with a flash, and much of the ship is not very well lit. I sometimes am wishing I had a wider aperture. I have looked at the 28, 35, and 50mm lenses. Does anybody have any input on the 28 and 35? I still may hold off, but just curious what everyone thinks. The 50mm seems kinda tough. I tried shooting with my lens zoomed to 50 yesterday and it kinda drove me nuts.

Thank you all again for all the input. I really do appreciate it. I will do my best to post some of my progress soon.

 

[Tiberius47]

I have been trying some different photos and learning about Depth of field. I am trying to focus on a point about 8' away, while making the foreground and the background out of focus.

For example; I was shooting my friend. He was sitting at a desk with his feet up on the corner. I was shooting from where his feet were. I wanted to focus on his face, leaving his feet out of focus and the stuff behind him out of focus.

From this same shot, I also tried shooting a wide aperture, with a high ISO about 1600 because the space isn't very well lit. So I have a great shot of his shoes, leaving his face out of focus. But how do I do the opposite?

Sounds like you have the camera set to use all the autofocus points. With this, the camera will focus as close as it can and still have one of the points establish focus.

What you should do is set the camera to use only the center point. Hold the camera so the part of your subject you want in focus is in focus and press the shutter halfway and hold it there. Then move the camera to get the composition you want and press the shutter button the rest of the way.