DOF (Depth of Field)

[Tywais]

I thought I would start a few technical discussions to start making good use of this new sub-forum. So my first topic is on DOF.

This one is on a very important aspect of photography, Depth of Field and when/how to make use of it. Since I upgraded from a P&S camera to an interchangeable lens camera DOF immediately became an issue with my 20mm f/1.7 prime and my Olympus M.Zuiko 45mm f/1.8 prime.

My P&S had huge DOF, due to sensor size and slow lens, from a couple of meters to infinity and I thought that was pretty cool. Until I started paying more attention to photos exploiting shallow DOF and the dramatic effect it had on a photo. So study time and lots of practice to get that 'feel' for cause and effect.

I took these photos of a research project I'm working on at the lab. f-stops (aperture) was consciously set incorrect for the conditions to show what happens. The 1st one was with the 20mm at f/1.7 and the 2nd shot with the same lens at f/3.2. Much better but you can see a bump up to f/4.0 would probably got all of the center of interest in focus at the expense of a longer exposure at a given ISO. The 3rd photo is with f/4.0 but you can see the effect of distance to the object has on the equation as this shot was closer in.

[Tywais]

Good article explaining the parameters and how they effect DOF.

Depth of field explained

What is depth of field?

Broadly, the term depth of field describes the distance in front of and behind a focus point that appears sharp in a photograph. When we focus on a tree in a field, it is rare that only that tree is in focus. You might find the grass between you and the tree is also sharp, and that the mountains in the distance have detail, too. However, with the right combination of lens and aperture it is possible to make sure that actually it is only the tree that appears focused, and all the other elements are blurred – or out of focus. When the photographer masters the skill of depth of field control, the options for what to show and what to hide are multiplied.

How to use depth of field

The purpose of depth of field control is not always to maximise it. Photographers spend far too long attempting to create complete front-to-back sharpness in their pictures at the expense of exploring the much more powerful effects of minimising depth of field. Even in landscapes where the depth of the subject might seem to encourage a desire to gain full focus from the foreground to the distance, selective focusing can be a more impressive creative tool. Using a very shallow depth of field can help direct the viewer to a single part of the scene by concentrating the focus of the lens there. It is a much more direct way of controlling the actions of the viewer and pointing out to them what you want them to see. When everything is sharp, you rely on their sense to see what is important.

Controlling depth of field

There are three main elements that help us to control depth of field – aperture size, focal length and focus point. In the broadest of terms, a small aperture (such as f/22) will produce a greater depth of field than a wide aperture (such as f/2.8). In the same way, a wideangle lens (such as 28mm) will produce a greater depth of field than a telephoto lens (eg 100mm). If you use a small aperture with a wide lens you increase depth of field, while a wide aperture with a long lens really restricts sharpness to a tiny area.

Read more at http://www.amateurphotographer.co.uk/how-to/tech-explained/536453/depth-of-field-explained#BbX5oSI0PbTEbusm.99

[MJP]

I've found the best way to learn depth of field apart from taking photos at different apertures is using this . . .

http://www.dofmaster.com/dofjs.html

[Tywais]

There are several different calculators available to calculate the DOF.

DOFMaster

Depth of Field Table

DOFMaster list of calculators. These include Android & iPhone and printable charts

Cambridge in Color Calculator

Another Android DOF Calculator

[Tywais]

I've found the best way to learn depth of field apart from taking photos at different apertures is using this . . .

http://www.dofmaster.com/dofjs.html

I was typing all that up and you slipped it in ahead of me.

[MJP]

I've found the best way to learn depth of field apart from taking photos at different apertures is using this . . .

http://www.dofmaster.com/dofjs.html

I was typing all that up and you slipped it in ahead of me.

You can get Android apps for DoF too!

More stuff to stick on that tablet. Our kid is already hiding the thing from me. I've already changed the wallpaper on it and removed loads of games!

See the attached screen shot. It's no wonder that 50mm f/1.2 is so tricky to focus at f/1.2. Focus is within a distance of 8 centimetres 2m from the subject.

Edited November 9, 2013 by MJP

[Guest]

It was not long ago when I realised that many photographers wish to have a short DOF to highlight the subject.

I thought that purpose of the photos was to give all the information available to the viewer. It's not always the case I have learned from this forum.

For technical images, like in OP, the whole image should be in focus. For the photogenic images, you could include mist from the liquid nitrogen mixed with water, which I'm sure you have in the lab, to show how the laser beams do. Can we have that picture as well

Off topic and utter curiosity: What does that setup do?

[Tywais]

It was not long ago when I realised that many photographers wish to have a short DOF to highlight the subject.

I thought that purpose of the photos was to give all the information available to the viewer. It's not always the case I have learned from this forum.

For technical images, like in OP, the whole image should be in focus. For the photogenic images, you could include mist from the liquid nitrogen mixed with water, which I'm sure you have in the lab, to show how the laser beams do. Can we have that picture as well

Off topic and utter curiosity: What does that setup do?

Yep, we do have liquid nitrogen but have to work out the logistics as it is tricky to handle.

The optical setup is a laser Michelson Interferometer. These are used to measure the wavelength or frequency of light and can be used to measure the speed of light. Uses a laser that is split, redirected in two directions and reflected back and combined to create an interference pattern. A motor is used to move one of the mirrors to change the phase interaction and thus the wavelength can be determined by watching the rings produced which are projected onto a screen.

We are talking very small numbers here. The motor I use is a piezo electric motor with a full scale range of 0 to 10 microns (human hair, 100 microns)

To keep on topic, a photo of the laser interference ring projected.

[skippybangkok]

DOF gets worse as focal length increases. This is a 2x macro with 105mm lens shot - subject 4mm high... And calc DOF was about + or - 2mm...... Hand held ( need to lock focus and move in and out )

DOF is quite digital , either you want max or min. Never seen someone use DOF calculator in the field

Sent from my iPhone using Thaivisa Connect Thailand mobile app

[MJP]

ImageUploadedByThaivisa Connect Thailand1383997950.481873.jpg

DOF gets worse as focal length increases. This is a 2x macro with 105mm lens shot - subject 4mm high... And calc DOF was about + or - 2mm...... Hand held ( need to lock focus and move in and out )

DOF is quite digital , either you want max or min. Never seen someone use DOF calculator in the field

Sent from my iPhone using Thaivisa Connect Thailand mobile app

I never use it in the field, but it's a good desktop way to figure out and learn your lenses and how they'll behave mounted to your camera.

You can probably tell I don't have a lot to do at the moment.

[Tywais]

DOF gets worse as focal length increases.

Curiously enough there are a lot of papers saying that it is a myth despite popular opinion. I have always thought that to be the case but find it may not be true, at least not as a fixed rule. In other words, it's highly debated it seems

This is the first article with empirical details of it that I had read a while back - luminous-landscapes

Another article

And on the opposite side of the fence is this article - theonlinephotographer

Though it depends from what he stated here "A good rule of thumb is that for just about any photography you do indoors, depth of field isn't going to be affected by focal length, just on-film magnification. But as you start photographic more distant subjects, the effect of focal length increases and eventually becomes as important as aperture."

[MJP]

DoF doesn't get worse, it gets shallower with increasing focal length and this can be a good thing if shallow depth of field is what you're after.

My Pentax-FA 77mm f/1.8 Limited is stunning for portraiture, extremely sharp wide open but producing the finest bokeh ever known to mankind at the same time.

[MJP]

[skippybangkok]

well, depending on what you want to achieve, DOF does get "worse". Here is an example of a shrimp on a anemone - shot macro, not double macro and on 35mm film. Was lucky in this shot, eyes and claws in focus, but impossible to get tail in focus too, even at f54 !!!!

Thats why i originally moved from film to DX format which offers better DOF

[MJP]

Image1301.jpg

well, depending on what you want to achieve, DOF does get "worse". Here is an example of a shrimp on a anemone - shot macro, not double macro and on 35mm film. Was lucky in this shot, eyes and claws in focus, but impossible to get tail in focus too, even at f54 !!!!

Thats why i originally moved from film to DX format which offers better DOF

I see what you mean. Start going above f/16 and you get diffraction with many digital cameras.

http://www.digitalversus.com/digital-camera/guide-diffraction-camera-sensors-a1010.html

Your FX should make it even easier than DX. The bigger the sensor format the less shallow the DoF.

Edited November 9, 2013 by MJP

[Guest]

Previously I thought that smaller F value equals that the lense can gather more light. Therefore with F1.0 it's possible to use faster shutter speeds while taking low light action photos. Is this not true?

Why does the better ability to collect or pass through the light effect to the depth of view?

[FracturedRabbit]

That Digital Camera diagram is great overview. It also illustrates something else that I didn't spot mentioned in the text; The depth of field will extend approximately 1/3 in front of the focus point and 2/3rd behing. This can be useful when shooting landscapes for example. If you are shooting a scene which ends in a treeline, for example, and want to maximise the scene being in focus; don't just focus on the trees. Focus on a point about one third into the scene and set the F stop so the trees will be in focus; this will maximise the in-focus areas of the scene.

"DOF is quite digital , either you want max or min." Not really. You want a DOF that produces the result you are looking for. You can focus on a face with a fast lens and get one eye in focus and everything else out of focus. Make look impressive; except to the person whose face you are photographing. You often have to dial in more than the minimum depth of field to produce the area you want in focus. Another danger with using minimum depth of field is that you can transform the background into a soft blur. Again, this can look impressive, even beautiful, but if your intention is to give your subject a sense of place, to tell a story, you will have to reduce that blur to allow the context of the place to come through, by increasing depth of field.

[MJP]

Previously I thought that smaller F value equals that the lense can gather more light. Therefore with F1.0 it's possible to use faster shutter speeds while taking low light action photos. Is this not true?

Why does the better ability to collect or pass through the light effect to the depth of view?

It is true. Lower the F number the wider the aperture.

[Guest]

But why? I used to dislike to study the optics.. and it seems to come back to haunt later on..

Edited November 11, 2013 by Guest
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[FracturedRabbit]

@MJP

You have an impressive collection of useful diagrams!

Edited November 11, 2013 by astral
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[MJP]

I just type the relevant word(s) into Google and then go to Google Images and 'View', Copy Image URL >

Makes me look an awful lot smarter than I am.

Edited November 11, 2013 by astral
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[MJP]

Previously I thought that smaller F value equals that the lense can gather more light. Therefore with F1.0 it's possible to use faster shutter speeds while taking low light action photos. Is this not true?

Why does the better ability to collect or pass through the light effect to the depth of view?

It is true. Lower the F number the wider the aperture.

But why? I used to dislike to study the optics.. and it seems to come back to haunt later on..

Because, because, because . . . because . . . the Wonderful Wizard of Oz!

Edited November 11, 2013 by astral
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[FracturedRabbit]

Try this: http://www.cambridgeincolour.com/forums/thread1357.htm

(I can use Google too!)

Edited November 11, 2013 by astral
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[MJP]

Google is the font of all knowledge.

[skippybangkok]

Your FX should make it even easier than DX. The bigger the sensor format the less shallow the DoF.

I think its the opposite......... DX gives you better depth of field. iPhone camera's with even a smaller chip has even a "better" DOF.

I saw a huge difference. 35mm film has less DOF than the sam shot on DX (smaller foot print than 35mm )

[Guest]

But why? I used to dislike to study the optics.. and it seems to come back to haunt later on..

Try this: http://www.cambridgeincolour.com/forums/thread1357.htm

(I can use Google too!)

This from that site, which explains if the aperture is large, there is more ways for light from one point to pounce to the sensor which makes the image blur.

Let's start with a limiting case: a pinhole aperture with no lens. When the aperture is effectively a single point, light which bounces off a given point on your subject, passes through the aperture, and then hits the camera sensor can only have taken one path: directly through the pinhole. This means that you can move the position of the sensor to pretty much anywhere and the light will take the same path -- meaning the image will remain in focus -- meaning there's effectively infinite depth of field.

Now, let's make the aperture a little wider and see what happens. If light bounces off of a particular point on your subject, this light can now enter the aperture by passing directly through the center of this aperture (as before), but can now also enter the aperture at a small range of angles, up to the point that the light passes just inside the outer edge of this circular aperture. This means that when you move your sensor, the image created will change focus (with the appropriate lens). The larger the aperture, the more pronounced this effect.

Overall: light which originates at a given point on your subject and passes through a larger aperture ends up being more divergent, which translates into a shallower depth of field.

This is a crude simplification, and is much better explained using a customized diagram for this purpose, but hopefully you get the idea.

Then again. Why the focused distance is not blurr?

The unwanted light from the focused point bounces off the sensor range, which makes the image clear? This way the essential of photography is not to collect light, but to avoid the scattering light?

[MJP]

Your FX should make it even easier than DX. The bigger the sensor format the less shallow the DoF.

I think its the opposite......... DX gives you better depth of field. iPhone camera's with even a smaller chip has even a "better" DOF.

I saw a huge difference. 35mm film has less DOF than the sam shot on DX (smaller foot print than 35mm )

Have a look at the two attachments.

DoF for a Nikon D7000 (DX, crop format) is front 0.12m and behind 0.13m, whereas a D800 FF sensor gives front 0.18m and behind 0.2m. Other factors being equal, 50mm lens, f/1.8, subject distance 3m.

[Tywais]

Your FX should make it even easier than DX. The bigger the sensor format the less shallow the DoF.

Think you may be phrasing it wrong. The larger the sensor format the more shallow the DOF. Suspect we are saying the same thing though.

Blurry backgrounds, Big Sensors and Bokeh.

And as linked previously by FR, the cambridgeincolor is an excellent site.

[MJP]

Your FX should make it even easier than DX. The bigger the sensor format the less shallow the DoF.

Think you may be phrasing it wrong. The larger the sensor format the more shallow the DOF. Suspect we are saying the same thing though.

Blurry backgrounds, Big Sensors and Bokeh.

And as linked previously by FR, the cambridgeincolor is an excellent site.

See my post above.

[Tywais]

So the bottom line - and all you really need to know - is that DOF is inversely proportional to format size. Note that format size is inversely proportional to the "digital multiplier". The higher the "digital multiplier", the smaller the format and thus the greater the depth of field. Note also that now you can see one of the reasons large format camera users need tilts and swings to get adequate depth of field. With an 8x10 camera you have about 8.5 times LESS depth of field than you do with 35mm for the same image. This also explains why consumer digicams, some of which have sensors 1/6 the size of 35mm film, have such a large depth of field and one of the reasons why it's almost impossible to get blurred backgrounds when using them.

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