Depth of Field ~ distances and zoom lenses

PJcam

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I have read Understanding Exposure by Bryan Peterson, a very good book, highly recommended

I have now purchased another of his books, Exposure Solutions, but I read something I am now sure about so ask you guys if you can confirm for me please.

[The books I purchase are Kindle ebooks, excellent and a fraction of the cost]

First it talks about single-focal length lenses, they have Depth of Field Scale that makes it easy to preset focus for a given scene. So far so good.

Then it says, most people go for wide angle lenses (I have), then he states that they don;t have the DoF scale, I agree. But he goes on the say they do however, have distance settings, which, similar to DoF scales, allow you to preset the DoF before taking the shot.

Are these the mm focal distance measurement?

He then continues and says... you'll find these numbers above the distance setting mark on the lens. He then says... set aperture to f/22 and then align a specific distance - 3 feet (1 meter) or 6 feet (2 meters) depending on the focal length you are using.

Can someone explain this please? I am aware of the lenses mm settings but not sure how this relates to the 1 or 2 meters he is stating.

Thanks in advance, I am very grateful.

All questions are easy... if you know the answer.
 

Dave442

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These settings were common on manual focus lenses. Many of my newer lenses have done away with these scales (if you in auto-focus mode it really throws the usefulness out the window).

If you have a lens with the numbers noted, then all you do is set your f-stop on the lens and then set your closest focus distance to that number and check that the farthest focus distance covers the required in-focus distance of the scene. If you need more in focus then stop down another stop and check again.

So he is saying to put the 3 feet under the 22 on the one side and you are probably past the Infinity mark at the 22 on the other side if using a wide-angle lens. I would not go to f/22 for difraction, but that is another issue. On some lenses the f-stop numbers are colored and then there are just notched lines that have a corresponding color where you would line up the distance scale.

The problem is that many of these lenses used a DOF scale based on a certain size of "Circles of Confusion" that with todays digital cameras is not adequate, so just be a bit more conservative.
 

Designer

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I have read Understanding Exposure by Bryan Peterson, a very good book, highly recommended

I have now purchased another of his books, Exposure Solutions, but I read something I am now sure about so ask you guys if you can confirm for me please.

[The books I purchase are Kindle ebooks, excellent and a fraction of the cost]

First it talks about single-focal length lenses, they have Depth of Field Scale that makes it easy to preset focus for a given scene. So far so good.

Then it says, most people go for wide angle lenses (I have), then he states that they don;t have the DoF scale, I agree. But he goes on the say they do however, have distance settings, which, similar to DoF scales, allow you to preset the DoF before taking the shot.

Are these the mm focal distance measurement?
No, the distance scale is in feet or meters, and sometimes both on the same scale. It is the distance to focus, from which you can figure the DOF. Get hold of a DOF app for your phone so you can check the DOF any time.
 
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PJcam

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These settings were common on manual focus lenses. Many of my newer lenses have done away with these scales (if you in auto-focus mode it really throws the usefulness out the window).

If you have a lens with the numbers noted, then all you do is set your f-stop on the lens and then set your closest focus distance to that number and check that the farthest focus distance covers the required in-focus distance of the scene. If you need more in focus then stop down another stop and check again.

So he is saying to put the 3 feet under the 22 on the one side and you are probably past the Infinity mark at the 22 on the other side if using a wide-angle lens. I would not go to f/22 for difraction, but that is another issue. On some lenses the f-stop numbers are colored and then there are just notched lines that have a corresponding color where you would line up the distance scale.

The problem is that many of these lenses used a DOF scale based on a certain size of "Circles of Confusion" that with todays digital cameras is not adequate, so just be a bit more conservative.

Thank you Dave442, all my lenses are brand new so your reply makes sense as to why I cannot see the details he is stating.
 

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First it talks about single-focal length lenses, they have Depth of Field Scale that makes it easy to preset focus for a given scene. So far so good.

Then it says, most people go for wide angle lenses (I have), then he states that they don;t have the DoF scale, ..
Single-focal-length lenses (also called "prime") have a simple calculation for DOF, which is easier for most people to read. Some zooms also have a DOF scale, but you have to remember to note your aperture in order to read it correctly.

The reason wide angle lenses don't have the DOF scale on them is because the DOF scale would be so compressed that it would be hard to tell one number from the next. The DOF, in other words, is quite deep, and therefore is almost irrelevant.
 
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PJcam

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I have read Understanding Exposure by Bryan Peterson, a very good book, highly recommended

I have now purchased another of his books, Exposure Solutions, but I read something I am now sure about so ask you guys if you can confirm for me please.

[The books I purchase are Kindle ebooks, excellent and a fraction of the cost]

First it talks about single-focal length lenses, they have Depth of Field Scale that makes it easy to preset focus for a given scene. So far so good.

Then it says, most people go for wide angle lenses (I have), then he states that they don;t have the DoF scale, I agree. But he goes on the say they do however, have distance settings, which, similar to DoF scales, allow you to preset the DoF before taking the shot.

Are these the mm focal distance measurement?
No, the distance scale is in feet or meters, and sometimes both on the same scale. It is the distance to focus, from which you can figure the DOF. Get hold of a DOF app for your phone so you can check the DOF any time.

Thanks designer, I have just downloaded two Apps, DOF Calculator Aimen RG and DOF Jonathan Sachs they both look good in their own ways, I will play with them more later. Thanks.
 
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PJcam

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I guess this leads to the next question.
With a modern AF lenses that I have are these items relevant?

The camera and lens will work it out depending which lens I am using and what aperture I have set.
 

Dave442

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You still need to consider the DOF. If you need to have focus from 6 feet to Infinity then check the numbers in a DOF Calculator that would give that range and then just auto-focus on something around the distance required, recompose and take the shot. With most DOF Calculators you may need to try some different distances as the focus point and different Apertures to find the combination that gives the near and far distances desired. Also check out Hyperfocal Distance if you want to have the far point of acceptable focus at Infinity with the maximum amount of the scene within acceptable focus.
 
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PJcam

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The author suggests focusing on something near, 3' or 6' when using a wide angle lens as he states everything from there to infinity would be in focus (with this lens type). He also states of you focus on the middle, the items in the foreground will be out of focus as it sets from focus point to infinity.

That's sounds reasonable to me and something I will test out, I then wonder about the other information, is it really needed. I will check the two Apps and learn more.

Thanks for your comments.
 

ac12

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A DoF scale would work on a Push/Pull zoom, but NOT on a 2-ring zoom where you zoom by turning the zoom ring.
This is because the DoF changes with the zoom position.
On a P/P lens, you have curved lines for the DoF scale, so you can see the DoF changing as you zoom.
Can't do that with a 2-ring zoom. The DoF would be correct at only ONE zoom setting, and wrong for everything else.

This is one thing that I miss on the old Nikon manual focus zooms.
 

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The author suggests focusing on something near, 3' or 6' when using a wide angle lens as he states everything from there to infinity would be in focus (with this lens type). He also states of you focus on the middle, the items in the foreground will be out of focus as it sets from focus point to infinity.

That's sounds reasonable to me and something I will test out, I then wonder about the other information, is it really needed. I will check the two Apps and learn more.

Thanks for your comments.

It sounds like this book isn't a patch on Bryan's 'Understanding Exposure', but that is a high standard to match.

Many lenses today don't have distance scales or aperture rings, but even when these where the norm then how DOF information was displayed could vary significantly from lens to lens.

If you focus on something at 6' with a wide angle then you might get everything from there to infinity focused acceptably, but there are far too many variables to assume so on any camera. A better approach may be to focus at the hyper focal distance for your lens/aperture. Then by definition everything from half that to infinity is focused. You may never need to refocus at all. There are actually a few lenses where focusing is based on this - such as the Olympus 9mm fisheye body cap which is fixed at f8.
 

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At this link:
Understanding Depth of Field in Photography
scroll down to where they have a chart that shows lens focal length and focus distance to maintain about the same DoF.
Note that the focus distance increases with lens focal length.
If the focal length doubles, so does the focus distance - to maintain the same DoF.

Right below that is a chart that shows how lens focal length also affects the distribution of DoF in front of and behind the point-of-focus (PoF).

The shorter the focal length of a lens, the deeper and less adjustable the DoF.
 
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PJcam

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The author suggests focusing on something near, 3' or 6' when using a wide angle lens as he states everything from there to infinity would be in focus (with this lens type). He also states of you focus on the middle, the items in the foreground will be out of focus as it sets from focus point to infinity.

That's sounds reasonable to me and something I will test out, I then wonder about the other information, is it really needed. I will check the two Apps and learn more.

Thanks for your comments.

It sounds like this book isn't a patch on Bryan's 'Understanding Exposure', but that is a high standard to match.

Many lenses today don't have distance scales or aperture rings, but even when these where the norm then how DOF information was displayed could vary significantly from lens to lens.

If you focus on something at 6' with a wide angle then you might get everything from there to infinity focused acceptably, but there are far too many variables to assume so on any camera. A better approach may be to focus at the hyper focal distance for your lens/aperture. Then by definition everything from half that to infinity is focused. You may never need to refocus at all. There are actually a few lenses where focusing is based on this - such as the Olympus 9mm fisheye body cap which is fixed at f8.

I totally agree, as will all on here I think, Bryan Peterson's 'Understanding Exposure' book or ebook is probably the best book anyone learning Photography could have, should have.

Interestingly the book mentioned, which I am referring to in the post here is by, Bryan Peterson, I am wondering if maybe an older book based on the rep;lies so far. That said, I don't feel I should judge the book based on this one item, time will tell as I work my way through the book.

I have today downloaded another App, called DOF easy, it has a rating of 5.0, very high. having downloaded it and checked it, along with explanations of every link, I can see why it is highly rated. There are areas in it I need to learn more about but it seems a very good App.

Meanwhile my reading as been distracted as I am currently looking to improve my understanding of the Hyperfocal Distance Hyperfocal Distance Explained

Thank you.
 

TCampbell

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Here's a link to an online DoF calculator:

Online Depth of Field Calculator

You supply a few ingredients such as:
  • The sensor size (this site asks for your camera model, but it really just needs to know the sensor size. If your specific camera model isn't on the list then just select any Canon "Rebel" because they all have APS-C size sensors.)
  • The lens focal length (if it's a zoom lens then enter the focal length you plan to use for the shot)
  • The focal ratio (f-stop) you plan to use for the shot
  • The lens focus distance to your subject
That's the info needed to compute the depth of field. BTW, there are several smart-phone apps that do this for you. So if you want an app when you're out shooting instead of at your computer... you can get an app to work this out.

Suppose we enter a few values by picking a Canon Rebel body, pick a 50mm lens focal length, pick f/8 as our focal ratio, and decide to focus the lens to 10 feet.

When you click the "calculate" button, the values on the right side of the table are updated and it tells us that everything from 8.46 feet to 12.2 feet will be in acceptable focus ... for a total depth of field of 3.77 feet.

But also notice that near the bottom of those values there's a number that says "Hyperlocal Distance: 54.1 ft".

Hyper-focal distance is something you would use if you wanted to get the maximum depth of field possible with that specific camera body + lens focal length + f-stop combination.

To show how that works, here's a couple of photos of my old Canon AE-1 35mm camera ... but I call your attention to the focus ring position, depth of field marks, and aperture ring on the lens.

In this first shot, suppose I want to shoot a landscape photo with my 50mm lens... so I focus to "infinity" and I select f/22 -- thinking this will maximize my depth of field (it turns out it will not... more on that in a moment). Here's the photo of the camera & lens showing how I've set the focus and f-stop:

Infinity.jpg


If you look at the the line that marks the focus (in the center of the yellow oval between the "22" and the infinity mark on the focus ring) you'll see a set of numbers that mirror each other... "22 16 11 8 4 | 4 8 11 16 22". Those are "depth of field" marks and were extremely common on old manual focus lenses. It means that if you select f/22 (as I have in this photo) then everything from the "22" on the left to the "22" on the right will be in acceptable focus.

But here's the thing... the "22" on the left is probably somewhere around the 12 ft distance (it's between the 10 and 15) and while that goes to "infinity" at the focus point, there's nothing beyond infinity. So there's a range of distance that could have been in focus ... but I'm not taking advantage of it if I set up my focus like you see in the image above. I am wasting some of my depth of field.

So here's another image and you can see I've changed my focus position in this next photo.

Hyper-Focal.jpg


I've annotated this image with a green oval, a yellow oval, and a blue rectangle.

First, I've selected f/22 -- as indicated by the green oval.

Second, and this is the important part... instead of focusing to "infinity", instead I adjust the focus ring so that the "infinity" mark is lined up with the "22" on the far side of the depth-of-field scale. I've circled in yellow in the photo above.

Third... as a result of doing this, everything between the "22" left of the focus position and the other "22" to the right of the focus position (on my depth of field scale) should be in acceptable focus. I've placed a blue rectangle over that range. You can see it's roughly everything from 6' to infinity that will be in focus. Recall in that in the first image... only subjects from 12' to infinity were going to be in focus. So I've increased my depth of field by doing this.

This "hyper-focal" distance only applies to this combination of lens focal-length and f-stop and for this film size. If we changed the film or sensor size ... or if we changed the lens focal length ... or if we changed the f-stop, then the hyper-focal distance would calculate to a different value.



Landscapes are often shot with wide-ish angles of view (short focal length lenses.) Short focal length lenses naturally increase the depth of field. If you were to punch in values for your 18-55mm lens and use the 18mm focal length, say... f/16... then the DoF calculator says that Hyper-Focal distance is 3.56 ft (meaning if you were to focus on something 3.56 ft away then you'd maximize the depth of field) At that combination, everything from 1.88 ft to infinity would be in acceptable focus. You can see how using wide-angle lenses makes it pretty easy to get a broad depth of field.
 
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PJcam

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@TCampbell

Many thanks for your detailed reply, the notes supplied and the images are very clear and most helpful.

Most modern lenses don't have the details you show in your example.

You mentioned obtaining Apps for a mobile phone, I downloaded two yesterday
DOF Calculator - Aimen RG and
DOF - Jonathan Sachs

Both look OK although one is better than the other.

DOF Easy is another App I found earlier today, it has a rating of 5.0 which is very high, most are 4 to 4.5 ratings. Having opened the App to look at it I can see why it is rated so well, not only is it easy to follow, every links has a detailed explanation to guide you through what they mean.

Back to :icon_study:
:encouragement:
 

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