Wildlife and Depth of Field

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Revet

Senior Member
As I was taking photos for this months challenge, Birds, and I got a little confused on Depth of Field. I have read and understand the 3 things that affect DOF (aperture, distance, focal length) but as I was putting this into action photographing the birds, I found out I didn't understand it as much as I thought.

Here is what happened, I set my camera up with tripod, speed light, and remote trigger. I started at a zoom of about 200 to stay back from the birds at my feeder. I got some great photos but I wanted to increase the DOF. I couldn't use a smaller aperture since I already was using a high ISO and max flash (already increased to +3), so i decided to put my depth of field knowledge to use. I said to myself, if I use a smaller focal length (ie. 70 mm) I will increase my DOF. But in order to get the same field of view, I would have to move in closer (less DOF!!!!). Oh No!!!

I could do some experiments but I am lazy and I don't have a DOF preview on my Nikon D3100 (and I don't know the distances I used to plug into a DOF calculator). In general, which is going to give me more DOF with the same field of view, 1) further back with zoom, or 2) closer with a wider angle (assuming same f/stop, etc).
 
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Revet

Senior Member
Eyelight said:
Based on the article @wornish refers to, I was playing with this a few weeks ago and posted some thoughts in the blog section, which may or may not be useful, as sometimes my thoughts don't hit the page so well.

Eyelight Plays with Depth of Field - Part 5
Read more: Eyelight Plays with Depth of Field - Part 5 - Blogs - Nikonites


I would say the pictures all have the same DOF. Thanks for doing this experiment!! I will see if I can repeat it (being the skeptic and perfectionist i am!!!!).


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hark

hark

Administrator
Staff member
Super Mod
wornish said:
Focal length does not affect DOF
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I disagree. f/4 on a 400mm lens will have far less DOF than f/4 on a 28mm lens. On a 200mm lens, the aperture's diameter is 50mm compared with the 28mm aperture diameter of 7mm at f/4. The smaller the diameter of the aperture, the greater the DOF. That's why wide angle lenses tend to have more in focus than telephoto lenses when using the same f-stop.
 
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wornish

Senior Member
hark said:
I disagree. f/4 on a 400mm lens will have far less DOF than f/4 on a 28mm lens. On a 200mm lens, the aperture's diameter is 50mm compared with the 28mm aperture diameter of 7mm at f/4. The smaller the diameter of the aperture, the greater the DOF. That's why wide angle lenses tend to have more in focus than telephoto lenses when using the same f-stop.
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Have you read the tutorial ?

If the object is taking up the same % of the frame there is no noticeable difference.
 
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Eyelight

Senior Member
Think of it this way. There are two things that influence DOF, aperture and distance. Distance is affected by the magnification of differing focal lengths, so if you stand in the same spot and change your distance by zooming your lens, the DOF will change. However, if you walk closer to the subject and zoom out to maintain the same subject/viewfinder ratio, the DOF remains fairly constant. Though you have increased your distance (and DOF) by zooming out, you have also decreased it by walking forward.
 
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Revet

Senior Member
Eyelight said:
I had an idea on showing the relation mathematically, put together a sketch and added a blog post with the info.


Eyelight Plays with Depth of Field - Part 7: DOF Based on View Size
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Nice chart, it also shows that the range of DOF is about equal in front and behind when using a zoom, but weighted more behind with wide angle (important for landscapes).

Why is it that so many photographers (Pros included) list focal length as one of the 3 ways to adjust depth of field. They show a beautiful chart/pictorial in Digital Photography School showing how focal length affects DOF, and that includes viewing the same subject/viewfinder ratio.


depth_of_field_photography_cheat_sheet.jpg
 
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wornish

Senior Member
The missing piece of the third part of this diagram is the person will take up a different percentage of the viewed image.
focussing on a person at 10m with a 28mm lens will show the the whole person and a lot of the surrounding area. Do the same thing zoomed in at 200mm and all you will see is the head.
Both shots will be in focus on the head and if you crop the head out of the 28mm shot you will see no difference in the focus compared to the 200mm shot.

To add even more complexity the size of the sensor also has an impact.
There are some DOF charts you can download here that covers most of the standard lens sizes. Just select your camera from the drop down and the lens.
Depth of Field Table

This stuff can drive you crazy so I just take pictures and stick to using the simple rules of smaller aperture gives more DOF and focus about 1/3 of way in for landscape shots.
 
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PaulPosition

Senior Member
Revet said:
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Why is it that so many photographers (Pros included) list focal length as one of the 3 ways to adjust depth of field.
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Probably just a consequence of how they test lenses by installing a target chart at the end of a range and a tripod-mounted camera at the other end. Same setup (and results) as the third part of that image you posted.
 
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Eyelight

Senior Member
Well, from a lens point of view, changing focal length is not the same as changing focus distance, but from the camera's point of view changing focal length is pretty much the same thing as changing distance.

Main thing is the real world application is: When framing a subject the same size, the same aperture produces nearly the same depth of field at different focal lengths. If a bird that occupies 50% of the view and fits in the DOF at f/11, the bird will fit in the DOF at 50% view and f/11 at all focal lengths.
 
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Eyelight

Senior Member
wornish said:
To add even more complexity the size of the sensor also has an impact.
Click to expand...

Actually, if the only thing you change is sensor size, the DOF is unaffected. If you frame the same subject size, the DOF is affected because you have to increase the distance by walking or zooming.
 
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WayneF

Senior Member
Revet said:
As I was taking photos for this months challenge, Birds, and I got a little confused on Depth of Field. I have read and understand the 3 things that affect DOF (aperture, distance, focal length) but as I was putting this into action photographing the birds, I found out I didn't understand it as much as I thought.

Here is what happened, I set my camera up with tripod, speed light, and remote trigger. I started at a zoom of about 200 to stay back from the birds at my feeder. I got some great photos but I wanted to increase the DOF. I couldn't use a smaller aperture since I already was using a high ISO and max flash (already increased to +3), so i decided to put my depth of field knowledge to use. I said to myself, if I use a smaller focal length (ie. 70 mm) I will increase my DOF. But in order to get the same field of view, I would have to move in closer (less DOF!!!!). Oh No!!!
Click to expand...


Lenses focus at ONE distance, period. Image is more blurry away from that distance.

Aside from aperture (which when smaller, directly reduces CoC to sharpen the image, less the effects of diffraction), Depth of Field is primarily about magnification (about how well we can see the blurry spot). The blur is a gradually increasing property, but we use an arbitrary CoC value to draw a sharp DOF border line (where there is no sharp line).

Wikipedia is quite good here. Depth of field - Wikipedia, the free encyclopedia

Says there: DOF is determined by subject magnification at the film / sensor plane and the selected lens aperture or f-number.

Magnification is increased with a closer subject or a longer lens.

Of course, focal length obviously affects magnification, and depth of field.

But there is one very special case. If you adjust whatever you have to adjust (focal length or subject distance) so that you create the SAME image magnification (subject fills the same percentage of the frame), you will have the SAME depth of field. It is about magnification.

So, changing focal length, and then changing where you stand to equalize it, gives the same DOF. Changing only the focal length affects DOF (and magnification).

That is very different than saying focal length does not affect DOF (which is completely laughable). There are some weird notions on the internet. People tend to make up things.

The accepted formula (down below there at Wikipedia) of course includes focal length, but can be simplified to magnification (also shown there). This includes viewing magnification - a small DX sensor requires more enlargement than a larger FX sensor (DX requires smaller CoC - and typically also uses a shorter lens to show the same view). Also whether you print 4x6 or 16x20 affects enlargement (magnification). It is about magnification (about how well you can see the blur, which is there, regardless of what you do).

So, there is of course NO ONE ANSWER, as so many fail to understand. DOF charts and calculators include Circle Of Confusion (CoC), to be an adjustment for sensor size (the expected magnification). Also the charts assume a standard viewing situation, typically 8x10 print size, viewed at a 10 inch distance. But more magnification of any type will show the blurriness better. If you blindly accept the DOF chart values, without matching their described setup, of course you will get different results. And of course, the CoC which determines the chart numbers, is an arbitrary number in the first place, judged to be the visual limit we can see (at that standard viewing distance).
 
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WayneF

Senior Member
Revet said:
Nice chart, it also shows that the range of DOF is about equal in front and behind when using a zoom, but weighted more behind with wide angle (important for landscapes).
Click to expand...

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It is not about wide angle. At typical landscape distances (whatever that means), a general rule of thumb is to focus about 1/3 into the scene. But at close distances, its more like 1/2 way. This varies with distance of course, but it won't be far wrong.


Why is it that so many photographers (Pros included) list focal length as one of the 3 ways to adjust depth of field. They show a beautiful chart/pictorial in Digital Photography School showing how focal length affects DOF, and that includes viewing the same subject/viewfinder ratio.


depth_of_field_photography_cheat_sheet.jpg
Click to expand...



Because those three factors (aperture, focal length, and focused distance) is simply how DOF works.

DOF is of course largely about magnification (when you want to reason it out, it explains how subject distance can balance out focal length when the magnification is the same), but we usually don't tend to think about magnification, not as such.

Your diagrams here about aperture, focal length, and focused distance is exactly the practical way to think of it.
 
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Revet

Senior Member
"This stuff can drive you crazy so I just take pictures and stick to using the simple rules of smaller aperture gives more DOF and focus about 1/3 of way in for landscape shots.[/QUOTE]"

I am the type that loves to know how stuff works. I think DOF was explained pretty well in this entire thread so know I can sleep well!! But in a couple of weeks, it is your last line there that I will remember!!
 
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Revet

Senior Member
Now that makes a lot of sense, if we think of changing distance or focal length as magnification, the topic of DOF comes into focus (no pun intended!!)
 
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Revet

Senior Member
"It is not about wide angle. At typical landscape distances (whatever that means), a general rule of thumb is to focus about 1/3 into the scene. But at close distances, its more like 1/2 way. This varies with distance of course, but it won't be far wrong."

Isn't that what that chart is showing? If you are shooting from a further distance (ie - landscape), the Depth of field will be weighted more behind the precise focal distance of the lens (in other words, more of the picture will be in focus (discernible by our eye) behind than in front of that exact distance where the focus is perfect for the lens and thus why we focus at 1/3 into the scene) as compared to a closer shot (ie, using zoom) where the DoF is somewhat more centered around that precise focus point. I don't think I used the correct terminology here but I think you get what i'm trying to say.
 
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