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07-06-2012, 11:05 PM   #1
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DOF Demonstration & Discovery

This post is kind of a 'statement' and also kind of a 'question' all in one...

The images below are not anything spectacular but they demonstrate a point that I would like others more in the know to possibly expand on so that I (and others) can learn more...

The images below were taken with a 50mm (Rokinon P) prime lens @ f1.4 ....I put the figuring out about 1 meter if I remember correctly (the yellow line is a tape measure)....(This is one of my many experiments...)

I am trying to learn how to make better use of the DOF at large apertures, well at any aperture really but that's a different story...

Now here is my 'point' so to speak...imagine if you had a large imaginary ice cream cone that extends out from your lens. When you get to your focal point it goes flat on the end thus creating a 'narrow DOF' (noting that the bigger the aperture the thinner the in focus plane, and smaller aperture the wider it is).

In my case as demonstrated in image 1 the DOF is just an inch or two thick. The figurine is maybe a couple inches tall...you can see it right there...I don't know the technical words for it but it appears to create a 'focal plane' at the point of focus...

The shot was taken on a level plane with the subject... It was as flat as I could get it...I created what I am calling a 'box shot'. I really am making up all sorts of words to try and describe what I am thinking...




Now in photo 2 I didn't change a single setting but I did raise my camera and have it mounted on a tripod looking down on the subject at an angle....

Look how much more of the image is 'in focus'...

I was shooting down and creating more of a 'flat plane' for the camera to look at... my 'imaginary ice cream cone' got a corner knocked off and became sort of a 'triangle' so to speak...my 'focal plane' was altered significantly by my angle of shot.

I don't know the technical term but I will say 'focal plane' for the sake of argument was changed drastically merely by the angle I pointed the camera...




Am I getting warmer? Anyone that knows more about this care to expand more?

07-07-2012, 03:28 AM   #2
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Did you just raise the camera perpendicular to the plane (what the doll is sitting on) or did you rotate the camera around the object (doll).
Going only by size clearly the doll is smaller (further away) in the second shot than the first.
07-07-2012, 07:20 AM   #3
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QuoteOriginally posted by wildman Quote
Did you just raise the camera perpendicular to the plane (what the doll is sitting on) or did you rotate the camera around the object (doll).
Going only by size clearly the doll is smaller (further away) in the second shot than the first.

I tried to just raise the camera....in its same location although it might have gotten pushed back a couple inches to accomodate the tripod...

I can do it again and measure from the tip of the lens to the subject so that I know for sure that the distance is the same. Now that I think about it the camera might have inadvertently been moved slightly back (away from the subject) by a little.

Also after thinking on it I demonstrated that I am very bad at geometry.

I used an online triangle calculator now that you mention it...If I lay the camera down 36 inches from the subject it is 36 inches from the subject. Period. Now if I raise the camera straight up 24 inches then the subject will no longer be 36 inches from the camera... it will be 43 inches from the camera...

I guess "finding the length of side C" did turn out to be useful after all...and my high school math teacher wasn't full of...

I will try again, next time using a piece of string so that I KNOW how far away the subject is. It is an experiment after all.

Last edited by alamo5000; 07-07-2012 at 07:26 AM.
07-07-2012, 08:36 AM   #4
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QuoteOriginally posted by alamo5000 Quote
if I raise the camera straight up 24 inches then the subject will no longer be 36 inches from the camera... it will be 43 inches from the camera...
Exactly.

Also realize that even if you maintain the same distance between the doll and the lens you are not necessarily maintaining the same distance between the lens and any given point on the plane the doll sits on. In fact in your second example you are increasing the distance between objects plane (the tape measure) and the lens thus increasing the len's apparent DOF of that plane.


Last edited by wildman; 07-07-2012 at 08:48 AM.
07-07-2012, 08:37 AM   #5
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Here is try #2 using the tried and true 'string method'...The figurine is a little out of focus but that is not really my point with the thread. My point is to demonstrate and understand my lens and/or any other lens with a bigger aperture and how to develop better techniques to use those apertures.

The camera lens was approximately 1 meter from the figurine on both attempts. I tied a string on the lens cap with it on the camera and measured both times. On the second attempt the camera lens was raised exactly 1 foot. I measured it to make sure.




Photo 2




Although less pronounced than my first flawed attempt the same principal is still there...
07-07-2012, 08:45 AM   #6
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Now for a bit of my own pontificating and analysis...

The brick plane the figurine is sitting on is flat and has been for say 30 something years. When I raise the camera up by 1 foot as was measured----

Parts of that flat plane are either closer or further away from the lens than in the first attempt, thus giving an 'appearance' of a variable...

The variable is 'still' distance I think, but I am putting it up for discussion.

Technically, in the same shot, in one frame I have multiple depth of field calculations that I 'could' make...hence in the second shot the bricks are way more pronounced and way more part of 'the picture'...

Maybe the DOF is not changing per se--just the distance in between the lens and objects in the frame...which ultimately effects DOF...or perception thereof...

That being stated I think it would be helpful to discuss techniques for proper visual effects using wide apertures...

Ready. Set. Discuss.

Last edited by alamo5000; 07-07-2012 at 08:59 AM.
07-07-2012, 10:29 AM   #7
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What you are taking about is a flaw in the camera systems (ones with lenses) that we use. The plain you are looking at is a spherical plain. At a distances it will start to resemble a flat brick wall but when you get closer like you are doing it will look like the inside of a ball. To illustrate take your tripod and a meter/yard stick. Place that stick on the tripod so it is just touching a wall. As you move the stick to the side the wall gets farther away. If you did this at say 10 feet/ 3 meters the change is much smaller and can be inside of what we call the DOF.


DOF is a fiction as it doesn’t exist in the “real world” but only in the syntax of the camera systems we like to use. It is the destruction of information. This fiction can be used in telling a story with a photograph. This can be used to highlight a truth or tell a lie. Both of these can be informative/entertaining or misleading/boring. As a photographer you should ask why are you destroying this information. More to the point what story are you trying to tell. It can be fun isolating an object with DOF but more often we need more DOF to keep the object in context to tell the story. As DOF is the destruction of information if we destroy to much with the lens when we take the photograph we can't get it back but if we need to destroy more information later we can do it with the computer in PP.


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07-07-2012, 11:12 AM   #8
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QuoteOriginally posted by DAZ Quote
What you are taking about is a flaw in the camera systems (ones with lenses) that we use. The plain you are looking at is a spherical plain. At a distances it will start to resemble a flat brick wall but when you get closer like you are doing it will look like the inside of a ball.
With a 50mm lens about what distances are we talking about to where it moves from spherical to 'flat'? Roughly...say with the lens I referred to above... a 50mm f1.4....just for example's sake...

At this point I am sheerly running experiments with this (and other lenses) so that I can learn more of the properties of the lenses and know in my head what I can and can't do for creative purposes. The above photos are not creative at all. Simple snap. But if I know the dynamics of the lenses I use I will be able to think through shots better and with more purpose...

QuoteOriginally posted by DAZ Quote
To illustrate take your tripod and a meter/yard stick. Place that stick on the tripod so it is just touching a wall. As you move the stick to the side the wall gets farther away. If you did this at say 10 feet/ 3 meters the change is much smaller and can be inside of what we call the DOF.
Sorry I didn't understand exactly what you meant here.


QuoteOriginally posted by DAZ Quote
DOF is a fiction as it doesn’t exist in the “real world” but only in the syntax of the camera systems we like to use. It is the destruction of information. This fiction can be used in telling a story with a photograph. This can be used to highlight a truth or tell a lie. Both of these can be informative/entertaining or misleading/boring. As a photographer you should ask why are you destroying this information. More to the point what story are you trying to tell. It can be fun isolating an object with DOF but more often we need more DOF to keep the object in context to tell the story. As DOF is the destruction of information if we destroy to much with the lens when we take the photograph we can't get it back but if we need to destroy more information later we can do it with the computer in PP.
Right now I am in learning overdrive. Some of the photos I have seen that I liked a lot actually didn't have a 'lot' of bohek so to speak... yes there was blur but it wasn't overwhelming... one shot I recall had the subject (a person) and in the background had some African troops that were slightly blurred out. You could still look at them and see what they were... they were not obliterated...but it kept attention on the subject and put the subject very much into context.

That was just one example of when not to 'over do it'...without the background being somewhat identifiable the photo lost a huge amount of significance.

On the other end of the spectrum I have seen some amazing shots where the subject was the subject and everything else was obliterated... those too were quite nice and appealing to me too because of the creative use of the background coloring. Say for example the subject was in front of a bunch of different colored christmas lights and in that instance the blurred colors added significantly to the meaning and didn't distract from the actual subject.

It can go either/or.... I just need to learn more so that I can control what I am trying to get in the end instead of just happening upon it by accident.

07-07-2012, 11:28 AM   #9
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From your first post...

QuoteOriginally posted by alamo5000 Quote
Now in photo 2 I didn't change a single setting but I did raise my camera and have it mounted on a tripod looking down on the subject at an angle....

Look how much more of the image is 'in focus'...
Actually if you look at the first two images, the DOF is very similar. Look at the rough brick along the wall.
You've merely compressed the depth of the first image by looking at it at that angle.

Last edited by amoringello; 07-07-2012 at 11:33 AM.
07-07-2012, 11:32 AM   #10
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Additionally, if you look closely at the wall on the second shot, you'll see that the focal plane is not vertical. It is at the same angle as your camera.
This cal cause a false perception to how much of the image may be in focus... you'll see focus area from one brick at the bottom of the wall to a location one or two bricks further at the top.

So you've actually got two potential issues going on, almost creating an optical illusion.
07-07-2012, 11:49 AM - 1 Like   #11
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This might be the most interesting thread i have ever seen in the forum. Thanks!

I'm going to throw in my simple hypothesis. I believe that, by altering the angle, you simply revealing to the viewer more of what is in focus. Would you mind trying the same shot, but with the doll and your camera flush against the verticL wall?

I personally have a depth of field crisis of faith. Conventional wisdom holds that there is moredepth of field behind a subject than in front. Yet, when I view images, I see more depth of field in front of the subject.
07-07-2012, 12:00 PM   #12
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I should have added more verbiage here. Rotate the stick from the tripod end. As you rotate the stick the end at the wall will move away from the wall. If you moved the stick and tripod closer (after you have rotated the stick) so the stick is just touching you will not be able to rotate it back without shortening the stick. This is showing that the distends to the flat wall is not a content.


From a technical point of view there is only one spherical dissidence with a lens that will be in focus. There is a plain in front and behind were the sensor and lens can't resolve any differences. This is the only thing in focus. Beyond this plain (both in front and behind) things just get less in focus as the information is destroyed. As a lens is stopped down only the center part of the lens can get to the sensor. This part is focusing vary close to all being in focus so the parts that are not are not destroying the parts that are in focus. When the lens is opened up the part of the lens at the sides can hit the sensor. These will be focused in front or behind the sensor. This will make for destructive interferences.


There is no point where this is absolutely flat other then at infinity. Just like the is no dissidence in focus other then the focal plain. You just get to a point were it is close enough that it is OK for you.


As this is most evident at closer dissidence’s the makers of the better macro lenses try to flatten the focal plain so on these lenses you may not see it as much. This is one good reason to use a macro lens if you have a 3D object you are trying to photograph.


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07-07-2012, 02:20 PM   #13
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QuoteOriginally posted by fuent104 Quote
This might be the most interesting thread i have ever seen in the forum. Thanks!
Don't know the most interesting but it's a good'un.

QuoteOriginally posted by fuent104 Quote
I'm going to throw in my simple hypothesis. I believe that, by altering the angle, you simply revealing to the viewer more of what is in focus.
I think this is right.
07-07-2012, 03:50 PM   #14
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QuoteOriginally posted by dadipentak Quote
I think this is right.
Easy enough to tell...
Online Depth of Field Calculator

Figure out if the few inches change makes that much of a difference.

50mm f1.4 at 36in: DOF = 0.7in

50mm f1.4 at 43in: DOF = 1.01in

IMOHO, most of the effect is perception due to change in angle, but the change in distance certainly makes a significant difference with nearly a 50% increase in DOF of 0.3in.
07-07-2012, 10:01 PM   #15
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QuoteOriginally posted by amoringello Quote
IMOHO, most of the effect is perception due to change in angle, but the change in distance certainly makes a significant difference with nearly a 50% increase in DOF of 0.3in.
I agree. My hypothesis:

Given the same distance from the subject for both shots:

1. The lower angle shot will show a shallower DOF because the DOF plane, or region, will be parallel to both the camera and the subject.

2. The higher angle shot will show what is apparently a wider DOF because the DOF plane, or region, will still be parallel to the camera, but also be in front of the subject for the area below the subject, and behind the subject for the area above the subject. Simple geometry.
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