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Technical question regarding depth of field

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bobgilbody

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I downloaded this:

Loading…

cpn.canon-europe.com

I understand that the physical size of the sensor will affect depth of field.

Also the f stop selected will, and the focal length of the lens will also.

So there are three things that affect depth of field.

In addition the distance of the sensor to the subject of the photograph will affect the depth of field.

My question is this:

Is there anything else that affects depth of field?
 
bobgilbody said:
I downloaded this:

https://cpn.canon-europe.com/content/education/technical/depth_of_field_calculator.do

I understand that the physical size of the sensor will affect depth of field.

Also the f stop selected will, and the focal length of the lens will also.

So there are three things that affect depth of field.

In addition the distance of the sensor to the subject of the photograph will affect the depth of field.

My question is this:

Is there anything else that affects depth of field?
Click to expand...
AFAIK, no. Sensor size, focal length, aperture and subject distance are the four factors that determine depth of field.

If you are trying to get a short depth of field to blur the background, then the distance from the subject to the background is important because it determines how much the background is blurred. Personally, I normally have the opposite problem when shooting wildlife - I often can't get enough depth of field to get everything in reasonable focus.
 
bobgilbody said:
I downloaded this:

https://cpn.canon-europe.com/content/education/technical/depth_of_field_calculator.do

I understand that the physical size of the sensor will affect depth of field.

Also the f stop selected will, and the focal length of the lens will also.

So there are three things that affect depth of field.

In addition the distance of the sensor to the subject of the photograph will affect the depth of field.

My question is this:

Is there anything else that affects depth of field?
Click to expand...
Only aperture and distance change the DOF, sensor size and focal length only affect the DOF if you change the distance to target to match the field of view changes they produce.

There are a number of urban myth misinterpretations with DOF.

All focal lengths from 100mm to 800mm give the same depth of field if you match the Field of View by changing the distance to target.(same aperture and sensor size).

All sensor sizes give the same DOF (same distance, aperture and focal length) they just change the field of view, If you match the Field of View by changing the distance the DOF changes.

The appearance of foreground and background blur is often misinterpreted as DOF but in wildlife terms DOF is the sharp bit on target not the blurry bits around it.

If you want to get more DOF and keep the same amount of pixels on target your focal lengths need to be below 100mm, preferably 24mm or less as wide angle lenses gain in DOF but you then have to get the camera close and use remote triggers.
 
The above is correct. Sensor size affects DOF only when it affects subject distance. If I put a full-frame camera side-by-side with a crop-frame camera with the same lens on each, then crop the full-frame by 1.6x in lightroom, the DOF will be the same. If I instead stand with the crop-frame at 1.6x the distance to the subject that I am with the full-frame, I'll get shallower DOF with the closer camera.

focal length also does not change DOF.It may change the perceptual intelligibility of the background due to compression, it your background will have the same amount of blur but with a very long focal length it's easier to make that blur into a wash because a very small amount of it is included in the frame. With a wider lens, you see more of the background and it becomes more intelligible.

One thing that will affect DOF is how you measure it, ie what your threshold is for acceptable sharpness. This can mean that having higher pixel resolution will decrease your DOF if you are adjusting your subjective standard for what you consider "in focus" between the higher and lower resolution systems.
 
Thanks for responding to the question.

It seems to me that in order to have a rational discussion regarding 'depth of field' it is first necessary to 'fix' our understanding of, and scope perhaps, of the words we are using.

I found this of particular interest:

"One thing that will affect DOF is how you measure it, ie what your threshold is for acceptable sharpness. This can mean that having higher pixel resolution will decrease your DOF if you are adjusting your subjective standard for what you consider "in focus" between the higher and lower resolution systems."

I once read an article about the optical abilities of the human eye. We all have different abilities, and these abilities change over time [ or level of alcohol in our blood stream ]. Anyway, the conclusion I drew from the article was that our brains process the images provided by our eyes to give an 'image'.

This is getting a bit complicated because it means that we each see the world slightly differently, but well enough that we tend to walk through open doorways rather than closed doorways.

Any photograph I see on my monitor is 'fixed' in the sense that the person that captured the image has decided what should be in focus and what is not.

I have seen some photographs that are composite images produced to give extended dynamic range. It maybe possible to do something similar with 'focus'. Whether or not this would provide a pleasing result I am unsure.

Thanks again Bob
 
The DOF measures we use are based on viewing distance and acceptable sharpness (3 times larger than the smallest detail a person with 20/20 vision could see). If you view the image from a closer distance or view your image at 100% on your computer screen, then the DOF for that situation will be much less than that given by the normal DOF calculators.

Attached is a simple example from when I was checking the focus accuracy of my 2X crop camera with a 420mm lens. The focus point was a nail head on my wooden walkway from 301.25 inches (ExifTools distance). The DOF obtained from typical calculator is 2.1 inches. The 100% crop shows that the DOF at that enlargement would be far less than 2.1 inches (about the width of the nail head).











--
drj3
 
Thanks for the example drj3.

Once I get set up in the granny flat at my eldest daughter's place I hope to be able to photograph small birds. There are fairy wrens there. It seems the only way I will be able to get detailed images of them is to get them to come close. I intend to use the Canon 80D attached to the Sinar. I can remotely trip the shutter on the Canon and have it set at say 10 seconds shutter speed, then trip the shutter on the Sinar using a solenoid. I have an old Metz 45 CT-1 flash that I will trigger via the shutter on the Sinar. Hopefully this will allow a flash duration short enough to 'freeze' motion yet still stop down to f22 or smaller to give depth of field.

Will have to wait and see if it works out.
 
bobgilbody said:
.

I have seen some photographs that are composite images produced to give extended dynamic range. It maybe possible to do something similar with 'focus'. Whether or not this would provide a pleasing result I am unsure.
Click to expand...
You can absolutely do something like this with focus. It is called Focus Stacking. The D850 even has a built-in mechanism to do this for you, semi-automatically. With AF-S lenses the camera can take a series of images all slightly shifted in focus point. The result is a series of images that you then can use in Focus Stacking software.

The difficulty, besides having to use software to combine the images, is that the subject matter needs to stay very still, though if shooting at very fast frame rates you might get a better result than expected.

Focus stacking is typically used in macro shooting where the DOF is so tiny.

Loading…

en.wikipedia.org
 
The easiest way to understand it is "larger reduces DOF." I.e. increased magnification/apparent subject size reduces DOF (shorter distance, longer FL, crop sensor); and larger apertures.

Crop sensors only increase DOF when you reduce the magnification/apparent size by using a shorter FL/longer distance in order to get the same composition (smaller size on a smaller sensor).

The other aspect that is often missed/overlooked is that DOF only describes what is "w/in acceptable focus" and it says nothing about how OOF areas are rendered. I.e. you can use a longer FL from a greater distance for the same composition/DOF, but how the OOF BG areas are rendered can be hugely different.
 
Bob,

The aperture diameter (the physical size of the lens opening) and the distance from subject are the two factors that most affect depth of field. The larger the aperture diameter and the nearer you are to the subject, the shallower the depth of field. The f-stop is relevant in that it allows you to determine the aperture diameter in use.

--
Bill Ferris Photography
Flagstaff, AZ
http://www.billferris.photoshelter.com
 
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Bill Ferris said:
Bob,

The aperture diameter (the physical size of the lens opening) and the distance from subject are the two factors that most affect depth of field. The larger the aperture diameter and the nearer you are to the subject, the shallower the depth of field. The f-stop is relevant in that it allows you to determine the aperture diameter in use.
Click to expand...
FL and subject distance both affect DOF significantly more than aperture does (2x more). But they act in opposition so that if you keep the composition the same the DOF will be (very nearly) the same... leaving you with only aperture to control DOF for a given composition.

But as I said before, that is only DOF at the subject/focus plane and not (necessarily) BG rendering/blur...
 
SKersting66 said:
Bill Ferris said:
Bob,

The aperture diameter (the physical size of the lens opening) and the distance from subject are the two factors that most affect depth of field. The larger the aperture diameter and the nearer you are to the subject, the shallower the depth of field. The f-stop is relevant in that it allows you to determine the aperture diameter in use.
Click to expand...
FL and subject distance both affect DOF significantly more than aperture does (2x more). But they act in opposition so that if you keep the composition the same the DOF will be (very nearly) the same... leaving you with only aperture to control DOF for a given composition.
But as I said before, that is only DOF at the subject/focus plane and not (necessarily) BG
Click to expand...
Compare equivalent compositions and shots of the same scene made from the same position by cameras of different sensor formats. Their focal lengths and focal ratios (f-stops) will be different but their depths of field will be equivalent because they are the same distance from the subject abys they are using the same aperture diameter.
 
Bill Ferris said:
SKersting66 said:
Bill Ferris said:
Bob,

The aperture diameter (the physical size of the lens opening) and the distance from subject are the two factors that most affect depth of field. The larger the aperture diameter and the nearer you are to the subject, the shallower the depth of field. The f-stop is relevant in that it allows you to determine the aperture diameter in use.
Click to expand...
FL and subject distance both affect DOF significantly more than aperture does (2x more). But they act in opposition so that if you keep the composition the same the DOF will be (very nearly) the same... leaving you with only aperture to control DOF for a given composition.
But as I said before, that is only DOF at the subject/focus plane and not (necessarily) BG
Click to expand...
Compare equivalent compositions and shots of the same scene made from the same position by cameras of different sensor formats. Their focal lengths and focal ratios (f-stops) will be different but their depths of field will be equivalent because they are the same distance from the subject abys they are using the same aperture diameter.
Click to expand...
In a DX/FF comparison the FF will have ~1 stop less DOF because it is using a lens that is 50% longer... i.e. 100mm vs 150mm; the 150mm is creating a larger image on a larger sensor in order to record the same composition. If you compare 4/3 vs FF it's ~2 stops because the FL will be 2x longer.
If you are also changing the aperture setting the DOF could be anything... unless you are talking about f-ratios in terms of "equivalence" (same f-#, different total light/DOF).

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

--
https://www.flickr.com/photos/skersting/
 
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BTW, that "larger reduces DOF" also applies to image display size and viewing distance... DOF is not a fixed quality of an image.
 
SKersting66 said:
Bill Ferris said:
SKersting66 said:
Bill Ferris said:
Bob,

The aperture diameter (the physical size of the lens opening) and the distance from subject are the two factors that most affect depth of field. The larger the aperture diameter and the nearer you are to the subject, the shallower the depth of field. The f-stop is relevant in that it allows you to determine the aperture diameter in use.
Click to expand...
Click to expand...
Click to expand...
http://www.dofmaster.com/dofjs.html

--
Click to expand...
The site you linked to confirms what I wrote.

Using the default 10-foot distance to subject, select a Nikon DX camera and a 100mm, f/2 lens. Click, Calculate. The result will show a depth of field of 0.24-foot.

Next, select a Nikon full-frame camera and a 150mm, f2.8 lens. Keep the same 10-foot subject distance. Click, Calculate, and you'll get a 0.22-foot depth is field.

Divide the focal lengths used by their respective f-stops (focal ratios) and you'll see the DX camera read using a 50mm aperture while the FX camera was using a 53mm aperture. If the online depth of field calculator allowed selection of f/3, the FX lens aperture and depth of field would match that of the DX.

Try this with other combinations of camera bodies and you'll consistently get the same outcome: keeping subject distance constant and selecting focal lengths & f-stops delivering equivalent images, cameras of different format use the same lens aperture diameter to achieve the same depth of field.
 
Thanks for all the information. I am getting a better idea now of the compromises required.

'focus stacking':

Thanks for this. I have seen photos of bugs that have had this technique applied. I assume the bug is dead and so doesn't move.

The focus stacking uses the lens to focus bits of the image, then the bits are put together to form a composite image. [ Hope I got that right ]

Maybe if the 'film plane' were not fixed and flat it would be possible to to capture the same image with one shot.

I'm not sure if this would be possible. Suggestion is that the sensor is not flat but is distorted to provide different focusing for different parts of the image.

Thanks again for all the info.

Bob
 
I took this photo using a Canon 750D glued to the Sinar. I posted it in the macro forum and it seems it's not an extension of DOF. Wouldn't work for birds anyway. Might be useful for flat fish or snakes or whatever.

Used about 15 degrees forward tilt on the lens plate.

Watch needs a clean.



ec8a9b421a134b51b0ff7076e955e9e3.jpg
 
Bill Ferris said:
The site you linked to confirms what I wrote.

Using the default 10-foot distance to subject, select a Nikon DX camera and a 100mm, f/2 lens. Click, Calculate. The result will show a depth of field of 0.24-foot.

Next, select a Nikon full-frame camera and a 150mm, f2.8 lens. Keep the same 10-foot subject distance. Click, Calculate, and you'll get a 0.22-foot depth is field.

Divide the focal lengths used by their respective f-stops (focal ratios) and you'll see the DX camera read using a 50mm aperture while the FX camera was using a 53mm aperture. If the online depth of field calculator allowed selection of f/3, the FX lens aperture and depth of field would match that of the DX.

Try this with other combinations of camera bodies and you'll consistently get the same outcome: keeping subject distance constant and selecting focal lengths & f-stops delivering equivalent images, cameras of different format use the same lens aperture diameter to achieve the same depth of field.
Click to expand...
It seems to me that you're convoluting multiple factors simultaneously in order to achieve "equivalence." Of the 4 factors, the only one you are keeping constant is the distance... how do you say which of the 3 changes had which affect (Ap/FL/SensorArea)?
In general, if you increase FL by 2 (2x) the DOF is reduced to 1/4. If you decrease distance by 2 (to 1/2) the DOF decreases to 1/4. If you open the aperture by 2 stops (1/2 the number) the DOF reduces to 1/2. And if you only change the image format (DX/FF) the DX sensor will have ~ 1 stop less DOF.
This holds true in any comparison as long as both are on the same side of hyper focal distance.

--
https://www.flickr.com/photos/skersting/
 
Last edited:
SKersting66 said:
Bill Ferris said:
The site you linked to confirms what I wrote.

Using the default 10-foot distance to subject, select a Nikon DX camera and a 100mm, f/2 lens. Click, Calculate. The result will show a depth of field of 0.24-foot.

Next, select a Nikon full-frame camera and a 150mm, f2.8 lens. Keep the same 10-foot subject distance. Click, Calculate, and you'll get a 0.22-foot depth is field.

Divide the focal lengths used by their respective f-stops (focal ratios) and you'll see the DX camera read using a 50mm aperture while the FX camera was using a 53mm aperture. If the online depth of field calculator allowed selection of f/3, the FX lens aperture and depth of field would match that of the DX.

Try this with other combinations of camera bodies and you'll consistently get the same outcome: keeping subject distance constant and selecting focal lengths & f-stops delivering equivalent images, cameras of different format use the same lens aperture diameter to achieve the same depth of field.
Click to expand...
It seems to me that you're convoluting multiple factors simultaneously in order to achieve "equivalence." Of the 4 factors, the only one you are keeping constant is the distance... how do you say which of the 3 changes had which affect (Ap/FL/SensorArea)?
In general, if you increase FL by 2 (2x) the DOF is reduced to 1/4. If you decrease distance by 2 (to 1/2) the DOF decreases to 1/4. If you open the aperture by 2 stops (1/2 the number) the DOF reduces to 1/2. And if you only change the image format (DX/FF) the DX sensor will have ~ 1 stop less DOF.
This holds true in any comparison as long as both are on the same side of hyper focal distance.
Click to expand...
 
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