DOF and distance from the object
May 28, 2012 09:36:53 #
The amount of Depth of Field one achieves is controlled by the distance from the subject besides the aperture setting, I have posted two images to demonstrate this, I hope this helps clear some confusion on this rather difficult subject for a new comer.
I hope we get some technical insights into the reason for this from the more enlightened.
These are taken with a D7000 and 70~300 4.5~5,6 G lens.
I hope we get some technical insights into the reason for this from the more enlightened.
These are taken with a D7000 and 70~300 4.5~5,6 G lens.
Butterfly - ISO 800 @ 1/400th F5.6. Full Zoom
Chameleon - ISO 200 @ 1/25oth F16 Full Zoom
May 28, 2012 10:48:45 #
Actual depth of field increases in relation to the distance from the subject. DOF is best expressed as a percentage of that distance, but I have never seen an actual formula. You can use the online DOF calculator to see this variation over greater distances.
May 29, 2012 08:18:17 #
This is how I understand Depth of Field.
A lens does not focus on a 'plane' but rather on 'space.' And, that 'space' is the Depth of Field. How deep, from front to back, that 'space' is varies with the focal length of the lens, the distance to the subject and the lens opening. A wide angle lens, focused at a 'reasonable' distance, and a 'smaller' lens opening, will have a great depth of field. For instance - 24mm, f16, focused @ perhaps 6ft could have a DOF of 2' to infinity. On the other hand, a telephoto lens, focused on a somewhat close subject, and using a wide lens opening, may have a DOF of only a few fractions of an inch. For instance 300mm, f4.5, @ 6ft - the DOF could only be, perhaps, 5 1/2' to 7'. (these are estimates, for example only) In general, the DOF, from the 'front' of the acceptable focus, to the subject, to the 'rear' of the acceptable focus is about 1/3 to 2/3. A 'box camera' with a fixed focus, fixed f8 lens, focused @ 15' could have a DOF of, perhaps, 5' to infinity.
A lens does not focus on a 'plane' but rather on 'space.' And, that 'space' is the Depth of Field. How deep, from front to back, that 'space' is varies with the focal length of the lens, the distance to the subject and the lens opening. A wide angle lens, focused at a 'reasonable' distance, and a 'smaller' lens opening, will have a great depth of field. For instance - 24mm, f16, focused @ perhaps 6ft could have a DOF of 2' to infinity. On the other hand, a telephoto lens, focused on a somewhat close subject, and using a wide lens opening, may have a DOF of only a few fractions of an inch. For instance 300mm, f4.5, @ 6ft - the DOF could only be, perhaps, 5 1/2' to 7'. (these are estimates, for example only) In general, the DOF, from the 'front' of the acceptable focus, to the subject, to the 'rear' of the acceptable focus is about 1/3 to 2/3. A 'box camera' with a fixed focus, fixed f8 lens, focused @ 15' could have a DOF of, perhaps, 5' to infinity.
May 29, 2012 09:38:56 #
DOF still confuses the heck out of me, and I am even pretty good at math! Hopefully someday someone will draw an explanation of DOF. That would be perfect!
May 29, 2012 11:50:07 #
One of my photo mentors stated this, DOF will go 1/3 before and 2/3 after the prime focal point, but at close distances it becomes very compressed.
May 29, 2012 12:20:39 #
twowindsbear wrote:
This is how I understand Depth of Field. br br A ... (show quote)
Just to clarify the terminology, given a specific focal length, a lens can only accurately focus on a point, plane or subject set a certain distance. There is no such thing as focusing on space. The depth-of-field or space as you call it, is simply defined as the distance in front and behind the subject that yields acceptable sharpness, but really never in precise focus.
May 29, 2012 21:33:22 #
May 29, 2012 21:36:04 #
The subject is really quite simple and straight forward, explaining it may not be. I found the best way to understand it is to play around with different setting and study the results, the clarity(!!!) will fall in place.
May 29, 2012 21:45:04 #
Thank you All, some interesting information there, certainly food for thought. The explanations by barryb and Julian seem to fit in with what I have observed.
The modern DSLR is a wonderful learning tool and it permits one to experiment with different settings and see the results immediately. This to me is the most practical way for any new comer to know what the different settings do for the image.
Cheers!
The modern DSLR is a wonderful learning tool and it permits one to experiment with different settings and see the results immediately. This to me is the most practical way for any new comer to know what the different settings do for the image.
Cheers!
May 29, 2012 21:55:49 #
This has been covered before, but bears repeating in this thread. DOF is NOT a direct function of lens length. It is a function of the size of the image on the sensor (or film) and aperture. If you took an image at 200mm and F4 and then took the image at 70mm but moved closer to make the image the same size on true sensor, the DOF would be virtually identical. I say"virtually" because there are some changes that occur from focal length, but they are minimal.
What does change is perspective, but not DOF.
Different lenses can change the look due to variations in the number of segments in the aperture diaphragm, but the DOF is still controlled by aperture and image size.
If is also worth noting that DOF is also subjective (despite its mathematical derivation) and the subjectivity is affected by print size. What might appear sharp in a 4x6 could be very soft in a 20x30.
The whole DOF thing is usually the victim of "over thinking." If it looks good , its good - if it looks out of focus, it is.
What does change is perspective, but not DOF.
Different lenses can change the look due to variations in the number of segments in the aperture diaphragm, but the DOF is still controlled by aperture and image size.
If is also worth noting that DOF is also subjective (despite its mathematical derivation) and the subjectivity is affected by print size. What might appear sharp in a 4x6 could be very soft in a 20x30.
The whole DOF thing is usually the victim of "over thinking." If it looks good , its good - if it looks out of focus, it is.
May 29, 2012 22:00:37 #
barryb wrote:
One of my photo mentors stated this, DOF will go 1/3 before and 2/3 after the prime focal point, but at close distances it becomes very compressed.
Julian wrote:
Both are correct. CaptainC is also correct (but it may take a few years for his point to sink in).Just to clarify the terminology, given a specific focal length, a lens can only accurately focus on a point, plane or subject set a certain distance. There is no such thing as focusing on space. The depth-of-field or space as you call it, is simply defined as the distance in front and behind the subject that yields acceptable sharpness, but really never in precise focus.
May 29, 2012 22:04:27 #
MT Shooter wrote:
Actual depth of field increases in relation to the distance from the subject. DOF is best expressed as a percentage of that distance, but I have never seen an actual formula. You can use the online DOF calculator to see this variation over greater distances.
Depth of field:
1. The premissible diameter of the circle of confusion in the negative-the larger the permissible diameter the greater the depth.
2.The angle subtended by the lens at the film, ie, for the most purposes, the f-number - the larger the f-number the greater the depth.
3. The square of the ratio of reproduction-the smaller the ratio of reproduction the greater the depth.
Focusing to cover two objects at different distances would finally read:
2xy over x+y.
From:"The Manual of Photography" formerly, "The Ilford Manual of Photography. First published 1890. My copy is from 1976. Rochester Insitute of Technology. :roll:
The circle of confusion is determined by using an optical lens bench. This tolerance is determined by the manufacturer. Why better lenses cost more. In general, telephoto lenses are easier to manufacture then wide angle lenses. As the depth of field decreases (telephoto) the depth of focus increases, as depth of field increases (wide angle) the depth of focus decreases.
May 29, 2012 22:13:55 #
henryl wrote:
quote=MT Shooter Actual depth of field increases ... (show quote)
All correct. And then there is the, "looks sharp / looks soft."
May 29, 2012 22:28:25 #
CaptainC wrote:
quote=henryl quote=MT Shooter Actual depth of fi... (show quote)
The problem with that statement is dependance of personnal visual ability and acutance. Also, in standard chemical photography the enlargement has been sent through another lens system. In digital, the dpi in relation to the print size, the magapixials of the receiver (camera), the the resolution of the lens being used.
May 29, 2012 22:41:18 #
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