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Q: Digital Photography - Depth of Field ( Answered ,   1 Comment )
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 Subject: Digital Photography - Depth of Field Category: Miscellaneous Asked by: nosredla-ga List Price: \$20.00 Posted: 19 Nov 2006 06:51 PST Expires: 19 Dec 2006 06:51 PST Question ID: 783986
 ```A common photographic technique is to isolate a focused subject against a blurred background by using a wide aperture to reduce the depth of field. This is much more difficult to do with a digital camera, and I would like to understand why. I believe the answer will have something to do with factors such as sensor size, lens size, focal length, distance between lens and sensor, etc. I would like to understand, but without being overwhelmed by technical terms. Thank you```
 ```Hi!! Let me start recalling that depth of field (DoF), in photography, is the distance in front of and behind the subject which appears to be in focus. The problem with DoF in digital cameras is due the usually small size of the sensors (chips). To start dealing with this problem we need to know about the called "Circle of Confusion": This concept is related to the "human eyes resolution", that is the smallest size of a point before it looks like a small disk rather than a point. On an 8" x 10" print viewed from a "lecture distance" of about one feet, assuming perfect vision and ideal light conditions, the size of such point is 0.25mm or 250 microns (1/100"). To get a point of this size on the 8" x 10" print we need to magnify our original image (negative or digital sensor surface). On a 35-mm film camera the frame size is 24x36mm, a typical good but non-SLR digital camera has a sensor of 2/3" (6.6×8.8mm), that is four times smaller. Therefore, to get the print, the magnification ratio for a digital camera with 2/3" sensor is about four times greater than the 35-mm film camera. How this affects the depth of field? Just see the following paragraph, I cannot copy it here due copyrights restrictions. Basically the problem lyes in since the small size of the sensors: they need, for a same field of view, a proportionally smaller lens focal length. "Basic Facts" & "What's so special about digital cameras?" at wrotniak.net "Depth of field and your digital camera": http://www.wrotniak.net/photo/tech/dof.html#BASIC Read this: "What About Digital? A common complaint about digital cameras is that when using one it's not possible to get nice out-of-focus backgrounds. Why therefore do digital cameras have greater Depth of Field? The reason for this is that the imaging chips on most consumer digitals is very small, around the size of ones smallest finger nail. This means that a normal lens for a format that small is as short as 15mm. A 15mm lens at f/5.6 has Depth Of Field from about 2.5 feet to infinity. Not too much opportunity for selective focus, is there? This is one of the unspoken drawbacks of low-end digital cameras. Only expensive SLRs like the Nikon D1x, Canon 1D and their ilk have chips close to the size of a 35mm frame, and therefore offer enough DOF to allow creative control over out-of-focus backgrounds." From "Understanding Depth Of Field" at The Luminous Landscape: http://www.luminous-landscape.com/tutorials/understanding-series/dof.shtml To complete the answer the better for you is to follow reading the wrotniak.net's article: "Depth of field and your digital camera": http://www.wrotniak.net/photo/tech/dof.html It has all concepts that you will need to completely understand this topic. In the case that you need further help with this just request for a clarification. At the mentioned article there are also links to tables that will be useful to use for estimate the depth-of-field. The tables are depth-of-field tables for four groups of Olympus digital cameras with different sensor sizes and they are also applicable to other cameras of similar sensor sizes. For example see the "Depth of field tables for the Olympus E-10/E-20 cameras"(2/3" sensor): http://www.wrotniak.net/photo/tech/dof-e10.html You can compare it with the "Depth of field tables for 24x36 mm cameras" (common film cameras): http://www.wrotniak.net/photo/tech/dof-35mm.html For further reading see: "Circle of confusion - Wikipedia, the free encyclopedia": http://en.wikipedia.org/wiki/Circle_of_confusion "Depth of field - Wikipedia, the free encyclopedia": http://en.wikipedia.org/wiki/Depth_of_field "Photo.net Depth of Field and the Digital Domain" by Bob Atkins: http://www.photo.net/learn/optics/dofdigital/ Search strategy: "Depth of field" digital "circle of confusion" digital I hope this helps you. Remember to not hesitate to use the clarification feature if something is missed in this answer. I will be glad to offer you further assitance on this topic if you need it. Best regards, livioflores-ga``` Request for Answer Clarification by nosredla-ga on 20 Nov 2006 16:09 PST ```Thank you for your efforts. However I must tell you, with great respect, that this is not what I had wanted. When I was a boy, I asked my parents "why does water boil". They replied that it boiled because heat was put under it. I did not find this to be an explanation because of course I could tell this from observation. I wanted to understand why the application of heat would have a specific observable effect on the water. I am having similar disatisfaction with explanations about the difficulty that digital cameras have in obtaining a shallow depth of field. I own several text books on digital photography, and have done a good deal of internet research through which I have already discovered the Luminous Landscape and Wikipedia sources that you referred me to. I already understand what depth of field is, and I already understand the concept of the Circle of Confusion. I will plough through the very lengthy wrotniak source you gave me, but at first glance it still seems to say only "digital cameras have difficulty allowing shallow depth of field because they have small sensors" (equivalent to "water boils because heat is applied") Perhaps my inability to understand is my fault, but I would really appreciate if you could try, in your own words, to give me in two short paragraphs of layman's language a simple explanation of why the small sensor of a digital camera makes it difficult to obtain a shallow depth of field. Please forgive any obtuseness on my part. Many thanks``` Clarification of Answer by livioflores-ga on 20 Nov 2006 21:36 PST ```Hi!! I am so sorry because my answer does not satisfy you; take into account that I am only a researcher not a photograph expert. So please give some time to prepare the requested explanation. I guess that some additional concepts must be included, a good explanation on this could take more than two short paragraphs. Regards, livioflores-ga``` Request for Answer Clarification by nosredla-ga on 21 Nov 2006 10:04 PST ```livioflores-ga I am sorry if my expectations were incorrect. I am usually quite effective myself at research, but had been unable to understand this issue to my satisfaction from the sources I found. I turned to Google Answers because I thought my question would go to a subject matter expert. I now feel it would be unfair to ask you to do a lot more work on this, so I am happy to thank you for what you have done, which certainly was very good research, and absolve you from further responsibility. Best wishes``` Clarification of Answer by livioflores-ga on 21 Nov 2006 20:33 PST ```Hi again!! Well, you did it. I hope that at least some smaill part of my work have been helpful. You relieved me from a huge research because I started to deal with some theoretical optics stuff. In order to satisfy my own need to bring something useful to you I want to add the following pages as additional sources: "Digital Depth of Field": This page gives some basic explanations and tells us that on some special circumstances "we can say that over the range of focus distances which aren't in the macro range (where D is close to F) and which aren't close to the hyperfocal distance (where D = F*F/fn*c) you can "guesstimate" that the depth of field ratio between two lenses used at the same aperture and focused at the same distance by assuming it's proportional to the size of the circle of confusion and inversely proportional to the square of the focal length. http://www.bobatkins.com/photography/technical/digitaldof.html The above confirms the fact that the focal length of the lens has the most dramatic effect on the depth of field. The other page is "Digital SLRs and Depth of Field": At this page an experiment is taken using the same lens on a 35mm-SLR and a Digital-SLR camera. Here is clear how the field of view change from one camera to another. http://www.dofmaster.com/dof_dslr.html Joining both above results your final conclusion follows. The following two related pages could add some additional background on this subject: "depth-of-field explanation": http://www.aesthetic-endeavors.com/photo/dof/ "depth-of-field example": http://www.aesthetic-endeavors.com/photo/dof/dof_eg.htm Again, I hope this could be on some help to you. Thank you for your understanding. Best regards, livioflores-ga```
 nosredla-ga rated this answer: ```Depth of Field is affected primarily by three factors: a) the aperture setting of the lens where wider apertures result in less depth of field, b) the distance from the subject, where the greater the distance the greater the depth of field, and c) the focal length of the lens where a shorter focal length results in greater depth of field. Of these three factors, it is c) that has the most dramatic effect. Because digital cameras have a smaller sensor (than 35mm film), they require a wider angle lens to give the same field of view. This means a shorter focal length, which results in a significant increase in depth of field, and consequent difficulty in obtaining a shallow depth of field. There - two paragraphs! I rate this answer three stars because despite livioflores-ga's best intentions, I had to answer my question myself from my own research.```
 ```Hi, To achieve a small DoF (which creates this blur effect), you have to combine wide aperture and long focale length. The problem with compact digital cameras is that the aperture is often small, and the angle wide. Great DoF effects appear when opening at f2.8 and below. You can also try to zoom because DoF is more perceptible when the focale length is greater. You will also have to use the manual mode of your camera, so you can try to set the lowest value as possible for the aperture. Try this indoor, because outdoor, you will get too much light for wide apertures (compact cameras also don't shut as lightspeed, generaly 1/1000 sec, while you would need 1/2000, 1/4000 or even 1/8000 to combine outdoor sjot + wide aperture). And don't fire the flash ;-) Exercise with objects very close to you, and far background. You have a macro-mode, try it, DoF in macro is very small. And well, if none of this helps, you'll have to consider buying a SLR camera with a great lens (if you love small DoF, you've got to try some f1.4 50mm or 85mm ;-)) Regards```