full frame deph of field vs small sensor depth of field

[william_bray1]

<p> Hi I was considering geting a canon 5d MK2 in the future. I have been thinking about how much it would improve my photography and I can only come up with one negative ( I think it's a negative ) about going full frame. It's the depth of field difference, I know the bokeh is better on the 5d and it can isolate your subject better. But when you have to shoot in low light and have to use a wide apature, like weddings, focusing, I would think must be critical. I have shot a few weddings and on a small sensor I only use 2.8 on a 70 200 lens when I have to, due to low light and not beacuse of the effect, I try to shoot about f4 normaly. Has any one come across this problem when switching to full frame.<br>

Thanks Bill</p>

[ed_k__north_carolina_]

<p>Depth of field is a function of the optics, not the sensor.</p>

[sheldonnalos]

<p>Not exactly correct, Ed. But that's a side discussion that would derail the thread from the OP's original question.</p>

<p>I haven't run into any DOF problems shooting full frame, but I actually prefer the shallow DOF. If you want to know the rough equivalents, it's about 1 1/3 stop less DOF for equalized FOV and aperture between 1.6 crop and FF. One other thing to think about is that you might be able to use a higher ISO with the 5D II and this would allow you to stop down for greater DOF.</p>

[alan_bryant1]

<p>Bob Atkins wrote a useful guide...</p>

<p>http://www.photo.net/learn/optics/dofdigital/</p>

[tdigi]

<p>I found it took a little getting used to ( especially with primes wide open ) but I consider it a huge benefit considering the 5D2s ISO performance. For weddings I think this is where the 5D2 would really shine. Most wedding people I know love it.</p>

[hal_b]

<p>All weddings, news, sports, travel, and nature photos were shot in "full frame" prior to 2001. I still shoot my 35mm all the time. I can't imagine this will be a limitation.</p>

[g dan mitchell]

<blockquote>

<p><em>"Depth of field is a function of the optics, not the sensor."</em></p>

</blockquote>

<p>Not so fast.</p>

<p>DOF is a much more complex and subjective thing than some imagine. It is not an objective thing at all. The original notions of DOF were essentially meant to be interpreted as "if you shoot film format X at aperture Y and make prints at dimensions Z then subjects within a certain range in front of and possibly beyond the actual focus point will be in sharp enough focus."</p>

<p>There is a plane of optimum focus. Anything in front of that plane and behind it (unless you focus at infinity) is not in focus. The question is how out of focus is this stuff. Stuff that is only out of focus to an extent that it doesn't look OOF in a print is said to be within the DOF zone.</p>

<p>Format very definitely makes a difference if you print at some specific size. It also makes a difference how large you print. Today we often push relatively small formats - like APS-C and full frame - to much larger sizes that photographers typically did in the past. This means that the old "rules of thumb" about DOF can't be directly applied to larger prints.</p>

<p>It is even more complicated than that...</p>

<p>... but you just want a bottom line answer about full frame. If you have other reasons for going to full frame, don't let concerns about DOF hold you back, particularly if you will print at the same size regardless of which format you use.</p>

<p>Dan</p>

[ed_k__north_carolina_]

<p><img src="file:///C:/Users/ETK/AppData/Local/Temp/moz-screenshot.png" alt="" /> <img src="file:///C:/Users/ETK/AppData/Local/Temp/moz-screenshot-1.png" alt="" /> I stand corrected.</p>

[bob_king2]

<p>DOF not only depends on sensor size but also distance to subject, lens focal length, enlargement size and viewing distance, and so on. In going from a 40D (which I still use) to a 5DII I have not had any DOF issues. As a positive, larger sensor sizes allow a greater range of useable apertures before diffraction starts to upset things. BTW I recently shot a wedding using available light only with the 5DII and 24-105L. Many church interior shots were f/4 at ISO 3200. No problems with IQ or DOF.</p>

<p>So in my opinion go ahead and get the 5DII, you'll love it!</p>

<p>Cheers, Bob</p>

[dogbert]

<p>When I picked up a 5D I guess the biggest difference I noticed was increased dynamic range. Better tonality and able to handle contrast better. It is subtle and I was surprised. As to overall IQ I think technique matters far more than whether you are using a 1.6 or a FF camera. Without careful techniqie I can't get a good 13x19 enlargement out of either and with good technique it is hard to tell the difference.<br>

Of course the viewfinder in the 5D is much better, though not good compared to plenty of old and cheap film cameras.<br>

To get the same DoF that you are used to, you will need to close down the aperture another stop approximately and therefore may need to bump up the ISO or work with lower shutter speeds.</p>

 

[ben_goren]

<p>William,</p>

 

<p>The short answer is that, all else equal, a larger format camera can do everything a smaller

format camera can and then some. If nothing else, you could always crop away the outer portion of

the larger format and be left with the exact same image as from the smaller format.</p>

 

<p>In your particular case, while it’s true that, at first blush, the larger format will have a

shallower depth of field with everything else set the same, what you’re missing is that you

could stop down the lens to get the same depth of field, boost the ISO to maintain proper exposure,

and still wind up with a higher-resolution image with at least comparable (and often, in the real

world, better) noise / grain characteristics. That is, you might shoot a certain scene with an 80 mm

lens at 1/100, f/8, ISO 100 on a small format, and the exact same scene with a 50 mm lens at 1/100,

f/11, ISO 200 on the larger format and get the exact same depth of field but a cleaner, sharper

image on the larger format.</p>

 

<p>Of course, there are advantages to smaller formats, else everybody would be shooting

8″ × 10″ view cameras. Convenience and price are the biggest and most

obvious. And, considering that the improvements in quality between APS-C and “full

frame” DSLRs really only start to show up at prints larger than 13″ ×

19″ — and that few people regularly print that large — the quality advantages of

full frame are mostly overshadowed by the cost and convenience advantages of APS-C.</p>

 

<p>Cheers,</p>

 

<p>b&</p>

 

<p>Cheers,</p>

 

<p>b&</p>

[john_deerfield]

<p>I have this same discussion with myself virtually everyday. And for weddings I keep coming back to the crop sensor. I like being able to shoot a group formal @ f/5.6 vs f/8. I like that extra stop of background light. No matter how you slice it, you will always have that extra stop. Sure, I could do ISO 800 on full frame instead of 400 (or 1600 vs 800)... but why? I like shooting f/2.0 or f/2.5 at a reception, along with that extra reach, and having a bit more DOF. If I were shooting only portraits, then I would be shooting nothing but full frame. As is, it is very hard to beat today's cropped sensor in terms of ROI. On a final note, I am seriously thinking about something like this:</p>

<p>http://www.dpreview.com/news/0910/09102102mamiyadm22dm28.asp</p>

<p>Now there would be some shallow DOF (as related to the sensor) along with a 12 f/stop range. Now that would be sweet for portraits. Funny though, it only goes to ISO 400 ;)</p>

[zafar1]

<p>This topic has been discussed many times before. DOF differences are not caused by sensor size, but are caused by optics. The thing is that with a crop sensor you are forced to use different optics. Since most people use zoom, they don't realize exactly at what length their lens is at any given time.</p>

<p>If I was using 85mm lens on FF, I would most likely use 50mm lens to get the approximate same field of view on APS-C. So now with 50mm I have more DOF and therefore I can open aperture to let more light in.</p>

<p>I can get the same effect on an FF if I use 50mm lens and crop my images to the size of APS-C. However after cropping I will be left with too few pixels (5MP for 5D1, and 8MP for 5D2) compared to a 500D/50D/7D.</p>

<p>The other difference to consider is the size at which final output is viewed/printed. If the size of final output is same for APS-C and FF sensor, and they are viewed from the same distance, then the output of APS-C sensor is getting enlarged 2.5 times more than the output of FF sensor. That has some impact on quality, but I am not quite sure how it impacts the DOF. I assume that the apparent DOF would be smaller, but I have never printed large enough for it to matter.</p>

<p>Of course, with the increase in level of enlargement we also see more diffraction, specially with high resolution sensors (because they may capture finer details).</p>

 

[g dan mitchell]

<p>Zafar:</p>

<blockquote>

<p><em>DOF differences are not caused by sensor size, but are caused by optics.</em></p>

</blockquote>

<p>Again, it isn't that simple. Keep in mind what I wrote above concerning what DOF actually means. It is not an objective property of lenses, etc. It is a subjective rule of thumb about how much OOF is acceptable in a print of a give size from a given size original and a rough correlation with how aperture choices will affect this.</p>

<p>Saying that DOF is "caused by optics" doesn't make much sense in a discussion of how a choice of format might affect DOF choices. I assume that you don't hold that DOF is the same at f/8 on a cropped sensor body and a 8 x 10 LF camera. Unless you do hold that to be true, you need to account for the difference by some factor other than "optics."</p>

<p>Interestingly you later in your post begin to acknowledge the non-objective and largely relative nature of this thing we call DOF when you discuss the need to consider the print size.</p>

<p>Dan</p>

[zafar1]

<blockquote>

<p>Saying that DOF is "caused by optics" doesn't make much sense in a discussion of how a choice of format might affect DOF choices. I assume that you don't hold that DOF is the same at f/8 on a cropped sensor body and a 8 x 10 LF camera. Unless you do hold that to be true, you need to account for the difference by some factor other than "optics."</p>

 

</blockquote>

<p>The simple question is, what does the recording medium (film, digital, APS, FF, MF) behind the lens has to do with how lens renders the image? Isn't an image taken by 5D.2 with 50mm lens and cropped to the center APS-C size, exactly the same as image taken by 30d and a 50mm lens?</p>

<p>The focal length of a lens is determined by the optics, not be sensor. Defocus gradient (how quickly things get out of focus as you move away from the plane of focus) is also determined by the lens. Aperture is one parameter that determines this, but the focal length is the other parameter. Remember the AOV formula uses focal length as the parameter. The higher the focal length, the less AOV, and therefore scene gets compressed less and OOF areas are more visible.</p>

<p>It is my understanding that 50mm on 8x10 body would have the same DOF. The problem for them is that the 50mm covers too much area and so to show the same angle of view as 35mm camera, they have to use a much longer lens. Because of the longer length MF and LF photographers always struggle more with limited DOF. On the other hand MF/LF photographers don't have to deal with diffraction that much, so they can stop down a lot for more DOF.</p>

<p>What you can argue is that the the DOF advantage that APS-C cameras get by using a shorter lens, is offset by the image having to be enlarged more. So while the 50mm hides OOF area better than 85mm, the extra enlargement needed in print really amplifies the OOF area more. I am not able to argue for/against this point right now but the experience of most photographers shows that this is not the case.</p>

 

[jeff_conrad]

<p>DoF depends on the subject distance, lens focal length, lens f-number, and the acceptable circle of confusion. The circle of confusion depends on the viewer's visual acuity, the viewing conditions, and the enlargement of the final image. How these interact is described in this Wikipedia article on <a href="http://en.wikipedia.org/wiki/Depth_of_field#DOF_vs._format_size_2">DOF</a> ; Factors affecting the choice of CoC are discussed in the article on <a href="http://en.wikipedia.org/wiki/Circle_of_confusion#Circle_of_confusion_diameter_limit_in_photography">Circle of confusion</a> .</p>

<p>To summarize: when essentially the same picture (i.e., same subject magnification) is taken in two different formats using the same f-number, the DoF is approximately in inverse proportion to the format size, as has been said. So the APS-C format has approximately 1.6× the DoF of FF 35 mm. Subject magnification can be held constant either by adjusting focal length to keep the same angle of view or by adjusting subject distance to maintain the same field of view (though the perspective will obviously be different).</p>

[mendel_leisk]

<blockquote>

<p>Depth of field is a function of the optics, not the sensor</p>

 

</blockquote>

<p>To achieve the same field of view with a 1.6 crop sensor you have to go to a wider angle optic (shorter focal length). These wider angle optics inheritantly give greater depth of focus at any given aperture.</p>

[jeff_conrad]

<blockquote>These wider angle optics inheritantly give greater depth of focus at any given aperture.</blockquote>

<p>It's not quite that simple. If the subject distance is held constant (so that magnification with the wider-angle optic is reduced), the DoF at the same f-number increases. But if the final-image size is the same for both formats, the greater enlargement of the image from the smaller sensor also comes into play.</p>

<p>Whether short-focus lenses give inherently greater DoF depends on what is assumed. If the subject distance doesn't change, the short-focus lens does give greater DoF, as previously stated. But at the same subject magnification, all lenses give approximately the same DoF except at distances approaching hyperfocal (where a short-focus lens does give slighter greater DoF).</p>

[zafar1]

<p>I think that it is fair to assume with anyone's statements, "all things being equal".</p>

<p>We are only discussing DOF differences between small and large sensors. All else being same, DOF will also be the same regardless of sensor size. However due to smalled FOV on small sensor, we are forced to use different focal length to keep the FOV same. When this is done, DOF changes (all else being equal).</p>

<p> </p>

[jeff_conrad]

<p>It seems to me that we're discussing the DoF that obtains from different format sizes.</p>

<p>It's more than just the focal length; were this the only factor considered, the DoF would be in inverse proportion to the <em>square</em> of the format size. When the enlargement (and hence the CoC) is also considered, the relationship is only inverse linear. So yes, size <em>does</em> matter.</p>

[zafar1]

<blockquote>

<p>It's more than just the focal length; were this the only factor considered, the DoF would be in inverse proportion to the <em>square</em> of the format size. When the enlargement (and hence the CoC) is also considered, the relationship is only inverse linear.</p>

</blockquote>

<p>Jeff<br>

Can you help me understand how you get these relationships?</p>

 

[jeff_conrad]

<p>It's really pretty simple. HTML has no math facilities, so it would be much easier to look at the the Wikipedia article on DoF linked above, which covers it pretty well. That article also derives DoF equations from scratch if you want to get into that much detail. The Circle of confusion article covers choice of CoC if you want more detail on that than the DoF article provides.</p>

<p>Bear in mind that the relationship is approximate, valid perhaps between about 10 times the focal length of the larger format and about 1/3 the hyperfocal distance of the smaller format (so the range of validity varies with aperture). But it's still useful for a general comparison.</p>

[william_bray1]

<p>Thanks for all ypur responses to be honest some of this went over my head.In simple terms I always thought sensor size was like apature the bigger it is the less depth of field you have. I found it hard to get my head around this in theory because a 100mm lens on 1.6 crop would be 160mm as oposed to 100mm on full frame. Normaly when you increase the focal lengh on a subject you automaticaly get less DOF. This doesn't seem to be the case when comparing sensor size.<br>

One point that interested me but I didn't quite understand it was Bob King's point about "larger sensor sizes allow a greater range of useable apertures before diffraction starts to upset things". Could anyone explain this please Thanks.</p>

[jeff_conrad]

<p>For a given lens, the angle of view changes with format, but the focal length doesn't. But as I said, it all depends on what is kept constant. If you keep the same lens, subject distance, and final-image size, you <em>do</em> get less DoF with the smaller format. Why? The magnification doesn't change, but the image from the smaller format needs greater enlargement, so the circle of confusion is necessarily smaller. Of course, when you keep the same subject distance, the angle of view is less, so you don't get quite the same picture. If you reduce the focal length to get the same angle of view, you get more DoF with the smaller format. Why? The effect of reducing magnification is greater than the effect of the greater englargement.</p>

<p>Again, article on DoF that I linked above shows the interaction of the various factors quite well (though it doesn't explicitly cover the case of keeping the same subject distance.</p>

<p>It's questionable whether you get a greater usable aperture range with FF. Again, it depends on what you assume. The larger format can use a smaller aperture before diffraction becomes a problem; again, the smaller format needs greater enlargement. But the larger format requires a smaller aperture to get the same DoF, so there's greater diffraction. So you end up with the same diffraction blur in the final image.</p>

<p>At the DoF limits, the tradeoff is between defocus and diffraction. In the plane of focus, the tradeoff is between aberrations and diffraction. With the same lens, the optimal aperture in the PoF doesn't change with format; if you consider the optimal aperture for the PoF as the minimum, you might actually get a slightly greater usable range of apertures.</p>

<p>But the optimal aperture for the PoF is usually in the middle of the range (e.g., f/8 to f/11), which doesn't apply if you're usually working close to wide open. For much practical photography, the loss of sharpness in the PoF when you use a smaller aperture for more DoF isn't even noticeable under normal viewing conditions. If you blow the image up on a monitor and go looking for trouble, it's usually easy to find. But is that really how images are usually viewed?</p>

<p>The tradeoff between PoF sharpness and DoF can be significant at magnifications greater than one. But it's usually not a big issue in general photography. So I don't think it's a big factor here in making the choice.</p>

[bob_osullivan]

<p>I'm with Jeff on this one. DOF is based on focal lenght, subject distance, aperture and media size. The larger sensor will have shallower DOF. Anyone who has shot MF or LF knows this from the challenge encountered getting adapquate DOF in low light. However, the difference between an APC and a FF sensor is not such a huge one as the difference in DOF from FF to say 4x5.</p>