MF- More shallower depth of field.

<p>I regularly look at photos on the internet. Something that struck me was how medium format cameras seemed to be able to generate a very shallow depth of field in portraits, with cameras that only have lens that are F4 apeture. Something that would require at least a F1.8 on a cropped digital camera. Is this your experience of the format and why is that ? </p>

<p>Yes. The larger the format, the narrower the depth of field.</p>

<p>One example to illustrate it: Concerning a 6x7 camera like the Pentax 67, you need a 100mm lens as your standard focal length, giving you the same angle of view like a 35mm on your crop camera. So you have the angle of view of a 35mm lens on a crop camera, but the depth of field remains that of a 100mm lens. A standard focal lenght on a medium format camera thus has already the shallow DOF that a tele lens on a crop camera would have.</p>

The easiest way to understand this is to think in terms of image size. Magnification.<br>DoF is a function of magnification and aperture.<br>To fill a larger frame, the subject must be rendered larger on film. So you get less DoF.<br>But if you enlarge a smaller format frame to get the same size as on a larger format frame, i.e. get the same image scale/magnification, DoF will be the same again.<br>So if you decide to change to 35 mm format to increase DoF, enlarge the resulting picture to the same size final image you would have done if you had used MF instead (say an 8x10 print), you'll find (though you probably will not, since you probably aren't going to compare) that it was a futile exercise changing to a smaller format, since the resulting DoF would have been the same had you used MF.

<p>Q.G...if that's the easiest way to understand it, I shudder to think of the complexity of the "hardest". ;-)<br>

<br />Sounds like you're saying that smaller formats don't lend themselves to larger DOF (or vice versa), which is just not the case.</p>

<p>A 4/3 25mm f/2.8 takes the same photo as a 50mm f/5.6 on FF and 100mm f/11 on 6x7. After all, they all have the same absolute aperture size, so DOF will be the same when framed identically (same subject distance).</p>

<p>The larger formats obviously have more headroom within the lens to open the aperture more to decrease DOF. And correspondingly, the larger format needs more total light energy to expose the greater film/sensor area. So longer exposures are necessary on the larger formats to achieve the same DOF as detailed in the above example.</p>

<p>The smaller formats have less area to capture the image, so image quality suffers at the same magnification, but less lens is "wasted" (by stopping down) to acheive the deeper DOF shots, so lighter equipment can be realized. I know nature photographers that have gone from FF to APS-C to 4/3 to get the extra telephoto range in a handholdable package.</p>

<p>I'm sure you know all this, so I'm just curious what you find "futile" about it, or really what it has to do with magnification.</p>

<p> </p>

<p>Yes there's less DOF with MF. Why? don't worry about it. You'll only get a headache. Alan</p>

I'll say it again, but shorter, Gregory ;-)<br><br>

(Given the same aperture), the higher the magnification, the smaller the DoF. Regardless of format.<br><br>That's it.<br>But a small extra explanation: MF has less DoF, because the in-camera magnification is higher (that same portraits sitter's head appears larger).<br>Enlarge an image made using a smaller format to the same size as one made using a larger format, the magnification will be the same, and so will DoF.<br>So a smaller format has more DoF, provided you keep (!) it smaller. If you don't, there is no such difference.

<p>Must be Monday...you still stymied me. <br>

<br />Does this have something to do with viewing distance? As in, for the same photo, the effective DOF for a 16x20 is less than an 8x10...when viewed from the same distance?<br>

<br />And are you talking absolute aperture, or F/stop?</p>

<p>It still sounds like you're saying you can print a 4/3 image at poster size and it'll have the same DOF as a LF camera. In the majority of cases (short of stopping the LF wayyyy down), this isn't a true statement.</p>

<p>I like Alan's response. :)</p>

No, you don't have to take the viewing distance into account, i.e. just assume it the same for any format.<br><br>Yes, if you print a tiny format camera image the same size as you print an 8x10", DoF will be the same. If it isn't true in the majority of cases you know, there's something seriously wrong with those cases. ;-)<br><br>Complicating factors however play along. DoF is apparent sharpness, and can be increased, not just by increasing sharpness of otherwise unsharp bits, but also by decreasing the sharpness of the in focus bits: that makes the out of focus bits not look that much different from the in focus bits, and DoF will be larger. Stuff like that.

<p>Another way of explaining it is that all lenses irrespective of format coverage, have the same depth of field at a given aperture, providing the image size (or image magnification) is the same on the film.</p>

<p>This isn't a matter requiring much experience; the difference in depth of field is readily calculable. Just note that, <em>at a given aperture</em>, the medium format camera will have less depth of field, but medium format lenses tend to be slower. The relationship is:</p>

<p>aperture adjustment in f-stops = 6.64 x LOG(controlling linear dimension of new format film or sensor / controlling linear dimension of old format film or sensor)</p>

<p>where LOG is the "common" or base-10 logarithm, and where a negative number means open up by that many stops and a positive number means stop down by that many stops. So, for example, comparing a DSLR with an "APS-C" sensor with a 1.53x crop factor relative to 35mm, with a 6x6, when both are used to make prints with a 4:5 aspect ratio (e.g., 8x10 or 16x20 inches), this is how it goes. The DSLR's sensor is 15.7 x 23.5 mm, but for the print, we can only use 15.7 x 19.6 mm; the 6x6's film is 56 x 56 mm, but for this print, we can only use 44.8 x 56 mm. So going from DSLR to 6x6:</p>

<p>stop-change = 6.64 x LOG(44.8/15.7) = 3.02</p>

<p>so you have to stop down about 3 stops from the aperture you used on the DSLR to get the same depth of field with the 6x6. Seen another way, a 6x6 at f/4 has about the same depth of field as an APS-C DSLR at f/1.4 (which is 2/3 stop wider open than the f/1.8 you mentioned).</p>

 

<blockquote>

<p>Yes, if you print a tiny format camera image the same size as you print an 8x10", DoF will be the same. If it isn't true in the majority of cases you know, there's something seriously wrong with those cases. ;-)</p>

</blockquote>

<p>You must be referring to images taken with the same lens, or at least the same focal length. Except, you can't take the same picture with the same lens on two camera formats. As in my example above, the smaller format camera has a lower focal length lens for the same FOV. I've never seen an 80mm on a P&S camera...let alone a 300mm.</p>

<p>Yes, if you used the same lens on the smaller format, you'd get the same DOF...once you backed up far enough to get the same framing/magnification. Assuming you had enough room. ;-)</p>

<p>I find this line of reasoning confusing, because nobody shoots this way, or thinks this way. The lenses I listed above are all considered "normal" for their respective formats, and would be used in a similar fashion. And in doing so, the larger format (and its attendant larger focal length lens), shot at the same f/stop and same distance, would have shallower DOF. </p>

<p>You can do mental gyrations with the optical physics to describe scenarios where they are "equal", but I don't find that at all useful. </p>

 

<p>Oh here we go again. Excuse me while I go get the aspirin. </p>

<p>OK I'm back. <br>

Now let's see. "<em>stop-change = 6.64 x LOG(44.8/15.7) = 3.02"</em><br>

Of course, Now I understand. Thanks Dave. How did I miss that before.<br>

Oh the other hand, since MF lenses can be stopped down further than other format lenses., you can squeeze out more DOF from MF.<br>

I think I'll go get a tranquilizer now.</p>

<p>Alan</p>

 

 

<blockquote>

<p><em>"... if you used <strong>the same lens</strong> on the smaller format, you'd get the same DOF...once you backed up far enough to get the same framing/magnification... "</em></p>

</blockquote>

<p>If you get the same <strong>framing</strong> in different formats, <strong>magnification</strong> cannot be the same. It is bigger on the bigger format. Anyway, if you <em>"backed up far enough to get the same framing"</em>, DoF will be different. It will be shallower on the larger format.</p>

<p>As Q.C. said above, DoF is related to magnification and lens aperture. Don`t think on focal lenghts. Longer focal lenghts are used to get higher magnifications. For a given aperture, the larger the subject the shallower DoF.</p>

 

 

 

<blockquote>

<p>As Q.C. said above, DoF is related to magnification and lens aperture. Don`t think on focal lenghts. Longer focal lenghts are used to get higher magnifications. For a given aperture, the larger the subject the shallower DoF.</p>

</blockquote>

<p>Right. Now you see my point about the semantics CAUSING confusion, and not solving it. :)<br>

But how do you get to:</p>

<blockquote>

<p>"Yes, if you print a tiny format camera image the same size as you print an 8x10", DoF will be the same." </p>

</blockquote>

<p>There's no sensible way to make this statement true. They aren't the same image, because you stood wayyyy too far back with the LF camera to keep the magnifcation down and cropped out 99.9% of the film.</p>

<p>I now return to my New Year's resolution to not discuss DOF. ;) Just like gravity...we all know how it works without knowing WHY it works.</p>

<p>Repeated post???</p>

<p>If you have a smaller format, and use a proportionally shorter lens and a proportionally smaller aperture, and enlarge it to that 8x10"...</p>

<blockquote>

<p>", DoF will be the same."</p>

</blockquote>

<blockquote>

<p>If you have a smaller format, and use a proportionally shorter lens and a proportionally smaller aperture, and enlarge it to that 8x10" , DoF will be the same.</p>

</blockquote>

<p>Well, you managed to change nearly EVERY technical aspect of the photo, didn't you? And in the process, you're 100% wrong.</p>

<p>Bbut once you figure out your mistake, I'll give you an example and we'll see if you can match it. :-)</p>

<p>Basically, you're saying that all images taken from the same spot of the same subject with the same perspective at the same f/stop will have the same DOF. Uh, nope.</p>

<p>Now, do you SEE why we should have left this at the first reply????</p>

<p>Typo; <em>"... and a proportionally <strong>larger</strong> aperture." </em></p>

<p>Nice catch. ;-)</p>

<p>Now, given that, what settings (focal length and aperture) on your P&S camera (pick a convenient sensor size) will match my FF 35mm camera shot at 50mm f1.4??<br /> <br /> I'll give you a tip. A better answer instead of "proportionally larger aperture" is "the same size aperture".</p>

<p>You caught me here, :) I know nothing about digital P&S sensor sizes, but...</p>

<p>A say, 8x10" print from a pic taken with your e.g.<br /> --Nikon film SLR 35mm camera, 50mm @ f1.4,<br /> will have a comparable DoF to another taken with a <br /> --Mamiya RB/RZ/7 6x7 format camera, 110mm lens @ f2.8.<br /> which will be also comparable to a <br /> --4x5" view camera, 210mm lens @ f5.6.</p>

<p>CoC are also doubled to get the same print detail; 0.03mm in 35mm, 0.06mm in 6x7, 0.1mm in 4x5".</p>

<p>You`re right, the "aperture diameter" (<em>entrance pupil diameter</em>, to be precise) is very close in all lenses. I wanted to use f/numbers to make it easier. Thanks.</p>

<p>Hey Alan, maybe if you'd bothered to learn more math in school or somewhere, you might have found that it is a useful tool, instead of getting a headache when somebody suggests using it for something more complicated than figuring out how much change you get at McDonald's.</p>

 

 

<p>(Normally I really don't like flame wars, but your comment was over the top, after I gave a very direct and precise way to compare depth of field between film / sensor sizes.)</p>

<p><em>ince MF lenses can be stopped down further than other format lenses., you can squeeze out more DOF from MF.<br /></em></p>

<p>Maybe yes, but probably no. The 35mm-style lenses most commonly stop down to f/22 or f/32. Put one of those on the OP's "APS-C" DSLR, and the lens on a 6x6 would need to stop down to f/64 or f/90 to get the same depth of field. Do yours? I didn't think so.</p>

<p><em>I think I'll go get a tranquilizer now.</em></p>

<p>Yes, please do. There are a lot of posts on photo.net that I don't find particularly interesting or informative, but unless they contain outright misinformation, ignoring them is usually the best approach.</p>

 

 

<p>Jose,</p>

<p>Right...those examples are correct. But you're going the wrong way.<br>

<br />Remember the comment was:</p>

<blockquote>

<p>Yes, if you print a tiny format camera image the same size as you print an 8x10", DoF will be the same."</p>

</blockquote>

<p>So, if we go the other direction, most P&S cameras have about a 6x crop factor. So, we'd be using a 8mm lens or so. To get the same DOF, we'd need the same aperture size, or around 50/1.4 or about 35mm. That would require an f/stop of around f/0.25. Now we all know that doesn't exist, and is probably physically impossible to build, at any cost.</p>

<p>To pick an example from large format, my calcs say the smallest f/stop of f/64 will result in an aperture of around 4mm. That would require an f/stop of a bit over f/2 on the P&S camera. Almost all P&S cameras I know of don't go to f/2. A few better ones might be able to, and/or have larger sensors. But we've essentially ruled out nearly all instances where the DOF can be made equivalent...certainly any "normal" examples at common f/stops.</p>

<p>Ergo...to make blanket comments as above that DOF "will be the same if a tiny format image is printed the same size" are misleading at best and physically impossible to create in most conditions at worst. And you'll notice in my math...nothing is said about print size, so that's a moot point which adds confusion.</p>

<p>Looking back to the original post, that sort of answer isn't at all helpful. </p>

<p>DOF has absolutely nothing to do with the size of print you have or the size of the format. It's all in the aperture and focus distance.</p>

<p>For example: A 100mm lens is a 100mm lens is a 100mm lens. The depth of field will not change because of a different format of film. Your focus distance and magnification will change, but DOF will remain the same. See attached image. It's that simple. Really.</p>

<p>Now, if your focus distance remains the same across formats, your DOF WILL change and the magnification will remain the same between formats so your subject will appear smaller on a larger format. See attached image.</p>