MF- More shallower depth of field.

[desmond_kidman]

<p>Jens, it shocks me how folks ignore truth or fact because it is too much work for them to actually learn, or do an experiment. Plus, it might challenge their "guru status" (thinking of one of the "experts" on this forum who NEEDS to be the expert) to admit they might have made a mistake.<br>

So, I have 2 shots from the identical spot, the first a 50mm, the second a higher quality 200mm, and it is so easy to see that the 50mm, despite being poorer quality and having to be enlarged much more (4x), still has much less blur in the out of focus areas. I am trying to post them here. They are of a map. Try to read the out of focus names on the map and it's immediately obvious that one lens renders much more readable names, despite the fact it is the lower quality lens and the image had to be enlarged 4x the amount of the image made with the 50mm lens. <br>

Both shots are at the same aperture. <br>

Again, notice I am not using terms like c of c, depth of field calculations, etc. Just compare the out of focus areas. The 50mm retains greater detail when you examine areas that are out of the image plane. <br>

<br>

</p><div></div>

[gregory_king1]

<p>Desmond/Jens,</p>

<p>Sigh...here we go.</p>

<p>You took different photos by not moving. You changed your field of view. Therefore, comparing DOF is rather moot.</p>

<p>Had you taken the same photo (moved back for the 200mm), the change in subject distance would have resulted in balancing the DOF. Yes, the nature of the OOF areas would change due to telecompression, but the DOF would be the same.</p>

<p>In short, head shots taken with the same camera will have similar DOF at the same aperture, regardless of focal length. Going to 200mm will not decrease DOF over using the 50mm, since the 50mm made you stand closer.</p>

<p>http://toothwalker.org/optics/dof.html</p>

<p>Look at the segment on "background blur"</p>

<p>Taking photos of flat objects and cropping photos isn't the best way to demonstrate the concept. ;)</p>

[desmond_kidman]

<p>Unfortunately I could not upload 2 images in the same post, so here is the 200mm lens. I was focused on the Congo with both images. Now, go left and look at the last 2 letters in Brazil (only "il" show) and "rica" and it's obvious. In fact, it gets much more obvious when you go further but I this forum will not accept the full width image as it limits you to 400 pixels wide. Still, it's quite obvious that the 200mm lens is more when moving away from the focus point. Despite the obvious inferior quality of the 50mm image, due to the lesser quality lens and a greater enlargement factor to get to the same image size, it is clearly sharper when way off the plane of focus. </p><div></div>

[jens_g.r._benthien]

<p>Gregory,</p>

<p>here is what the original post said:</p>

 

<blockquote>

<p>Something that struck me was how medium format cameras seemed to be able to generate a very shallow depth of field <strong>in portraits</strong>...</p>

</blockquote>

<p>When speaking of portraits, we talk about 85 - 105 mm lenses on 35mm systems and 180 - 240 mm lenses on MF systems (that's why they are called 'portrait lenses' or 'portrait tele'). Nobody would seriously shoot a portrait with a 6x9 and a 85mm lens, unless he doesn't have anything else in his bag or is close to being brain dead :-)</p>

<p>Again, identical FOVs result in different DOFs for 35mm and MF or even LF if shot at the same distance.</p>

<p>Makes sense? </p>

<p>Forget all the CoC and viewing distance stuff here, it's only hot air to distract from the physics here.</p>

[desmond_kidman]

<p>Gregory, your point is good but is off from the original subject. When comparing MF depth of field to smaller formats, the assumption of course is that the images are taken from the same point! The assumptions are equivalently frame-filling lenses will be used on each camera (so of course the mf camera will have a longer lens), the same camera position, therefore same subject distance. <br>

If we start using different subject distances for the comparison of mf and smaller formats then we are no longer comparing formats for the same shot. <br>

You are correct, of course: for the same image size on the film or sensor (meaning we are changing subject distance) DOF will be the same, but the image will not be the same due (it will be compressed) due to a change in subject distance. Again, this ir not relevant to the original posters question. <br>

To be painstakingly clear, the following is unequivocal:<br>

From the same camera position using lenses that fill the frames equally, a medium format camera, relative to a 35mm camera, will have more blur in the print, assuming equal sized final prints and equal f-stop settings, in the out of focus areas. <br>

Therefore, for any given image, there is an advantage to the medium format camera if blurring of the out of focus areas is desired.<br>

Unfortunately, there is caveat: If the 35mm camera has a larger aperture (numerically smaller) then the medium format camera could lose some, or all, of its "blur advantage". <br>

</p>

[desmond_kidman]

<p>Jens, you are absolutely right-on here, as you know. I wrote my last post while you were posting your last! I am surprised most people have been wrong in this thread....many photo books to through this in great detail.<br>

When switching to digital (full frame 35mm size) one thing I've lost, and I've noticed it many times, is the gorgeous blur when shooting a portrait with Hasselblad with a 120 lens or an RZ with a 140 lens.<br>

I've heard a lot of folks say that with a view camera you can really get great depth of field with a lens that goes to f64 or f90. What they don't realize is that you NEED those small apertures to get good sharpness away from the image plane since the depth of field is so limited with a big format....because, as we both know (but few others seem to!) DOF gets really limited with the long lenses. </p>

[jens_g.r._benthien]

<blockquote>

<p>Unfortunately, there is caveat: If the 35mm camera has a larger aperture (numerically smaller) then the medium format camera could lose some, or all, of its "blur advantage". </p>

 

</blockquote>

<p>Nope. Reason: shooting a portrait with a 1.4/85mm wide open won't work unless you intend to have only the nose tip or iris of the eye(s) in focus. That means you **must** stop down to at least 4.0 or even 5.6 (depending on the object distance). With a MF or LF you can (depending on the lens) shoot wide open at 4.5 or 5.6, but the focus 'falls off' rapidly.</p>

<p>On one hand this is a nice feature of my 6x9 cameras, on the other hand it might turn into a real problem if you need huge DOF and don't have a monorail or field camera where you can 'adjust' the DOF with the Scheimpflug principles.</p>

[desmond_kidman]

<p>Hey Nee, I missed your post! Another shooter of many formats, great so "meet" you!<br>

Yes, once you have run into this over and over you start taking it for granted just as you take it for granted that when you drop something it goes down, not up! I can't believe I actually went a ran a little test, knowing what the results would be! It's always fun to observe things, though. <br>

I have the focusing rail marked up on my monorail for DOF measurements using different length lenses and formats. Life would have been much easier if reality really was what many have posted here!<br>

I'd live a compact like a micro 4/3, but that DOF thing! You just can't blur an image background because of the small format and the fact that for that small format you would need super fast lenses, which they don't make. <br>

</p>

[jens_g.r._benthien]

<blockquote>

<p>I've heard a lot of folks say that with a view camera you can really get great depth of field with a lens that goes to f64 or f90. What they don't realize is that you NEED those small apertures to get good sharpness away from the image plane since the depth of field is so limited with a big format....because, as we both know (but few others seem to!) DOF gets really limited with the long lenses.</p>

 

</blockquote>

<p>Again *nope* ;-) - sorry for that...</p>

<p>You don't need the small apertures, not really. In the past people didn't think about diffraction, but later they did. Here is the strength of LF systems that comes into play: you can shift, tilt, rise, fall with the front and back standard to place the focus plane (almost) anywhere you want. </p>

<p>Example: Landscape. Everything is in focus from front to back - with open aperture! The trick: tilt the front lens until the film plane, the lens plane and the ground meet in one single point.</p>

<p>Try to read something about the 'double Scheimpflug' - for newbies and beginners (sometimes even for experienced) photographers it is **extremely** confusing, but once you've experimented with your own LF you know how to do it without all the math behind it.</p>

[desmond_kidman]

<p>Yes, Jens, it does cut both ways. When I'm looking for great sharpness away from the image plane I then love this advantage of small formats.<br>

Tilting the lensboard is the ultimate, of course, but do you think we should be bringing up Scheimpflug here? Think of the opinions and confusion that could be generated! The horror! The humanity! </p>

[jens_g.r._benthien]

<p>Desmond,</p>

<blockquote>

<p>Think of the opinions and confusion that could be generated! The horror! The humanity!</p>

</blockquote>

<p>Hahahaha, I almost fell from my chair ;-))</p>

<p>Let the fun begin :-o</p>

[gregory_king1]

<p>Desmond,</p>

<p>Of course it's off the original topic, but YOU were the one guilty here. You just posted two shots from the SAME CAMERA, using different lenses, did you not?</p>

<p>I was just trying to limit the confusion you were perpetrating. </p>

<p>The original topic got lost LONG LONG AGO.</p>

<p> </p>

[q.g._de_bakker]

I gave up on you lot where DoF is concerned, but will chime in about Scheimplug.<br>Tilting will only change DoF in that there's less of it in the parts of the tilted plane of focus nearer to the camera, more in the parts further away. Has all to do with the only factor besides aperture that governs DoF: magnification.<br>Ignoring that effect, all tilting does is redistribute DoF in space.<br><br>Oh, and Gregory,<br>The original topic only got lost in the minds of those who (and yes: that means you) refused to think about the correct answers about it that were given repeatedly.

[jens_g.r._benthien]

<p>Gregory,</p>

<blockquote>

<p>You just posted two shots from the SAME CAMERA, using different lenses, did you not?</p>

 

</blockquote>

<p>Yes, he did, but it is a perfect illustration for the difference of DOF between focal lengths, i.e. a 'normal' lens for 35mm systems and a 'normal' lens for a 4x5 LF system.</p>

 

<blockquote>

<p>The original topic got lost LONG LONG AGO.</p>

 

</blockquote>

<p>Yup, because most people here didn't read the original post, or didn't understand it at all.<br>

Just my two cents.</p>

[q.g._de_bakker]

Worst of all, some people do understand the question but still don't understand (nor know) the answer.

[desmond_kidman]

<p>Thanks Jens, I just did not want to have to explain that I demonstrated clearly that a longer lens, when shot from the same spot, would yield less sharpness away from the plane of focus than a shorter lens.<br>

I did not want to have to explain that this therefore perfectly simulates what happens when you use a MF from the same spot as a 35mm camera, since the MF has to have a longer lens to get the same field of view. <br>

I did not want to have to explain that since more of my sensor area was used for the crop of the 200mm lens than was used for the crop of the 50mm lens that I indeed was making my sensor act like 2 different format cameras during this test, perfectly demonstrating the point of different formats using different lenses for the same field of view!<br>

Your comment hit the nail on the head, obviating my need to explain this all.<br>

Oops, I just did......<br>

Tying it all back to the original post, which I've done many times, this all demonstrates the advantage of blur, away from the plane of focus, that MF cameras have.<br>

Now, getting off the subject, it was great that we got that education (or was it a correction to something we did not even write? How is that possible? Maybe in a different universe?) by one poster of Scheimpflug! Now we both know! Wow...how did we get sharp images front to back before when tilting? Must have been luck all those years ..... Anyway, excuse me while I go Scheimpflug my butt off with my new education! This will be a real Scheimpflug-a-rama! <br>

</p>

[q.g._de_bakker]

Yes, Desmond, even in an attempt at being flippant, you manage to display something that 'really' installs confidence in your opinions.<br>:D

[desmond_kidman]

<p>Confidence is not something folks need to have re: my opinions. They can look at the results on screen, or simply do the test themselves, something I've encouraged several times in this thread. I'm a believer in everyone doing their own research whenever possible. Don't just blindly trust what strangers say or write. Learn by testing and experimenting. The memory lasts much longer when you teach yourself. </p>

[AlanKlein]

<p>Well I just got back from McDonald's after straightening out the change thing. What's this about <em>Scheimpflug</em>? Did I miss something?</p>

[gregory_king1]

<p>Desmond,</p>

<p>The sad part is...you think that changing focal length without changing image size is the same as changing focal length AND changing image size. It's not.</p>

<p>The sadder part is...I gave you a detailed technical link that explained it, and you were too lazy to read it.</p>

<p>The saddest part is...you are arrogant enough to impune others with childish comments as a result of your ignorance.</p>

<p>I'll say it one last time, but I don't expect it to sink in. For the same framing and aperture, you can change focal length all you want, but it won't change depth of field. You can shoot a head shot at 20mm f/2.8 (close up) or 200mm f/2.8 (far away) and the DOF will be THE SAME. The background will look different, but the zone of acceptable focus won't change.</p>

<p>So your example was misleading at best, and fully incorrect at worst. Maybe go read the link I presented, and play around with a DOF calculator to prove me correct.</p>

<p>If this is what you were trying to cover your ass on on your longwinded, equally flippant explanation, so be it. It's still not helpful.</p>

 

[gregory_king1]

<p>PS...if we don't agree on this topic, we never will. If we do agree, then obviously our inability to communicate via semantics won't be fixed anytime soon.</p>

<p>Either way, there's no point in continuing this discussion. Only one person here seems to think tiny formats produce shallow DOF, and he won't defend his position. :-)</p>

<p>So, I'm gone. I've got VC160 to burn. Peace out.</p>

[jens_g.r._benthien]

<p>Gregory King,</p>

<p>you are more than lousy! How much of a nuisance must a human be to repeat his dumb and wrong thoughts?</p>

<p>For God's sake, check these 3 tables and see yourself how absurdly wrong you are:</p>

<p><strong><a href="http://toyotadesigner.wordpress.com/2011/01/22/dof-comparison/">http://toyotadesigner.wordpress.com/2011/01/22/dof-comparison/</a></strong></p>

<p><strong>And after checking these tables please stop annoying us with your hot air.</strong></p>

[q.g._de_bakker]

Jens,<br><br>How, do you suppose, makes the fact that you managed to find a DoF Calculator on the internet you right?<br>How does using formulae to calculate hyperfocal distance a DoF calculator make?<br>Explain, please.

[AlanKlein]

<p>Here's an interesting explanation of DOF with pictures between different lenses. I won't volunteer if its answers the OP's question. I'll let the experts here do that. Alan.</p>

<p><a href="http://www.luminous-landscape.com/tutorials/dof2.shtml">http://www.luminous-landscape.com/tutorials/dof2.shtml</a></p>

[ondebanks]

<blockquote>

<p><a rel="nofollow" href="http://toothwalker.org/optics/dof.html" target="_blank">http://toothwalker.org/optics/dof.html</a></p>

</blockquote>

<p>Excellent link, Gregory. I think that this article perfectly answers the OP's post - although not the section you quoted earlier, but rather the section starting with the subtitle "Digital Depth of Field" (where he explains that "Digital" is irrelevant - it just means any format smaller than his reference format, 35mm).</p>

<p>Can I just pull out extracts which settle this matter? And embolden the font on the really key bits:</p>

<p>"A fair comparison requires <strong>'identical' pictures</strong>, i.e. the <strong>object distance (perspective) and field of view (FOV) must be the same</strong> in both cases....In the light of a fair comparison we also want to consider eventual <strong>prints or screen displays of the same size</strong>, which implies that the digital image needs a linear magnification four times as high as that of the 35-mm image....<strong> <br /></strong></p>

<p><strong>Although the perspective, composition and F-number are the same, the depths of field differ greatly.</strong> The digital image has 5 meters of DOF, the 35-mm image barely 1 meter. This is due to the very short focal length of the digital camera, which outweighs the smaller COC criterion....<br>

So, in addition to the larger DOF, <strong>the digital image also has less background blur. (Both absolute and relative.)</strong>...</p>

<p>When the <strong>F-numbers are the same, the smaller format brings inherently more DOF and less background blur...</strong><br>

...the larger format requires a focal length that is <em>R</em> times as large as the lens focal length for the smaller format, where <em>R</em> is the ratio of the format dimensions...<strong>rule of thumb: <em>The smaller format employed at an F-number N yields the same DOF as the larger format at an F-number of R × N."</em></strong></p>

<p>(end of quotations)</p>

<p>Well, I don't think it could be any clearer than that - here's the killer line again: "<strong>the smaller format brings inherently more DOF and less background blur."</strong><br>

<strong><br /></strong><br>

And, directly answering the OP's question, which let's remind ourselves was:</p>

<blockquote>

<p>...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. ...why is that ?</p>

</blockquote>

<p>- the answer is the "rule of thumb" given above:<br>

<strong><em>The smaller format employed at an F-number N yields the same DOF as the larger format at an F-number of R × N."</em></strong><br>

which I rewrite as<br>

<strong><em>Cropped digital employed at an F-number f1.8 yields the same DOF as medium format at an F-number of about f4</em></strong><br>

...since R is approx. 2.5 for say 645 or cropped 6x6 format in comparison to APS-C.<strong><em> </em></strong></p>

<p>Mr. van Walree, take a bow. <strong><em> </em></strong></p>