Compressing background, function of sensor size?

[veronica_lodge]

<p>If you shoot with from the SAME EXACT location then the perspective is already defined. Thus focal length; color of camera or moon phase do not matter. This was well known 10,000 years ago by most hunters, but somehow many many modern folks like to tie perspective to goofy parameters like focal length. Eons ago the lay caveman did this too. The dumber ones lied perspective to spear size. If you shoot from the SAME EXACT LOCATION the perspective is the same, Thus with a cellphone one has the same perspective as a 8x10 view camera. The cell phone has a focal length of 1 to 2 mm; the 8x10 view camera has lens of 200 to 400mm. Sadly the lay masses equate perspective to focal length, but fail to fathom that THEY MOVE the camera.</p>

[Two23]

<p>I've also tested and found less DoF on an FX camera than a DX camera. This makes total sense to me as there is less DoF on my 4x5 camera than my medium format camera, and there was more DoF on my 35mm cameras than my medium format. Sensor size does affect DoF. But, that't not really what the OP was after here.<br>

Kent in SD</p>

[richardsnow]

<p>Everyone here seems to have bits and pieces of the puzzle correct, and bits and pieces of the OP's original question missing or omitted. Here are the concepts that must be understood to give an accurate answer:</p>

<p><em><strong>Concept 1: </strong>Focal length has nothing to do with perspective.</em> It's only a matter of distance from camera to subject. <br /> Tested and confirmed: If you shoot a subject with a variety of lenses from the same distance and crop to the same framing, the perspectives will be the same.</p>

<p><em><strong>Concept 2:</strong> Depth of field has nothing to do with the camera you are using. </em><strong> </strong> Depth of field is determined by focal length, lens aperture, and distance to subject. <br /> Tested and confirmed: If you shoot with a 35mm lens from 6 inches with the same f/stop on large format, medium format, 35mm/FX, or DX, then crop to the same framing, the DOF is the same.</p>

<p><em><strong>Concept 3:</strong> Using lenses that produce the same field of view on different format cameras produce different results</em><em> from the same distance</em><em>.</em><strong> </strong>Because perspective is controlled by the distance from your subject to the camera, your perspective (magnification/compression of the background) will be the same, <em>however</em> because you will be using a different focal length your depth of field will be different (assuming you are using the same f/stop).<br /> Tested and confirmed: If you shoot different lens/camera combinations to achieve the same framing from the same distance with the same aperture, you will retain the same perspective, but will achieve a shallower depth of field with the larger format medium & longer lens combination.</p>

<p>So, using the three principles above, we can answer the OP's question.</p>

<p>Conditions: Subject is a static distance from the camera. Background is also a static distance behind the subject.<br /> Camera combinations (these are not 100% correct, but since the lens in question has markings for 135mm and 200mm we'll use them since it's nearly impossible to get 133.3mm accurately) :<br /> D300s with 80-200mm f/2.8 lens zoomed to 135mm @ f/4<br /> D700 with 80-200mm f/2.8 lens zoomed to 200mm @ f/4</p>

<p>Since your distance to your subject is static your perspective would not change. (Your background magnification/compression would remain the same assuming the crop was identical) What would change is your depth of field. The background would be slightly blurrier on the D700.</p>

<p>I hope this helps and eliminates any confusion.</p>

<p>RS</p>

[mauro_franic]

<p>It is very simple so not sure where the confusion is. This is more basic than shutter speed.</p>

<p>Perspective is obviously independent from sensor/film size and focal length. It only depends on your position relative to the subject (i.e. stand somewhere and look at an object - no combination of camera or lens will see it any different).</p>

<p>Focal length determines what portion of the image is projected on the sensor/film plane (i.e. now make a little frame with your hands and pull it farther-telephoto or closer-wide_angle to your eye). If you bring your hands all the way until they touch your face where you don't see them anymore you have the eq to 40mm in FF. Wider than that and you will have to rotate your head around and stitch what you see.</p>

<p>Sensor size determines the cropping on the image plane. (i.e. now from everything you can see through your hands pick just a small section in the center and discard the rest).</p>

<p>It is not true that with FF you would walk closer to take the picture. If you get closer you would change the perspective and the picture you intended to take will no longer be there.</p>

<p> </p>

[veronica_lodge]

<p>Considering the decade's worth of Photo.net threads I have read; the belief that focal length causes perspective is actually quite common. The average poster believes that focal length causes perspective changes and the trend is worse is a dumbing down trend</p>

[richardsnow]

<blockquote>

<p>It is very simple so not sure where the confusion is. This is more basic than shutter speed.</p>

</blockquote>

<p>The confusion is that not everyone understands the concept of perspective. It comes from a generation of photographers that have learned on zoom lenses because they come with the camera and are easier to use for most situations. </p>

<p>How perspective works is simple, but unless you are shooting with primes, it can be hard to grasp. It's the reason people, (myself included), use improper terms like "foot zoom" even though I know that changing my position changes the perspective of the image and you can't "zoom with your feet".</p>

<p>And people still wonder why I suggest a prime lens as your first lens purchase if you want to become a better photographer.</p>

<p>RS</p>

[mauro_franic]

<p>Those people might have magic lenses... I want one.</p>

[mauro_franic]

<p>Maybe your comment about zooms is true but still weird since looking through a zoom makes it easy to understand that perspective doesn't change when you zoom in and out. The confusion escapes my understanding. </p>

[jose_angel]

<p>I still don`t see the concepts crystal clear. Please help me if I`m wrong:</p>

<p>I`d say perspective refers to the <strong>relationship</strong> between all elements in the space, as seen by the photographer. Not only the <em>camera to subject</em> distance. Matt mentioned it in the first posts. I assume you`re ommiting this to make the concept more understandable.</p>

<p>We can say that Depth of Field is determined by focal length, lens aperture, and distance to subject... <strong>and if we are talking about different cameras, format</strong>. Different formats will require different enlargement factors for a viewing distance, where the Circle of Confusion is another unavoidable parameter.</p>

<p>Focal lenght determines the <strong>magnification</strong> on the film/sensor plane. Depending on the covering angle, some lenses will project a wider or narrower field over the sensor/film plane. FX have a wider covering angle than DX lenses. As mentioned, if you use a FX lens on a DX camera, what is restricting the portion of the image is the format, not the lens.</p>

<p>(I don`t want to hijack the OP thread; I think his question has been extensively answered).<br /> ---<br /> Edit; for years I have been also confused with the perspective concept. It was drawing, and not making photos where I found the answer. There are not bad students, but bad teachers.<br /> PNet is a good source where I like to learn.</p>

<p> </p>

[veronica_lodge]

<p>Maybe folks get confused because few took drawing, or read older books on photography.</p>

<p>The concept of perspective and the concept of DOF are different and should be learned without confusing the two subjects.<br>

One can shoot the same scene from the same spot with all the different cameras in the world and the perspective is EXACTLY the same.</p>

<p>If one sits in row 34; seat W one gets the same view of the football field too. Lenses and sensors do not cause compression, your location does to the subject.</p>

<p>It is basic ratios; how far object A and object B are to the viewing point. If two men are both 6 feet tall; the man twice as far away covers one half the arc angle.</p>

[richardsnow]

<blockquote>

<p>Those people might have magic lenses... I want one.</p>

</blockquote>

<p>Me Too :p</p>

 

<blockquote>

<p>Maybe your comment about zooms is true but still weird since looking through a zoom makes it easy to understand that perspective doesn't change when you zoom in and out. The confusion escapes my understanding.</p>

</blockquote>

<p>While looking through a zoom should make it easy to understand that perspective doesn't change, it doesn't always. My reasoning comes from a statement made to me by a professional photographer years ago. I penciled it down in "Understanding Exposure" by Bryan Peterson since it's my go-to when I'm trying to get inspiration. </p>

<p>"The real difference between professionals and amateurs is an understanding of light, perspective, and your subject's background. Taking someone's photo is easy...taking someone's portrait is entirely different. This is what makes photography art and a professional a professional."</p>

<p>Jose, I don't think you're wrong. You've added a few wrinkles like CoC which I was hoping to avoid to make the concepts easier to understand. I do like your definition of perspective as well...I am posting while at work, so I've got a few disjointed concepts and would probably have re-worded my post if I was teaching a class...lots of words in only a small amount of time. :D</p>

<p>RS</p>

[bruce_rubenstein]

<blockquote>

<p>...or read older books on photography.</p>

</blockquote>

<p>Bingo! Before there was an internet and somebody wanted to learn something on there own, at some point they probably bought a book. (The photography book I bought in the late 70's made a very clear illustration of why perspective is strictly a function of camera to subject distance.) Now with the internet lots of folks are more than happy to parrot what some other clueless wanker posted.</p>

[richardsnow]

<p>Clueless Wanker:<br>

http://photoinf.com/General/Klaus_Schroiff/Perspective.htm</p>

[mauro_franic]

<p>Funny. I guess since he omits to say that the changes in perspective are due to his walking closer or farther away (and implies the change in perspective is due to using a different lens) it can be confusing. Especially confusing to those people that think that light curves and never walked around in the real world... Just kidding.</p>

<p>Those trees must be made out of dark matter to bend light that way... Just can't stop joking about it.</p>

[mauro_franic]

<p>His example is like showing 1-> a picture of a person's face and 2-> a picture of the back of the head and explain the differences by saying they were taken with different lenses.</p>

[brian_hooks]

<p>Using A FF camera would help, in the sense that you would move closing to the subject due to the wider FOV of FF, with respect to the same FL used.<br>

Thanks Leslie,<br>

I think you actually caught on to what I was asking. Still can't afford to go FF but interesting to know how things work.<br>

Brian</p>

[mauro_franic]

<p>"Using A FF camera would help"</p>

<p>Nope. Same compression... FF will capture more of the surroundings with the same lens (since the crop sensor is discarding part of the image) but compression will be the same.</p>

<p>Walking closer to the subject with a FF camera will not give you the same picture as using a crop sensor from farther away.</p>

[leslie_cheung]

<blockquote>

<p>Thanks Leslie,<br />I think you actually caught on to what I was asking. Still can't afford to go FF but interesting to know how things work.</p>

 

</blockquote>

<p>No problem, Brian. In this forum, people often forget the practically side of photography and argue the physics and optics behind it. I just yawn and work with the "magic" sorta speak...</p>

<p><img src="http://static.zooomr.com/images/10114452_c0b4cc1768_o.jpg" alt="" width="700" height="462" /> </p>

<p> </p>

[zack_zoll]

<p>Richard and Mauro illustrate the idea I mentioned that a Kia may be as good as a BMW on paper, but it isn't really. Both of them made compelling and totally true arguments on page three of this thread that basically boil down to, "perspective and DOF are not affected by lens choice because taking the same image from the same distance at the same aperture, and cropping to the desired composition gives you the same DOF and perspective." On paper this is totally accurate, just as a lighter Kia with a 150 horsepower engine might be as fast as a heavier BMW with a 250 horsepower engine when you work out the power to weight ratio.</p>

<p>But in the real world, it doesn't work this way. The fact is that unless you can afford to shoot everything with an 8x10 view camera, you can't just, "crop to the desired composition" every time. Those of us without near-limitless funds must rely on a variety of focal lengths to get different compositions, and those different focal lengths change the relationship between camera, subject, and background; thus altering perspective and DOF. Much in the way that a BMW's superior handling allows you do brake less, and the better build quality means that it retains much more horsepower as it ages. In the real world, the BMW is way faster than the Kia, and lenses affect perspective and DOF.</p>

<p>If it makes you happy to know that the theoretical physics support your argument, then by all means continue. You are, technically, correct. But if you wonder why so many people are posting photos that "disprove" you or can't understand what you're saying, then go test drive a Kia and a BMW.</p>

[scott_ferris]

<p><em>" In the real world, ..........., and lenses affect perspective and DOF."</em></p>

<p>No, in the real world your position and distance to subject and background dictate the perspective, your position, however, might be dictated by lens availability, but that is a side issue. Don't confuse the correct physics and understanding of the thing with emotional irrelevancies.</p>

<p>The truth is if Brian was to buy a FF camera after listening to half the answers here in the belief that his pictures would be "different", he would be sadly disappointed.</p>

<p>Brian, you might like Leslie's answer, but it is still wrong. If you changed position because you changed sensor size while keeping the same lens, your pictures would be different, but only because you changed position, not because you had a more expensive camera. Shoot from the same spot and you get essentially the same picture, try it with a camera phone and your DSLR. Same spot, different lenses, different sensors but the same picture. In that instance, where there is a very large difference between sensor sizes, there will be a difference in DOF at the same f-stop, but only because of the magnification ratio differences, the subject is reproduced much smaller on the phone.</p>

<p>The same is true of APS and FF cameras but if you stand in one place and frame the subject the same (use different lenses, or a zoom) the ratio difference is normally small enough to amount to one stop of aperture. That is, two 12"x 18" prints made from: 1, a FF sensor shot at 150mm and f4 at 200iso and: 2, an APS sensor at 100mm and f2.8 at 100iso are<strong> identical</strong> when shot from the same place.</p>

[zack_zoll]

<blockquote>

<p ><a name="00ZeiS"></a><a href="../photodb/user?user_id=657840">Scott Ferris</a> <a href="../member-status-icons"><img title="Frequent poster" src="../v3graphics/member-status-icons/3rolls.gif" alt="" /></a>, Nov 26, 2011; 12:16 a.m.</p>

</blockquote>

 

<blockquote>

<p><em>" In the real world, ..........., and lenses affect perspective and DOF."</em><br>

No, in the real world your position and distance to subject and background dictate the perspective, <strong>your position, however, might be dictated by lens availability</strong>, but that is a side issue. Don't confuse the correct physics and understanding of the thing with emotional irrelevancies.<br>

(my emphasis)</p>

</blockquote>

<p>That is all I need to say. As far as I'm concerned, your argument is akin to saying that guns don't kill people: blood loss does. Shooting someone might not <em>technically</em> kill them, but it sort of sets the whole thing in motion.</p>

 

[richardsnow]

<p>Zack -</p>

<p>You are completely and totally WRONG!</p>

<p>Let me break it down for you:</p>

 

<blockquote>

<p>perspective and DOF are not affected by lens choice because taking the same image from the same distance at the same aperture, and cropping to the desired composition gives you the same DOF and perspective.</p>

</blockquote>

<p>I never said this. I said that your perspective doesn't change. Your DOF is dictated by focal length, aperture and distance to subject. Your PERSPECTIVE is only dictated by distance to subject and distance to background. Therefore, what I said is that your DOF may change, but your PERSPECTIVE WILL NOT.</p>

<blockquote>

<p>But in the real world, it doesn't work this way. Those of us without near-limitless funds must rely on a variety of focal lengths to get different compositions, and those different focal lengths change the relationship between camera, subject, and background; thus altering perspective and DOF.</p>

</blockquote>

<p>While lens and camera choice may dictate where you stand, it is only where you stand that dictates perspective. Focal lengths have nothing to do with the relationship between camera, subject and background. If you're standing in the same location with 3 different format cameras and three different focal lengths, the perspective DOES NOT CHANGE! Your DOF may change, but your perspective will not.</p>

<blockquote>

<p>The fact is that unless you can afford to shoot everything with an 8x10 view camera, you can't just, "crop to the desired composition" every time.</p>

</blockquote>

<p>Again...wrong.<br /> I do not have an unlimited budget. What I have is a camera and lens selection that gives me the freedom to shoot from 24mm to 200mm (FX) seamlessly. This allows me to choose the perspective I want and zoom accordingly. You see...this is the true power of zoom lenses. They allow the photographer to choose the perspective they wish to create and then frame the shot accordingly using the zoom ring...essentially "cropping to the desired framing"</p>

<p>While this may seem like it would be expensive, most new photographers buy a kit that gets them from 24-70 (FX) in their DX 18-55mm. They then only need to spend another $200 to get a 55-200mm. While this is not optimal for low light shooting, it gives the photographer all the freedom they need to choose the perspective and zoom to crop.</p>

<blockquote>

<p>If it makes you happy to know that the theoretical physics support your argument, then by all means continue. You are, technically, correct. But if you wonder why so many people are posting photos that "disprove" you or can't understand what you're saying, then go test drive a Kia and a BMW.</p>

</blockquote>

<p>This is not theoretical physics. It's a LAW of physics. Please keep in mind that I wouldn't be posting about theory...I only post what I have tested and what I have practiced. I am technically correct and I am correct in practice. Also do not assume that I disapprove of people's photos. There are not many photos that I "disapprove of". Every person is creatively free to express what they desire to. If they ask for critique, I will give my opinion...but it is always asked for before it is given.</p>

<p>BTW, there's a big difference between a Kia and a BMW...just like there's a difference between a D3100 and a D3s. The thing is, a Kia and a BMW both get you from point A to point B. That's their intended purpose, and in no way do they defy the laws of physics to do so. The same goes for a D3100 and a D3s...both achieve the same perspectives from the same physical position in relation o the subject and background and neither defy the laws of physics.</p>

<p>RS</p>

[richardsnow]

<blockquote>

<p>That is all I need to say. As far as I'm concerned, your argument is akin to saying that guns don't kill people: blood loss does. Shooting someone might not <em>technically</em> kill them, but it sort of sets the whole thing in motion.</p>

</blockquote>

<p>This is useless rhetoric and has no place in this forum... You're very wrong and it's time you come to grips with this.</p>

<p>I see no reason why your lens availability would dictate your position when, for about than the cost of dinner and a movie for a family of four, you can add a 55-200mm lens to the kit lens on most cameras and achieve unlimited focal lengths from 18-200mm.</p>

<p>More likely your position dictates your focal length choice...and your position should be chosen by the perspective you wish to convey. The only exception to this is when you physically cannot get to a position to achieve the perspective you desire. Examples would be a photographer being restricted to a press box at a sporting event or the OP being restricted by a wall to his back. These situations mean that the photographer's limitations will dictate the focal length used...but the photographer's position is still what dictates the perspective captured.</p>

<p>RS</p>

[veronica_lodge]

<p>If one is on the goal line of LSU and there are 6 foot high players on every 10 yard lines to the Arkansas goal line the farthest one away appears the smallest. The chap at the Arkansas goal line is 100 yards away. The chap at the 50 yard line is of course 50 yards away and appears twice as big. The player at the LSU 10 yard line is 10 yards away and "appears" 10 times as big as the chap at the Arkansas goal that is 100 yards away. One's camera, shoe color, or beliefs do not change this basic geometry of perspective. Maybe some photographers cannot understand "ratios" thus they believe focal length changes perspective? :) Sadly this was once taught in art in grade school.</p>

[richardsnow]

<p>I completely forgot that Nikon has a tool that demonstrated how perspective does not change based on focal length.</p>

<p>http://imaging.nikon.com/lineup/lens/simulator/</p>

<p>Notice how when focal length changes, the perspective stays the same.</p>

<p>Also note that this is not just one image...the water, the shadows, and the woman reading the book change as you zoom in/out.</p>

<p>This is exactly what was mentioned by using a zoom lens to understand how perspective does not change. You just have to pay attention to realize this.</p>

<p>If this still doesn't make sense, I will have to demonstrate this weekend when I have the time to go out and make photos.</p>

<p>RS</p>