Compressing background, function of sensor size?

<p>Hello all,<br>

Lately I have been exploring compressing the background in shots by using longer lenses. I currently shoot Nikon D300s and have been using my 80-200 (push pull) lens. I really like the effect but I find that many times I cannot get far enough away from my subject to get anywhere near 200mm where the greatest compression would tend to be. My question is would someone shooting say a D700 or D3 full frame camera have the same amount of compression at the same distance or would the crop sensor magnify the compression just as it does the effective reach of the lens. For example would a shot taken with a crop sensor camera at 200mm have the same compression effect as one taken at 300mm on full frame? I hope I'm explaining my question correctly. Just trying to understand the physics.<br>

Brian</p>

<p><img src=" alt="" />Example...</p>

<p>Focal length being constant, field of view becomes narrower as sensor size decreases: but depth of field is not affected.</p>

<p>The way you are using the work "compression" is perspective. Perspective is not DOF. Perspective is controlled by the distance between the subject and the camera. Nothing else. Sensor size and focal length will effect image size and field of view (FOV), but not perspective.</p>

<p>The word "compression" has been used to refer to the fact that distant objects seem to be on much the same plane as one another when photographed with a lens of long focal length. Here, however, it seems to mean something else: "I cannot get far enough away from my subject...". This is confusing. I'd like to see a photo taken from not "far enough away". That should help in understanding the problem.</p>

Agree 100% with Bruce. It's a matter of your distance to the

subject - perspective. So going FX would not make a

difference, if you stay at the same spot and change focal

length to have the same composition with your main

subject, i. e., field-of-view.

<p>The larger sensor wouldn't change the relationship between you, your subject, and the background unless you move. And to get your subject to fill the frame the same way, using the same focal length, you'd have to move <em>closer</em> to the subject (while using a larger sensor), and thus increase the perspective effect (making the background less "compressed" and close-in to your subject).</p>

<p>Shooting longer focal lenghts on larger formats, you get the same field of view and perspective, but a shallower DOF at the same f-numbers.</p>

<p><em>"With longer focal lenghts on larger formats, you can get the same field of view and perspective, but a shallower DOF at the same f-numbers" </em>- Not quite. Once you get the same field of view on large sensor, by cropping, you get the same DOF as in the small sensor camera. </p>

<p>If you compare small and large sensors complete pictures with te same distance and focal length, you get different DOF, just because you measure DOF at two different areas, where lens sharpness differs the most at edges of FX sensor.</p>

<p>If you consider DOF over common picture area in small and large sensors, then Mukul Dube is correct. The lens sharpness property does not change with the sensor size. What changes is how you measure DOF on small and on large sensor, and your perception of sharpness.</p>

<p><em>"Once you get the same field of view on large sensor, by cropping, you get the same DOF as in the small sensor camera."</em><br /> <em></em><br /> Not in my experience. Check the pics below; first, the DX one, shot at a FL= 35mm. Second the FX one, FL= 55mm (I know the FX should have been shot with a FL of 35x1.5= 52.5mm, but I dont have such lens). Both at the same distance, f2.8.<br /> The difference is 1.5 times more DoF (roughly) for the DX lens. It`s not a huge difference, but it can be noticed at the Air Duster can or in the "seconds" watch marks.</p>

<p>DX shot:</p><div></div>

<p>FX shot:</p><div></div>

<p>Depth of field is determined not by field of view but by focal length (see my first post here). For the same field of view, a smaller sensor will use a shorter focal length, which will of course give more depth of field.</p>

<p>Perspective is not DOF, but I tried to achieve<a href="../photo/14225718"> large DOF by focus bracketing</a> with a 100 mm lens on a crop body and the effect is similar. I do not know whether this is what you are after.</p>

<p><em>"Depth of field is determined not by field of view but by focal length... "</em><br /> Right; but I`d better say that is determined by <em>magnification</em> (instead of focal lenght) and aperture.</p>

<p>About your first post,<br /> <em>"Focal length being constant, field of view becomes narrower as sensor size decreases: but depth of field is not affected... "</em><br /> Exactly; if you don`t change your focal lenght, nor your shooting distance, there is no change at all (magnification remains the same). You only get a "cropped" frame with a smaller camera (or a larger frame with a bigger camera).</p>

<p><em>"For the same field of view, a smaller sensor will use a shorter focal length, which will of course give more depth of field."</em><br /> I assume that you don`t change your shooting distance, hence with a shorter lens you get smaller magnification, then larger DoF.</p>

<p> </p>

<p>The degree of compression (or perspective) is the same with the same subject to camera distant regardless of focal length. However, the framing is different for fx or dx camera and thus photographing an object at the same distance. The 300mm lens on fx camera would give you very much the same photo as a 200mm lens on dx camera.</p>

 

<p>Sorry, apparently the image I was trying to post is too large and I'm not certain of how to make it small enough to fit, but in essence my question was that in the shot i was trying to take I wanted to shoot at or near 200mm to compress the image as much as possible and bring the background in closer but I was limited in how far I could back away from my subject and thus the amount of zoom I could use. It had occured to me that a full frame sensor would have less extension (?) than my crop sensor camera which would allow me to shoot the same shot closer to the 200mm max of my zoom. I just wasn't sure if the background would be pulled in the same amount as with the crop sensor camera.<br>

Hope that helps</p>

<blockquote>

<p ><a name="00ZeKo"></a><a href="../photodb/user?user_id=977463">Frank Skomial</a> <a href="../member-status-icons"><img title="Frequent poster" src="../v3graphics/member-status-icons/3rolls.gif" alt="" /></a>, Nov 24, 2011; 12:59 p.m.</p>

</blockquote>

 

<blockquote>

<p><em>"With longer focal lenghts on larger formats, you can get the same field of view and perspective, but a shallower DOF at the same f-numbers" </em>- Not quite. Once you get the same field of view on large sensor, by cropping, you get the same DOF as in the small sensor camera. </p>

</blockquote>

<p>DOF is the same regardless of sensor size in the same sense that a Kia is as good as a BMW; yes, it is often true on paper. But in practice, it doesn't happen that way. A 50mm lens has less DOF on an FX sensor not because of any magical interations between the sensor and lens, but because the larger sensor requires moving much closer to frame the shot in the same way. Moving closer reduces your DOF; thus, a larger sensor produces a shallower DOF with the same lens.</p>

<p>I'm going to use 150mm as an example, since I have that range for several cameras. Framing a face to more-or-less fill the frame with that lens on by 4x5 puts me something like two feet away. On my Hasselblad it's closer to 4 feet. With FX it's more like 6, and closer to 10 or 12 with a DX sensor. A quick check with the online DOF calculator tells me that at f/8 I would get a DOF of .07 feet with the 4x5 (just under an inch), while a D300 would give me about a half a foot.</p>

<p>This is why view camera users need crazy powerful studio strobes - so they can shoot at f/32. Which is still only 3 inches, compared to a couple feet on the Nikon.</p>

<p>In order for multiple formats to have the same DOF from the same lens with the same composition, they all need to be focused at infinity. In which case, the discussion of DOF is moot.</p>

<p>Compression is based on the relationship between camera, subject, and background. A wider lens will usually place the subject closer to the camera than the background. A longer lens places the subject closer to the background than the camera, which is what creates the compression effect.</p>

<p>Picture someone standing 10 feet from a tree. With a fisheye lens, you'll be right on them ... that tree looks like it's way out there, since it's several times further away than the subject. A 300mm lens will require you standing much further away, and suddenly the tree is only 120% as far away as the subject, and they look much closer.</p>

<p>Compression is also affected by sensor size (since you will have to move to recompose), but it is not the same as DOF. That 300mm lens is going to give you more compression, regardless of whether you shoot it at f/2.8 or f/64.</p>

 

<p>Here's a website with some examples: http://toothwalker.org/optics/dof.html</p>

<p>The degree of compression is totally related to the distance from subject. So using a FF camera would not help. </p>

<blockquote>

<p>The degree of compression is totally related to the distance from subject. So using a FF camera would not help.</p>

 

</blockquote>

<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. </p>

 

<p>I tend to agree with everything Zack is saying. I started into digital photography with a 40D, and when I went to a 5D mkI, I immediately noticed that the depth of field with my 5D was much shallower than using the same lenses on my 40D. Compression is all about focal length. I can shoot with two lenses, say a 50 prime and then my 70-200. Even if if I move back while shooting at 200mm to compose the same shot, the background will appear significantly closer than with the 50mm lens.</p>

<p>An image made with a super-telephoto lens makes objects far away and objects nearby <em>appear </em>to be closer together.  This is my understanding of "compression".  I think it is what the original poser is referring to.<br>

 <br>

For example these runners appear to be closer to each other than they actually are.  Approximate focal length equivilent is 576MM in this shot.<br>

 <br>

<a href="../photo/11091952">http://www.photo.net/photo/11091952</a></p>

<p>J. Harrington, nothing wrong with it; this is certainly a perspective effect. As mentioned, it`s a camera/ subject/ background relationship.</p>

<p>In the pic you`re showing, there is a large distance between the camera and the subject, but short between the subject and background... here it is a given "compression effect".</p>

<p>If the photographer have to use a shorter lens to get the "same" picture, a shorter shooting distance must be achieved. The relationship is then changed; the focus distance is shorter, the subject to background (relative) distance is (proportionally) larger... but actually, the picture will never be the "same" because <em>perspective</em> have changed.</p>

<p>If in the same scenario you simply choose a longer focal lenght, without changing your position nor your camera, you just get the subject bigger on the screen (we could say a "cropped"/tighter framing or narrower viewing angle). Change the format to a larger one, and you will get the very same scene, very same "compression", at a higher magnification.</p>

<p><em>"Compression is all about focal length... " </em><br /> <em> </em><br /> Imagine the scene J. Harrinton provides. We are in a stand at the sports stadium; you have two cameras, one with a wide angle (say, 24mm) and the other with a tele (400mm) lens.</p>

<p>Shoot both cameras at a time. Check the prints; if you enlarge the detail of the the athletes runing in the curve on the 24mm lens` print, you will see that the "compression" is the same on both 24 and 400mm prints, the image is the same... the "only" difference is that the 24mm shot is a much wider viewing angle.</p>