Another post on DX vs FX

[martinangus]

<p>I know this must seem tiring to those who have a clear understanding of the two formats and what equates to what...</p>

<p>I, (not a beginner), generally have the concepts clear until some expert says something such as "I like DX for the extra reach it gives me". "Reach" to me would refer to "zoom" rather than "crop"...no?<br /> I would like to achieve clarity on this issue by making a few statements and getting concensus as to their accuracy....so here goes:</p>

<p>1.<strong> A 100mm FX lens used on a DX body</strong> will yield the same zoom factor (level of detail) as the same lens on an FX body. The image will be cropped (reduced field of view) on the DX body, but the lens will create the same image detail.</p>

<p>2. <strong>A 100mm DX lens used on a DX body</strong> will yield the same zoom factor (level of detail) compared to a 100mm FX lens used on the DX body, Field of view will be the same as if a 100mm FX lens was used on an FX body.</p>

<p>3. <strong>A <em>160mm</em> DX lens used on a DX body</strong> will produce the same zoom factor (level of detail) AND field of view as a 100mm FX lens on the same DX body.</p>

<p>So, what do we think...does an FX lens on a DX body give "extra reach"?</p><div></div>

[bob_sunley]

<p>Yes, purely due to the build in cropping of the DX body as compared to an FX body.</p>

[martinangus]

<p>So, you are saying that "reach" has something to do with "crop"?</p>

[matttonkin]

<blockquote>

<p> </p>

</blockquote>

<p>Your use of "zoom factor (level of detail)" is a little confusing as I would think the level of detail is dependant on the body as well.</p>

<blockquote>

<p>3. <strong>A <em>160mm</em> DX lens used on a DX body</strong> will produce the same zoom factor (level of detail) AND field of view as a 100mm FX lens on the same DX body.</p>

</blockquote>

<p>This statement is wrong, a 160 mm DX lens used on a DX body produces the same field of view as a 160 FX lens used on a DX body. The difference is the DX lens projects a smaller image circle since the sensor it needs to cover is smaller. The first and second statements seem correct to me but again I'm a little confused by what you mean by "zoom factor (level of detail)"</p>

[martinangus]

<p>Is "field of view" and "image circle" not the same thing? Perhaps its all in the terminology. Zoom factor = "magnification" = "reach" to me</p>

[matttonkin]

<blockquote>

<p>Is "field of view" and "image circle" not the same thing?</p>

</blockquote>

<p>No field of view is dictated both by the lens and the sensor that is being projected, this is why a smaller sensor will 'crop' the image projected from the lens compared to a full frame sensor and will yield a smaller field of view. The image circle is the image itself that is projected by the lens. With FX lenses this circle needs to be large enough to cover the full frame censor to avoid vignetting. A DX lens however is only to be used on a DX body and thus the circle the lens produces can be smaller since it needs to cover a smaller area, a DX lens on a FX body would not produce an image large enough to cover the entire sensor. </p>

[martinangus]

<p>Ok, Matt, that is logical and I kinda new that... I was oversimplifying the relationship between the lens size (mm) and field of view. I agree with everything you just said. I am still not bought into the fact that a smaller sensor increases reach...if that was true, would it not hold that making a sensor even smaller would really increase reach...? Sounds crazy.</p>

[Wouter Willemse]

<p>Focal length is focal length is focal length. Let's start there. 100mm is 100mm. No matter what size of sensor you line up behind it.</p>

<ul>

<li>Between using a lens on DX and FX, the <strong>ONLY</strong> thing that changes is the "field of view". The key word in understanding FoV is <a href="http://en.wikipedia.org/wiki/Angle_of_view"><em>angle</em></a>. The angle is the thing that changes - it's less for a smaller sensor, more for a bigger one.</li>

<li>Between a lens designated DX and FX (or EF-S and EF for Canon), the ONLY difference is the size of the image it can project onto the sensor. FX/EF lenses project a circle at least large enough for a 36mm * 24mm sensor, DX/EF-S lenses project a circle at least large enough for 24mm * 16mm. So, a DX lens might not cover the whole frame of the FX sensor. This is the image circle. It has no effect with regards to focal length, or angle of view.</li>

</ul>

<p>And that's it.<br /> So, a FX lens on a DX body does not give more reach than a similar focal length DX lens on a DX body. As said before, focal length is focal length. By converting everything to 135 format (or FX/FF), people make things overly complicated. A 50mm lens remains a 50mm lens, regardless of body. It's a 50mm lens whether I put it on a 6x6 Medium Format camera or a Nikon 1.<br /> The angle of view it achieves can differ, though. On DX, a 50mm lens is similar to what a 75mm lens would show on FX. This is what people perceive as the 'extra reach' - for each focal length, on DX bodies, the angle of view is smaller. Smaller angles <em>resemble</em> longer focal length.<br /> In the very same way cropping an image in an editor does the exact same thing. And that's why '<em>crop factor</em>' is not a bad chosen word. It is really like cropping an image. Try it in Photoshop, and it suddenly becomes obvious. If you crop a photo in photoshop, the lens you used did not change - and so the only difference is that the camera itself already makes a crop.<br /> ____ <br /> Unrelated note: since you use the Nikon DX/FX terminology, for Nikon cameras the "crop factor" is 1.5, not 1.6.<br>

____<br>

Edit:</p>

<blockquote>

<p>if that was true, would it not hold that making a sensor even smaller would really increase reach</p>

</blockquote>

<p>Yes, look at using Nikon F-mount lenses on the Nikon 1 with its smaller CX sensor (crop factor 2.7x). Maybe it sounds crazy, but it's real all the same.</p>

[bebu_lamar]

<p>Making the sensor smaller does increase reach. P&S camera has something like 12x zoom and the lens is a mere 80mm or so at the long end. Many of these cameras have the same number of pixels as an FX camera. Of course you have noise and stuff but that's still an increase in reach.<br>

When someone said that he/she gets a dx camera to get more reach from his/her lenses he/she understood the trade off. If both cameras have the same number of pixels you can't achieve what you get on the DX camera with the same lens by cropping.</p>

[lwg]

<p>The easiest way to see this is to take a magnifying glass, or other simple lens, and hold it in front of a window where the outside is brighter than the inside of the room. Daytime with the lights off is good. Put a white piece of paper behind the lens and move the lens or the paper until you have formed an image on the paper. The distance from the lens to the paper is the focal length. The size of the projected circle is the "image circle". Now draw some little squares on the paper. These will represent the sensor (or film). Draw a 24x36mm rectangle for an FX sensor. Draw a 16x24mm sensor for Nikon DX (Canon is slightly smaller). Now move these squares into the image circle projected by the lens. You can see that the image lens projects stays the same, but how much of the image is seen by the sensors depends on their size. If you go to an even smaller sensor size you can see how things appear to be magnified because the sensor only sees a small bit of the image, all without changing the lens at all.</p>

<p>DX lenses project a smaller image circle than FX lenses, but the relative size of features in the circles is the same assuming the same focal length.</p>

<p>As to the 12x Zoom lenses, Zoom is not a measure of magnification in camera lenses (unlike binoculars). All it means is the long end of the lens has a focal length that is 12 times longer than the short end. So a 12X lens that starts at 24mm will be 288mm at the long end. A 12X lens that starts at 35mm will be 420mm. Assuming the same size sensor you will get more magnification out of the latter lens, but it won't be able to see as wide as the former.</p>

[ljwest]

<blockquote>

<p>So, you are saying that "reach" has something to do with "crop"?</p>

</blockquote>

<p>In a nutshell, <em><strong>yes</strong></em>!</p>

<p>Think about it like this: You are photographing something with a 200mm lens on an FX (full-frame) sensor. You frame it up nice, but you're still a little too far away, and you cannot move closer physically. You take out a 300mm lens and get the framing you like and take the shot. The 300mm lens gets you more "reach" by magnifying the image that hits your full-frame sensor.</p>

<p>Now, take <em>the same 200mm lens</em>, and put it on a camera with a DX (crop sensor, 1.5x since you're talking Nikon) size sensor placed in the same location, and you will get the same image framing as if you had the 300mm lens on the full-frame body. The crop sensor camera gets you more "reach" by<em> "seeing" a smaller part of the image from the lens</em>. </p>

<p>As for Depth of field, that is purely a function of the lens, and does not change one bit when using a DX sensor vs a FX sensor, given the same focal length, aperture and <em>focus distance</em>. What make is seem that DoF changes with a DX sensor camera, is that when you try to obtain the same scene framing, you have to change your distance to your main subject, which changes the focus distance, and thus, affects the DoF. If you kept the same focal length, aperture and focus distance, but changed from an FX body to a DX, the DoF of the image would not change, but the framing would (the DX would be "zoomed in" or cropped).</p>

<p>Some folks, like myself, do like the extra reach of a crop sensor camera. I use a Canon 7D (crop factor 1.6x) to shoot wildlife, primarily birds, in my case. The "Crop Factor" on my camera of 1.6 turns my 100-400mm lens into a 160-640mm lens! That's quite a good bonus at the long end, considering Canon's 600mm lens costs ten times what their low-end 400mm lens does! A 500mm lens on my camera becomes effectively an 800mm lens, and I could still add a 1.4x converter to get past 1,000mm.</p>

<p>But I never think of my 100-400 as my "160-640". That's just too much work! I know that, for me to grow as a bird photographer, I'm going to have to bite the bullet and purchase a 500mm or 600mm lens. I'd never go through the rigamarole of figuring out effective focal lengths to come up with a solution. I have a 400, I know I need longer, so 500 or 600 are the next choices...</p>

<p>No matter which format you have, if you need more reach, your next lens needs to have a focal length larger than what you already have, and if you need to go wider, your next lens needs to have a smaller focal length than what you have.</p>

[JDMvW]

<p>The only difference is in the size of the sensor. These are simply two different formats, analogous to 2 1/4 vs 35mm back in the old film days.</p>

<p>The only time you need to worry about "equivalence" is if you are shooting with both a 24x36mm sensor (FX, "full frame") and a ~25.1 × 16.7mm (the old APS-C film format, "crop") DX camera.<br>

Otherwise, just get a handle on what each of your lenses does on your body. "Conversion" whether of measurements or different currencies is always a trap and a source of error. Just learn how much you can buy with 10 Euros, or whatever.</p>

 

[bebu_lamar]

<p>Once again most P&S with a 12x zoom lens usually started out with the short end angle of view around 60 degree (similar to a 35mm lens on a 35mm camera) so the long end would have the similar angle of view as a 420mm lens on a 35mm camera.</p>

 

[lwg]

<p>BeBu, that is just a generalization. Many now start with 24 or 28mm equivalents, so if reach is important you can't just compare the Zoom X rating.</p>

[martinangus]

<blockquote>

<p>Think about it like this: You are photographing something with a 200mm lens on an FX (full-frame) sensor. You frame it up nice, but you're still a little too far away, and you cannot move closer physically. You take out a 300mm lens and get the framing you like and take the shot. The 300mm lens gets you more "reach" by magnifying the image that hits your full-frame sensor.<br>

Now, take <em>the same 200mm lens</em>, and put it on a camera with a DX (crop sensor, 1.5x since you're talking Nikon) size sensor placed in the same location, and you will get the same image framing as if you had the 300mm lens on the full-frame body. The crop sensor camera gets you more "reach" by<em> "seeing" a smaller part of the image from the lens</em>.</p>

</blockquote>

<p>Larry, I still don't agree sir...so why not just crop the FX version down to the 300mm equivalent size the DX version is? In fact, why not crop the image so much it looks like you must have used a 1000mm lens? I don't get how this is "reach"? Sorry... </p>

[Matt Laur]

<p>Martin: cropping the larger image to get the faux reach isn't the same because to do so, you're throwing away pixels. The idea is that for some people, getting that same 16mp on a smaller sensor is a worthy tactic, because you <em>are</em> getting a narrower angle of view while still keeping all of those pixels. Obviously there are trade-offs - most immediately seen in noisier low light performance, the inability to achieve DoF quite as shallow, and the need to buy DX-oriented ultra wide lenses (since what's wide on FX doesn't feel as wide on DX).<br /><br />But if you're shooting wildlife in broad daylight (where the low-noise FX doesn't have as much of an advantage), and you're stopping down while using a lower ISO, why not use every pixel you've got coming to achieve a composition you'd otherwise have to crop (from an FX exposure) to get? That's the idea.</p>

[jim_momary]

<p>Focal length <strong>never</strong> changes.<br>

The amount of the intercepted image area changes with sensor size, as illustrated below.<br>

It only 'appears' that we 'magnify' everything with DX, but as stated it's cropping really.<br>

Maybe the pic will help.<br>

Jim M.</p><div></div>

[James G. Dainis]

Yes, it is better if what you see in the viewfinder is what you get. A 16MP frame filling shot with DX is better than a loosely framed 16MP shot in FX. The former generally looks better and the former can be printed directly at 300ppi to get a finished photo. The latter has to be cropped and then printed at 200ppi to get the same size photo and image.

[martinangus]

<p>Well, it appears this comes down to the definition of terms then. "Reach", to me, is the ability of a lens to get closer optically - as in magnification - as in being able to count the eye lashes on a fawn in the woods. I still believe that to get closer you need bigger glass not a sensor that crops giving the impression that one is closer. So, I suppose I will have to continue rolling my eyes when I read that, someone who should know better, suggests FX on a DX body is a great way to get (better reach) ie closer.</p>

[bob_sunley]

<p>Well a 300mm lens on an 8x10 inch camera has no reach at all. :)</p>

<p>In fact is is a normal lens, same as a 50mm is a normal lens on full frame 35mm film.</p>

 

[johnw63]

<p>Optically, there is NOT gain in reach with a DX sensor camera. The "reach" is when you have to zoom into the shot to fill the 8X10 print or 800 X 600 screen image or what ever the final output will be. To get the same NARROWED field of view of a 200mm lens on an FX camera, you would have to use a longer lens, but that would get you closer than the 200mm lens on the DX camera.</p>

<p>The lens is the lens. The focal length is still the focal length. It's what you DO with the image after it is captured that makes and difference. If you took 2 shots, one on FX and the other on DX, and you kept the raw image size, you could paste the DX image right on the FX image and it would line up fine. the FX shot would extend around the DX one. No change in "reach" at all. Now, if you wanted that DX shot to be the same SIZE as the FX shot, you would have to enlarge it and THAT is where the supposed reach gain comes from. </p>

<p> </p>

[James G. Dainis]

Yes, an FX camera with a 300mm lens is a crop camera. It crops out a 36 x 24mm section of that 12 inch image circle.

 

With a 300mm normal lens on 8x10 film, a deer might be 3/4 inch high on the film. Cut out the section of the film with the deer, a 36 x 24mm section, and you have the same result as if you used 35mm film, a frame filling shot. Or use a 35mm film roll back on the 8x10 camera and you crop out everything but the 36 x 24mm section of the image that strikes the film.

 

Any camera not using the normal lens for the format is a crop camera.

[frank_skomial]

<p>In digital cameras picture sizes are expressed in pixel dimentions. So it becomes more important to talk about picture sizes on sensors expressed in pixels, and not in other measures like mm, inch, etc.</p>

<p>Your statement # 1, (or #2) wil be true if you clearly say that you mean picture size in millimeters, but not in pixels.</p>

<p><em>"he same image detail</em>" - is not defined precisely enough to say that your statement is correct or not. In digital world, the optical image detail can result in a larger number of pixels detail in the picture file, and as a result your statement will not be correct, from practical point of picture manipulation on a computer.</p>

<p>Your statements, e.g. #1, hold true for film cameras, where picture sizes are usually expressed in mm.</p>

<p>Your example in the table is wrong on many items...but just enjoy the photography..and do not get bothered by the crop things.</p>

<p>As someone mentioned, Nikkor AF_S lenses get 2.7 x crop on Nikon 1 cameras, and appropriataly more "image details" afforded by the much denser pixel count. Regardless if the actual image size expressed in mm is the same, pixel counts is that matters to image detail.</p>