confusion between DX and FX lense Focal length

[joe_c5]

<blockquote>

<p>I have a D90 and the 17-55 DX and 18-105 DX lenses. Will the Nikon 24-70 FX lens produce the same image in the viewfinder on my D90 at 35mm that my 17-55 lens produces set at 35mm?</p>

</blockquote>

<p>Yes; on a D90 any of those three lenses at 35mm focal length will have the same framing and magnification.</p>

<blockquote>

<p>Will the 24-70 produce the same image in my viewfinder set at 70mm as my 18-105 lens produces at 70mm? I'm taking in regards to framing and magnification, not DOF, color rendetion, etc.</p>

</blockquote>

<p>Yes; the 24-70 at 70mm will have the same framing and magnification as the 18-105 at 70mm.</p>

<blockquote>

<p>All the confusion on my part led me to believe that the 24-70 would reach out to ~105 like my 18-105 lens does.</p>

</blockquote>

<p>No; on your D90 the 24-70 will not reach out to 105mm like the 18-105 lens does. Put in terms of "35mm equivalent" focal lengths the 24-70 goes to 105mm equivalent but the 18-105 goes to 157.5mm equivalent.</p>

 

[tveck]

Thank you Keith, my conclusion was wrong. But I was thinking with a macro point of view, and I am still puzzled by it. I have only a questions about the dept of field, that the field of view changes was not my question. But my puzzleling is not over, if you take macro pictures you need to be nearer to the subject with a DX then with a FX camera (say a DX with 100mm and a FX with 150mm(Nikon) or 160( Canon)). How closer you get to a subject the more dept of field you loose. Can anyone explain my puzzleling about the DOF.

[Matt Laur]

<p>Ted: at the same aperture, using the same lens, yes... as you get closer, you lose depth of field. But that has nothing to do with camera sensor format. <br /><br />But I think you are confused about needing to be closer (for macro) using DX than you would need to be with an FX. For a given subject (let's say an insect), and given a the same focal length lens (say, 100mm), you will need to get closer to the insect using an FX camera than you would using a DX camera in order to have that same insect fill the frame in the same way. That will change the perpsective and the depth of field, yes. But in terms of framing the subject the same way using the same lens, the FX will require you to be closer than the DX. Or, it will require you to use a longer focal length lens on the FX to achieve the same framing - one or the other.</p>

[tveck]

Thank you Matt. My conclusions are:

- that you with a DX camera you always need to be closer to the subject than with a FX, filling the same frame.

- So at longer distance's from a subject a DX camera has more DOF.

- With macro a DX camera has less DOF, because you are nearer to the subject.

So at some focal lenght the DOF should be the same for FX and DX. Could that be 35mm, the meaning of 35mm format?

If my conclusion are right, it could be something to consider when choosing between a FX or a DX format camera.

[joe_c5]

<blockquote>

<p>My conclusions are: - that you with a DX camera you always need to be closer to the subject than with a FX, filling the same frame.</p>

</blockquote>

<p>This isn't quite right. With the same lens, for example the 105mm F/2.8G, a DX camera will fill the frame from <em>farther away </em> than an FX camera. If your goal is to be using the lens for true 1:1 macro, then the working distance will be the same for both cameras and the DX camera will just have a narrower field of view.</p>

<blockquote>

<p>So at longer distance's from a subject a DX camera has more DOF.</p>

</blockquote>

<p>This is correct at most distances; if the DX camera uses the same lens from farther away from the subject then it will have more DOF. At extremely close focusing distances, the depth of field tends to depend more on the magnification than on the focal length.</p>

<blockquote>

<p>- With macro a DX camera has less DOF, because you are nearer to the subject.</p>

</blockquote>

<p>This is not correct. If at macro working distances you fill the frame with either camera, then the DOF will be roughly similar with either camera (perhaps slightly larger DOF for the DX camera). If you use both cameras from the same macro working distance, the DX camera will have less DOF because of the higher magnification when an image is captured by the smaller DX sensor and displayed at the same size.</p>

<blockquote>

<p>So at some focal lenght the DOF should be the same for FX and DX. Could that be 35mm, the meaning of 35mm format? If my conclusion are right, it could be something to consider when choosing between a FX or a DX format camera.</p>

</blockquote>

<p>There is no focal length where the DOF should be the same for both a DX and FX camera, aside from the similar macro DOF. If you want the same DOF on both cameras, the FX camera should use a lens that has 1.5x the focal length and set just over one f stop slower aperture (e.g. 50mm f/4 on DX and 75mm f/5.6 on FX).</p>

 

[tveck]

Thanks Joe. If I make a (right) conclusion of your explanation with using a 50mm/5.6 on a DX, and 75mm/5.6 on FX:

(the same aperture 5.6!, then there should be the same amount of light on the sensors)

- a DX camera has always more DOF, when with macro it is not a point of interest because the

differences are to small.

[joe_c5]

<blockquote>

<p>Thanks Joe. If I make a (right) conclusion of your explanation with using a 50mm/5.6 on a DX, and 75mm/5.6 on FX: (the same aperture 5.6!, then there should be the same amount of light on the sensors) - a DX camera has always more DOF, when with macro it is not a point of interest because the differences are to small.</p>

</blockquote>

<p>That is correct, though it is the intensity of the light that will be the same. The total amount of light hitting the sensor will be greater on the FX camera because its sensor is larger.</p>

[david_earle]

<p>I have been trying to follow some of these threads on the FX / DX discussion. Does anyone have two lenses of the same focal length, one DX and one FX, and a DX and FX camera? Could they take the same picture with each and post - this might help with understanding the crop factor / focal length / sensor size discussion? <br>

Thanks,<br>

David.</p>

[kelly_flanigan1]

<p>To All;<br /> <br /> Consider how folks are confused about hammers on clawhammer.net:<br>

<br /> One could have three folks each holding a 16 oz claw hammer; each hammer is the same 16 oz model hammer.<br /> To the homeowner the 16 oz hammer is the one to use; the normal hammer.<br /> <br /> To the burrly Paul Bunyan pro framer dude; he might always use a 24 oz model; thus the 16 oz seems whimpy and small.<br /> <br /> The next person might be a 5 year old little kid helping dad build a dog or bird house. The 16 oz hammer seems huge and heavy to the little kid.<br /> <br /> IN all three cases the hammer is the same weight and model; but the end user is different.<br>

LETS LOOK AT LENSES NOW :<br>

One might have some 35mm focal length lenses; and place each on a different camera that has a different film or sensor size.<br /> <br /> The first Case might be the lens is on a standard 35mm still camera with a 24x36mm film or sensor; here this combo covers a wide angle; its called a wide angle lenses.<br /> <br /> The next case might be the 35mm lens is on my Epson RD-1 with a 1.6x crop factor. This means the sensor is smaller than full frame; thus this combo "acts" like a 35 * 1.6 = 56mm lens IN ANGULAR COVERAGE on a 35mm still camera. The lens is still a 35mm lens; the light just falls on a smaller sensor. One can get the same effect by cropping; or cutting ones negatives up too.<br /> <br /> The same 35mm lens can be used on a 4x5 Speed Graphic; here the is so short it jsut makes a round image on film. With th3 35mm F2.8 GN lens in the photos way below; it makes a circle on 4x5 film. This lens has a tad more coverage than a regular 35mm lens; since it is a shift lens that is designed for shifting 11mm.<br /> <br /> Another case is where I take the same 35mm lens and use a Nikon F to C mount adapter and place the combo on my 16mm Bolex Cine camera. Here ANGULAR coverage is less; because the film is smaller. For a 16mm cine camera; a 25mm is considered a normal lens; thus a 35mm is considered a telephoto; a lens with less angular coverage than a normal lens.<br /> <br /> Yet another case is I add a C mount to D mount adapter to the above config; and place the 35mm lens on my 8mm cine camera. Now one has a really long telephoto lens; because a Normal lens is 12.5mm for 8mm cine.<br /> Yet another example is one attaches the same 35mm on a cellphone. One rips on the stock 1.5 to 2 mm lens; and uses epoxy and balsa;) and attaches the 35mm lens. Now one has a super telephoto lens; maybe good for moon shots; girls on the beach; celeb shots for TMZ. With a 35mm lens on a cellphone's sensor; the angular coverage is tiny. If the normal lens is 2mm; then the 35mm lens is 17.5 x longer than a normal lens; roughly like a 900 mm lens onm a 35mm still camera IN ANGULAR COVERAGE.<br /> <br /> IN PRO CINE WORK; folks *want* a certain angular coverage for each scenc shot. They just select the proper focal length for each film format used; adn do not get all confused.<br /> <br /> A 35mm lens is a 35mm lens still in focal length; no matter if used on a 4x5 Speed Graphics or cellphone. The lens doesnt not change; what changes is the sensor/film size. The lens stays the same focal length when used on any camera. Here is a Nikon 35mm F2.8 lens mounted on a 4x5" Speed Graphic. The lens does not cover a 4x5 frame; it makes a ROUND circle. In like manner a 16 oz claw hammer is the same mass no matter who uses it; or on what planet used.</p>

<p>All a crop factor is a math crutch for folks to use. It does not work well when the different formats have different aspect ratios; or the output is a round circle too. IF ON THINKS in angular coverage there is no confusion. Note too that a 7 grade teenage girl has NO CONFUSION and this subject when using her cellphone cam; she just moves the phone to cover what she wants. PLUS she does not know the focal length or sensor size either; all she knows is the angular coverage; ie what she sees on the screen. Thus the teenage girl and Pro Hollywood film director are above the still users confusion on this thread; they think in what they see on the screen.</p>

<p>It is quite baffling why the angular coverage; focal length and crop factor is so confusing to so many folks today. I can take a 7 1/4 " saw blade and place it on my 10" Big Foot circular saw; and it still is a 7 1/4 " blade. I can give way 1000 16 oz hammers; and they still are 16 oz hammers. One can use a 35mm focal lengtth lens on a 1000 different cameras; and it still is a 35mm focal length lens. The problem is folks drop *qualivalent* lingo; the 16oz claw hammer *seems* like a Sledge Hammer to a little kid; but IT STILL IS A 16 oz hammer!<br /> t</p>

<p><img src="http://i4.photobucket.com/albums/y148/ektar/Speed%20Gr%2035mmPC/tripods-298.jpg?t=1258548857" alt="" width="398" height="424" /> <br /> <img src="http://i4.photobucket.com/albums/y148/ektar/Speed%20Gr%2035mmPC/tripods-296.jpg?t=1258548343" alt="" width="487" height="381" /></p>

[ShunCheung]

<p>To David Earle: DX lenses have a smaller image circle designed to only cover the smaller DX sensor (which is roughly 16x24mm), while the FX sensor is 24x36mm. Essentially that is the only difference for DX lenses. Of course there are other issues such as difference lens designs, etc., but let's not confuse the topic in this thread.</p>

<p>Focal length is focal length and there is no difference between a 35mm DX lens and a 35mm non-DX lens (and for the sake of convenience, let's call non-DX lenses FX lenses, although Nikon does not officially use the terminology "FX lenses").</p>

<p>In other words, theoretically, if you mount a 35mm DX lens and a 35mm FX lens on a DX (16x24mm sensor) body, you will get exactly the same image.</p>

<p>If you mount those same two lenses onto an FX body (24x36mm), you should see darkened corners in the frame with the DX lens since its image circle cannot cover the entire FX frame. The attached image was captured on the D700 (24x36mm FX frame) using the 35mm/f1.8 AF-S DX at f8. I added the yellow box inside to indicate the DX frame area.</p><div></div>

[garner_par]

<p>Hi guys! Sorry but I'm a bit confused. I only use a DX camera (d5100) so please forget about the FX camera for now. I just need to know how tight will it get when I use other lenses. I can only compare the focal length to my 18-105vr lens for now so my questions are;</p>

<p>1. If I set my lens(18-105vr) to 35mm, will I also get the same when I buy the 35mm DX f/1.8?<br>

2. If I set my lens to 50mm, would that be the same if I use the 50mm 1.8G?<br>

3. I guess I just want to clarify that whether I use a DX or non-dx lens, it would still be the same focal length compared to my 18-105vr</p>

<p>Thanks in advance,<br>

Garner</p>

[andylynn]

<p>Lens focal length is lens focal length. A zoom lens that's set to 35 has the same magnification as a 35mm lens, etc., and it doesn't matter whether the lens is labeled DX or is a full frame lens.</p>

<p>So you'd see roughly the same image on your camera if you mounted the 35mm DX lens, or any 35mm full frame lens, or any zoom lens that's set to 35. Likewise, your zoom at 50 shows roughly the same image as a 50mm f/1.8G lens would. (I say roughly because I'm only talking about magnification. Other factors, like the aperture, are of course different.)</p>

[ShunCheung]

<blockquote>

<p>1. If I set my lens(18-105vr) to 35mm, will I also get the same when I buy the 35mm DX f/1.8?<br />2. If I set my lens to 50mm, would that be the same if I use the 50mm 1.8G?<br />3. I guess I just want to clarify that whether I use a DX or non-dx lens, it would still be the same focal length compared to my 18-105vr</p>

</blockquote>

<ol>

<li>yes</li>

<li>yes</li>

<li>yes</li>

</ol>

<p>35mm is just 35mm. It does not matter whether that 35mm is from your 18-105mm DX lens, 35mm/f1.8 DX lens or 35mm/f1.8 FX lens; it will give you the same coverage on your DX body.</p>

<p>However, when the camera is FX, those DX lenses may generate a certain degree of vignetting, i.e. darkened corners as well as low image quality along the edges and corners.</p>

[garner_par]

<p>Now I understand that part finally! Thanks guys! I'm excited to get either the 35mm or 50mm. Now I can set my lens to 35mm or 50mm so that I would know which would fit my need. I'll be using it mostly for video by the way, probably outdoor shots. Do you have any inputs about this? Any idea would be a big help! Thanks again!</p>