confusion between DX and FX lense Focal length

Discussion in 'Nikon' started by sun_p, Jun 18, 2009.

  1. Hi experts,
    I have the nikon D40 and 18-55 kit lens. I was looking at buying a good portrait lens and as per expert advice I had two options, 50-150 sigma and 28-75 F2.8 Tamron. However, both these lenses are just not available here and will have to wait for someone travelling to the US or UK to get it but then the problem is if there is an issue then I am stuck.. Now, I am having a change of mind and thinking of playing it safe and going in for the 50mm 1.4AF/S and probably 105 F2.8 nikkor prime lenses so that even if something is wrong, atleast I have authorised service stations here. Tamron/Sigma are not yet here and i am getting grey models for ridiculous prices without warranty.
    1. The reason I am choosing 50mm1.4AF/S is I can shoot in Low light and also i can stop up to shoot regulr protraits indoor under stobes. My space restriction is 18 feet by 7 feet (I am managing).
    2. The reason I am choosing 105 2.8 is so that I can get some good face shots and probably shoulder length shots under strobes indoors and can be used outside also in
    3. Both are nikon and robust in build without many moving parts and also I have proper repair facilitites. The other zooms etc are ridiculously expensive here, almost half the cost of a car!
    4. My 4 issue is with focal length. I am a little confused about the lengths. The crop factor mentioned for DX bodies, is that the real FL or we need to manually calculate. E.g, the 18-55 kit lens for my d40 when I take a shot, in the Exif data I see FL as 50 when I shoot at 50. So does that mean that the snap is shot at 50 FL or do I need to multiply that by 1.5 or is the snap already cropped at 50mm! What I was trying to ask is that are all lenses expecially for DX (AF-S) ones showing the FL the correct one or are they shown for FX bodies and we need to multiply. Does it mean that my Kit DX 18*55 is actually 18*1.5 to 55*1.5?
    Please advice
    Thanks,
    Sunil
     
  2. Firstly the focal length of the lens remains the same for whatever format.
    On DX the 50mm will have the same angle of view as a 75mm lens on FX, so the 1.5x is correct.
    However, as others will probably chime in, it isn't as simple as that. :)
     
  3. Sunil,
    All Nikon lenses indicate the same focal length be they DX lenses or FX lenses - the actual focal length of any given lens remains the same wether it be mounted on a DX body or an FX body.
    On DX bodies there is the crop factor or multiplication factor (1.5x in Nikon's case) as you are aware. DX designated lenses are specially designed to produce a smaller circle of light through the lens which only covers the smaller foramt DX sensors but fails to 100% cover the larger format FX sensors.
    A 50mm f/1.4 lens will produce a 50mm frame on an FX body but on a DX body the same lens will crop the frame to effectively give the equivalent of a 75mm frame on FX. So in effect, when mounted to a DX body - any lens be it DX designated lenses or other non designated DX lenses like the Ai, AiS, AF, AF-D, AF-S etc will produce an FX equivalent focal length imaged frame 1.5 x l'onger' (or tighter) than the actual lens focal length. So your current 18-55mm kit zoom is actually giving you what would be in FX equivalency a focal range of 27mm - 82mm, therefore your last line in this post is indeed correct.
    To put it another way - I have a D700 FX body camera / you have a D40 DX body camera. If you and I were to stand side by side with a 50mm f/1.4 lens on our respective cameras, and we shoot the same subject in front of us - my camera will produce an image which is 1.5 x wider framed than your cameras image or alternatively, your camera will produce an image which is 1.5 times tighter framed than my camera.
    I think 50mm focal length will suit you well given your stated studio dimensions.
     
  4. Can someone answer this, please? There are DX and FX lenses. If I have a DX body and a DX lens, say the 18-105, I actually get 18-105. But if I put a FX lens on there, like the 24-70, that is different than using a 24-70 if it were built for a DX camera, right? Putting the Nikon 24-70 on a DX body is really like putting a ~35-105 DX lens on it, right? So the 70mm on the current FX 24-70 lens would frame up exactly like the 18-105 DX lens at 105mm. Is that correct?
     
  5. Jason: as mentioned above, at 24-70 is a 24-70 no matter what camera you put it on. When you use a DX-format sensor, you're just recording a smaller piece of the image projected by the lens into the camera body.

    To be clear: a 70mm lens mounted on a DX body will result in the same angle of view as a 105mm lens mounted on an FX format body. When you put an 18-105 on a DX body, you'd need to use a 27-157 on an FX body to see the same angle of view.
     
  6. Jason, no. The 24-70 at 70 would frame up the same as the 18-105 at 70. The only difference between DX lenses and all the rest is that DX lenses generally won't cover a full frame (film or FX digital). See Matthew's post for more details.
    If you only use a DX camera, you can just ignore the DX/non-DX distinction.
     
  7. However, as others will probably chime in, it isn't as simple as that.​
    Why not :). It's a crop factor not a change in focal length. So if you compare a 200mm on a DX body to a 300mm on an FX body, you won't have the same depth of field and you won't have the same background compression.
    I find it funny when cheap point and shoots talk in 35mm equivalents.
     
  8. Unless you use, or have used, both formats and want to compare 35mm/FX angles of view with DX angles of view, forget about crop factors. They're meaningless and only serve to cause confusion.
    50mm is 50mm on DX, FX, 35mm, 120, etc. The new AF-S 35mm f/1.8 DX and the "FX" AF 35mm f/2D for example, will give the exact same framing when mounted on a DX body. They'll also give the exact same framing when mounted on an FX or 35mm body, but the DX lens will not project a large enough image circle to cover the format, so there will be severe corner vignetting.
    Putting the Nikon 24-70 on a DX body is really like putting a ~35-105 DX lens on it, right? So the 70mm on the current FX 24-70 lens would frame up exactly like the 18-105 DX lens at 105mm. Is that correct?​
    No. The FX 24-70 at 70mm will frame up exactly like the DX 18-105 lens at 70mm, not 105mm. Zoom the 18-105 from 24mm through 70mm, and that's the exact same framing you will see if you mounted the 24-70 on the same body and zoomed it through its full range. You will probably see slight differences in framing at close focus distances, but that has nothing to do with "crop factors".
     
  9. Nikon lenses have worldwide warranty so even if you purchase one in the US or UK, it will still be respected by Nikon in your country. As long as it was not gray market in the country of purchase.
     
  10. this is a really good resource regarding the field of view difference between DX and FX bodies:
    http://support.nikontech.com/app/answers/detail/a_id/2596
     
  11. Okay, thanks for the clarification. Everytime I read about a FX lens on a DX, people always mention the other numbers (ex 24-70 roughly = 35-105). I just didn't understand why I should care. I'm not an FX shooter, so I guess I should disregard those statements. Thanks again.
     
  12. I read the link that William provided, and this is what I don't understand. Maybe I am mixing up words and saying the wrong thing. Quote from article above regarding using a FX lens on a DX camera:
    The image circle produced by the lens is larger than the sensor area, therefore the field of view is cropped and the image appears magnified. This means that the lens has an apparent focal length magnification of 1.5 times the quoted figure, the actual focal length of the lens has not changed.​
    It sounds like that is saying that even though the lens is at a certain focal length, it appears as though it is not. It appears 1.5 times bigger. That's why I keep thinking that FX lens at 70 would produce the same framed image as a DX lens at 105.
    I don't have any experience with this, so I am trying to learn. Sorry for all the questions.
     
  13. It sounds like that is saying that even though the lens is at a certain focal length, it appears as though it is not. It appears 1.5 times bigger. That's why I keep thinking that FX lens at 70 would produce the same framed image as a DX lens at 105.​
    In a nutshell, yes. As stated above, a 50mm lens is a 50mm lens. As long as the distance from the camera to the subject does not change, the only difference from one format (DX,FX,MF,LF, etc.) to another is one of cropping. Nothing is magnified, only the framing is different from one "sensor" size to another.
    Back in the film days, no one had much of a problem understanding the difference between 35mm and MF. Digital has apparently created a"problem". Therefore, digital is bad. ;-) (That was a joke!)
    Good luck, Doug
     
  14. Jason: you're in the right conceptual neighborhood, you've just got it backwards.

    Take the example of a 50mm lens. A simple prime. It projects an image into an DX body that would allow you (with the camera in portrait/vertical orientation) to fill the frame with a standing human figure from about 15 feet away.

    Now, stand in exactly the same place, and use exactly the same lens, but put it on an FX body. The lens is projecting the exact same image into the body (because the lens hasn't changed), but now that projected image is falling on a bigger sensor. Some of that image was being ignored on the DX's smaller sensor, but is being recorded on the FX's larger one. So that means that your human figure no longer fills the frame, but instead has more scenery around it.

    In order for the FX camera's framing (with regard to how much of the frame the human figure fills) to look like the DX's, you'd have to walk closer to the person, to again make them fill the larger frame. But that also changes your perspective. Your other option (on the FX body) would be to use a longer lens... so that your human figure again fills the frame, but your perspective (which is a function of how close you are to the figure, and has nothing to do with lenses and cameras) remains the same.

    So in that scenario, the DX camera can fill the frame with a human from 15 feet while using a 50mm lens, but the FX camera needs a 75mm lens to make that figure land on the sensor in the same proportion.
     
  15. You must be thoroughly confused by now !
    It is all based around the diagonal of the sensor or film and a lens that has a focal length of the diagonal is deemed normal and has a 40 deg angle of view regardless of camera.
    An 8x10 camera is around 12" A 4x5 is 160mm 6x9 is 100 mm FX is 43 mm DX is 30 mm. All are approximate as I am to lazy to figure exactly.
    All see the same angle of view if you look through the camera
    A crop factor is just a way to to tell 35 mm film photographers what focal length they need to make the DX camera see the same as a film camera. It is about 1.5 x. So if you like 50 mm on film, get a 35 mm for DX. If you like 105 on film, get 70 for DX.
     
  16. So if I use a 70mm/5.6 on DX camera, and a 105mm/5.6 on a FX camera, the only difference will be the depth of view. May I concude that the DOF on a DX camera is less, because you are nearer to the subject?
     
  17. Ted, I think that's field of view that varies, not depth of field.
     
  18. Ted, you get a larger DOF the smaller the sensor is.
     
  19. Ted, I think that's field of view that varies, not depth of field.​
    Yes.. because the focal length changes, the field of view change, just as if switching to a longer lens.

    But smaller sensors do provide a larger depth of field.
     
  20. So if you compare a 200mm on a DX body to a 300mm on an FX body, you won't have the same depth of field and you won't have the same background compression.​
    This is incorrect. The depth of field will be different at the same f stop, but telephoto compression depends only on field of view and has nothing directly to do with focal length. So those two examples will have the same amount of compression.
     
  21. Joe C,
    So you're saying if I use an FX camera and take an image with a 200mm lens, then crop the image so I have the same *field of view* the lens would have given me with 300mm (which is what a DX body does), I will also have the same background compression I would have had if I shot at 300mm to begin with on the FX body? That doesn't make any sense. It would follow that taking any image and cropping it changes the background compression.
     
  22. So you're saying if I use an FX camera and take an image with a 200mm lens, then crop the image so I have the same *field of view* the lens would have given me with 300mm (which is what a DX body does), I will also have the same background compression I would have had if I shot at 300mm to begin with on the FX body? That doesn't make any sense. It would follow that taking any image and cropping it changes the background compression.​
    That is correct, cropping any image will increase the telephoto compression (or reduce the wide angle expansion if the cropped image is still wide angle). The perspective distortion is because of the difference in field of view between the camera (including any form of cropping) and the final photograph as seen by the person looking at it. Changing the viewing distance of a photograph also changes the perspective distortion. If one gets close enough to a wide angle photograph (and can still focus one's eyes from that close, it helps if the photograph is big) then the wide angle expansion disappears.
     
  23. ShunCheung

    ShunCheung Moderator

  24. Thanks for the links, all.
    I just want clarification on one thing. The reason I'm asking is that I want more of a good portrait lens than what I have. 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? 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.
    I don't think my 17-55mm is long enough for protraits at 55mm, and I would like a larger aperture then what my 18-105 provides. Although if the answers to my above questions are "yes", then I'm not sure 70mm is enough, either on the 24-70. I tend to stay above 70mm on my 18-105 when I am taking portrait-type pictures. 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.
     
  25. ShunCheung

    ShunCheung Moderator

    Jason, any Nikon F-mount lens at 35mm, regardless of whether it is a fixed 35mm DX, a fixed 35mm non-DX, a DX zoom that covers 35mm, or a non-DX zoom that covers 35mm will produce "the same image" in the viewfinder on your D90. (In reality, the quality from each lens could be a bit different in terms of sharpness, flare resistence, etc., but you shouldn't be able to tell the different looking into the viewfinder perhaps except for flare resistence.)
    As it has already been mentioned, whether a lens is DX or not indicates the size of its image circle. Otherwise a 35mm DX and a 35mm non-DX projects the same image (in terms of magnification) on the sensor.
     
  26. 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?​
    Yes; on a D90 any of those three lenses at 35mm focal length will have the same framing and magnification.
    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.​
    Yes; the 24-70 at 70mm will have the same framing and magnification as the 18-105 at 70mm.
    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.​
    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.
     
  27. 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.
     
  28. 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.

    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.
     
  29. 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.
     
  30. 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.​
    This isn't quite right. With the same lens, for example the 105mm F/2.8G, a DX camera will fill the frame from farther away 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.
    So at longer distance's from a subject a DX camera has more DOF.​
    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.
    - With macro a DX camera has less DOF, because you are nearer to the subject.​
    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.
    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.​
    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).
     
  31. 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.
     
  32. 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.​
    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.
     
  33. 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?
    Thanks,
    David.
     
  34. To All;

    Consider how folks are confused about hammers on clawhammer.net:

    One could have three folks each holding a 16 oz claw hammer; each hammer is the same 16 oz model hammer.
    To the homeowner the 16 oz hammer is the one to use; the normal hammer.

    To the burrly Paul Bunyan pro framer dude; he might always use a 24 oz model; thus the 16 oz seems whimpy and small.

    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.

    IN all three cases the hammer is the same weight and model; but the end user is different.
    LETS LOOK AT LENSES NOW :
    One might have some 35mm focal length lenses; and place each on a different camera that has a different film or sensor size.

    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.

    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.

    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.

    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.

    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.
    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.

    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.

    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.
    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.
    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!
    t
    [​IMG]
    [​IMG]
     
  35. ShunCheung

    ShunCheung Moderator

    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.
    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").
    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.
    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.
    00V2VQ-191955584.jpg
     
  36. 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;
    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?
    2. If I set my lens to 50mm, would that be the same if I use the 50mm 1.8G?
    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
    Thanks in advance,
    Garner
     
  37. 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.
    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.)
     
  38. ShunCheung

    ShunCheung Moderator

    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?
    2. If I set my lens to 50mm, would that be the same if I use the 50mm 1.8G?
    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​
    1. yes
    2. yes
    3. yes
    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.
    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.
     
  39. 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!
     

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