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  1. #1
    Senior Member
    Moab Man's Avatar

    DX - FX photo explanation of crop zoom

    DX - FX photo explanation of crop zoom
    Wrapping your head around the crop mode can be difficult. After participating in a thread on choosing a next camera, it was asked if the crop sensor is simply cropping down. Now that is an oversimplification, and there were other questions, so I decided to offer a photo explanation so that it may help clear the confusion. All photos were shot from a tripod placed over second base. The hot model, myself, stood in two foot prints for consistency.

    On a side note, who would have thought photography was so good for exercise as I ran back and forth between home base, second base, and my camera bag with lenses in the grassy outfield.

    Cameras: Nikon D7100 (crop sensor) and a Nikon D600 (full frame). Photos were not edited, auto focused, and no settings were adjusted in the camera other than compensating (shutter speed) for the sunlight fading. Effective focal length calculated using an online calculator.

    1. "DX is great for the extra zoom it gives."

    No, there is a not an actual zoom happening. The smaller sensor area is taking a smaller slice of the image coming through the lens. This smaller slice is what makes a 50mm lens on a crop sensor have an effective zoom range of 76mm. On a full frame sensor the full breadth of the image coming through the sensor is used thereby keeping it at 50mm.

    This image is a 50mm lens on a full frame sensor capturing the full image from the lens.
    DX - FX photo explanation of crop zoom-50mmfx.jpg

    This image is a 50mm lens on a crop sensor. The crop sensor is only pulling a slice from the center area of the lens and not the full image. This produces an effective zoom of 76mm.
    DX - FX photo explanation of crop zoom-50mmdx.jpg



    2. "So it's just a matter of cropping down the image."

    Incorrect, it is not "just" a cropping down of the image. The D7100 and D600 are standing on the dividing line between crop and full frame. Each uses a 24mp sensor.

    This image is a 35mm DX lens on a crop sensor camera. The smaller sensor at 24mp allows for this image to be printed at 300dpi (high resolution) at 20"x13.3".
    DX - FX photo explanation of crop zoom-35mmd7100.jpg

    Putting this same lens on a full frame camera, triggering a crop mode, gives us the same image. However, due to a small portion of the image being used there are fewer megapixels coming into play. This image has a high resolution print size of 13.1"x8.7" at 300dpi.
    DX - FX photo explanation of crop zoom-35mmincropmoded600.jpg



    3. "You need much more zoom on a full frame to achieve the same of a crop sensor."


    This image is a 35mm lens on a crop sensor. Effective zoom due to a crop sensor is 53mm.
    DX - FX photo explanation of crop zoom-35mmd7100.jpg

    To achieve the same "zoom" of a crop sensor we must use a 50mm lens on full frame.
    DX - FX photo explanation of crop zoom-50mmfx.jpg

    The difference between a 35mm and a 50mm lens may not seem like that much. But, when you are talking serious telephoto reach it become quite substantial in reach and cost to achieve the same image on full frame. A 500mm lens on a crop sensor effectively becomes a 759mm lens. To achieve the same for full frame you're shopping for an 800mm lens. In other words, a crop sensor gives you free additional reach through the "crop factor." However, it bears repeating, there is no actual mechanical zoom happening.


    4. "There are benefits to using an FX lens on a DX camera."

    Putting a full frame lens on a full frame camera gets you the effective zoom listed on the lens - 200mm is 200mm. As I showed above, triggering the crop mode on the camera with a DX lens loses a lot of pixels. Further pixels are lost when you crop down on the image you want such as sports. Generally, sports shots are cropped tight. for this reason, when it can be afforded, FX lenses are desired because they can give you the additional "zoom" on a crop sensor camera and on a full frame camera pixels are not being lost through the triggering of crop mode.

    This image is an FX lens (500mm) on an FX camera and cropped in tight for a sports shot. High resolution print size of 6"x9".
    DX - FX photo explanation of crop zoom-500mmd600sportscrop.jpg

    This image is an FX lens (500mm) shot on a DX camera and sports cropped. High resolution print size of 9"x13". This is a substantial 3" and 4" difference respectively.
    DX - FX photo explanation of crop zoom-500mmd7100sportscrop.jpg



    5. How substantial is the difference?

    This first image is the 500mm lens on a full frame sensor and then crop sensor.
    DX - FX photo explanation of crop zoom-500mmd600.jpg DX - FX photo explanation of crop zoom-500mmd7100corrected.jpg



    6. So how much difference in size are the two sensors? (shot through a 500mm lens)

    The inner area boxed in red is what the crop sensor sees. The entire photo is what full frame sees. To create this image I reduced the D7100 crop sensor image until it overlaid the image content of the full frame image. Therefore it is not a "mathematical" sensor size overlay but a content overlay.
    DX - FX photo explanation of crop zoom-sensoroverlay.jpg


    7. If I buy a DX specific lens does the crop factor still apply?

    Yes, the crop factor and effective resulting zoom is still present.

    This image is from a DX specific lens: Tokina 11-16mm shot at 14mm. The effective zoom due to the crop factor gives us an image approximating 21mm.
    DX - FX photo explanation of crop zoom-14mmdx.jpg

    This image is from a Rokinon 14mm FX lens. On a full frame it will give us a 14mm photo. Putting this FX lens on a crop sensor camera would give us an image like the image above because a crop sensor pulls a small slice from the center of the image.
    DX - FX photo explanation of crop zoom-14mmfx.jpg



    **My personal thoughts and opinion.

    When I shoot sports I prefer a crop sensor for the effective zoom of a crop sensor. However, if I am shooting in lower light I have to make the decision between having quite a bit less zoom with no high ISO noise and improved low light capability. Or, do I live with the higher noise in low light on my crop sensor to get better reach. With that said, the low light capability of the D7100 is pretty darn good. But... full frame is still clearly king in low light and high ISO.

    In my opinion, buy FX lenses when able. Generally, it's better glass and the lens can be used equally on both crop and full sensor cameras. DX lenses can be used on both, but you sacrifice image print size when used on full frame due to the triggering of crop mode because a DX lens is only putting through a smaller image in the center of the FX sensor leaving the outer area of the FX sensor with no image coming through.

    And I have no idea as to why this image below has attached itself to this thread. So I guess you can all take a moment to stare at me, the eye candy in each photograph.


    › See More: DX - FX photo explanation of crop zoom
    Attached Thumbnails Attached Thumbnails DX - FX photo explanation of crop zoom-500mmd7100.jpg  

    Last edited by Moab Man; 07-24-2014 at 11:35 PM.
     
    D5100, D7100, D600, D750, Df
    Lenses: Nikon DX 18-55mm, 55-200mm, 55-300mm, Tamron SP 70-300mm F4-5.6 Di VC USD & 200-500mm
    Prime: Nikon 35mm, 50mm, & 85mm f/1.8G, 300mm f/4
    Wide Angle: Tokina AT-X116 Pro DX-II 11-16mm f/2.8, Rokinon f/2.8 14mm (chipped)
    Macro: Nikon 40mm, Tamron 90mm
    ​Flash: Nissin MARK II Di622
    Stuff: Expodisc Neutral & Portrait
    ​Editing: CS6, CC, Nik Tools, Portrait Pro 12, Topaz
    Spyder4Pro
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  2. #2
    Senior Member
    Philnz's Avatar

    Re: DX - FX photo explanation of crop zoom

    Quote Originally Posted by Moab Man View Post
    Wrapping your head around the crop mode can be difficult. After participating in a thread on choosing a next camera, it was asked if the crop sensor is simply cropping down. Now that is an oversimplification, and there were other questions, so I decided to offer a photo explanation so that it may help clear the confusion. All photos were shot from a tripod placed over second base. The hot model, myself, stood in two foot prints for consistency.

    On a side note, who would have thought photography was so good for exercise as I ran back and forth between home base, second base, and my camera bag with lenses in the grassy outfield.

    Cameras: Nikon D7100 (crop sensor) and a Nikon D600 (full frame). Photos were not edited, auto focused, and no settings were adjusted in the camera other than compensating (shutter speed) for the sunlight fading. Effective focal length calculated using an online calculator.

    1. "DX is great for the extra zoom it gives."

    No, there is a not an actual zoom happening. The smaller sensor area is taking a smaller slice of the image coming through the lens. This smaller slice is what makes a 50mm lens on a crop sensor have an effective zoom range of 76mm. On a full frame sensor the full breadth of the image coming through the sensor is used thereby keeping it at 50mm.

    This image is a 50mm lens on a full frame sensor capturing the full image from the lens.
    DX - FX photo explanation of crop zoom-50mmfx.jpg

    This image is a 50mm lens on a crop sensor. The crop sensor is only pulling a slice from the center area of the lens and not the full image. This produces an effective zoom of 76mm.
    DX - FX photo explanation of crop zoom-50mmdx.jpg



    2. "So it's just a matter of cropping down the image."

    Incorrect, it is not "just" a cropping down of the image. The D7100 and D600 are standing on the dividing line between crop and full frame. Each uses a 24mp sensor.

    This image is a 35mm DX lens on a crop sensor camera. The smaller sensor at 24mp allows for this image to be printed at 300dpi (high resolution) at 20"x13.3".
    DX - FX photo explanation of crop zoom-35mmd7100.jpg

    Putting this same lens on a full frame camera, triggering a crop mode, gives us the same image. However, due to a small portion of the image being used there are fewer megapixels coming into play. This image has a high resolution print size of 13.1"x8.7" at 300dpi.
    DX - FX photo explanation of crop zoom-35mmincropmoded600.jpg

    To get the same zoom factor of the 35mm on a crop sensor camera we have to step up to a


    3. "You need much more zoom on a full frame to achieve the same of a crop sensor."

    This image is a 35mm lens on a crop sensor. Effective zoom due to a crop sensor is 53mm.
    DX - FX photo explanation of crop zoom-35mmd7100.jpg

    To achieve the same "zoom" of a crop sensor we must use a 50mm lens.
    DX - FX photo explanation of crop zoom-50mmfx.jpg

    The difference between a 35mm and a 50mm lens may not seem like that much. But, when you are talking serious telephoto reach it become quite substantial in reach and cost to achieve the same image on full frame. A 500mm lens on a crop sensor effectively becomes a 759mm lens. To achieve the same for full frame you're shopping for an 800mm lens. In other words, a crop sensor gives you free additional reach.


    4. "There are benefits to using an FX lens on a DX camera."

    Putting a full frame lens on a full frame camera gets you the effective zoom listed on the lens - 200mm is 200mm. As I showed above, triggering the crop mode on the camera with a DX lens loses a lot of pixels. Further pixels are lost when you crop down on the image you want such as sports. Generally sports shots are cropped tight. for this reason, when it can be afforded, FX lenses are desired because they can give you the additional "zoom" on a crop sensor camera and on a full frame camera pixels are not being lost through the triggering of crop mode.

    This image is an FX lens (500mm) on an FX camera and cropped in tight for a sports shot. High resolution print size of 6"x9".
    DX - FX photo explanation of crop zoom-500mmd600sportscrop.jpg

    This image is an FX lens (500mm) shot on a DX camera and sports cropped. High resolution print size of 9"x13". This is a substantial 3" and 4" difference respectively.
    DX - FX photo explanation of crop zoom-500mmd7100sportscrop.jpg



    5. How substantial is the difference?

    This first image is the 500mm lens on a full frame sensor and then crop sensor.
    DX - FX photo explanation of crop zoom-500mmd600.jpg DX - FX photo explanation of crop zoom-500mmd7100.jpg



    6. So how much difference in size are the two sensors? (shot through a 500mm lens)

    The inner area boxed in red is what the crop sensor sees. The entire photo is what full frame sees. To create this image I reduced the D7100 crop sensor image until it overlaid the image content of the full frame image. Therefore it is not a "mathematical" sensor size overlay but a content overlay.
    DX - FX photo explanation of crop zoom-sensoroverlay.jpg


    **My personal thoughts and opinion.

    When I shoot sports I prefer a crop sensor for the effective zoom of a crop sensor. However, if I am shooting in lower light I have to make the decision between having quite a bit less zoom with no high ISO noise and improved low light capability. Or, do I live with the higher noise in low light on my crop sensor to get better reach. With that said, the low light capability of the D7100 is pretty darn good. But... full frame is still clearly king in low light and high ISO.

    In my opinion, buy FX lenses when able. Generally it's better glass and the lens can be used on both crop and full sensor cameras. DX lenses can be used on both, but you sacrifice image size for print when used on full frame in crop mode.
    Wow. Thank you for all the time that you must have put in to this post. It has helped my understanding a great deal. I am buying all the old film lens that I can get my hands on.( if the price is right.) so am I right in thinking they are all Full Frame Lens?
    "On a side note, who would have thought photography was so good for exercise as I ran back and forth between home base, second base, and my camera bag with lenses in the grassy outfield." Now that is a good excuse to "Give Her in Doors" for getting more gear

    Thanks/Like PaulPosition, Moab Man, traceyjj, Lawrence Thanks/liked this post
     
    Phil. Ngatea New Zealand
    Life is like a camera
    Focus on what is important
    Develop from the negatives
    And if things don't work out
    Take another shot.

  3. #3
    Senior Member
    carguy's Avatar

    Re: DX - FX photo explanation of crop zoom

    Great info - thank you for putting this together
    Joe

    D750 | 50mm f1.8G | Tamron 70-200 2.8 VC
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  4. #4
    Senior Member

    Re: DX - FX photo explanation of crop zoom

    Quote Originally Posted by Philnz View Post
    Wow. Thank you for all the time that you must have put in to this post. It has helped my understanding a great deal. I am buying all the old film lens that I can get my hands on.( if the price is right.) so am I right in thinking they are all Full Frame Lens?
    You're right, at least as long as you're talking 35mm film camera's which full frame sensors are sized like (I have no idea what sort of lens "large-format" camera used to use).

  5. #5
    Happy to be Canadian
    Super Mod
    Marcel's Avatar

    Re: DX - FX photo explanation of crop zoom

    Quote Originally Posted by PaulPosition View Post
    You're right, at least as long as you're talking 35mm film camera's which full frame sensors are sized like (I have no idea what sort of lens "large-format" camera used to use).
    Normal lens on a 2-1/4" camera was 80mm, 4x5 around 190mm, 8x10 350mm is my memory serves me well.
    Thanks/Like PaulPosition Thanks/liked this post
     
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  6. #6
    Senior Member

    Re: DX - FX photo explanation of crop zoom

    I'm sorry...I totally got distracted by the fact that he's not actually holding a bat.

    This is a great post, though. It'll help us make the decision on whether we want to go full frame or not for the next camera. Thanks!

  7. #7
    Staff
    Moderator

    Re: DX - FX photo explanation of crop zoom

    Very useful indeed - thanks

    So to summarise really I would say;


    • 50mm FX lens on a FX body = equivalent 50mm (1x zoom)
    • 50mm FX lens on a DX body = equivalent of 75mm (1.5 zoom)
    • 50mm DX lens on a FX body = equivalent 50mm (1x zoom)
    • 50mm DX lens on a DX body = equivalent 50mm (1x zoom)



    It's important to remember that the focal length does NOT change on a lens - its the equivalent length that is chaging
    Last edited by §am; 07-24-2014 at 11:37 AM.
    Sam
    I've had brain surgery, what's your excuse.
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    mm f/2.8 VC (Tamron)
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  8. #8
    Senior Member
    PapaST's Avatar

    Re: DX - FX photo explanation of crop zoom

    Thanks for that great write up. But, we really need to work on your stance. Leaning into the plate too much and your strike zone is a mile high.
    Thanks/Like Eyelight, Moab Man Thanks/liked this post
     

  9. #9
    Senior Member
    Moab Man's Avatar

    Re: DX - FX photo explanation of crop zoom

    Quote Originally Posted by skater View Post
    I'm sorry...I totally got distracted by the fact that he's not actually holding a bat.
    It was my job to bring the camera equipment and my imaginary friends job to bring the baseball equipment. I'm not sure if he let me down or not.
    D5100, D7100, D600, D750, Df
    Lenses: Nikon DX 18-55mm, 55-200mm, 55-300mm, Tamron SP 70-300mm F4-5.6 Di VC USD & 200-500mm
    Prime: Nikon 35mm, 50mm, & 85mm f/1.8G, 300mm f/4
    Wide Angle: Tokina AT-X116 Pro DX-II 11-16mm f/2.8, Rokinon f/2.8 14mm (chipped)
    Macro: Nikon 40mm, Tamron 90mm
    ​Flash: Nissin MARK II Di622
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  10. #10
    Senior Member
    Moab Man's Avatar

    Re: DX - FX photo explanation of crop zoom

    Quote Originally Posted by PapaST View Post
    Thanks for that great write up. But, we really need to work on your stance. Leaning into the plate too much and your strike zone is a mile high.
    LOL, this is my I'M TRYING TO BREATHE stance. I was in a literal race against the setting sun to get these shots finished. My daughter laughed her butt off because in the photos I have this belly hanging out. I don't actually have a belly but learned to belly breathe to extend the lungs when bike racing. However, none of that matters to the camera or my laughing daughter.

    As for the stance... I don't play imaginary baseball very well.
    Last edited by Moab Man; 07-23-2014 at 03:54 PM.
    Thanks/Like PapaST, Eyelight Thanks/liked this post
     
    D5100, D7100, D600, D750, Df
    Lenses: Nikon DX 18-55mm, 55-200mm, 55-300mm, Tamron SP 70-300mm F4-5.6 Di VC USD & 200-500mm
    Prime: Nikon 35mm, 50mm, & 85mm f/1.8G, 300mm f/4
    Wide Angle: Tokina AT-X116 Pro DX-II 11-16mm f/2.8, Rokinon f/2.8 14mm (chipped)
    Macro: Nikon 40mm, Tamron 90mm
    ​Flash: Nissin MARK II Di622
    Stuff: Expodisc Neutral & Portrait
    ​Editing: CS6, CC, Nik Tools, Portrait Pro 12, Topaz
    Spyder4Pro
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