DX Camera and DX Lens question?

Discussion in 'Photography Beginners' Forum' started by LiamMason, Dec 1, 2020.

  1. LiamMason

    LiamMason TPF Noob!

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    Was listening to a YouTube photographer and he said that pictures taken with a DX Camera and DX lens can be cropped easier than FX camera pics. Not sure I am wording this statement correctly. It has something to do with the sensors ability to write information from a long DX lens.
    But my question is why. Why is it easier to crop a DX picture over an FX picture.

    He also mentioned that National Geographic photographers are using DX cameras with FX lenses.

    Thank you,


     
  2. RVT1K

    RVT1K Been spending a lot of time on here!

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    I'm afraid that the question doesn't make much sense to me. Cropping an image is done after the fact and I can't see how the size of the sensor in your camera can make a difference.

    Are you familiar with the difference between a FX and a DX sensor?
     
  3. PJM

    PJM Been spending a lot of time on here!

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    Because of the smaller sensor size on a DX camera body the subject of an image taken with any given lens will cover a greater portion of the sensor on a DX camera than it would with the same lens on an FX camera. To create an image of a specific size on a screen or print you would have to crop less if the image were taken with a DX camera body than if it were taken with an FX camera body. This may be what they mean by "cropped easier".

    The size of the subject produced by a DX camera is about 1.5x the size produced on an FX camera. Wildlife photographers (i.e. Nat Geo) use this to their advantage as it essentially extends the reach of their telephoto lenses. A 300mm telephoto on a DX body will produce an image the same size as at 450mm on an FX body.

    DX lenses are designed to cover a DX sensor. They will not typically cover an FX sensor so DX lenses are not used on FX bodies. FX lenses are designed to fill FX sensors and therefore will also fill the smaller DX sensors. This makes FX lenses a good choice for people who have both FX and DX bodies or plan to switch from a DX to an FX body at some point.

    I hope this helps.
     
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  4. Space Face

    Space Face Been spending a lot of time on here!

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    That's pretty much nail on head when it comes to crop v full frame sensors. Very well put.
     
  5. PJM

    PJM Been spending a lot of time on here!

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    Thanks @Space Face.

    And as a follow up... this "enlargement" effect can work against you if you are into landscape or astrophotography and like to take wide angle shots. You would lose the wide angle going from an FX camera to a DX using the same lens.
     
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  6. Space Face

    Space Face Been spending a lot of time on here!

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    Being a mainly wildlife photographer I used to be of the crop sensor school (I'm a Canon user). I have however changed my opinion on this after reading an article on another Forum a few years ago which went into great technical detail in explaining that the crop factor was really a false economy.

    I can't remember all the specific in's and out's but it made sense at the time and I moved to a higher resolution full frame set up and am currently considering a full frame mirrorless. I find that the ability to crop into the FF image is better than the cropping effect on the smaller sensor. Lowlight performance is generally better too. Hope that makes sense.

    I still have a 1D MK IV which is only a 1.3x crop but has a high frames per second burst so I'd use that if need this function but that apart I'm a FF convert.
     
  7. Ysarex

    Ysarex Been spending a lot of time on here!

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    This is incorrect. Magnification is a function of lens focal length and subject distance -- two variables, period. The format size is meaningless. Therefore a 300mm lens will project the exact same size image onto both an FX and DX sensor.

    Think of it this way. Swap out the sensors with transparency film. One camera has a larger piece of film than the other. Photograph the same subject at the same distance with the same lens and then develop the film. Lay the two pieces of film on top of each other and the image of the subject on both will align perfectly as both will be the same size.

    An Xmm lens will always be an Xmm lens.
     
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  8. Ysarex

    Ysarex Been spending a lot of time on here!

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    Post a link to the Youtube video for us. That does sound like nonsense.
     
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  9. Strodav

    Strodav TPF Supporters Supporting Member

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    A FF (or FX) lens is designed to focus the image on a roughly 35.9mm x 23.9mm sensor. An aps-c (or DX) lens is designed to focus the image on a roughly 23.5mm x 15.7mm sensor. If you use a FF lens on an aps-c camera, the outer edges of the image fall outside the sensor area, so only the center part of the image is being used, hence the "crop factor". If you use a aps-c lens on a FF camera the image will be smaller than the sensor size, so you will see a black border on the outer edges of the frame. See the image below. So, FF lenses work fine on a aps-c camera, but not the other way around. I use FF lenses on both my D500 and D7200 DX bodies all the time.

    Let's say you have 2 24mp cameras, one FF and the other aps-c and you are going to use the exact same prime FF lens on both shooting your subject from the exact same distance with both cameras. Because of the sensor size difference, the subject covers less of the frame on the FF camera and more of the frame on the aps-c camera, i.e., the crop factor. So, you are putting more sensor pixels on the SUBJECT with the aps-c camera than with the FF camera. Pixels = Detail. So, the aps-c camera will give you better detail than the FF camera here in our thought experiment. This is why I use a D500 DX body for wildlife / birding and a D850 FX body for everything else.

    There are tradeoffs. Since the pixels density is higher on the 24mp aps-c sensor, the light buckets that convert photons to electrical signals are smaller. Smaller light buckets means higher noise and less dynamic range compared to the larger light buckets on the 24mp FF sensor. As long as you have good light, no problems, but you will see more noise from the aps-c body in lower light conditions. Higher resolution FF cameras are getting close to the pixel density of DX cameras, but are not quite there. For example, my 20.9mp D500 has a 7% higher pixel density than my 45.7mp D850, but as the pixel density goes up, the light buckets get smaller compromising noise and dynamic range, so there are limits. DX 24mm.jpg
     
  10. Ysarex

    Ysarex Been spending a lot of time on here!

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    Not necessarily. That will be more likely than not but it depends on the specific cameras being compared. It's true for your D500/D850 pair but would not be true if your D850 were instead a Sony A7R IV. Your D850 was released in 2017. In that year there were still 16 and 18 megapixel APS-C cameras being sold. Even cropped your D850 would have a higher pixel density. You're right that the sensor pixel density is what matters in this case. In your next paragraph you note that FF cameras are getting close to the pixel density of DX cameras but are not quite there -- that's a game of leap frog in which you're right one minute and wrong the next. That Sony I just mentioned has a 61 megapixel FX sensor.
    It's correct that the DX sensor camera will be noisier and the smaller pixel size is a factor in that however the primary reason the DX sensor is noisier is because the sensor is smaller.
     
  11. wfooshee

    wfooshee No longer a newbie, moving up!

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    I swear I'm having heavy deja vu with this thread, but search as I might, I don't find what I thought this was a copy of. I thought it was an old thread when I read post 1, then I saw the date.
     
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  12. Ysarex

    Ysarex Been spending a lot of time on here!

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    It's a perennial topic and surfaces with regularity. And unfortunately it always manages to stir up a fair amount of misunderstanding. After all the OP did introduce the topic by referencing a YouTube video.
     

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