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Thread: Crop Factor

  1. #1
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    Crop Factor

    I'm kinda confuse with this one.

    They say APS-C has 1.6 crop factor (Canon Camera) and 1.5 crop factor (Nikon Camera)
    I have XTi and my question is : does EF-S lens comply to 1.6 crop factor too? or just for EF Lens.

    Because after a while using EF-S lens @ 50mm focal length i feel that what i see in viewfinder @ that focal length is the same as i see with my eyes (since they say what you see through viewfinder @ 50mm focal length is the same with what your eyes see). if EF-S comply to crop factor, what i see through viewfinder @ 50mm focal length should be different with what i see with my eyes

    thank you for helping me.

  2. #2
    project forum co-moderator Frog's Avatar
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    Re: Crop Factor

    I found this......don't know if it helps
    http://kwc.org/blog/archives/2006/20...ersus_efs.html
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  3. #3
    Senior Member Dylan8i's Avatar
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    Re: Crop Factor

    i believe the crop is due to a smaller sensor size and nothing to do with lenses.... unless you use a crop specific lense (not sure the canon name but nikon is DX) on a full frame camera.
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  4. #4
    Learning more with every "click" mjs1973's Avatar
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    Re: Crop Factor

    What you are seeing in your viewfinder is "pre cropped" by the camera. When you have your lens set on 50mm with your XTi, your are seeing the same field of view as if you had an 80mm lens on a 35mm camera.

    Don't let the crop factor get more complicated than it has to be. A 50mm lens is still a 50mm lens no matter what camera you put it on. You're just seeing a little bit less of the image in your XTi than you would if you had it on a 35mm or full frame dSLR.
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  5. #5
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    Re: Crop Factor

    You may get your answer here, Jeff

    http://www.kenrockwell.com/tech/crop-factor.htm
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  6. #6
    Senior Member readingr's Avatar
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    Re: Crop Factor

    The EF-S is designed for the 1.6 crop factor so the 50mm EF-S lens on an XTi will give the same result as the 50mm EF lens of the 5D full frame camera.

    Only apply the crop factor to EF lenses as they are designed for the full 35mm frame. so a 50 EF on the XTi will have the same view as a 80mm EF-S lens on the XTi.

    Hope thats clear.

    Roger
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  7. #7
    Be serious Franglais's Avatar
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    Completely wrong

    Quote Originally Posted by readingr
    The EF-S is designed for the 1.6 crop factor so the 50mm EF-S lens on an XTi will give the same result as the 50mm EF lens of the 5D full frame camera.

    Only apply the crop factor to EF lenses as they are designed for the full 35mm frame. so a 50 EF on the XTi will have the same view as a 80mm EF-S lens on the XTi.

    Hope thats clear.

    Roger
    No. That's not right.

    As someone else stated, a 50mm lens is a 50mm lens whether it is EF or EF-S. But the view you get through it is not the same on a 450D as on a 5D

    - The EF lens gives an image circle that fully covers the 24x36mm frame of a "full frame" camera like the 5D.
    - The EF-S lens gives a smaller image circle that fully covers the 22.2x14.8mm frame of an APS-C camera like the 450D. If you put an EF-S lens on the 5D you would see that the corners were dark.

    Put an EF lens on an APS-C camera and you are only using the central part of the image. The rest is outside the edges of the sensor and is lost. The effect is as though you had put a more telephoto lens on the camera. Multiply the actual focal length of the lens by the crop factor and you get the corresponding focal length if you were using a "full-frame" camera.

    A 50mm lens on an APS-C camera gives the same view as a 50x1.6=80mm lens on a full-frame camera (in other words it's a moderate telephoto)

    The "normal" view on a full-frame camera is the 50mm. On an APS-C camera the equivalent of a 50mm is a 50/1.6 = 31mm lens.
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  8. #8
    Senior Member readingr's Avatar
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    Re: Completely wrong

    Quote Originally Posted by Franglais
    No. That's not right.

    As someone else stated, a 50mm lens is a 50mm lens whether it is EF or EF-S. But the view you get through it is not the same on a 450D as on a 5D

    - The EF lens gives an image circle that fully covers the 24x36mm frame of a "full frame" camera like the 5D.
    - The EF-S lens gives a smaller image circle that fully covers the 22.2x14.8mm frame of an APS-C camera like the 450D. If you put an EF-S lens on the 5D you would see that the corners were dark.

    Put an EF lens on an APS-C camera and you are only using the central part of the image. The rest is outside the edges of the sensor and is lost. The effect is as though you had put a more telephoto lens on the camera. Multiply the actual focal length of the lens by the crop factor and you get the corresponding focal length if you were using a "full-frame" camera.

    A 50mm lens on an APS-C camera gives the same view as a 50x1.6=80mm lens on a full-frame camera (in other words it's a moderate telephoto)

    The "normal" view on a full-frame camera is the 50mm. On an APS-C camera the equivalent of a 50mm is a 50/1.6 = 31mm lens.
    I knew when I read it back it wasn't clear and your explanation is excellent but Isn't that what I said?

    View:

    50mm EF on XTi = 80mm EF on 5D which is 35mm?

    Therefore 50mm EF on XTi = 80mm EF-S on XTi

    Roger
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  9. #9
    project forum co-moderator Frog's Avatar
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    Re: Crop Factor

    I get a headache reading this thread
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  10. #10
    Be serious Franglais's Avatar
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    OK now I see

    Quote Originally Posted by readingr
    I knew when I read it back it wasn't clear and your explanation is excellent but Isn't that what I said?

    View:

    50mm EF on XTi = 80mm EF on 5D which is 35mm?

    Therefore 50mm EF on XTi = 80mm EF-S on XTi

    Roger
    When you say it like that it comes out right. First time I read it the other way round.

    Frog is right. This is really something really simple that is hard to explain.
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  11. #11
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    Re: Crop Factor

    oh.. yeah it's kinda confusing.
    when i see through viewfinder with EF 50mm, what will I see? 50mm view or 80mm view?

  12. #12
    Learning more with every "click" mjs1973's Avatar
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    Re: Crop Factor

    If you are looking through a 50mm lens on your XTi, you will see the same thing that you would see if you looked through an 80mm lens on a full frame dSLR or a 35mm SLR. This is the same for both EF and EF-S lenses on your XTi.
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  13. #13
    Senior Member readingr's Avatar
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    Re: Crop Factor

    Quote Originally Posted by mjs1973
    If you are looking through a 50mm lens on your XTi, you will see the same thing that you would see if you looked through an 80mm lens on a full frame dSLR or a 35mm SLR. This is the same for both EF and EF-S lenses on your XTi.
    Just one thing more to remember the EF-S lens will not fit a 35mm sensor camera, it doesn't allow enough room for the mirror to pop up, so if in the long term you plan of buying a 35mm 5 or 1 series camera then stick with the EF lenses. They work on all the EOS bodies.

    A 50mm EF will look like an 80mm on the XTi
    A 50mm EF-S will look like a 50mm

    or another way 31mm EF will look like a 50mm on the XTi

    Hope that helps

    Roger
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  14. #14
    Learning more with every "click" mjs1973's Avatar
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    Re: Crop Factor

    Quote Originally Posted by readingr
    A 50mm EF will look like an 80mm on the XTi
    A 50mm EF-S will look like a 50mm
    This is not correct. A 50mm lens, no matter what it is, EF or EF-S will look exactly the same on the XTi. On the XTi they will both give you the field of view equal to an 80mm lens on a full frame camera.

    The "crop" itself has nothing at all to do with the lens. The crop is taking place at the sensor. The EF-S lenses are designed to produce a smaller image circle because they don't have to cover a FF sensor, but the image within that circle isn't magnified. If you were to lay the image circle from a 50mm EF lens, on top of 50mm EF-S lens, the only difference would be the size of the circle. The image within both circles would be the same same size. The only difference would be that the EF lens would give you a larger circle, and therfore project a wider field of view. The EF-S image would line up perfectly with the EF image, other than the part that is cropped off do to the size of the image circle.
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    Senior Member Dylan8i's Avatar
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    Re: Crop Factor

    also to note, as per my understanding, its not really like using an 80 mm lense, that may be the field of view you get, but the compression (front to back- not sure if thats the right word) stays the same as a 50mm.
    like how flat the image looks, with wide angle lenses giving more depth and tele making it flat
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  16. #16
    Senior Member readingr's Avatar
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    Re: Crop Factor

    Quote Originally Posted by mjs1973
    This is not correct. A 50mm lens, no matter what it is, EF or EF-S will look exactly the same on the XTi. On the XTi they will both give you the field of view equal to an 80mm lens on a full frame camera.

    The "crop" itself has nothing at all to do with the lens. The crop is taking place at the sensor. The EF-S lenses are designed to produce a smaller image circle because they don't have to cover a FF sensor, but the image within that circle isn't magnified. If you were to lay the image circle from a 50mm EF lens, on top of 50mm EF-S lens, the only difference would be the size of the circle. The image within both circles would be the same same size. The only difference would be that the EF lens would give you a larger circle, and therfore project a wider field of view. The EF-S image would line up perfectly with the EF image, other than the part that is cropped off do to the size of the image circle.
    Mike,

    Thanks for the correction - I should have put 80mm view into the text. I didn't mean magnification.

    Roger

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  17. #17
    Be serious Franglais's Avatar
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    This is an interesting point. Let me have a go

    Quote Originally Posted by Dylan8i
    also to note, as per my understanding, its not really like using an 80 mm lense, that may be the field of view you get, but the compression (front to back- not sure if thats the right word) stays the same as a 50mm.
    like how flat the image looks, with wide angle lenses giving more depth and tele making it flat
    When you talk about "compression" I think you mean depth of field - the foreground is blurred (out of focus), the area the lens was focussed on is sharp and the background is blurred again. Any 50mm lens at a given aperture will go from blurred to sharp and back to blurred at exactly the same distances. It seems simple, doesn't it?

    In reality the image doesn't look exactly the same on an APS-C sensor as on a "full-frame" sensor, even with the same lens :

    1. On an APS-C sensor the image is enlarged more than on a FF image. Any slight blurring is more obvious so the depth of field appears to be less
    2. The in-camera sharpening of the image is usually set stronger on APS-C cameras than on FF. This tends to make the cut-off between in-focus and out-of-focus parts of the image more abrupt
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  18. #18
    Senior Member Dylan8i's Avatar
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    Re: Crop Factor

    no i don't mean DOF. I mean telephoto lenses compress the image while wide angle exagerate the picture.

    imagine a crowded street several blocks long. If taken from different spots on the street with a wide angle and a telephoto lense so that the same field of view occurs. The wide angle will have a greater dof, but will also have much more seperation between the closest subjects and the ones several blocks away, while the telephoto will compress the image via "telephoto effect" seeming to create a more crowded jammed up street, with the farther blocks seeming much closer to the close one.

    its a change in the perspective of the photograph.

    you can also see it if you take a close up of a face with a wide angle lense and the nose (or what ever is closest to the camera) appears much larger than the further back parts of the face.


    this perspective does not change with the crop factor. the perspective of the 50 mm stays the same, just the angel of view changes with the crop.
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  19. #19
    Nature/Wildlife Forum Co-Moderator Loupey's Avatar
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    Re: Crop Factor

    Quote Originally Posted by Dylan8i
    If taken from different spots on the street with a wide angle and a telephoto lense so that the same field of view occurs.
    That's the difference. Changing the camera postion to compensate for the focal length has a HUGE effect and is NOT the same as the crop factor. The former is what gives the patented "Alfred Hitchcock" camera move where the frightened main character stays about the same size while the background moves in or out (depending on the emotion portrayed).

    Remember that a focal length is simply the magnification/reduction of an image. As long as you stay in the same position, the crop factor is identical to what a telephoto lenses does.
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  20. #20
    Nature/Wildlife Forum Co-Moderator Loupey's Avatar
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    Look at it this way...

    Here’s my explanation for this topic – with illustration of course!

    As stated previously, a 50mm is a 50mm. On the image below, imagine that the image circle is what is produced by a 50mm EF (full frame) lens. A full frame 5D would have the imaging sensor (and viewfinder) covered by the larger white rectangle. But the same 50mm on a 30D (APS-C sensor) would have the imaging sensor (and viewfinder) covered by the smaller white rectangle.

    The smaller white circle is what might be covered by a 50mm EF-S lens (if there were such a thing) manufactured specifically for a APS-C dSLR.

    Again, at the imaging plane, the image “magnification” is the same. The smaller area covered by the smaller sensor (and viewfinder) is the same as if a longer telephoto was used with the larger (full frame) camera. The effect is the same – so long as your shooting position remains the same.

    Hence why the viewfinder of the 5D looks so much larger and "wider" than that of the 30D, 40D, XTi, etc.


    If it helps to visualize, think of it in reverse. With medium format equipment, the image area captured is even larger than what is shown here. So what it would “see” is wider than what the full frame 5D would record. So to put the same amount of “stuff” into the frame of the medium format camera would require you to magnify the image. Hence why a 75mm is considered normal for a 6x4.5cm format camera. So the larger the imaging area, the longer the focal length to get the same amount of “stuff”. The converse is true - the smaller the imaging area, the smaller the focal length required to put the same amount of the scene into it.
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  21. #21
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    Re: Crop Factor

    hm, by reading your reply, loupey.
    I think i understand now.
    EF lens in full frame works like using both of our eyes, we can get wider view.
    EF lens in APS-C is like using one eys, right?

    so even if i use EF 50mm in XTi the view that i will get is the as big as that small white box in your explaination right?

  22. #22
    Senior Member Dylan8i's Avatar
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    Re: Crop Factor

    yes. the lense will produce the larger circle, but the sensor will only pick up whats in the smaller box
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  23. #23
    Nature/Wildlife Forum Co-Moderator Loupey's Avatar
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    Re: Crop Factor

    As the name implies, a “crop factor” is just that and only that. Nothing special – it doesn’t change what the lens is doing nor does it change the perspective or image characteristics.

    On point-and-shoot cameras, the focal ranges are all over the place. My wife’s Sony Cybershot has a zoom range of 6.7mm to 20.1mm. Does that mean it only shoot ultra-wide angle shots? Absolutely not - but it would if I stuck a full frame 24mm x 36mm imaging sensor in there. It would be a simple calculation to figure out the equivalent crop factor but what good will that do? It would only tell me the exact size of the imaging sensor.

    It is what it is. Mental conversion is not necessary – just understand what look you are after and what your equipment will give you. If I had a 5D, 1DmkIII, and a 40D (corresponding to 1.0x, 1.3x, and 1.6x crop factors) slung over my neck at the same time, I wouldn’t carry a chart of focal length conversions – I would just use what camera with what lens to get the image width that I was looking for. You can see that cropping the full frame 5D image down would have the same effect as using the 1.3x or 1.6x cameras. Whether the image resolution would hold up is a different matter though.


    Use the metric system analogy: The US is, I believe, the last country on this planet to still not use the metric system. Why? Because I always hear people saying “How many MPH’s is that?” or “How many feet is that?”, or “How many gallons is that?”. As long as one tries to compare one convention to another, undue effort and confusion will occur.

    Just adopt and use would be my philosophy :thumbsup:
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