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Thread: Crop Factor?

  1. #1
    Senior Member melvin's Avatar
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    Default Crop Factor?

    Hi!

    Check wif all experts here camera having a crop factor of 1.6 What does it mean heard from my friend that not suitable for lens with f2.8 or f2 n below or no point using them due to crop factor? How will it affect the picts? They say lens wif f2.8 below is only for full-frame like 5D etc....... please enlighten, still a newbie n learning!

    Thanks a million in advance!
    Last edited by melvin; 26th October 2007 at 05:53 PM.

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    Default Re: Crop Factor?

    http://en.wikipedia.org/wiki/Crop_factor

    wiki still e best friend.. just read this... usually we use crop factor 1.6x to multiply lens focal length
    example 17mm 1.6x = 27mm
    17mm lens will be 17mm for Full Frame camera
    It will be field of view of 27mm on a 400D
    Canon 400D + 50L - Everyone was once a Noob

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    Default Re: Crop Factor?

    Quote Originally Posted by melvin View Post
    Hi!

    Check wif all experts here camera having a crop factor of 1.6 What does it mean heard from my friend that not suitable for lens with f2.8 or f2 n below or no point using them due to crop factor? How will it affect the picts? They say lens wif f2.8 below is only for full-frame like 5D etc....... please enlighten, still a newbie n learning!

    Thanks a million in advance!
    Regarding to this question: What does it mean heard from my friend that not suitable for lens with f2.8 or f2 n below or no point using them due to crop factor? That is not true, that's nonsense. It would not affect the pics. f/2.8 lenses work well with DSLRs with the crop factor e.g. 40D, 400D, 350D, D300, D80 etc. A f/2, f/2.8 lens can work with cameras with crop factor, lenses made specially for cameras with crop factor do have some f/2.8 lenses in the range, so that's rubbish, and they are the best lenses around. I would recommend you look at Wikipedia about crop factor. Here is the linkhttp://en.wikipedia.org/wiki/Crop_factor
    Nikon D80|Nikon 18-135 AF-S DX|Nikon 70-300 AF|Nikon 50 f/1.4 AFD|Nikon SB-800|Canon IXUS 70

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    Senior Member zac08's Avatar
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    Default Re: Crop Factor?

    Quote Originally Posted by melvin View Post
    Hi!

    Check wif all experts here camera having a crop factor of 1.6 What does it mean heard from my friend that not suitable for lens with f2.8 or f2 n below or no point using them due to crop factor? How will it affect the picts? They say lens wif f2.8 below is only for full-frame like 5D etc....... please enlighten, still a newbie n learning!

    Thanks a million in advance!
    The crop factor has NOTHING to do with the aperture size of the lens. Pls ask your fren to read up more and dun go around confusing people..
    Michael Lim
    My Flickr Site

  5. #5

    Default Re: Crop Factor?

    I think your friend means that it may not display the full qualities of a lens for full frame?
    like you buy EF 17-40mm f/4L USM and put in on a Canon 40D.
    den u put a EF 17-40mm f/4L USM on Canon 5D.

    On canon 40d it is actually a 27.2 - 64mm (1.6 x 17 - 1.6 x 40)
    for a start, go read the newbie sticking guide.... better than listening to ya dear friend.

  6. #6

    Default Re: Crop Factor?

    Put a 17-40/4 on a 40D and you get 27.2-64 F/6.4

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    Default Re: Crop Factor?

    Don't worry about what your friend said. All lenses used on full frame cameras can be used on 1.6x crop cameras. The converse is not true though. Not all lenses used on 1.6x crop cameras can be used on full frame cameras, and for canon, those lens starts with a EFS instead of a EF, eg efs 18-55mm usm II kt lens.

  8. #8
    Senior Member creampuff's Avatar
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    Default Re: Crop Factor?

    Quote Originally Posted by grantyale View Post
    Put a 17-40/4 on a 40D and you get 27.2-64 F/6.4
    Are you sure the aperture size is reduced? Please go check.

  9. #9
    Senior Member zac08's Avatar
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    Default Re: Crop Factor?

    Seriously...go read up more.

    The crop factor is actually a good thing, esp for those mediocre lenses which works best in the middle area. Think about it, when the problem areas of the corners are actually cropped off, you get better image quality straightaway, no need to crop further.

    On the other hand, if you use film cameras or FF DSLRs, then you NEED to ensure that the lenses you use are of TOP quality or else the edge quality of your pics will suffer.

    And the aperture is NOT affected by the crop.
    Michael Lim
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  10. #10
    Senior Member creampuff's Avatar
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    Default Re: Crop Factor?

    Quote Originally Posted by zac08 View Post
    Seriously...go read up more.

    The crop factor is actually a good thing, esp for those mediocre lenses which works best in the middle area. Think about it, when the problem areas of the corners are actually cropped off, you get better image quality straightaway, no need to crop further.

    On the other hand, if you use film cameras or FF DSLRs, then you NEED to ensure that the lenses you use are of TOP quality or else the edge quality of your pics will suffer.

    And the aperture is NOT affected by the crop.
    This is true only you're using lenses that were originally designed for 35mm film format and used on a camera with a cropped sensor as these lenses project a bigger image circle than the size of the sensor.

    This is not true for lenses designed for cropped sensors (digital only) where the image circle is matched to the smaller sensor size, i.e. the lens is resolving to the edge of the image circle of the entire lens. What you mention in your second para also applies to lenses designed for cropped sensors when used on cropped sensor DSLRs.
    Last edited by creampuff; 27th October 2007 at 01:40 AM.

  11. #11

    Default Re: Crop Factor?

    Quote Originally Posted by creampuff View Post
    Are you sure the aperture size is reduced? Please go check.
    Yes, a 17-40 F/4 lens is always a 17-40 F/4 lens regardless of sensor size.

    I think from what grantyale have posted in the past, I can guess that he is speaking from a different angle.

    1) If both the full frame user and the Canon 40D user are both using 17mm on this lens, then the 40D user will have to stand 1.6x further away to get the same composition.

    As we all know, light fall off by a factor of 1/2 (1 stop exposure) for each squareroot(2) increase in distance.

    So the 1.6x further distance for the 40D user means that he is getting the [1.6/squareroot(2)] stops less light than the full frame user who is standing nearer to the subject.

    So in terms of exposure, the 40D user's exposure at 17mm @F/4 is the same as the full frame user's exposure shooting the same composition at 17mm @F/6.4. [ i.e. 1.6/(SqRoot(2) x SqRoot(2) x F/4).

    The perspectives however are different between the 2 users since the full frame user is nearer to the main subject when compared to the 40D user while the other subjects's relative distance to the main subject do not change with the shooting distance. For e.g. 1 secondary subject 2m behind the main subject will always be 2m behind regardless of your shooting distance. The nearer you're to the main subject, the bigger the difference in its apparent size with the other subjects within the frame.

    2) If now, the Full frame user is using a 27.2-64mm F/4 lens instead while the D40 user still uses the 17-40mm F/4 lens, both of them will get the same field of view and therefore have the same composition when they stand together at the same distance away from the subject.

    However, the Depth of Field will be different. The full frame will have a much shallower DOF.

    The DOF of 17mm @F/4 on the D40 is about the same as the 27.2mm @F/6.4 on the full frame.

    So from a DOF point of view, the 17-40 F/4 on the D40 is like a 27.2-64mm F/6.4 on a full frame.

    Perspective wise, both users are the same because perspective is only affected by shooting distance and both users now stand at the same distance away.

    So the picture taken by 17-40mm @F/4 on the 40D will be the same as the one taken by a 27.2-64mm F/6.4 lens on a full frame in terms of DOF and perspective.

    Although the physical aperture (diaphragm) of the 27.2mm @F/4 is bigger than the 17mm @F/4, the exposure is the same for both cameras at F/4 because more light through the bigger lens is spread over a corresponding bigger sensor on the full frame. So in terms of exposure, the F/4 on the 40D from the same distance is the same as F/4 on the full frame and will have an 1.6/sqRoot(2) stops advantage over the F/6.4 on the full frame.

    ===
    So although the 17-40mm F/4 lens remains a 17-40mm F/4, some photographic effects of this lens on a small sensor is equivalent to a 27.2-64mm F/6.4 lens on a full frame.

    So I guess grantyale was speaking from a photographic effect angle (point 2 above) rather than a physical dimension or exposure point of view.
    Last edited by Clockunder; 27th October 2007 at 06:38 AM.

  12. #12
    Senior Member creampuff's Avatar
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    Default Re: Crop Factor?

    Hmm, a long dissertation but suffice to know the actual focal length of a lens remains the same due to its optical construction, and does not change with the format of the sensor that is used behind it.

  13. #13

    Default Re: Crop Factor?

    Quote Originally Posted by creampuff View Post
    Hmm, a long dissertation but suffice to know the actual focal length of a lens remains the same due to its optical construction, and does not change with the format of the sensor that is used behind it.
    The photographic effects are more important than the physical dimension of the lens or exposure.

    Afterall, people only look at the picture and its photographic effects to judge/feel whether it's a good picture and not whether your lens is 17mm or 27.2mm or your sensor is 1.6x crop or full frame or you used F/4 or F/6.4.

    The physical dimensions etc. of a lens and camera are important to a photographer only as far as it pertains to the photographic effect (details resolved, dynamic range, noise, DOF, perspective etc.) it can achieve.

    We buy the lenses and any photographic equipment not for its physical dimension but for what they can achieved in photograhic effects.

    (p.s. just in case some people again jump in to say it's all about the photography skill of the person behind the camera, I would say that while it is is true that nice pictures can also be produced by compact PnS, the person behind the camera must also have the right/appropriate equipment to produce what he wants. It is not the equipment he should be after but the photographic effects the equipment can bring about.)

    A wide F/2.8 lens is nothing if it's on a compact PnS camera which cannot get the shallow DOF or other possible effects possible on bigger sensor camera. This is also the prime reason why people go for bigger sensor/format cameras like DSLR and medium format etc. If not, everyone would have just use compact PnS which is much more portable, cheaper and easier to be maintained or even disposal cameras.

  14. #14
    Senior Member creampuff's Avatar
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    Default Re: Crop Factor?

    Clockunder no any disagreement with what you've written at length. My response to grantyale is that no matter whether one uses a cropped sensor camera or FF camera, the description of the lens always remains the same irrespective of whatever sensor it is used with (ie. f/4 remains f/4). We're not talking about the photographic effect arising from a smaller sensor, which is obvious and it would be confusing to describe it as a 27.2-64mm F/6.4 in this example.

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    Default Re: Crop Factor?

    Well, some people feels that it is better to differentiate between the effects produced by the instrument, and the instrument itself. Afterall, using a 17-40mm lens on a 1.6x crop sensor does not give a 27.2mm-64mm lens. It just gives the same effective field of view of a 27.2-64mm lens used on a full-frame camera.

    Well, this may be confusing for a beginner, doesn't it? Some times it will be better to just ignore the technical aspects, and just make the most of the equipment that you have? As long as you do not use a EFS lens on a full-frame or 1.3x camera, the rest are just bothersome details to be picked up later.

  16. #16
    Senior Member melvin's Avatar
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    Default Re: Crop Factor?

    Thanks guys for all the great effort n knowledge input! really learn alot from u all, really appreciate it thanks!

    Can i request if anyone would be kind enough to post picts for comparision thanks!

  17. #17
    Senior Member xunjas's Avatar
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    Default Re: Crop Factor?

    http://web.canon.jp/imaging/cmos/fullframe-e/angle.html - comparisons of angle of view for FF sensor, H Sensor and C sensor

  18. #18
    Senior Member xunjas's Avatar
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    Default Re: Crop Factor?

    http://web.canon.jp/imaging/cmos/technology-e/size.html - Sizes of different Canon CMOS sensors.

  19. #19

    Default Re: Crop Factor?

    ... I thought only a few over the other forum disagree on this...

    Anyway, F/4 is F/4 as long as there's no "35mm equivalence" involved. Similarly, 17-40 is 17-40. But it's nice to have a common way to describe a setup in terms of its ability to deliver images, isn't it?

    The equivalence should be

    Xmm F/Y @ISO Z on 1.6x
    is equivalent to
    1.6Xmm F/1.6Y @ISO 2.56Z on 1x
    Assuming similar circuit design and fabrication.

  20. #20

    Default Re: Crop Factor?

    Quote Originally Posted by Clockunder View Post
    ... I think from what grantyale have posted in the past, I can guess that he is speaking from a different angle...
    It's kinda scary to realize others actually check out what you've written long ago


    And just to clarify, this discussion and that F/6.4 comment isn't meant to "bash" cropped formats. This is just what I think the right way of presenting the "equivalence". That said, all formats are compromises between image quality and size/cost/usability. The evolution of film made 35mm a great balance point for the majority, while other formats are still being used (bigger ones for the quality, smaller ones for ultimate portability - spy cams?). As we moved on to digital, a few new possibilities have emerged, say, APS(a failed film format), 4/3... I believe there's much a personal preference involved and picking one that works for you is the key.
    Last edited by grantyale; 27th October 2007 at 10:46 PM.

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