Question + Thoughts on Crop Factor.

Discussion in 'Photography Beginners' Forum' started by Innocence, Mar 4, 2007.

  1. Innocence

    Innocence TPF Noob!

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    I have heard time and again different things but I came to my own conclusion that:

    A APS-C(? 1.6x or 1.5x crops) literally crop the field of view - but does not do anything regarding magnification. [1]

    But I hear many many experienced shooters say that crops are better if you want more reach. [2]

    I completely rejected [2] based on [1].

    Now.
    I have just then thought of something else.

    The crops give a higher erm - forgive my bad terminology but - pixel density within the same frame compared to a FF when cropped.

    Which means that the person with the FF would have to zoom in, or step closer to get the same FOV as on the crop with the same resolution.

    Thus, I have now decided to reject [1] in favour of [2] because it seems that it does "bring things closer" if you think about it. (since the FF would have to zoom or walk in further towards the subject)

    And I know that there are quite a few followers of each view here, so thought I'd share and ask for help. :heart:

    Note [2] doesn't really say anything about the increased "reach" or maginification but purely by the above argument would it be wrong to conclude that they are one and the same?

    I surely hope I haven't lost anyone. :mrgreen:

    Haha, after so much thought, I want the answer - and the reasoning behind it, preferably with lots of equations haha. (jk about last bit).
     
  2. fmw

    fmw No longer a newbie, moving up!

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    You are right in your first conclusion. Focal length (and camera to subject distance) determines magnification on any camera and in any format, film or digital. However, the field of view can be quite different depending on the image circle (coverage of the lens on the film) and the frame size.

    A 50mm lens shooting an image of a person produces the same size person on any format at the same distance between camera and subject. However, on a medium format, the image circle and frame size are larger than on a 35mm camera and the result is a wide angle of view. You see more of the surrounding area around the person. On a 35mm camera, you would describe the angle of view it produces as "normal" and on an APS sized digital would describe it as modest telephoto. So a 35mm camera crops the subject from medium format just like APS crops it from 35mm.

    Two things affect magnification. The first, as you know, is the focal length of the lens - a longer lens brings subjects closer. The other is the distance between the subject and camera. This is what affects perspective. If you fill the frame with the 50mm lens on the APS sized frame, you will get a reasonably nice portrain perspective. If you fill the frame with a 50mm lens on a medium format camera, you will introduce perspective distortion, not because of the focal length of the lens, but because of the shorter camera to subject distance.

    All 50mm lenses have the same amount of "magnification." However what size frame you use to project the image upon and how you use the lens in terms of subject distance can greatly affect the result. Hope this helps clarify it a little.

    Sorry, I don't do equations. I just do photography.
     
  3. Orgnoi1

    Orgnoi1 TPF Noob!

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    fmw hit it directly on the head... there is no "advantage" to shooting with a cropped camera really over a FF camera... because of exactly what you said... since there is no magnification whatsoever with using a camera with crop. The only thing really you ARE doing is making it so you CANT crop as much... I routinely shoot wildlife with my 5D and 500L... do I need to get closer? No... because if I want to crop the edges of the image it would make the exact same image as say with a 20D or 30D... yet its a choice *I* have... not the camera forcing me to move forwards or backwards...
     
  4. Alex_B

    Alex_B No longer a newbie, moving up!

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    :grumpy:

    I am too late, all has been said

    ;) :)
     
  5. Alex_B

    Alex_B No longer a newbie, moving up!

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    Ok, still I want to say at least something ;)

    [1]: true, in the same way as MF does not magnify compared to LF, and 35mm film does not magnify compared to MF .. given you use a lens of the same focal length on all of them.

    However, when you print from all three of them to the same sized print, then the object will appear larger on the print from 35mm film than on the
    print from MF or LF. Of course resolution will be lower then on the print from 35mm, given that you use the same type of film in all three cameras.

    With sensors things are a bit different, since smaller sensors often have higher pixel density, but then again this gives other disadvantages.

    So [2] holds true composition wise when you want to use your whole frame for your later prints.

    If you use full frame 35mm or a crop camera depends on personal taste, your type of shooting, and, unfortunately on your bank account.
     
  6. Don Simon

    Don Simon TPF Noob!

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    I still find the term 'crop factor' a bit misleading. I don't see how it literally crops; to my mind cropping is removing parts of an image, whereas the 'crop' sensors simply do not capture an image with the same field of view as a 35x24mm area of film/sensor. In particular I don't see how 'cropping' is relevant if you use a lens specifically designed for these smaller sensors. I guess what I'm trying to suggest is that the concept is only comparative, which is often misunderstood since people often talk about lenses of one focal length 'being' another on a digital body.
     
  7. Alex_B

    Alex_B No longer a newbie, moving up!

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    Oh yes, in people's brains it is all messed up, but that is partially to be blamed by companies and shops, who often either don't properly explain it to people or explain it in strange ways that would even confuse you or myself :p

    I think one of the problems is, that on smaller compact digital cameras with tiny sensors, you hardly ever have the true focal length printed. Normally you read the 35mm equivalent, whereas for dSLRs the true focal length is given on the lens.

    I remember some people on here were asking if on Canon EF-s lenses the focal lengths were given as "corrected focal lengths" .. it is all a great confusion among beginners ...
     
  8. Orgnoi1

    Orgnoi1 TPF Noob!

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    If you look at an image circle for a camera... it is a little easier to understand... but yes... a crop camera DOES crop the sides of the images... the way that they get around "seeing" it is through a smaller view finder... a crop camera does not use the full lens... only the center portion of the element in its image (which is why you will NEVER see vignetting on a crop camera image no matter how hard you try) where as a full frame sensor or 35mm camera uses the whole lens (and is more sensitive to vignetting)
     
  9. Orgnoi1

    Orgnoi1 TPF Noob!

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    The reason for EF-s lenses goes two fold.. they are cheaper to make and they make use of the full piece of glass vs. a 35mm lens on a crop camera where it only uses the center portion... it does not change the focal length...

    The easiest way to explain that... is to do it with a fisheye lens... the center of a fisheye is somewhat "normal" where as the outside edges are somewhat (ok very) distorted. If you take 3 cameras... a 5D, a 1D (mark II) and a 20D/30D and use the same lens to take the same picture you will notice that the 5D has almost a 180 degree image (FOV)... the 1D will have somewhere around a 150 degree image (guesstamating), and the 20D/30D will look like you arent even using a fisheye... the reason is that the smaller sensor is only reading the center portion of the lens (as I stated earlier) so its not getting the same fishy effect... but if you look at the EXIF the focal length never changes... its still a 15mm fisheye... you arent magnifying... you are taking away from the full size of a perceived image on a full frame sensor because the sensor is smaller
     
  10. Don Simon

    Don Simon TPF Noob!

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    Surely, the "crop camera" only uses the centre of the lens but only assuming the lens was designed for 35x24mm? The lenses designed for these "crop" sensors (like EF-S) are for a smaller image circle.
    Even when using lenses designed for 35mm "full frame" cameras on smaller sensors, I'm not sure if it's actually "cropping" anything, that part of the image simply wasn't captured by the sensor in the first place. But this part is basically just me being diffifcult and pedantic about my definition of a "crop". if on the other hand it's a lens designed for the smaller sensor being used on a smaller sensor then I'm not sure how there's any cropping.
     
  11. Orgnoi1

    Orgnoi1 TPF Noob!

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    I agree cropping is probably a bad term... but for lack of a better one you are correct... you arent *technically* cropping the image... you just arent receiving the data in the areas that the sensor doesnt *see* which is effectively cropping the image that the lens can see... the reason they do different lenses is that they adjust (in some instances) the curvature of the glass and put a much smaller rear piece of glass on so the image circle is adjusted to the smaller sensor... but no matter which way you look at it... 18mm is still 18mm... as well as 600mm is still 600mm
     
  12. fmw

    fmw No longer a newbie, moving up!

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    I never liked the term "crop factor" either. APS is simply a different format from 35mm. The fact that you can use a lens designed for a 35mm camera is irrelevant. The fact that the lens may have an image circle larger than necessary is irrelevant. It is just a different format just like 120 medium format is a different format. But I guess the term is useful when comparing 35mm cameras to APS digitals. The only reason people get confused is that cameras in the two formats look similar and can use the same lenses in some instances.

    People don't seem to get confused when comparing 35mm to medium format. The reason, I assume, is that they don't normally share the same lenses even though they may share the same focal lengths.
     

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