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FF vs M43 compression with lenses and focal length

Discussion in 'Open Discussion' started by RamblinR, Jan 26, 2015.

  1. RamblinR

    RamblinR Mu-43 Top Veteran Subscribing Member

    Aug 16, 2012
    Qld Australia
    Have done a bit of search and can't seem to find what I'm after.

    I shot the following image

    View attachment 405528 P1252063.jpg by Noonan Photo & Video, on Flickr

    Exif data shoes focal length was 25mm (equiv to 50mm compositional view to FF)

    Would this image look the same on a FF 50mm lens. Her feet and legs seem wrong, more like a wide angle lens (which the 25mm really is if it was on a FF camera)?
    Do the characteristics of a lens (according to the focal length) still come into play?
    I thought having to stand back further would correct this.

    Your thoughts on the image.

    (Shot with an EM1 with 2 YN560II flashes through umbrellas using the TX560 transmitter)

  2. The problem is relative distance and perspective. Her feet, which are closer to the camera relatively speaking, will look bigger. The effect is compounded by the fact that the subject is a child, meaning you have to get even closer to fill the frame compared to an adult. The reason why telephoto lenses reduce this effect is that by backing away and getting the same framing, the relative distance between her feet and head will be closer, thus reducing the size difference. Because you'll be at the same distance to get the same framing with a 50mm lens on a 35mm camera, the relative size difference will be the same.
    • Like Like x 2
  3. Amin Sabet

    Amin Sabet Administrator

    Apr 10, 2009
    Boston, MA (USA)
    Hi Maria, yes it would look the same. 25mm on 4/3 and 50mm on FF give the same perspective distortion for a given subject distance. If perspective distortion were a function of actual focal length, imagine how crazy iPhone pictures would look with that 4mm lens.

    It's one of the inherent qualities of a "normal" lens that is can look more like a wide or more like a tele depending on how you use it. For this kind of shot with a small child, I'd lean towards the Sigma 60mm and Olympus 75mm lenses. Any number of telephoto zooms would also work well given the controlled lighting.
    • Like Like x 3
  4. fredlong

    fredlong Just this guy...

    Apr 18, 2011
    Massachusetts USA
    I'll add to what Amin said. Perspective and perspective distortion are determined ONLY by distance. Focal length may determine what distance you need to be at to frame the image the way you want, but it is the distance that determines perspective.


    EDIT: I just looked back and see wjiang said pretty much the same thing too.
    • Like Like x 1
  5. lightmonkey

    lightmonkey Mu-43 Veteran

    Dec 22, 2013
    50mm on ff would look identical. pure function of distance. you could stand further away and crop in.
  6. bikerhiker

    bikerhiker Mu-43 All-Pro

    Dec 24, 2013
    Hi Maria,

    Nice shot, but I do agree the legs do not look all that natural.

    Anyhow, a quick explanation on compression and perspective. People confuse the two terms quite a bit. Perspective defines how a foreground element appears in relation to other elements in the scene. Perspective changes not because of a change in focal length, but because of a change of camera to subject distance. If you do not move away from your subject and simply zoom in more, you are not changing the perspective at all! And what about compression? The term “compression” has been historically wrongly associated with focal length. There is no such thing as “telephoto compression”, implying that shooting with a longer lens will somehow magically make your subject appear more isolated from the background. When one changes the focal length of a lens without moving, all they are doing is changing the field of view – the perspective will remain identical.

    So your conclusion is correct. You need to move away from the subject and use a slightly longer lens like a 45 to 50 or a 75 depending upon how far you can move back to retain the similar view. I use my 35-100 for this kind of photography and usually end up with 50 or 75 to get a more natural look.:biggrin:
    • Like Like x 2
  7. RamblinR

    RamblinR Mu-43 Top Veteran Subscribing Member

    Aug 16, 2012
    Qld Australia
    Thanks everyone.
  8. Klorenzo

    Klorenzo Mu-43 All-Pro

    Mar 10, 2014
    Just a couple more examples: move your face close to a mirror and try to notice what you actually see. Crouch near the front headlight of a car: you'll see that the close wheel is bigger than the other. Or you can also look down to the point of your feet keeping a finger close to your nose: they should have about the same size. It's just the way our eyes work.

    About compression: if you have a person at 1 meter from you and one at 10 meters you should clearly see that one appears smaller then the other and using this information you can estimate the distance. If you go back of 100 meters you are 101 meters from the first and 110 from the second: the relative difference is so small that they appear at the same distance. Add 10 more person and they will appear all "compressed" in a tight space. Usually this is hard to notice because they are too small but using a tele lens you just magnify this "view" giving you something you are not used to see.

    So you can move back and crop the picture if resolution is not important or if you want to make a few quick experiments. Also consider that your model is quite small :)  so you had to go closer than you would usually do with a full size one.
  9. dwig

    dwig Mu-43 Top Veteran

    Jun 26, 2010
    Key West FL
    +1, and both a 25mm on m4/3 and a 50mm on FF are too short to give pleasing perspective at the overly close distance you need to frame a picture like this.

    You need to shoot from a greater distance to get the pleasing perspective and you would then need a longer lens on either format to get the desired framing, probably 45-50mm on m4/3 or 90-100mm on FF.
  10. Paul80

    Paul80 Mu-43 Veteran

    Jul 6, 2014
    This is why in the days of 35mm film or FF as you know it today the most popular size of lens used for portraits was between 85 and 105mm or 150mm if you used medium format. Subjects looked better with the compressed perspective those short telephoto lenses gave, 50mm was just too wide, especially for head shots where it made noses look big. For m4/3 I would recomend not using anything less than 42mm, which most will have as it's the long end of the standard zoom or the 45 or 60mm lenses available, the Sigma 60mm being a prime example of a fine portrait lens, although it can be a tough too sharp for some subjects, but it's easier the soften a sharp picture, unlike trying to sharpen a soft image ;) 

  11. tomO2013

    tomO2013 Mu-43 Top Veteran Subscribing Member

    Oct 28, 2013
    Sigma 60mm is a lovely lens and may be more along the lines of what you need here.
    It's a bit of a bargain too! I'd even go so far as to say I prefer it to the Oly 75 :biggrin:
    Compression itself is a feature of the focal length of the lens itself. It's often mistaken with DOF. 25mm on m43 will compress the image similarly to a theoretical 25mm on FF, just the field of view and DOF will be different.
  12. dwig

    dwig Mu-43 Top Veteran

    Jun 26, 2010
    Key West FL

    The perspective (the so called "compression") is a factor of the relative distances from the camera to the various objects in the scene. It has absolutely nothing to do with the focal length, or the focal length relative to the format.

    Any FL lens used on any format camera will yield exactly the same perspective if the pictures are shot from the same position. Other than sharpness, these will also be identical if cropped to yield the same framing.
    • Like Like x 2
  13. tomO2013

    tomO2013 Mu-43 Top Veteran Subscribing Member

    Oct 28, 2013
    Not sure what I originally said that was incorrect?!?!
    Compression is a characteristic/feature of a particular focal length irrespective of sensor type the lens is attached to!
    Obviously as a photographer you have control over perspective etc... distance to subject and subject to background etc... but there is an inherent compression effect associated with each focal length lens regardless of format. This was my original point above!

    A 25mm on m43 compresses the images to the same extent as a 25mm lens would on FF. The difference is the angle of view and DOF. Shooting the same subject with a hypothetical 25mm 2.8 on m43 and a 25mm 2.8 on FF taken at the same distance to subject and subject to background, will show the 35mm format having a much wider angle of view but with she same DOF as the m43 25mm lens and the background objects will look equally compressed. I.e. the lens will behave the exact same.

    If you were to even out the FOV and DOF by shooting the FF format with a 50mm @ 5.6 and m43 with a 25mm @ 2.8 , then you will still see that while the FOV is similar, the background subject matter on the FF is compressed more than the 'equiv' 25mm shot on m43 - even though similar FOV and similar DOF (ignore crop aspect ratio for a sec!).

  14. It isn't a function of focal length. It's a function of distance. Even the article you linked to spells it out.

  15. tornado

    tornado Mu-43 Veteran

    Nov 6, 2012
    I have heard of this 25mm m43 effect stated as "Franken-Hand"...when the subject's hand is nearer the lens than the body/face.

    Here's my contribution:

    Subscribe to see EXIF info for this image (if available)
  16. EarthQuake

    EarthQuake Mu-43 Top Veteran

    Sep 30, 2013
    Right, perspective compression has everything to do with distance to subject and no inherent tie to focal length. The only role focal length plays is that for a given framing (ie, a headshot), a certain focal length (more specifically, a lens with a certain angle of view) means you'll have to be a certain distance from the subject. With wide angle lenses you need to get closer to the subject, which produces more perspective distortion. The common observation here is that the focal length is what causes this distortion, but this is completely incorrect, its the distance to subject and nothing else, as has been correctly stated many times in this thread.

    This is demonstrated very clearly in the following thread: http://photography-on-the.net/forum/showthread.php?t=672913

    I've shot with FF, APS-C, M43rds, and various smaller formats, and with a lens that provides the same angle of view, shooting the same subject at the same distance, the perspective will be exactly the same. It's very easy to test, so I would recommend anyone who disagrees with this to try it themselves. The DOF will be different with the various formats, but not the perspective. The idea that smaller sensor cameras provide different perspective is a myth.

    Here is a quick test I did, though the POTN thread above shows the same effect.

    FF 50mm:
    Subscribe to see EXIF info for this image (if available)

    M43 25mm (50mm equiv):
    Subscribe to see EXIF info for this image (if available)

    FF 200mm:

    M43 100mm (200mm equiv):

    Subscribe to see EXIF info for this image (if available)

    As shown above, this is demonstrably false.
    • Like Like x 1
  17. tomO2013

    tomO2013 Mu-43 Top Veteran Subscribing Member

    Oct 28, 2013
    THAT is what I was trying to say... or should I say, that was where I went ass ways with what I said! Typically longer focal length do not have the same minimum focus distance to subject so typically force you to shoot the scene further back. Either way I put my hand up - I got this one majorly wrong.
    Optics lesson 101. I stand completely corrected.
    Thanks for edu-ma-acting me!
  18. edmsnap

    edmsnap Mu-43 Veteran

    Dec 20, 2011
    Edmonton, Alberta
  19. bikerhiker

    bikerhiker Mu-43 All-Pro

    Dec 24, 2013
    Focal length, usually represented in millimeters (mm), is the basic description of a photographic lens. It is NOT a measurement of the actual length of a lens, but a calculation of an optical distance from the point where light rays converge to form a sharp image of an object to the digital sensor or 35mm film at the focal plane in the camera. The focal length of a lens is determined when the lens is focused at INFINITY.

    So therefore, focal length has no relevance whatsoever to perspective whereas subject distance is.
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