Mirrorless focal length question

Discussion in 'Mirrorless Cameras' started by Dhalevi, Nov 20, 2015.

  1. Dhalevi

    Dhalevi TPF Noob!

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    Can anyone explain me how to choose a mirrorless lens?
    How does the mm (like 18-55) works?
    If regular dslr uses 18-200 mm what does it mean Ib mirrorless cameras?


     
  2. jaomul

    jaomul Been spending a lot of time on here!

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    Focal length is done the same on dslr and mirrorless. It's based on full frame or 35mm lens. You then apply crop factor.

    18-55 mm lens on apsc dslr gives field of view of approximately 27-82mm on Nikon, or 28-85 approx on Canon.

    If you use a mirror less apsc 18-55 is same, if you use m43, crop factors differ so it's approx 14-42 lens , Fuji or Sony is 18-55 mm
     
  3. Dhalevi

    Dhalevi TPF Noob!

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    Can you explain it again please?
    Lets say I'm buying 18-55 lens.
    What do I need to look at in the camera ( sensor Size/...) and what calculation do I need to do?
    Thanks!
     
  4. astroNikon

    astroNikon 'ya all Bananas I tell 'ya Supporting Member

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    You have to first understand what size of sensor you are buying in the camera.

    Mirrorless comes in all sizes from a FullFrame 35mm sensor to small sensors.

    The size of the sensor determines the "crop"
    35mm FullFrame sensor = 1 to 1
    APS-C sensor = 1.5x (or 1.6x) to 1
    other smaller sizes increase that amount ==> https://lensvid.com/wp-content/uploads/2014/01/Sensors-size-01-01.jpg
    as below - crop factor is the 4th row.
    [​IMG]

    You then take that crop factor, such as 1.5x for APS-C and multiple it to the lens focal length.
    So a 18-55 on a APS-C sensor would
    18 x 1.5 - 55 x 1.5 = 27 - 82.5 in perceived field of view
     
  5. astroNikon

    astroNikon 'ya all Bananas I tell 'ya Supporting Member

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    So just looking at SONY mirrorless cameras ONLY
    ==> DSLR-like Cameras | Full Frame Mirrorless Cameras | Sony US

    the first & second row is all FF sensors. Thus a 1x crop factor. 18-55 would be 18-55

    the 3rd, 4th rows are APS-C and thus are 1.5 crop factor. 18-55 would be 27-82.5

    A Canon EOS M10 is supposedly a APS-C sensor

    PowerShot G9x is a 1.0 inch sensor which is a 2.7x crop factor, thus a 18-55 would be 49 - 149

    Thus you have to first determine the sensor size before you figure out the crop factor.
     
  6. Dhalevi

    Dhalevi TPF Noob!

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    Thank you very very very much!
     
  7. Bebulamar

    Bebulamar No longer a newbie, moving up!

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    The crop factor made the assumption that people are familiar to 35mm camera. They made the assumption that people would know what it looks like in the viewfinder for a certain focal length lens when mounted on a 35mm camera. For example it makes the assumption that you know what the view is when you have a 50mm lens on the 35mm camera.
    For people who are not familiar with the 35mm camera and in fact nowaday many people never used a 35mm camera then it may be easier to describe by angle of view / focal length.
     
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  8. petrochemist

    petrochemist TPF junkie!

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    astroNikon has pretty much covered it. It's exactly the same for mirrorless than for DSLRs except for the sizes of the sensors.
    I don't think there are currently any mirrorless cameras with sensors bigger than full frame, or any DSLRs with sensors smaller than 4/3. The most common sizes are covered by both alternatives.
     
  9. beagle100

    beagle100 Been spending a lot of time on here!

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    true, I don't think there are any medium format mirrorless models (yet)
    www.flickr.com/photos/mmirrorless
     
  10. Ysarex

    Ysarex Been spending a lot of time on here!

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    Sure there are -- you just got to pay to play with the big boys:

    [​IMG]

    That's a Phase One A series mirrorless medium format digital (film too) that uses an Alpa body.

    Joe
     
  11. astroNikon

    astroNikon 'ya all Bananas I tell 'ya Supporting Member

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    It's kinda funny. My P7800 is a full DSLR featured pocket camera with no mirror box. It even has CLS (which the D3x00's don't) and a bright Digital ViewFinder, but isn't considered mirrorless as it does not have an interchangeable lens.

    And isn't the Nikon V1/J1 things have a sensor smaller than 4/3rds at 1" (13.2 x 8.8mm) and an interchangeable lens ?
     
    Last edited: Dec 10, 2015
  12. beagle100

    beagle100 Been spending a lot of time on here!

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    I stand corrected !

    www.flickr.com/photos/mmirrorless/
     

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