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Is the 2x Crop Really What It Implies?

Discussion in 'This or That? (MFT only)' started by Clint, Jan 23, 2016.

  1. Clint

    Clint Mu-43 All-Pro

    Apr 22, 2013
    San Diego area, CA
    Clint
    I just read through Robin Wong’s review of the new 300mm f/4.0 lens. An excellent review with incredibly sharp images. Robin’s knowledge and skill levels certainly paid off for this review of a very fine lens. If I regularly shot with a super telephoto or if I had professional requirements – I would have preordered the lens!

    One thing really caught my attention, and that was when he started discussing the MC-14 1.4x Tele convertor and his moon shot.

    What hit home with me was two things – the 2x crop factor that so many rely on or believes in.

    When I moved from 4/3s to Nikon, I never found a way to do an accurate comparison that would be hard to disparage. Is that 2x crop really 2x? Does it really make a difference? Take into account the cameras, the internal processing, the crop factors, the actual diagonal measurements of sensors and how those play out with the differences in the final number of megapixels actually produced – and it really gets pretty complicated. In all, I moved to Nikon because Olympus’s dismissal of the 4/3s format cameras. But I really wanted lighter and smaller – and so eventually I moved to and predominately use m4/3s.

    However the second thing that that caught my attention was Robin’s moon shot. Wow, I had something that I could make a comparison with! Yet again, considering all factors – the tools become a choice of the user – and the tools are outstanding. Again - If I regularly shot with a super telephoto or if I had professional requirements – I would have preordered the lens! It just depends what you want and how the final result will be used.

    To my point – a photo of the moon – (an interesting comparison with Robin Wong’s shot - if this does not directly to the intended photo, the moon shot is 28 of 43 of his posted shots )

    Below is a photo taken May 3, 2012, came from a D7000 (16mp), 1/250, f/8.0, ISO 100 with the Nikkor 80-400mm f/4.5-5.6 VR at 400mm, a 2002 lens. Original image size was 4928 x 3264, cropped to 1658 x 1244, and reduced in size to 1200 x 900 in Lightroom. To get the best out of the lens I should have been at f/11 or f/13, but I wasn’t.

    full.

    All said and done, the 50-200mm just isn't getting to the equivalent of a 400mm lens anyway you look at it.
     
  2. wjiang

    wjiang Mu-43 Hall of Famer

    It comes down to the elements presented here:
    Optical resolution - Wikipedia, the free encyclopedia

    Cropping digitally by removing pixels simply degrades the sensor resolution component of the system resolution. You can't avoid severe degradation from cropping the pixels out. If your lens is excellent, and you don't crop too many pixels out, results might still be good.

    Getting a longer focal length lens or using a dedicated teleconverter may or may not significantly degrade the optical resolution, depends how good the new optical combination is. e.g., cropping the 75mm f/1.8 compared to using the 35-100mm f/4-5.6.

    Going to a different sensor format may or may not degrade the sensor resolution. Despite the talk of 'crop sensor', it isn't cropping. It depends on the sensor size, pixel pitch, number of pixels, noise, cross-talk, etc. It may also degrade the optical resolution due to diffraction. Your lenses are also likely to be different, making the comparison rather difficult. e.g., trying to compare a cheap 75-300 on 24MP APS-C to the 40-150 PRO on 16MP m4/3... :confused:
     
  3. sesser

    sesser Zen Master

    489
    Mar 10, 2015
    Portland, OR
    randy
    From my understanding, a 200mm lens on a 4/3 sensor does not equal 400mm lens on a FF camera in terms reach. Id est, the focal length of a 200mm lens is still 200mm no matter the sensor size. What you do get is a 400mm angle of view (about 5º). If you want the reach of a 400mm lens, then you'll need a 400mm lens... which on a 4/3 sensor, has a viewing angle of about 2.5º.
     
  4. budeny

    budeny Mu-43 All-Pro

    Mar 4, 2014
    Boulder, CO
    That is 2.85 diagonal cropping, so your effective focal length would be 400 * 2.85 = 1140mm.
    I'm not sure how Mr. Wong defines 50% crop, but if he goes by area (rather than by diagonal) then his lens effective length will be to 300 * 1.4(MC-14) * SQRT(2) = 1187mm
    Pretty close and images look similar.



     
    Last edited: Jan 24, 2016
    • Like Like x 2
  5. wjiang

    wjiang Mu-43 Hall of Famer

    Reach has no technical meaning in optics and imaging. Usually people take it to mean 'how small a subject will fill the frame at a given distance with this lens' or 'how close do I need to be for a given subject with this lens', both of which are entirely related to angle of view.

    The correct terms are focal length and angle of view, but rarely does true focal length matter for imaging (especially digital) except when talking about aperture and f/stop, or when doing macro where the simple equations break down.
     
    • Agree Agree x 1
  6. wjiang

    wjiang Mu-43 Hall of Famer

    Great comparison. You can see that at the end of it, the 300mm + TC + 16 MP (cropped to 4 MP) 4/3 clearly has more resolution than this particular 400mm + 16 MP (cropped to 2 MP) APS-C. What made the difference? Probably both the optics combined with the huge difference in the number of pixels.
     
    Last edited: Jan 24, 2016
  7. budeny

    budeny Mu-43 All-Pro

    Mar 4, 2014
    Boulder, CO
    Ups, I didn't count in APS-C crop, so it should be 400 * 2.85 *1.5 = 1710mm for Clint's image (2 MP)
    So, Mr Wong must be using 50% crop by diagonal that will give us 300 * 1.4(MC-14) * 2 *2 = 1680mm (4 MP)
     
  8. Klorenzo

    Klorenzo Mu-43 All-Pro

    Mar 10, 2014
    Lorenzo
    The 2x crop factor is just a simple number commonly used. To get that number you need to take the 18x13.5 sensor, cut it to a 3:2 format (18x12) then you compare the diagonals.
    Otherwise you can choose to consider the uncut sensor diagonal, the height or the width getting 1.92x, 2x, 1.77x respectively.

    If you look at diagonal angle of view of an 85 and a 42.5 you get 28.6 degrees on FF and 28.6-29.7 (Panasonic declares 29) on m43. With the Olympus 45 you have 27-28.6 degrees (Olympus declares 27) (the two values are with 1.92x and 2x conversion). Seems like Pana went with the 2x and Oly with the 1.92x.

    Then you could have a little focus breathing, but considering the Moon you were almost at infinity.
     
  9. tkbslc

    tkbslc Mu-43 Hall of Famer

    Short answer to thread title = Yes.