"Normal" definition and application to m43s vs. FF equivalent; maybe why 20mm/1.7 is so perfect

Discussion in 'This or That? (MFT only)' started by LovinTheEP2, Oct 1, 2013.

  1. LovinTheEP2

    LovinTheEP2 Mu-43 Top Veteran

    Feb 15, 2011
    I was today trying to understand why the 20mm focal of the 20/1.7 seems to render very nice photographs. Outside of the quality of the lens build and design. There is just some about how it composes images I find.

    So I was looking into what the definition of what a Normal lens is mathematically and why it's typically 35mm (on a full frame equivalency with respect to focal length due to crop).

    I didn't realize the definition was based on the diagonal size of a 35mm frame. ie a 36x24 frame yield a length of 43.3mm (never really thought about it) so Normal (not wide or telezooms) is about 45mm and not 35. 35mm could be common due to some really good glass at the focal having been selected way back when and everyone got used to composing with it.

    So taking that into consideration..what's a NORMAL view on a 35mm shouldn't be the same on a CROP sensor by definition.

    On a m43 sensor of 17.3x13, yields a 21.6mm focal for NORMAL.

    Exactly where the 20mm/1.7 renders. Additionally, apply the 2x crop yields 42.8mm; pretty much equivalent to a 43.3mm full frame normal by definition which is expected.

    That might be why I don`t particularly care for the images taken with the 17mm prime lens but the 20 seems to be a sweet spot. I feel the crop effect is more pronounced for smaller focal lengths due to the compression effect and to get a similar `Feel` of a full frame 35mm, taking it a 20mm on a m43 might be more stylistically the same.

    So for me.. I consider the 20mm focal length the real normal on a m43 system vs. 17mm when attempting to achieve the same image of 35mm full frame image. Yes it will be a tighter composition but a more normal less compressed rendering.

    Curious what others think..
  2. LovinTheEP2

    LovinTheEP2 Mu-43 Top Veteran

    Feb 15, 2011
    Applying the math to the Sigma DPx cameras, I have struggled with which one to get if I had been my only camera as I didnt feel like either the DP1 or DP2 seem to be perfect with respect to normal range images (not talking sensor performance of RED shift, iso etc).

    Looking at the math:
    Sensor yields a Normal lens of 25mm (24.8mm) for the non-Merrills editions (DP#, DP#s, DP#x).

    DP1: 19mm (32mm equivalent using 1.7x crop)
    DP2: 30mm (51mm equivalent using 1.7x crop)
    DP3: 50mm (85mm equivalent using 1.7x crop)

    So Sigma went purely route of std 35mm typical std lens of 35mm, 50mm, 85mm and created a system whereby there is no NORMAL street camera for its sensor size.

    DP1: 19mm is 6mm to wide for normal. Which is fine, as I always considered it wide and good for landscapes etc.
    DP2: 30mm is 5mm to LONG for a pure normal based on the sensor size. I guess thats why I never really clicked with it and finally understand why.

    The Sigma DP merrills have a larger sensor and 1.5x crop, the DP2m (28.2mm and lens 30mm and 45mm equivalent if 1.53 is used for crop factor) is near the sensor normal and I guess I should look at the DP2m more. For some reason, I didn't pay close attention to the fact the Merrills sensor was significantly larger then its previous variant.

    I realize the definition of practical wide, normal and zoom is a Range and not just 1 number for each and there is overlap. So normal can be 25mm-40mm full frame equivalent and wide is 8mm-30mm etc.
  3. Tilman Paulin

    Tilman Paulin Mu-43 Veteran

    Jun 10, 2013
    I think you may have got your numbers mixed up in regards to the Foveon cameras:

    The "first generation" (e.g. DP2, DP2s, DP2x) had a 1.7 crop factor.
    The newer DP merill generation has a 1.5 crop factor.

    The DP2,DP2s and DP2x were advertised as 41mm equivalent. They actually had a 24.2mm focal length.
    (Loved that focal length, just as I now like the Pana20mm on m43.)

    The DP2m went up to 45mm equivalent (30mm with 1.5 crop factor), part of the reason why I didn't upgrade to it...
  4. LovinTheEP2

    LovinTheEP2 Mu-43 Top Veteran

    Feb 15, 2011
    As I was writing the post I double checked my understanding of the FOVEON and noticed 1.7 and 1.5 so I looked into further and amended my post before I saw yours. Thanks for the heads up. I don't know why I never realized it wasnt just an improved sensor but a larger one to boot.
  5. Tilman Paulin

    Tilman Paulin Mu-43 Veteran

    Jun 10, 2013
    no problem... doesn't happen every day that a camera manufacturer changes the sensor size from one generation to the next :)
  6. cmpatti

    cmpatti Mu-43 Veteran

    May 8, 2011
    Berkeley, CA
    I think this is a false attempt to apply some mathematical rationalization to your preference in focal length. It's really just a coincidence that you're preferred focal length (mine too, by the way) happens correspond to the image diagonal. Others prefer 35mm equivalent and others 50mm equivalent (and some longer), but those are just personal preferences. There's no mathematically provable "correct" answer. Same applies to some people's obsession with the "golden mean."
    • Like Like x 2
  7. meyerweb

    meyerweb Mu-43 Hall of Famer Subscribing Member

    Sep 5, 2011
    To the OP:

    I don't think a 35mm lens has EVER been considered a "normal" lens for 35mm cameras. 35mm refers to the length of the frame, not the lens. 35mm lenses are, and always have been in my experience (with my first 35mm camera coming about 1967) considered wide angle. Every vendor of 35mm SLR cameras that I am aware of offered "normal" lenses around the 50mm mark. I recall a few in the 47-49mm range, and a few as long as 58mm, but never a 35mm "normal."

    Many small P&S cameras did come with a non-interchangeable 35mm lens, but even those were considered slightly wide, and that focal length was generally a compromise of a number of factors, including small size, greater DOF to lessen the importance of focusing errors, and an FOV that offered a somewhat wide angle, but could still be cropped to a "normal" FOV without much loss in quality.

    As far as the definition of "normal lens," you can find several. The diagonal of the frame is one. But in the early days of SLRs the "normal" was often the focal length that matched the view through the viewfinder with what the unaided eye saw, making it relatively easy to keep both eyes open while shooting.

    As for the framing of the 20 vs. the 25 (which nominally corresponds to a 50mm "normal" on 35mm cameras), I think it may have more to do with the difference in aspect ratio. A 20mm on 4:3 matches more closely the horizontal field of view of a 50mm on the 3:2 aspect ratio of 35mm film. And we typically notice the horizontal FOV much more than we notice the diagonal.
    • Like Like x 2
  8. jloden

    jloden Mu-43 Hall of Famer

    May 15, 2012
    Hunterdon County, NJ
    Pretty much my thoughts.

    You could argue that the images from a 20mm on m4/3 look more 'natural' to you because the focal length is closer to the human eye, but I don't believe there's any correlation between that and successful or compelling images. I think what you're seeing is mostly about what your preference in focal length is - and that's largely borne of familiarity (the rest is down to artistic vision).

    I've shot with all sorts of focal lengths over the past few years and my experience has been that you can feel natural and create successful compositions with a wide range of focal lengths, given the requisite time and effort. Most people decide at some point they like 50mm, 35mm, etc. and very rarely decide to step out of that box for long enough to get past the initial discomforting feeling of unfamiliarity.

    I won't bore you with all the details, but suffice to say that at various points I've thought for sure I was dedicated to a specific focal length that resulted in better compositions, a more natural look, etc. Finally after enough experience shooting different focal lengths for a long enough period of time, I realized that it had a lot more to do with just getting past the "learning curve" - or perhaps "comfort curve" would be more accurate - of a specific FOV.
  9. mh2000

    mh2000 Mu-43 Veteran

    Jul 3, 2010
    >>I think this is a false attempt to apply some mathematical rationalization to your preference in focal length.

    I agree with this. Going from one format to another is not an exact science when it comes to actually composing real shots. Just the ratio of the sides being different changes how you have to compose for balance.

    I mostly grew up with 50's on 35mm film and am quite comfortable with them. I shot a 58mm Biogon for a while and thought it was too tight, but now on m43 I am loving my Sigma 30 as my go to "normal" lens. Instead of worrying about the FoV's, I'm just shooting it.

  10. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    I like normal lenses. Over the years I've owned several (XPan, Contax). It feels completely neutral with no real compression or expansion in the image relative to my eyes interpretation. I would choose a normal over either a 35 (sometimes called a wide normal) or a 50 (long normal). But if I can't get one I tend to choose a 50. I don't get on with 35's. Never have.


    p.s. the maths is correct. A 43mm lens (35mm format) is a normal (neutral) for most, but not all people. But I agree that it doesn't necessarily translate to a real reason to choose one, although many people do prefer the 43mm length over the more common 35's and 50's.
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