An uphill battle, but ...

Discussion in 'Native Lenses' started by bassman, Dec 17, 2013.

  1. bassman

    bassman Mu-43 Top Veteran

    682
    Apr 22, 2013
    New Jersey
    Scott
    ... I'll give it a try anyway.

    There are endless arguments on this and other forums about whether a lens is "really" a 24mm or a 12mm, or "equivalent" to f/1.8 or f/3.5. This, of course, comes from our habit of describing two attributes of lenses - the angle of view, and the relative depth of field, by reference to the standard of 35mm film cameras. So I thought it would be interesting if we could start a movement to describe lenses by their inherent and useful properties rather than trying to describe the field of view, for instance, as "the same for this camera as if you mounted a lens with this different focal length on a 35mm film camera".

    This table starts by talking about the field of view on the left, and then tells you what lens you would need to mount on each of several formats to achieve that.

    I realize a couple of things about this:

    1. None of us are used to talking about, for instance, an 63 degree lens when we mean our 17/1.8 on a m43 body. But all of the conversations about choosing the 17 vs. the 20 or the 25 include a discussion of the field of view, and some posters make the point that this is often the most important characteristic.

    2. This table isn't precise, in that we don't reall have a 17.5mm lens for m43, we have a 17mm lens. I would argue that the lens makers round anyway, and often ignore the fact that a DX18-200 doesn't really have the field of view implied by 200mm on a DX camera at all focusing distances. So this table would just be a start.

    3. We need to develop a similar nomenclature to talk reasonably about Depth of Field without getting bogged down into the light-gathering which is the actual feature measured by maximum f-stop. It also ignores the fact that DoF is highly dependent on a whole host of other variables, including subject distance, print size vs. sensor pixels ("enlargement"), etc. I'm pretty sure I'll get flamed to death over my much simpler FoV proposal, so I'm not going further. Yet.

    So ... what do you think? Can we start talking about whether an 84 degree FoV is enough, or we really need a 114 degrees? (For those of you who have converted yet, that means 12mm or 7mm on m43.)

    Edit: I note that I mislabeled the Width and Height rows at the top ... unless you're holding your camera in portrait orientation, in which case they're correct ;0)
     

    Attached Files:

  2. Cruzan80

    Cruzan80 Mu-43 All-Pro

    Aug 23, 2012
    Denver, Co
    Sean Rastsmith
    From what I understand, when you get into the UUWA (Ultra-Ultra-Wide Angles) the FoV tends to be more lens dependant. For example, I believe the Minolta 8mm fisheye has closer to a 180degree FoV. If you are talking rectilinear, then I apologize. Also, remember that various lens makers have different crop dimensions for APS-C.
     
  3. bassman

    bassman Mu-43 Top Veteran

    682
    Apr 22, 2013
    New Jersey
    Scott
    Ah ... 180 degrees on what sensor?

    FoV is only an approximation in any case: the diagonal is different than the horizontal which is different than the vertical, all of which are different than points in between. And the relationship amongst them changes with the different aspect ratios of FX/DX (3:2) and m43 (4:3), or the aspect ratios we can choose on some of our cameras. So I wouldn't get hung up on that degree of precision. My point is that the thing we mostly care about is field of view, and focal length is just a means to an end. So if you want a zoom which goes from about 84 to 45 degrees, you would choose a 24-70 (FX) or 12-35 (m43). Or 17-55 (DX, but not exactly for Canon's crops). And so on.
     
  4. biomed

    biomed Mu-43 Hall of Famer

    Aug 22, 2013
    Seattle area
    Mike
    I ran into this with 1/2 frame 35mm cameras. I have just about lost that "crop factor/35mm equivalent" frame of mind. It is similar to learning another language. If you can't think in the language you will probably never speak it very well. Just my opinion and not meant to offend anyone.

    Mike
     
  5. bassman

    bassman Mu-43 Top Veteran

    682
    Apr 22, 2013
    New Jersey
    Scott
    I agree, except that many of us have cameras which use different size sensors. I have DX, m43, CX, an XZ1 and an iPhone. I have no idea what "crop" those last are, nor do I really care as the lenses are not changeable. But I do care what their FoV is. In fact, the XZ-1 has the FL printed on the lens, which is pretty useless information without the crop factor.
     
  6. EarthQuake

    EarthQuake Mu-43 Top Veteran

    836
    Sep 30, 2013
    Fisheye lenses will always have a dramatically wider AOV than a rectilinear lens of the same focal length, this isn't specific to the Minolta (rokkor 7.5mm?) lens, so I assume the OP is only account for rectilinear designs here.
     
  7. bassman

    bassman Mu-43 Top Veteran

    682
    Apr 22, 2013
    New Jersey
    Scott
    Yes, the table describes the FLs needed in each format to match a desired rectilinear FoV. However, the argument is more useful for non-rectilinear lenses, where the FL merely tells you ... the FL. You always need to specify FoV for a non-rectilinear lens, as this can vary widely for a given FL depending on the actual lens design.
     
  8. jamespetts

    jamespetts Mu-43 Top Veteran

    803
    May 21, 2011
    London, England
    This is a very interesting table. It is certainly an interesting exercise. Two suggestions: firstly, might I suggest using more standardised terms for the sensor size? "FX" and "DX" are proprietary terms of Nikon (I am not sure about "CX", but I assume that that is similar). "35mm", "APS-C" and "1 inch" would be better terms. As to Micro Four Thirds, since the "Micro" part describes the registration distance, not the sensor size, "Four Thirds" might be a better description.

    Also, to have a good multi-format comparison, it might be sensible looking at the common medium format sizes and large format sizes, too.
     
  9. pdk42

    pdk42 One of the "Eh?" team

    Jan 11, 2013
    Leamington Spa, UK
    It would be great of we could get away from all this "crop factor" and "equivalence" confusion. Personally, I only shoot with one format now (u43 of course) and try to equate FOV and DOF to the native FL without going through some 35mm equivalence. Defining lenses in terms of their FOV and DOF rather than FL would be a great step forward, but I doubt the industry will accept it - the whole FL thing is embedded into the brains of too many photographers and manufacturers the world over. I even noticed that Leica Vario X (that's the one with an f6.3 fixed zoom and a $3000 price tag) has the zoom marking in 35mm equiv rather than the actual FL - bizarre!

    Of course, producing a definitive position on DOF will be hard, but I would think some approximate scale would be possible.
     
  10. bassman

    bassman Mu-43 Top Veteran

    682
    Apr 22, 2013
    New Jersey
    Scott
    It's trivial to include any format, as the calculation is very straightforward. I chose those listed as the ones most likely to be used by this crowd.

    The "crop" thing is particularly interesting or annoying, depending on your point of view, as their sensors are slightly different sizes. Nikon's DX is 23.6x15.7, as are Fujifilm, Sony and Pentax cameras. Canon is 22.2x14.8. Since they all offer the same FL lenses (eg 50mm), the FoV on the Canon sensor is slightly narrower. Maybe I should round the FoV column a bit more?

    I chose the names based on my personal Nikon inventory, but don't really care. Sony also sells cameras with the so-called 1" sensor, and doesn't call them CX.
     
  11. bassman

    bassman Mu-43 Top Veteran

    682
    Apr 22, 2013
    New Jersey
    Scott
    Ok, here's an updated spreadsheet which renames the sensor sizes, adds the Canon APS format, and suggests some convenient rounded FoV measures.
     

    Attached Files:

  12. bassman

    bassman Mu-43 Top Veteran

    682
    Apr 22, 2013
    New Jersey
    Scott
  13. dwig

    dwig Mu-43 Top Veteran

    624
    Jun 26, 2010
    Key West FL
    Since the table is calculated for only rectilinear lenses the Nikkor 10.5mm and 4/3 8mm entries in their "primes" columns should be omitted as they are fisheyes.
     
  14. Ulfric M Douglas

    Ulfric M Douglas Mu-43 Hall of Famer

    Mar 6, 2010
    Northumberland
    Edit. This was my post, I guess someone already mentioned that stupid names nonsense so I'll just quote my rant ;
     
  15. bassman

    bassman Mu-43 Top Veteran

    682
    Apr 22, 2013
    New Jersey
    Scott
    Ulfric:

    Constructive feedback is always welcome, but there's no need to rant. The first post was just a place to start the conversation.

    As you can see, I've updated the table to include both Nikon and Canon APS-C sizes, and also renamed some of the columns. I chose commonly used names, and in some cases, I'm not sure what they even mean.

    Nikon uses CX to describe their 1" sensor format for the 1 Nikon series. What is 1", anyway? It's used by both Nikon and Sony, but I don't see any measurement that approximates 1" in the spec.

    "Full Frame" is, and has been, a common name for so-called 35mm film cameras for many years, and was carried forward to describe the digital sensors that approximated that size.

    There are a whole set of "medium format" cameras and image sizes: 60x45, 60x60, etc. Each would need to be listed separately, just as the two APS-C sizes are above. And given the tiny number of cameras in that class used by the members of this forum, I elected to omit them. I think it would just clutter the table.

    The formula is pretty simple, and anyone can do the calculation:

    =2*arctan({sensor dimension} / (2*{focal length})) * (180/3.14159) )

    The last term (180/pi) converts radians into degrees. The actual formula I used in Google docs for arctan is atan. As I said above, I deliberately rounded some of the numbers for convenience.


    Dwig:
    I included the two fisheyes as they are the only way to get that wide FoV in those formats. I admit to not knowing what they would really show after rectilinear-izing and/or cropping. Anyone know the answer?
     
  16. bassman

    bassman Mu-43 Top Veteran

    682
    Apr 22, 2013
    New Jersey
    Scott
    I've been working on a project to shoot my guitar collection, and I think I'll continue with the 40 degree view on the E-M5, so the 12-35 will be my lens of choice. I could go to 45 degrees and use the 25/1.4, but that would mean stepping back some more in the room. I like being this close. And I don't need nor want the shallower DoF, as I'm shooting at f/8 anyway.

    Just sayin' ...
     

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  17. dwig

    dwig Mu-43 Top Veteran

    624
    Jun 26, 2010
    Key West FL
    In m4/3, and most formats today, life revolves around zooms. You might consider adding a column, similar to the one in the m4/3 section of my mockup, to indicate the range of FLs availble in zooms.
     

    Attached Files:

  18. WT21

    WT21 Mu-43 Hall of Famer

    Feb 19, 2010
    Boston
    I honestly don't care, personally. I've got a good feel for 135 format, so I can translate pretty easily.

    If everyone started talking about FOV, that'd be fine, too.

    However, what's the point of "diagonal" FOV. Most people who are mathematical can grasp the 35mm eq dialog. They can also understand diagonal FOV. However, most of the time, you aren't choosing a lens based on a diagonal FOV. You are choosing it based on either horizontal (landscape) or vertical (portrait) FOV. Of course, there are different aspect ratios, but if you get too technical, you'll loose people again, in which case -- what's the point?

    So, if you stick with just horizontal FOV, and people can get comfortable with 45 degree, 90 degrees, 12 degrees, etc. That could be good. But, when you get to telephoto, can you really make sense of 5 degrees vs. 1.5 degrees? You start to lose the power of the descriptor.

    Lastly -- you'd have to convince all the manufacturers to make changes, and what do you do with legacy lenses that are already inscribe with FL?

    People want a magic bullet around this, but IMO there just isn't one. At least, not as long as there are such a variety of aspect rations and sensor sizes.
     
  19. fredlong

    fredlong Just this guy...

    Apr 18, 2011
    Massachusetts USA
    Fred
    In video, a 1" sensor's height and width total 1". The standard predates wide screen so 3x4 image ratio is assumed. I believe it goes back to vidicon tubes, the 1950s version of a sensor.

    Fred
     
  20. beanedsprout

    beanedsprout Mu-43 Veteran

    429
    Apr 13, 2013
    north central Ohio
    Ok one thing iim sort of confused on. f2.8 lets in twice as much light as f4. Our sensor size is 1/2 of 35mm, therefor we need 1/2 the focal length to get equivalent field of view. But how does the aperture translate to dof? Do you double it f2.8 becomes f5.6, (effectively decreasing the amount of light four times) or do you double it f2.8 becomes f4? Assume subject distance is the same for each.