Sensor Format Nomenclature: Sakes No Mense! Or does it?

Discussion in 'Open Discussion' started by acnomad, Feb 29, 2016.

  1. acnomad

    acnomad Mu-43 Veteran

    284
    Jan 5, 2016
    Andy
    Stop me if you've heard this one.

    A little logic problem, for your amusement.

    GIVEN: The sensor size known as "Full frame" is 36mm x 24mm
    AND: A "Crop frame" sensor, such as APS-C, is CROPPED somewhat smaller to 23.6mm x 15.6mm

    DERIVE:
    A solution to the mystery as to why a 4/3" sensor is 17.3mm x 13.0mm?
    And while you're at it, why is a 1" sensor 12.8mm x 9.6mm?
    And surely, the 1/1.7" sensor couldn't be 7.6mm x 5.7mm, right? (but it is!)

    Hint 1: It's not a metric conversion issue.
    Hint 2: It's not a failure to understand the Pythagorean Theorem.
    Hint 3: Long ago, in a TV station far, far away...
     
    • Useful Useful x 1
  2. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    Sensor size is given as the perimeter of the sensor, thus 4/3" is one and a third inches around if you trace the edge, a one inch sensor is one inch, etc.
     
  3. Clint

    Clint Mu-43 All-Pro

    Apr 22, 2013
    San Diego area, CA
    Clint
    Hint 3 = The Twilight Zone :)
    and is not a TV station. It does have to do with tubes.
     
    • Like Like x 1
  4. acnomad

    acnomad Mu-43 Veteran

    284
    Jan 5, 2016
    Andy
    Good guess, but the math doesn't quite work out.
     
    • Agree Agree x 1
  5. heli-mech

    heli-mech Mu-43 Top Veteran

    959
    Mar 9, 2012
    Vancouver Island, Canada
    Andrew
    Diameters of old tv camera tubes, actual sensor size diagonally is a percentage of the named size based on the usable areas of the tubes, can't remember the percentage off top of my head. Either way its goofy and should been replaced as a naming convention awhile ago.
     
    • Like Like x 1
  6. heli-mech

    heli-mech Mu-43 Top Veteran

    959
    Mar 9, 2012
    Vancouver Island, Canada
    Andrew
    Little googling to refresh the memory and its 2/3 the named size (roughly, its not exact)
     
    • Like Like x 1
  7. acnomad

    acnomad Mu-43 Veteran

    284
    Jan 5, 2016
    Andy
    Well that didn't take long. Nicely done! Though, I have to admit, it would have been entertaining to see some more creatively incorrect guesses.
     
  8. heli-mech

    heli-mech Mu-43 Top Veteran

    959
    Mar 9, 2012
    Vancouver Island, Canada
    Andrew
    Lol, sorry. I looked that up years ago as I am reasonably good at math but couldn't make any sense of the designations. I'm sure there is some reason it made sense to carry over this naming convention to the digital world but I've never heard one.
     
  9. Hypilein

    Hypilein Mu-43 Veteran

    296
    Mar 18, 2015
    The reason is probably that naming conventions are just that. People agreeing on how to name a certain thing. Once everyone agreed to a standard it's hard to move away from it, even if the reasons for that naming convention are no longer valid.

    If we changed the names for formats now, people would be very confused very quickly as to which sensor is actually bigger when compared to older cameras.
     
  10. Bruce McL

    Bruce McL Mu-43 Veteran

    I think camera makers like having naming conventions that are not easy to understand. It makes it easier to claim that any camera is really, really good, and you should buy it right now. The weird fractions with decimals in the denominator just add to the confusion. If whole numbers were used, it would be obvious to anyone and everyone which sensor is bigger and, theoretically at least, better.

    What is even more optimum from camera makers perspective is to use different naming conventions than your competitors. They love that. How long has image stabilization been around? We still have IS, VR, OIS, SR, VC, and probably a couple more I forgot. There is no good reason for this, other than to make it easier for individual companies to sell cameras.

    To end this on a more positive note, I think the best naming convention for sensors would be based on sensor area. Square millimeters for example.
     
    Last edited: Mar 1, 2016
    • Agree Agree x 1
  11. barry13

    barry13 Super Moderator; Photon Wrangler

    Mar 7, 2014
    Southern California
    Barry
    Speaking of old conventions... Wouldn't it be much easier if aperture were expressed as
    1, 2, 4, 8, 16, 32, ...
    Or
    1/1, 1/2, 1/4, ...

    E.g. what we now call f/2.8 is 3 stops slower than f/1, resulting in 1/8 the light, so why not call it A8 or 1/8 or something like that?

    An f/0.75 lens could be 0.5 or 2/1 or whatever the math comes out as.

    ND filters are using similar notation already, iirc.

    Barry
     
  12. acnomad

    acnomad Mu-43 Veteran

    284
    Jan 5, 2016
    Andy
    Yes, I think that would be ideal. If that were the convention, manufacturers could tout the megapixel count and quietly mention the sensor area in mm^2. Thus, as they squeeze more and more pixels onto sensors, they can still advertise MP prominently (as they do now) and capture mainstream buyers who are already conditioned to looking for high pixel count, while at the same time stating sensor area for those who are looking for a specific format.
     
    • Like Like x 1
  13. pdk42

    pdk42 One of the "Eh?" team

    Jan 11, 2013
    Leamington Spa, UK
    F-stops are a ratio so whilst you can change their absolute value, you can't change the relationship to others in the series without spoiling the ratio.
     
  14. acnomad

    acnomad Mu-43 Veteran

    284
    Jan 5, 2016
    Andy
    Inverse logarithmic relationship to focal length, if I recall. Right? Going slightly OT, but my inner nerd is stretching as it awakens.
     
  15. heli-mech

    heli-mech Mu-43 Top Veteran

    959
    Mar 9, 2012
    Vancouver Island, Canada
    Andrew
    focal length/entrance pupil
     
  16. acnomad

    acnomad Mu-43 Veteran

    284
    Jan 5, 2016
    Andy
    Ah, yes. Now it's coming back to me. Multiply by 1/sqrt (2) to reduce each stop. Lots of dust accumulated on that knowledge over the years that I've just used those numbers without questioning them. I suppose that's the way we all got stuck with Qwerty keyboards too.
     
  17. Bruce McL

    Bruce McL Mu-43 Veteran

    I like the idea that the same f-stop and exposure time give you the same degree of lightness or darkness from any scene using any camera. I think this standard is one that the film makers strongly enforced, preventing the camera makers from messing it up.

    As the digital era began the film makers became less important. Still, at this time a big priority for camera manufacturers was to keep their lens sales strong. That meant not changing the mounts, or any of the writing on the lenses. :) So that opportunity for change passed.

    I think there is another standard called EV that could be used. For rating lenses, you could assume 1 second as the exposure time. That would make ƒ1.0 = EV 1, ƒ5.6 = EV 5, ƒ22 = EV 9, etc. Follow the line of 1’s in the chart below for details.

    Exposure value - Wikipedia, the free encyclopedia
     
  18. gr6825

    gr6825 Mu-43 Veteran

    277
    Oct 10, 2012
    If a Ford F-150 is a "full size truck" then what do you call an F-350 or a dump truck? I think our naming conventions are well intentioned but imperfect.
     
  19. barry13

    barry13 Super Moderator; Photon Wrangler

    Mar 7, 2014
    Southern California
    Barry
    Re apertures... Changing to
    Yes, I'd want the numbering to be consistent across all lenses and cameras... An F/2.8 lens should start at 8 or 1/8 wide open.

    I think f/5.6 is ev6, BTW.

    EV already means something else though, so a new label might need to be chosen.
    But also, I think that 1/8 is easier to grasp than '3' (aka 1/3^2), or ev4 which has an even less simple formula afaict: 1/(4-1)^2 , assuming we're starting from 1... 0 would be easier/same as above.

    Barry
     
    Last edited: Mar 2, 2016
  20. Bruce McL

    Bruce McL Mu-43 Veteran