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Focal lenght double or not?
  • Rivo_KikkulRivo_Kikkul

    We all know that with the m4/3 sensor all m4/4 glass we have to double the marked focal length but I remember I did a test in the spring with 14mm Pana and 28mm FD and field of view was almost the same as far as I can remember or I make this up and the FD was ~56mm for me? Little confused right now...

  • 18 Replies sorted by
  • Vitaliy_KiselevVitaliy_Kiselev

    14mm is 14mm, 28mm is 28mm. They are not the same on same camera, even if first is m43.

    http://www.personal-view.com/faqs/camera-usage/general-camera-usage-faq

    And we also have flame topic about it somewhere.

  • goannagoanna

    http://filmsbyshaun.com/the-switch-to-micro-43-and-super35-equivalent-fov/

  • Vitaliy_KiselevVitaliy_Kiselev

    @goanna

    Your link is good, but confusing related to the original question.

  • goannagoanna

    image

    CROP FACTOR & FOCAL LENGTH MULTIPLIER

    The crop factor is the sensor's diagonal size compared to a full-frame 35 mm sensor. It is called this because when using a 35 mm lens, such a sensor effectively crops out this much of the image at its exterior (due to its limited size). http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

    Math: To calculate comparable angles of view new lens mm = (new format diagonal / old format diagonal) times old lens mm - FDTimes

    (There's also a lot of other stuff on this link about other effects of sensor and lens sizes - on image quality, lens weight etc. I do hope expressing the same message of focal length and crop factor in slightly different ways will help clarify the issue ..)

  • BurnetRhoadesBurnetRhoades

    Most of the references incorrectly state a crop factor for MFT which has no crop factor being that it's a mount not a sensor definition. Almost all assumptions based on common sensor sizes for MFT get the GH2, the BMCC and BMPCC totally wrong.

    It's also a term and a short hand that really only has relevance for stills photography. It's totally inappropriate when discussing motion pictures and video where the reference there is not 135-format film and a 36mm effective sensor size. If one were using reference material discussing a particular DP's selection of lenses for a particular film then this "crop factor" is not relevant or accurate.

  • goannagoanna

    @BurnetRhoades

    I'm surprised (and pleased) to still hear of comparisons to lens sizes from motion picture film. I still - or would like to think - I still shoot on film. (I maintain my two 35mm movie cameras, a couple of working 16 and super-16s, and a fridge of film stock in forlorn hope of TV commercial shoots)...

    However, I personally have come to think of "35mm equivalent" benchmark, just as most people do nowadays. As far as I'm concerned, a 50mm lens or equivalent is normal and it'll stay that way, just as a 25 equiv is wide, an 85 is portrait and a 300 is for bird watching.

    See Wikipedia on Normal Lens

    In cinematography, a focal length roughly equivalent to twice the diagonal of the image projected within the camera is considered normal, since movies are typically viewed from a distance of about twice the screen diagonal. Anton Wilson, Anton Wilson's Cinema Workshop, American Cinematographer, 2004 Page 100.

  • BurnetRhoadesBurnetRhoades

    But that's just it, "35mm equivalent" has two different meaning. One for stills, generally. A few for motion pictures. They're being mixed here. That also doesn't change the fact that the FOV calculations in the linked sites aren't correct for the GH2 or address the fact that MFT is a mount, not a sensor size.

    "Normal" is another issue entirely. It also doesn't help, any more than the standard definition of "crop factor", anyone referencing the lens package for a given film and wanting to match FOV as close as they can with the camera they possess. 'Sall I'm sayin'.

  • goannagoanna

    "35mm equivalent" has two different meaning. One for stills, generally. A few for motion pictures.

    They must not be mixed, of course. But, other than in American Cinematographer Magazine, I rarely hear any reference to film lens sizes.

    For me, a "normal" lens is a wonderful thing. You need to get a feel for which size is just right (for each camera) to put the viewer right amongst the scene.

    http://www.personal-view.com/talks/discussion/comment/103182#Comment_103182

    "Normal" is another issue entirely. It also doesn't help

    Yes, it does. It helps - and is really all a thinking photographer needs to know. The "normal" lens for your camera is your benchmark, from which you extrapolate what sized lenses will be wider or longer.

  • vicharrisvicharris

    Is it me or does this topic come up every 6 months?

  • jpbturbojpbturbo

    Only every 6?

  • BurnetRhoadesBurnetRhoades

    other than in American Cinematographer Magazine, I rarely hear any reference to film lens sizes.

    You'll read more references to the lenses used on films reading about films. ACM is but one source. If someone wants to know what's used on films and why movies look and feel the way they do, well, there you go.

    Why else would anyone even want to do FOV conversions between MFT and Super-35? Unless they're reading about the use of cine lenses (and 85mm is 85mm no matter cine or SLR) it's not likely to ever come up. It's not relevant unless you're reading about the use of specific focal lengths in motion pictures.

    It's the kind of question one might ask and look for the answer to when they read something like Harris Savides talking about shooting The Game with David Fincher. They shot the wides on a 27mm. They shot the close-ups on a 75mm. "Crop Factor" (at least relative to 36mm format film) or "normal" aren't part of the equation when what you want to know is "how do I achieve the same FOV on the GH2?"

    What's important is knowing the film was shot on Super-35mm, so a 24.89mm film width. The GH2 has a 19mm sensor width shooting video. That means you'd need a 20-21mm lens for the wides and a 57-58mm for the close-ups, if you were looking to match the FOV on the GH2.

    That "Films by Shaun" link you posted on Oct. 10 gets it wrong, because he's using the AbelCine calculator which isn't accurate for MFT cameras in general, the GH2, or the BMPCC in particular. Both MFT cameras of entirely different sensor sizes.

  • BurnetRhoadesBurnetRhoades

    @vicharris

    Is it me or does this topic come up every 6 months?

    You're likely right. The same bad links keep getting sent around too that don't help. It's one of the worst side effects of DSLRs leading the revolution. Too much baggage from stills conventions.

  • goannagoanna

    @BurnetRhoades

    Which of the motion picture formats would you like to compare your M4/3 lenses to?

    image

    • Super 35?
    • Panavision 35mm standard?
    • Academy (1:33:1)?

    (or any of the others: Cinemascope, different perfs, etc etc?)

    • My academy 2" (35mm motion picture film camera) lens (51mm) shows the same FOV (top to bottom*) as my GH2 at 35mm
    • My academy .7" (35mm movie camera) lens (18 mm) shows the same FOV (top to bottom*) as my GH2 at 28mm

    *Top to bottom FOV is used for reference. However, sideways, my movie cameras use a 2X anamorphic, whereas the GH2 is usually set at 1.77:1

  • Vitaliy_KiselevVitaliy_Kiselev

    Is it me or does this topic come up every 6 months?

    May be law makers could make something with special tax for talking about crop factors?

  • goannagoanna

    May be law makers could make something with special tax for talking about crop factors?

    I believe such discussions just naturally get moved to the far end of the barbecue area, carrying on until midnight while all the dancing takes place on the patio..

  • Vitaliy_KiselevVitaliy_Kiselev

    @goanna

    Nope, it'll be special places hidden deep inside Chinatown :-) with bodyguards and special payment and face check required to enter.

  • BurnetRhoadesBurnetRhoades

    Which of the motion picture formats would you like to compare your M4/3 lenses to?

    Okay, now I think we have a language barrier. Nevermind.

  • goannagoanna

    This has been said before: One day we could all use different, universal numbers to describe a lens besides its focal length.**

    I was just checking the specs of my binoculars and was reminded how the fraternity of (non-photographer) lens users use a refreshingly simple way of expressing some measurements:

    from Guide to Binoculars - Opticron:

    image

    from Nikon USA Support:

    Question: What do the numbers that appear on a binocular mean?

    There are three basic descriptive and performance numbers on every binocular. These include magnification/power, objective lens diameter in millimeters, and real angle of view. For example the Nikon 8x25/5.6 Travelite V binocular has 8x magnification, 25mm objectives, and a real angle of view of 5.6 degrees.,

    The first number (8x) is the magnification, meaning the image of the subject you see through the binocular is 8 times larger than visible with the naked eye. Objects at 100 yards appear only 12.5 yards away (100 yards divided by 8).

    [of less use to us photographers:]: The second number (25) is the diameter of the objective lenses in millimeters. This is a major factor in determining how much light enters the binocular. For example a 25mm lens will capture less light than a 50mm lens.

    The third number printed on all Nikon binoculars is the real angle of view in degrees (5.6 in our example). It represents the segment of a 360-degree circle that the binocular is designed to view. The higher this number, the more of the subject you see from side to side.

    Naturally, the lens should be measured on its own, in underscan (showing the frame borders, even if it vignettes), so as to show its degrees. What happens on a camera is up to the manufacturer.

    **or should I say, "focal "lenght" ? ;-)

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