Confusion

Discussion in 'Panasonic Cameras' started by vintageslrs, Jan 5, 2011.

  1. vintageslrs

    vintageslrs Mu-43 Regular

    65
    Dec 13, 2010
    I have read elsewhere on the internet and, I believe here at this forum too, that when using legacy lenses on let's say a G1--the f stop changes as viewed by the camera. Example a Hexanon 40mm F1.8 becomes (35mm terms) an 80mm F3.6.
    But I just read on page 183 on David Busch's book on the GF1, that although the focal length doubles--the f stop remains the same. So in the example used it is (again in 35mm film thought process) an 80mm f1.8.
    Which is the truth?
    From the few photos I have taken with my G1---I always thought it appeared not the change the aperture size effect....but up till today everything I read says it does.
    Confusion.

    thanks
     
    • Like Like x 1
  2. grebeman

    grebeman Mu-43 All-Pro

    Mar 13, 2010
    South Brent, south Devon (UK)
    Barrie
    Hi Bob,
    The aperture of an adapted lens on m4/3 will be the same as when the lens is used on it's intended format, that is a physical property of the lens, however the depth of field that the lens produces will change, so in judging the depth of field the f/4 mark on the lens barrel will be actually f/8 when used on m4/3, the f/5.6 mark on the lens barrel will be actually f/11 on m4/3 and of course the focal length will give the equivalent of a lens of twice the focal length when judged in 35mm format terms.

    Barrie
     
  3. Grant

    Grant Mu-43 Veteran

    Well, I hope David Busch didn't say it exactly like that.

    The F value and the focal length of the lens remains the same regardless of what camera you have it on.

    What changes is the crop factor. A 40 mm F/1.8 on a M43s camera behaves like an 80 F1.8 camera on a 35 mm system as far as magnification goes. This is regardless of where it is a legacy lens or not.
     
  4. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    SoCal
    Well said Grant ... but, (the big but), technically speaking ... isn't it the crop factor which changes the FOV?

    Gary

    PS- I enjoyed scrolling down your photo site.
    G
     
  5. Grant

    Grant Mu-43 Veteran

    You are absolutely right! I only chose the term crop factor over FOV because I figured, for new people, it would be easier to visualize. Of course I could be wrong :rolleyes:
     
  6. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    SoCal
    Gotcha ... things start getting sorta weird when talking about crop sensors.

    G
     
  7. Streetshooter

    Streetshooter Administrator Emeritus

    Dec 15, 2009
    Phila, Pa USA
    Hmmmmm, crop factor... field of view...
    Now I'm confused....
     
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  8. BBW

    BBW Super Moderator Emeritus

    As long as we don't get into crop circles.:biggrin:
     
  9. vintageslrs

    vintageslrs Mu-43 Regular

    65
    Dec 13, 2010
    Crop factor, field of view and now crop circles--LOL.
    You folks are great...I got a big smile from that!!! :biggrin:

    so, if I understand correctly the aperture does not change (for exposure purposes).
    but the effect of the aperture's depth of field does--that is where the f1.8 acts like an f3.6---for depth of field purposes only.

    Do I have have it right now?
    Thank you all for trying to end my confusion! :thumbup:
     
  10. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    SoCal
    Circle of Confusion anyone?

    (and technically it's not your Chem Study Group - aka drinking buds - from college ... but in retrospect the shoe seems to fit ...)
     
  11. Streetshooter

    Streetshooter Administrator Emeritus

    Dec 15, 2009
    Phila, Pa USA
    Bob,
    You have it right enuff to make photos.

    Gary, Circle of confusion. Hmmm
    Depends on the Aspect Ratio. My GF1 does square and rectangles.
    Where did ya find the circle thing?
    Don
     
  12. carpandean

    carpandean Mu-43 Top Veteran

    827
    Oct 29, 2010
    Western NY
    I like to think about it this way:

    Say, I have a 40mm f/1.8 and I put it on a full-frame camera and take a picture. Then, in software, I crop out the center of the picture (half the height, half the width), and blow it up x2, the resulting image is exactly what I would get from that lens on a :43: camera. Technically, the pixel density (MP/sensor size = pixels/in^2) of the two sensors should be the same and the same aspect ratio should be selected (technically, :43: only specifies the diagonal) for the equivalence to hold.

    As pointed out above, this would not be exactly the same as the image that you would get from an 80mm f/1.8 (or 80mm f/3.6) on the FF camera. It has similarities, but is not 100%. FOV-wise, it would be similar to any 80mm lens on the FF and light-wise, it would be similar to any f/1.8. These are relatively simple geometric properties.

    However, DOF-wise, it is not so easy to tell without doing a bit of geometry and calculations. It would actually have a smaller DOF than the 40mm f/1.8 on the FF, but that's not a fair comparison, because the FOV is different, too. What f-stop 80mm on the FF would it have the same DOF as the ? I don't know exactly. There are two offsetting effects: shorter focal length (40mm on :43: as opposed to 80mm on FF) leads to increased DOF, but smaller sensor size leads to decreased DOF. I've read that the focal length effect would be larger, meaning that the DOF would be higher on the :43: image. In other words, the 40mm f/1.8 on :43: would have an equivalent DOF of an 80mm with a larger f-number (smaller aperture) on a full-frame camera. I don't believe (but haven't verified) that it works out to 2x.
     
  13. grebeman

    grebeman Mu-43 All-Pro

    Mar 13, 2010
    South Brent, south Devon (UK)
    Barrie
    Yes

    Barrie
     
  14. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    SoCal
    lol ... Thank you Barrie
     
    • Like Like x 1
  15. Streetshooter

    Streetshooter Administrator Emeritus

    Dec 15, 2009
    Phila, Pa USA
    Gary, no more coffee for you....
     
  16. vintageslrs

    vintageslrs Mu-43 Regular

    65
    Dec 13, 2010
    OK....Great!
    now for the sake of accuracy--this is what David Busch said "Yet, your f/stop remains the same (that is, a 300mm f/4 becomes a very fast 600mm f/4 lens)."

    I did not want to mis-quote David.

    thanks
     
  17. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    SoCal
    ... sigh ... but it's Columbian Supremo, fresh ground and French pressed ...
     
  18. Streetshooter

    Streetshooter Administrator Emeritus

    Dec 15, 2009
    Phila, Pa USA
    Yeah right, like that's coffee.....
    Get some Kona...... that's coffee.
    .......sheeeesh
     
  19. carpandean

    carpandean Mu-43 Top Veteran

    827
    Oct 29, 2010
    Western NY
    It's funny, because "that is, a 300mm f/4 becomes a very fast 600mm f/4 lens" seems to imply that you are getting something that you couldn't get as easily as before. Something like "wow, 600mm f/4, can you imaging how much that would have cost for a full-frame system?!" When, in reality, all you had to do was blow up the center of the image from your 300mm f/4 on the full-frame camera to get roughly the same thing (again, assuming roughly the same pixel density on the sensor.) You're not getting something for nothing. In fact, you're leaving out a lot of the image that you were getting from the same lens.
     
  20. Amin Sabet

    Amin Sabet Administrator

    Apr 10, 2009
    Boston, MA (USA)
    Current 4/3 sensors have higher pixel density than any of the current 35mm format cameras. So if the lens is sharp enough to outresolve both sensors and the subject distance is fixed, then the 4/3 camera with the 300mm lens is going to capture more detail than the blown up center crop from the 35mm format camera with the same 300mm lens.