75mm Summilux and the M8

Discussion in 'Leica and Rangefinders' started by jim_cain, Nov 18, 2006.

  1. It's well known that this lens (which I own) has a very thin depth of field when used wide
    open and at short distances. When used with an M8, it would be an effective 100mm.
    Am I correct in assuming that the depth of field would be even thinner then at 75mm with
    an M7? Ir sound neat to have a 100mm effective lens with f1.4! What are the trade offs?
    Thanks
     
  2. DOF is the same for the M8 and any other camera. It's physics. You can use the same DOF scale you are accustomed to.

    That said, since the original image is smaller than FF, when you enlarge (print) to the FF equivalent (use the horizontal for scale), you MIGHT (more below) require a slightly more conservative DOF (it's based upon the Circle of Confusion (CoC)) because you have to 'enlarge' more.

    And finally, what makes this all so uncertain is we don't know what your expectations were with film, what film you used, whether you enlarged optically or scanned, and so-forth. Digital is 'cleaner' for many people and they find that with reasonable print sizes they are happier with the outcomes.
     
  3. The lens itself does not change, so its depth of feild doesn't eiter.

    The smaller sensor needs a bit more enlargement when compaired to film, this will slightly

    decrese the dof. but in effect, daily use there will not be that much different.
     
  4. The short answer - yes, there will be slightly less apparent DOF using any given lens on
    the M8 (including the 75 'lux) than on a film M. The DOF will be slightly MORE than one
    would get using a true 100mm f/1.4 lens on film (if such existed).

    The long answer - the image the lens projects onto the imaging surface does not change a
    bit (the light-bending properties of the glass are not magically influenced in any way by
    what lies behind the lens - air, silver, or silicon), but factors like final enlargement (a 27
    x18mm image from the M8 will need more for a given print size than a 36x24mm image
    from film), and whether you change shooting distance to account for the framing
    difference between "75mm" and "100mm" will also affect what you see as blurred or sharp
    in a final print.

    My practical experience is that it is a bit trickier to focus, and you lose a bit of final
    resolution (that extra enlargement factor again). I'll dig up a 75/M8 shot and add it here
    when I get a moment.

    Despite my clear and succinct explanation, I predict this thread will now descend into one
    of those screwy "DOF" debates fueled by people who don't know the difference between
    "focal length" and "field of view". Seasoned by others waving countless DOF formulas and
    spreadsheets. (circle of confusion 0.03 or 0.02mm??)

    With luck I'll be wrong.

    There are 75mm lenses (engraved such on the barrel). There is no such thing as a "75mm
    field of view" unless one also defines the format - on a 4x5 a 75 is a superwide, on a
    classic Rollei it is a "normal", on a 35mm camera it is a short tele, on the M8 it is a longer
    tele, and on a Panasonic FZ-50 it is a LONG tele (400+ equivalent crop).
     
  5. M8 it is a longer tele
    Andy, I promise not to drag this into silliness, but I do not think the 75mm is a tele lens. It simply a long lens. It has a nominal/normal nodal point. No?
     
  6. I have a 75mm Summilux and waiting for my M8... I just picked up a 1.25x magnifier to help focusing the 50 and 75 lux. The results I get from film are nice. Make sure you shoot it with high shutter speed ...
     
  7. I sort of agree with Andy but. If you use a depth of field charts for your M3 or baby brownie it does not ask you how big a print you are going to make. The focal length and fstop determine the depth of field.
    I think it's too late to change the definition now. (The same with marriage.)
     
  8. But never too late to change the definition of bigotry.
     
  9. ...must resist comment...can't resist...must resist...
     
  10. here is a shot with the combi you mention.

    more dof would have been better, but it gives you the idea.
     
  11. Andy's right. DOF will be reduced owing to the increased magnification needed to get the same print size from a smaller image area. I'd have gone into DOF formulas, spreadsheets, and the .02 vs. .03 blur circle issue, but I would't want to prove Andy any more right than he already is. :<)

    To use your fast 75's and 90's, I'd say do like Charles, and get a magnifier; or stop down one stop. Even a .72 finder is marginal with such fast, long lenses. The M8 focusing will be bang-on at infinity, however. :<)
     
  12. i disagree on the focusing. i focused on the eye that is in focus in the pciture. it is th eonly
    thing in focus. the accuracy is there if you are patient.
     
  13. Pico: I think you are right regarding the 75 'lux - it is not a "telephoto" optical design. I was
    using the looser sense of a longer-than-"normal" lens.

    Charles: Many DOF references (including, for that matter, the scales permanently engraved
    into lens barrels) do not specify an enlargement size, as you say.

    But I think if you research it a bit you'll find that those 'fixed' references tacitly ASSUME a
    given print or enlargement size (8 x 10 I think). Which is why some people use the formulas/
    spreadsheets to figure DOF - the formulas include enlargement as one of the variables.
     
  14. Look here (same question):

    http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00IKyS
     
  15. Okay, what does "telephoto" mean? I always thought it meant a non-zoom lens longer than the "standard" 50mm on a 35mm camera. If there is a more technical definition (which I guess there is), let's have it.
     
  16. "... what does 'telephoto' mean?"

    Put simply (by definition), a telephoto lens is physically shorter than its effective focal length.

    Look here:

    http://en.wikipedia.org/wiki/Telephoto_lens
     
  17. Focusing the 75mm on the M8 is easy with a 1.25x magnifier and not really very hard without the magnifier. Framing is a different story. The 75mm frameline on the M8 is really almost vestigial, and it's also very close to the much more visually "active" 50mm frameline. I find myself using the 50mm frameline "accidentally" when I'm using the 75mm lens - it definitely is a problem. Depth of field isn't "very thin" - at least compared to the 50/1.2 which I've also used for a couple hundred shots on the M8 now. It's thin, but if you have no trouble using a 90/2 on your M6, M7, or MP, you'll have no trouble with the 75/2 on your M8.
     
  18. Marc: A "telephoto" design, as mentioned, is a lens designed so that the effect focal length
    or magnification is longer than the lens's physical length, making it more compact. It's
    usually done by adding negative, or concave, or inwardly curving glass at the back - and in
    fact "teleconverters" do exactly that. By adding 30mm of length with concave glass in it to
    the back of, say, a 200mm lens, you make it into a 400mm lens (adding 200mm of focal
    length with a physical increase of only 30mm).

    "Retrofocus" wideangle lenses are the reverse - with more backfocus than their effective
    focal length (to clear SLR mirrors or allowing metering in a Leica M). In those lenses, the
    negative elements are added in FRONT of the lens to "minify" the scene, making everything
    smaller and fitting more into the frame. The "wide" and "fisheye" converters for digicams
    do the same thing, except not built into the original design.

    "Telephoto" (which just means "long light", literally) has come to be applied by the huge
    majority of people (including you and me) to any lens longer than a "normal" lens - but
    technically it should only be applied to lenses with a telephoto optical design.

    E.G. despite its name, the Leitz 400mm TELYT that is basically a fancy 2-element
    magnifying glass at the end of a 400mm-long tube, is NOT a "telephoto" design. It really
    does have to be 400mm from the film/sensor to be in focus at infinity.
     
  19. The depth of field issue wrt to various digital format sizes is covered in great detail here: http://www.bobatkins.com/photography/technical/digitaldof.html

    Whether a lens has more or less DOF on 35mm vs. APS-C digital depends on how you use it (i.e. whether you shoot from the same position or you back up to get the same framing).

    For the same framing (field of view), at the same aperture, the M8 shot will have LESS DOF than on film (but of course you'll be standing further away from the subject).

    The cited article goes into all this stuff in depth (no pun intended), along with a discussion of what the circle of confusion is and what it really means [briefly it's a number calculated on the assumption that you'll be viewing an 8x10 print from about 15" and you have average eyesight!]
     
  20. DOF is a set of calculations, based on certain parameters (CoC, viewing distance, enlargement, etc), and expressed on a lens barrel through DOF markings.

    Since it's hard to change DOF markings on a barrel after the lens has been made, some people argue that DOF doesn't change whatever you put behind a lens.

    Well, the physics of where the light falls does not change because of digital, but the enlargement factor will change. Since that violates now the assumptions made when Leica engraved the lens barrel, it can logically only mean that your DOF markings are no longer valid.
     
  21. If DOF does not change, then shooting the same object from the same distance, same aperture, using both film and digital, should result in an object at the edge of the DOF marking to be rendered just acceptably sharp in both cases. How could that be when the print from digital will be a cropped version of the print from film, and thus will magnify any out of focus areas even more, incl. the portion at the edge of the DOF?
     
  22. To drive a nail into the DOF issue as it regards degree of enlargement consider that Hasselblad once published a caveat regarding their earlier SWC (their 38mm wide-angle camera). That lens has a mechanical pointers that describe the DOF - it changes depending upon F-Stop. 'blad wrote that if one is going to do large prints, then one must use a more pessimistic interpretation of the given scale ...presuming the viewers will not be at 'normal' viewing distance, and they very often are not.

    Anyway, to the OP. Take pictures. Be happy. If you notice a difference, then repeat the situation. If you still notice it, then stop down one. Then be happy.
     
  23. The depth of field issue writ to various digital format sizes is covered in great detail here: http://www.bobatkins.com/photography/technical/digitaldof.html
    Concise! I like laying out the facts in a case manner like that. Beats the heck out of a Truth Table, and with a quick read the reader doesn't have to understand the Why; he can go right in with confidence knowing it is so.
     
  24. roger, that's a great photo. i think the focus is *perfect*.
     
  25. "The focal length and f stop determine the depth of field."

    This is not totally correct.

    Depth of Field is a function of aperture and reproduction ratio.
    An object photographed at 1:1 with a 25mm lens at f8, provides the same depth of field as that object photographed at 1:1 with a 300mm lens at f8
     
  26. Good Lord! All this fuss over a definition when it was a simple question that was posed.
    Does DOF change when you crop an image? The answer is NO. DOF is defined by the focal
    length of the lens, the aperture, and the SELECTED circle of confusion. PERIOD. Cropping of
    an image, the equivilent of a smaller than full24x36 mm sensor, does not change the DOF
    defined for the lens.
    If you want to change the definition of DOF to account for the selection of different circles of
    confusion, you will end up with a huge mess.
    It was a simple question and it deserved a simple answer.
     

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