Selective Focus with fast lens

Discussion in 'Portraiture' started by Hamster, Jan 2, 2010.

  1. Hamster

    Hamster Member

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    A lots of people, (myself included) thens to overuse the the thin DoF possible with fast lens.

    Now I think I am getting into the habit of abusing thin DoF without thinking about how it suits my imaging objectives.

    Do you find yourself in a similar situation?
     
  2. Pinholemaster

    Pinholemaster Member

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    Abusing?
     
  3. modafoto

    modafoto Subscriber

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    I use thin DOF a lot when shooting people. Portraits with the eyes sharp and the ears more or less blurred are great. Am I abusing it, then?
     
  4. WetMogwai

    WetMogwai Member

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    I don't think you can abuse an artistic technique. Was Picaso abusing cubisim? Was Adams abusing dodging and burning? If that is your style, embrace it. If you don't like the results you are getting, practice more or experiment with other techniques.
     
  5. fotch

    fotch Member

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    Is there a DoF Anonymous? :tongue:
     
  6. 2F/2F

    2F/2F Member

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    Sounds like a bad habit; letting your work be guided by technical matters instead of by concept or vision, etc. I don't get it. How does that even happen? If you want more D of F, do what it takes to get more D of F. It is not as if you are out of control.
     
  7. Chazzy

    Chazzy Member

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    Hamster seems to be talking about miniature format, since he refers to fast lenses. In miniature format, one does indeed have something of a choice about how shallow depth of field might be. But in the larger formats, relatively shallow depth of field is more or less a given—depending on how long an exposure is feasible.
     
  8. Rudeofus

    Rudeofus Subscriber

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    Is this really the case? I know of no medium or large format lens comparable (in terms of DOF) to the 50 F/1.0 or the 85 F/1.2 for "miniature format" as you call it. While it may be more difficult to get everything in focus with MF/LF, insanely shallow DOF may actually be more feasible with 35mm cameras.
     
  9. keithwms

    keithwms Member

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    The mamiya rz 110/2.8 gives extremely shallow DOF, as does the m645 80/1.9; there are numerous others e.g. the contax 645 lenses.

    Then there is the issue of tilts, which make it very easy to produce extremely shallow DOF on some MF and most LF cameras.

    Finally, one must also consider the tonal smoothness of in-focus / out-of-focus transitions. MF and LF give up nothing to 35mm in that department. If you want very shallow DOF and good sharpness and good bokeh in 35mm, you are going to pay big bucks for it, tnere are only a handful of lenses that deliver all three. With LF just about any lens will deliver all of the above. And LF doesn't have to be huge, I played these games with an itty bitty horseman VH, for example: here or here. IIRC the first one was done with a 360 tele Nikkor and the second a 150 convertible.

    .... mind you, I am a guy who uses his Nikon 50/1.2 very happily :wink:
     
  10. benjiboy

    benjiboy Subscriber

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    I find that a lot of people who have fast lenses for 35mm cameras use them habitually at far too big an aperture for their subject, and think that because they have paid for an 85mm f1.2 lens, for example that it must always be used wide open with the result that their pictures constantly suffer from insufficient depth of field.
     
  11. AgX

    AgX Member

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    That abusing thing may have two sides:
    Making exposures where ones technique does not fit the matter (whatever that means...)
    Or selecting only subjects where ones technique fits.
     
  12. JBrunner

    JBrunner Moderator Staff Member

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    Yes, it really the case. Because of the larger film area "normal" on my 8x10 for example, is around 300mm, and thus I have 300mm DoF at the same distance that I would use a 50mm for with 135. It takes more than a stop or two to make that up, hence part of the usefulness of swings and tilts.
     
  13. Rudeofus

    Rudeofus Subscriber

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    If you look here, you'll find the equation: c = m*A*|S2-S1|/S2, with c being the circle of confusion in the focal plane (i.e. the film plane), m being the magnification, A being the diameter of the aperture, S2 the distance in perfect focus and S1 being the object distance.

    What does this mean: for equal subject framing and equal DOF impression on the final print you keep c/m constant. The larger the film, the larger the circles of confusion may become before a section looks blurry, but at the same time the larger the magnification m becomes. After all is said and done, only the aperture diameter determines your DOF. And that's exactly where the myth comes from that long focal length lenses or large format have narrow DOF: it's easy to have A=1mm with a 14mm lens (just dial in F/14), but next to impossible to find a 300mm lens with that aperture diameter.

    When it comes to really narrow DOF, 35mm cameras rule at the moment. You get normal lenses with A=50mm, portrait focal legths (85, 135mm) with A=70mm, and longer focal lengths with A>100mm, even A>150mm. No medium or large format camera can offer you that. Your 8x10" normal focal length lens may be f=300mm, but with F/8 you get A=37.5mm, which is nice but not extraordinary.

    All you have with large format is DOF too thin for reasonable hyper focal distances, that's why you need camera movements to get a landscape shot in focus, where 35mm cameras would just stop down a little.
     
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  15. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member

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    Anyone who actually shoots 35mm, medium, and large format knows that really, no foolin', no myth, even without tilts and shifts, it's easier to do short DOF with a larger format and ordinary lenses.

    Running some numbers through f/calc (available from http://fcalc.net), which is a handy program for calculations like these with all the formulas included in the help screens, I get a DOF range of slightly less then a three inches using a 300mm lens at f:8 on an 8x10" camera (acceptable CoC=0.188022mm) with a subject distance of six feet. I get a DOF range of slightly more than a three inches using a 50mm lens at f:1.0 on a 35mm camera (acceptable CoC=0.02501mm) at the same subject distance, which would be typical for a portrait. So if we call that even, you need an exotic f:1.0 wide open lens on a 35mm camera to do what you can do with a typical modern plasmat made some time since the 1970s (300mm/5.6) on an 8x10" camera stopped down one stop. Tessars in that range would usually be 300mm/4.5, and a 12" Dagor is f:6.8.
     
    Last edited by a moderator: Jan 21, 2010
  16. Rudeofus

    Rudeofus Subscriber

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    Funny thing is dofmaster comes to different conclusions: at 2 meters distance the 300/8 has a DOF of 0.12m, where the 50/1.0 would have only 0.09m. At a distance of 6 feet I get 0.33ft vs. 0.26ft. While the 50/1.0 may be a freak lens, a 50 F/1.2 is not, and is still comparable to the 300 F/8 on 8x10 cameras. And that's only at normal focal lengths. Once you compare a 200/2.0 or a 600F/4 to the lens lineup for MF/GF, you blow anything MF/GF out of the water.

    The reason for this is not any inherent superiority of 35mm cameras. It's just that due to high market volume a lot more research effort is put into these small format lenses, providing us with insane lens designs. Look at the complexity in some of the newer 35mm lenses!
     
  17. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member

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    Sorry, I misread the f/calc result. That should be a quarter of a foot or about three inches, rather than a quarter inch. I've corrected the post above.

    Also DOFmaster is rounding the 8x10" CoC value (.2) more than 35mm CoC (.03) just following the normal rounding conventions, but that aside, the most common 300mm lenses for 8x10" aren't wide open at f:8, so at f:8, there is usually room to spare. The exceptions would be Artar and process type lenses or compact lenses like the Fujinon C, which are usually around f:9. Most 50mm lenses for 35mm cameras are f:1.4 or f:1.8, so even if an f:1.2 isn't quite as exotic as an f:1.0, they're still pretty unusual.
     
    Last edited by a moderator: Jan 21, 2010
  18. Rudeofus

    Rudeofus Subscriber

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    F/1.2 is not all that unusual in a Canon gear bag and would be even more commonly seen if the 50L didn't suffer from its dreaded and much written about focus shift issues. Ok, let's settle this with: GF gets smaller DOF in the normal to wide range, 35mm format rules the DOF arena in the longer focal length range.
     
  19. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member

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    Maybe, but only because there are no vaguely equivalent long lenses as you go up in format, and they get pretty impractical to work with. The long end of 35mm or 8x10" is around 1200mm--Canon tele, Nikon tele for 8x10", and then there are a few monster process lenses longer than that.
     
    Last edited by a moderator: Jan 21, 2010
  20. JBrunner

    JBrunner Moderator Staff Member

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    I just set up my 8x10 and my 35mm side by side on the same subject. The 8x10 is wearing a 14 inch Heliar about (350mm), set at f/4/5.6 split (it's WFO), no movements. The 35 is equidistant and set to the same approximate FoV, happening in this case to be about 70mm on a 24-70, making the subject (a small doctor Dr. Suess christmas tree on my window sill) the same size relative to the vertical part of the aspect ratios (the Heliar could easily cover a longer ratio), at f4/5.6 split. Only front part of the tree is in focus on the 8x10. The window frame behind it is decidedly bokehed. Nothing outside the window is discernable at all. With the DoF preview pressed to set the 35mm aperture to 4/5.6, focused on the christmas tree, similar FoV, all of the tree and the window sill are sharp, and I can easily make out the house number on the house next door. The exposures would be exactly the same, the FoV's very similar, and that's what even is where the rubber meets the road outside of a calculator. Dropping the aperture on the 35mm to 2.8 (thats as fast as my 24- 70 is) doesn't buy much of anything at all. Another stop and a half still wouldn't get it even close, and indeed stopping the Heliar to f8 doesn't change much in relation to the deep DoF of the 35mm camera at 2.8, which is still has far greater apparent DoF, and that's three stops of difference.

    In practical application both my experience as a multi-format shooter and this test indicate that no matter what you calculated, the reality doesn't fit your interpretation. At similar apertures and similar FoV's larger formats have far less apparent DoF. What I think is overlooked is that while DoF is a constant relationship to aperture and focal length, in application across formats, FoV for film size for a given focal length isn't, and so apparent DoF for the same FoV isn't either.

    When I put up the Turner Reich Triple at 25 inches, at a portrait distance, I'm lucky to get more than an eye without stopping down.

    Don't make me make these negatives.


    :smile:
     
    Last edited by a moderator: Jan 23, 2010
  21. erikg

    erikg Member

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    There is always a risk to letting some element of style become a crutch. It's pretty normal to go back to things you've had success with, but when you do so without questioning why and find that you have done one thing when something else may have been a better choice, then there is a problem. But, if you can see that has happened, then you can try something else next time.
    As someone who shoots formats from 35mm to 8x10 and also likes to use some shallow DOF at times with all formats, I can say with certainty that David and J Brunner are right, LF rules for shallow DOF, even without movements. That's why folks are using speed lenses on Graflex SLRs and Aero ektars are hot lenses for graphics. If the formula doesn't fit that, then the formula is missing something.
     
  22. Lee L

    Lee L Member

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    Doesn't hold. Here's a 50mm and 100mm comparison, both at 25mm aperture diameter (f:2 and f:4 respectively), both at 0.0101 magnification and same CoC on 35mm film. Same formulae and results as DoFMaster. DoF doesn't match between images.

    See: http://theonlinephotographer.typepa...er/2009/06/depth-of-field-hellthe-sequel.html

    Lee
     

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  23. df cardwell

    df cardwell Subscriber

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    Wonder what happens when the magnification of the subject = magnification image in the PRINT ?
     
  24. Lee L

    Lee L Member

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    You can play around with different lenses, apertures, CoC, etc with Schneider's spreadsheet: http://www.schneideroptics.com/software/DOF_Calculator.xls

    If you don't have MS Excel, this spreadsheet (and nearly all others) works fine in the free (in multiple senses) openoffice calc spreadsheet, available at www.openoffice.org

    You could set up your spreadsheet numbers however you want to get the print magnification / reproduction ratios you want to try.

    Lee
     
  25. Leighgion

    Leighgion Member

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    If you think you're "abusing" thin depth of field, you're obviously being brainwashed by the f64 crowd. :smile:

    Resist! You use as thin a depth of field as you want to. No more.
     
  26. JBrunner

    JBrunner Moderator Staff Member

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    Sometimes I'm f64 and sometimes I'm f1.3. The only thing I abuse is myself. Hmm.. that didn't come out the way I meant it...:tongue: