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Which one produces shallower depth of field.....

Discussion in 'Photography Techniques' started by TraamisVOS, Oct 5, 2013.

  1. TraamisVOS

    TraamisVOS SC Hall of Famer

    Nov 29, 2010
    Melboune, Australia
    ...(without referring to a depth of field calculator) .. a 50mm lens, f/1.4 wide open:

    (i) on a full frame body

    or

    (iii) on an APS-C (x1.6) crop body which would make it a mild telephoto at 80mm.
     
  2. Luckypenguin

    Luckypenguin SC Hall of Famer

    Dec 24, 2010
    Brisbane, Australia
    Nic
    On the basis that each image will be printed/viewed at the same size for comparison, the APS-C body will produce the shallower depth of field using the same lens. Bit academic really when the fields of view produced are so different.
     
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  3. HeatherTheVet

    HeatherTheVet SC All-Pro

    Apr 23, 2011
    Scotland
    Heather
    Who would win a fight between a shark and a crocodile?
     
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  4. renatoa

    renatoa New to SC

    9
    Oct 5, 2013
    You statement is not right, especially because you specified "printed/viewed at the same size".
    There is an optics law saying that for any focal length, if the subject has same size in the frame, the DOF is the same and depends on aperture only. What changes is perspective, probably bokeh.
    The above would be right if both shots are from same distance, thus different subject size.
     
  5. Luckypenguin

    Luckypenguin SC Hall of Famer

    Dec 24, 2010
    Brisbane, Australia
    Nic
    Exactly, therefore the statement is not "not right".
     
  6. Luke

    Luke Super Moderator

    Nov 11, 2011
    Milwaukee, WI USA
    Luke
    I'll put my money on the crocodile.

    And I just checked a DOF calculator. I thought it was easier to get a shallow DOF with a bigger sensor, but unless I used the calculator wrong, the APS-C yields a shallower DOF. Now I feel like verything I thought I knew was wrong. Effing great.
     
    • Like Like x 1
  7. flash

    flash SC Veteran

    372
    May 6, 2011
    Gordon
    This assumes that the sensor size remains the same for the DOF to be the same. In this case the sensor size changes so the equivalence of DOF between focal lengths does not apply. His statement was correct.

    The full version is: DOF will remain constant for a subject shot at the same aperture, subject size and format regardless of the focal length used to take the shot. You missed the bit about the format, which changes in the OP's question.

    35mm vs 4/3.

    If you stay in the same postion and shoot the same lens and view the image at the same size, the smaller sensor will have LESS DOF as it needs to be enlarged more. But the content of the frame will be radically different and the subject will be a different size when enlarged.

    If you move to reframe the shot so the subject size is the same then the larger sensor will have LESS DOF. This is because the movement made by getting further away on the smaller sensor will be greater than the difference in the enlargement amount of the paragraph above.

    Gordon
     
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  8. bartjeej

    bartjeej SC Hall of Famer

    Nov 12, 2010
    bart
    I'm not sure I agree with this part entirely. I think it should state: DOF will remain constant for a subject shot at the same aperture (note: this is about physical aperture size, not f-number), subject distance and equivalent focal length. The equivalent focal length is a function of absolute focal length and sensor format. For instance, an m43 camera with a 25/2 lens (which is 50mm equivalent, with a physical aperture opening of 12.5mm) has the same DOF as a full-frame camera with a 50/4 lens (obviously 50mm equivalent, with physical aperture opening of 12.5mm), provided subject distance remains the same.

    Conversely, keeping the physical aperture size, subject distance and sensor format the same while using different focal lengths (for instance, comparing the 25/2 and a 50/4 on the same camera body) will give different results, because the effective focal lengths will be different.

    This I agree with.
     
  9. Luckypenguin

    Luckypenguin SC Hall of Famer

    Dec 24, 2010
    Brisbane, Australia
    Nic
    The results from the calculator are correct, but the resulting image from the APS-C is cropped so the comparison isn't equal, hence you substitute a shorter focal length lens to get the same angle of view, on which the depth of field is now greater and the planets and stars are all aligned again.
     
  10. TraamisVOS

    TraamisVOS SC Hall of Famer

    Nov 29, 2010
    Melboune, Australia
    See, this is why this question stumped me for a while.

    At the most rudimentary level of understanding, a larger sensor will give you shallower depth of field.

    On the other hand, a telephoto lens will also give you shallower depth of field.

    So by going with a crop sensor you would be increasing depth of field .... but would the increase in depth of field be ultimately cancelled out by the telephoto which is caused by the crop?
     
  11. TraamisVOS

    TraamisVOS SC Hall of Famer

    Nov 29, 2010
    Melboune, Australia
    PS. Some of you cheated by referring to a depth of field calculator.

    EWKG6E3.
     
  12. TraamisVOS

    TraamisVOS SC Hall of Famer

    Nov 29, 2010
    Melboune, Australia
    Also, I noticed in my original post I provided the option of (i) and (iii). Apparently I can't count using the letter 'i' either.
     
  13. TraamisVOS

    TraamisVOS SC Hall of Famer

    Nov 29, 2010
    Melboune, Australia
    The question in my original post refers to circumstances where you're photographing with your 50mm f/1.4 wide open spontaneously on the street.

    In a real world sense if you're on the street and snapping shots on the fly you're going to be snapping these shots from wherever you happen to be standing at the time, perhaps without the luxury of time or space to reframe your shot, ie. you may be observing a spontaneous event unfolding right in front of you that you want to capture asap before the moment passes.

    In those circumstances would you tend to see shallower depth of field in the photos from the photographer with (i) the full frame camera or (ii) from the photographer with the same lens on a crop sensor camera?

    I refused to use a depth of field calculator, I wanted to work it out conceptually rather than mathematically.
     
  14. wt21

    wt21 SC Hall of Famer

    Aug 15, 2010
    My head hurts reading the replies, but here's what I know from experience, and I'm avoiding the DOF Calc.

    If you use the same exact lens, and you shoot the subject at the same exact distance, DOF should be the same, but the APS-C will give a tighter crop. It's the same as if you shot it with the FF camera, and then just cropped in LR. DOF does not change just because you cropped the picture.

    If you move positions (i.e. getting closer with the FF or moving further away with the crop) to get similar framing, then the DOF should be less on the FF, because you are now closer to the subject. The focal length and the physical aperture size has not changed. If, however, you grabbed a 75mm lens to shoot with the FF and a 50mm lens on the crop (assuming a 1.5 crop), and you kept distance to subject the same, then DOF will be driven by the physical aperture size, so if f/stops were the same (e.g. both 1.4), then the FF should have shallower DOF because 50/1.4=35.7mm vs. 75/1.4=53mm.

    That's the way I understand it, but actually don't really care, lol. I have the lenses I have (50/1.4 and 85/1.8 on FF and 22/2 on my EOS-M) and I like the look of these lenses a lot, so if I'm wrong, I'm wrong :)

    Also, if "viewing distance" to the picture comes into play here, well then I'll just keep quiet. My viewing distance is just about always 2 feet (distnance from my chair to my monitor) ;)
     
  15. bartjeej

    bartjeej SC Hall of Famer

    Nov 12, 2010
    bart
    So if I understand you, subject distance is fixed, absolute focal length and physical aperture* are also fixed? Then the smaller sensored camera will have the shallower DOF.

    As I said in my previous post, DOF is a function of:
    -subject distance [closer = shallower DOF]
    -physical aperture size (so not f-number) [larger = shallower DOF]
    -equivalent focal length. [longer = shallower DOF]

    In your example, the subject distance, physical aperture size and absolute focal length are fixed, but due to the smaller sensor, the crop sensor camera has a longer equivalent focal length and therefore a shallower DOF.

    The statement that a larger sensor in and of itself gives shallower DOF is wrong; if all else is fixed, it's the smaller sensor that gives you shallower DOF. Thing is, larger sensors need longer absolute focal lengths to achieve the same field of view; and if you couple that longer focal length with the same f-number, you have by definition a larger physical aperture opening. That's what gives larger format cameras shallower DOF for the same equivalent focal length and f-number.

    *50/1.4=35.7mm, regardless of sensor size
     
  16. wt21

    wt21 SC Hall of Famer

    Aug 15, 2010
    I don't understand this statement. If all else is fixed, then isn't DOF equal, but the crop pic is, well, cropped.

    This is how I understand it.
     
  17. TraamisVOS

    TraamisVOS SC Hall of Famer

    Nov 29, 2010
    Melboune, Australia
    I'm just thinking aloud now.

    Generally speaking, a larger sensor will give you shallower depth of field.

    But if you only have one lens, and you want to do some street photography at night where you have to stay wide open, and you don't want to be constantly dealing with razor thin depth of field ... you're better off with a full frame sensor rather than a crop sensor because the crop sensor is going to have shallower depth of field than a full frame sensor.
     
  18. flash

    flash SC Veteran

    372
    May 6, 2011
    Gordon
    What I stated is correct. Have a read of this thread from mu4/3 this week where the same subject was covered.

    http://www.mu-43.com/showthread.php?t=53469

    Your statement is also correct. However, I will not get involved in a discussion about absolute aperture. It's just too confusing for most. We've got enough people arguing over the meaning of "bokeh". I'm going to stick to the accepted photographic description of aperture (the relationship between the focal length and the diameter of the aperture blades.

    Gordon
     
  19. TraamisVOS

    TraamisVOS SC Hall of Famer

    Nov 29, 2010
    Melboune, Australia
    oh man I didn't even know people discussed aperture blade diameters or that it even existed as a discussion point.
     
    • Like Like x 1
  20. flash

    flash SC Veteran

    372
    May 6, 2011
    Gordon
    The smaller sensor will require more enlargement to get to the same viewing size as the shot from the larger sensor (comparisons and DOF calculations are made at a fixed viewing size). So the *apparent* DOF will be thinner due to the greater degree of enlargment. This is why DOF calculators use a CoC value that depends on the size of the sensor,

    Gordon