Depth of field of 45/1.8 vs 60/2.8

Discussion in 'Native Lenses' started by Timos L, Jul 6, 2013.

  1. Timos L

    Timos L Mu-43 Top Veteran

    721
    Dec 26, 2011
    Athens, Greece
    Timos :)
    My question is whether the depth of field of Olympus 45/1.8 is shallower or not to Olympus/Sigma 2.8, for the same dimentions of the photographed object (let's say a portrait, which will be the same size in the frame in both cases).

    I consult dofmaster.com, talking into account that for the same dimentions of the subject, the distance from the subject is proportional to the focal length.

    And the results are:

    45/1.8 -> 10m distance -> DOF = 2.67m
    60/2.8 -> 13.3m distance -> DOF = 4.25m (in the second case, distance = 60/45 * 10 = 13.3)

    So this shows that if I want to photo the same portrait (same dimentions in both cases) with these two lenses, 45/1.8 gives me a much shallower DOF comparing to 60/2.8.

    Is there anyone who has both lenses and has compared them regarding their DOF, to certify the above?
     
  2. MAubrey

    MAubrey Photographer

    Jul 9, 2012
    Bellingham, WA
    Mike Aubrey
    I think you'll actually find them to be more similar to dofmaster.com states. That isn't to say their numbers are incorrect, but that subject isolation is more than just narrow DOF. The 60mm is going to give you more background compression since its a longer lens. The effect is such that the 60mm isn't much different at all in terms of isolation and you have the added benefit of more of your subjects face in focus than you otherwise would.
     
  3. madmaxmedia

    madmaxmedia Mu-43 Veteran

    335
    Feb 20, 2010
    Maubrey answered it pretty well.

    DOFMaster will give you the literal depth of field. But which appears to have a narrower or deeper DOF is not the same. There's a good online article that shows this really well with examples, if I can find it I will post here.
     
  4. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    Gordon
    I have both the 45 and 60mm Olympus lenses and I notice the difference, quite clearly. Although what's stated above is correct, there just isn't that much difference between the focal lengths for the changes in perspective to mask the 1.5 stops of DOF difference. Assuming the same sensor size and size of the subject in the frame, lenses of any focal length with have the same DOF at the same aperture, but you'll have to move to acheive this (as you correctly showed above, although I haven't bothered to check your maths. I'll assume you got it right.).

    The change in aperture will effectively double the amount of DOF with a 1 stop increase (100%) but your change in position is only 30%, by your calculations. So the DOF difference will be more noticable than the change of position, in this case.

    Gordon
     
  5. MAubrey

    MAubrey Photographer

    Jul 9, 2012
    Bellingham, WA
    Mike Aubrey
    The increase of 1 stop in aperture does not double the depth of field. That requires two stops.

    45mm f/2 at 37.4inches = 1 inches of DOF
    45mm f/2.8 at 37.4inches = 1.42 inches of DOF
    45mm f/4 at 37.4inches = 2 inches of DOF

    Depth of field increases by 1.42x, which is the same ratio of doubling the area of a circle, but the size of DOF isn't a circle it's depth.

    This is from a Voigtlander 58mm f/1.4, but they're all shot at f/2.8. It should give you an idea what you'd get with a 60mm f/2.8. Obviously the farther the background is from the subject the more out of focus it will be, so here are a few with varying background distances.

    _1020805.

    _1020807.

    _1010990.

    _1020007.
     
  6. usayit

    usayit Mu-43 Hall of Famer

    I"m guessing you would actually be further back with the 60mm. Distance = (1 + 45/60) * 10 = 17.5m which dofmaster ends up reporting as 4.53m behind the subject. This is versus 45mm f/1.8 @ 10 m with dofmaster 1.51m behind the subject.

    I think the difference between 1.51m and 4.53m is significant enough to explain flash's observations.

    I think its important to use the DOF behind the subject distance because in general its the background DOF behind the subject that people notice in a photo rather than the foreground. Portraits in general having limited foreground (artistic vision excluded).
     
  7. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    Gordon
    Sorry. You are correct. I hadn't had a coffee yet (that's my excuse and I'm sticking to it...) Double the number double the DOF (ie: 2 stops).

    So we are looking at a 1.5 stop gain in DOF (approx 75% more) and a 30% difference in shooting distance. DOF difference should be generally quite noticable at these settings.

    gordon
     
  8. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    Gordon
    I checked and it's 30% more distance (approximately). With both lenses at 2.8 and the same DOF you'd have the 60mm at 6.5 meters if the 45mm was at 5 meters. Subject size would be the same. Perspective would change.

    Gordon
     
  9. MAubrey

    MAubrey Photographer

    Jul 9, 2012
    Bellingham, WA
    Mike Aubrey
    And all these variables would still result in roughly the same amount of blur as this completely ad hoc, quick and dirty comparison shows. Yes, the 45mm f/1.8 has slightly more background blur, but the difference is hardly within the realm of being "quite clearly [noticeable]."

    edit: so quick and dirty, in fact, that I didn't realize that I didn't notice my ISO was so high that I clipped the highlights with the fast shutter speed.

    45mm f/1.8
    _7060012. 5mm

    58mm f/2.8
    _7060016.
     
  10. usayit

    usayit Mu-43 Hall of Famer

    If the background in those two photos are well beyond the far limit of the DOF then of course the differences will be difficult to notice.

    You can already see that the DOF is quite different if you ignore the far limit background and look at the window frame just behind the cup.
     
  11. usayit

    usayit Mu-43 Hall of Famer

    Ok... if you say so... 30% it is...

    If at f/2.8 the DOF (total I assume) is 6.5 and 5 respectively, then it seems that as already stated, the perspective/focal length differences are not making up for the DOF differences introduced by the difference between f/2.8 vs f/1.8 aperture. I guess deep down, I believe the math more than I believe uncontrolled/adhoc experiments.
     
  12. MAubrey

    MAubrey Photographer

    Jul 9, 2012
    Bellingham, WA
    Mike Aubrey
    Hey, hey, slow down...nobody said not to believe the math. If you've read my posts, you'll have seen the math in them. I'm using both math and images. And your observation about the window frame, I reject. Who in the world, with either a 45mm lens or a 60mm lens, is going to put their background an inch behind their subject when doing portraiture?

    As for the math, it can be reduced to a simply contrast: virtual size of the entrance pupil: 25mm in the case of the 45mm and 21mm in the case of the 60mm. That's the number that motivates all background blur, whether caused by telephoto compression or by f-number. And 4mm isn't so significant as to matter.

    Since I apparently need to repeat myself over and over again:

    There's a real difference.

    It isn't that big.
     
  13. usayit

    usayit Mu-43 Hall of Famer

    I am not moving fast.... didnt intend on being confrontational... Its not that I expect anyone to place the background an inch behind the subject its that you can begin to see the difference at that point. Its pretty noticeable and if there was something between that point and the far limit (rather than beyond it ) the difference would be more visible.

    ... also CoC...

    I am pretty confident in what dofmaster and similar calculators report.
     
  14. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    Gordon
    My very unscientific test based on dodgy technique and shaky hands. About 1 meter with a tripod based EM5. Out of camera jpeg resized to 1000px for display.

    45mm 1.8 @ 1.8.

    GTC70475.JPG

    60mm 2.8 macro @ 2.8.

    GTC70476.JPG

    But as Mike said. There are ways we can fluff the overall look ( a very close subject and very far background, for example.). I've chosen to hide the background as much as possible here to concentrate things on the differences between the apertures.

    Gordon
     
  15. DHart

    DHart Mu-43 Hall of Famer

    Jan 7, 2010
    Scottsdale, Arizona
    Don
    Gordon... this visual demonstration is quite effective in conveying the visual difference of attempting to achieve a similar result with the two different lenses.

    Differences in compression are quite visually evident, as well as differences in DOF. Nice visual example!
     
  16. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    Gordon
    For me it wouldn't be the difference between the subject and the background (most of the time). It would matter more for an object with depth. It'll be obvious in a tight head shot where the ears would be much softer with the 45 wide open compared to the 60 wide open. A head and shoulders portrait is a place where I would use either of these lenses a lot.

    Personally I consider 1.5 stops significant enough that I sold the Panny 45mm 2.8 macro and purchased the 45mm 1.8 and 60mm 2.8 because I specifically wanted the thinner DOF the 1.8 lens could provide, because I specifically shoot these focal lengths at short to moderate distances, where the difference is obvious. I understand it doesn't matter as much to others.

    Gordon
     
  17. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    Gordon
    Thanks Don,

    I do what i can.... :smile:

    Gordon

    p.s. the real problem is I'll do something like this and prove myself wrong. :eek:
     
  18. MAubrey

    MAubrey Photographer

    Jul 9, 2012
    Bellingham, WA
    Mike Aubrey
    It was my failure. I didn't make clear that my purpose was to think in terms of how someone would do portraiture.

    Me too.

    @Flash, thanks for the extra images!
     
  19. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    Getting back to the original post, there's an implicit assumption in the question that the lens is going to be used wide open. OK, it's also apparent that we're being asked about the shallowest DOF obtainable from each lens but the OP does say "…for the same dimentions of the photographed object (let's say a portrait, which will be the same size in the frame in both cases)" and then they give a comparison of DOF calculations based on distances of 10 m and 13.3 m respectively. I really have to ask whether such distances are realistic if we're discussing a portrait and if they aren't realistic then what information is the OP really trying to get.

    It seems to me that if I'm going to be taking a portrait at a distance of 10 to 13 metres and the depth of field is going to extend somewhere between 1.8 and 2.8 metres behind the subject (based on the principle that one third of the DOF is in front of point of focus, two thirds behind) then I'm most probably going to have something behind the subject in focus regardless of which lens I choose if I'm working indoors. After all, if you're indoors and need to be 10 to 13 metres away from your subject, what are the odds that there's going to be something that will make a difference to the portrait that is going to be between 1.8 and 2.8 metres behind the subject?

    Anything that's closer than 1.8 metres will get picked up in the depth of field with both lenses, and anything further than 2.8 metres away is outside the depth of field of both lenses. The only observable difference is going to be with anything between 1.8 and 2.8 metres behind the subject and if there's enough space for you to be working at a distance of 10 to 13 metres indoors, then what are the odds that you're going to be able to have enough free space behind for there not to be an issue over lens choice? I think there's an equally fair chance of there not being any issues if working outdoors because there may not be anything closer than 3 metres or so behind the person under those conditions.

    In other words, I don't think there's likely to be much of a difference in practical terms with these 2 lenses if you want to use them for portraits at the stated distance.

    So, if the aim is portraiture and the distances are significantly less than 10 to 13 metres, say 3 to 4 metres, then the DOF is a lot shallower, extends nowhere near as far behind the subject, and you tend not to have things in front of the subject to distract if you're taking a portrait. Once again, is there going to be a difference in practical terms? There definitely shouldn't be an issue if you've got some control over where the subject is placed in relation to the background. If you can't control where the subject is within the environment, then you may still be able to solve any problems if you can choose which angle you shoot the subject from because that may enable you to minimise the effect of any problematic background objects.

    And if we're not talking portraits then everything is going to turn on what the subject is, how it relates to the background and foreground, how much control you have over subject placement in the environment, and your working distance. If you've got control over subject placement and working distance you may well be able to arrange things so that the difference in the depth of the DOF zone simply is irrelevant and won't be an issue. If you can't arrange things in order to achieve that and you have to take what you get, then I'd suggest that the most important thing determining whether you choose the 45mm or the 58mm is going to be the distance you need to work at and how large you want the subject to be in the frame. DOF may very well not be the deciding factor.

    I've got no problems with Gordon's math or Mike's images, I just have problems with the question. Portraiture with the 45mm or 60 mm at 10 to 13 metres doesn't seem realistic to me. At those distances I'd be reaching for my 75mm or something even longer, definitely longer if I wanted head and shoulders only.