What am I doing wrong? (large aperture)

Discussion in 'Digital Photography' started by JDDavis, Mar 17, 2010.

  1. JDDavis macrumors 65816


    Jan 16, 2009
    OK. Need some help. Two pics below. Both were taken with my D90 and 50mm 1.8D. The first one (orchid) was shot at 1/4000, f/2, ISO 100 and is decently sharp. The second was shot at 1/1000, f/1.8, ISO 400. Both were shot at near minimum focusing distance on the 50mm.

    Why is the second so blurry? (not the bokeh but the flower...I was focusing on the center of the flower) Is there that much a difference between f/2 and f/1.8? I wouldn't think the ISO and shutter would've had that much to do with it. 1/1000 was plenty fast. Is there something else I'm missing? I know the 50mm is in now way a macro lense but I'm usually able to get good shots with it at it's minimum distance. I shot a bunch of these today trying to get f/1.8 to produce something nice but no luck. My one thought was that there was a slight breeze and that f/1.8 at minimum distance produced such a shallow DOF that the flower was moving in and out of focus as I shot??

    Thanks for the advice.

    Attached Files:

  2. JNB macrumors 604


    Oct 7, 2004
    In a Hell predominately of my own making
    At 12 inches, there's effectively no difference in the DOF for those two apertures. However, what you didn't mention was the distance to the subject and the distance to the relative backgrounds. Seems to me the second one had objects outside the far distance but still close enough to render some detail, while the first didn't. You can't really compare different subjects with different fore- and background objects, at different shutter speeds, ASA ratings, and apertures and try to figure out why one component ended up different. Gotta compare apples to apples.

    Try identical shots using the same subject with a tripod and just change the lens. You should see similar—although not exact—results.
  3. H2Ockey macrumors regular

    Aug 25, 2008
    This is a very likely cause. Need a much larger DOF i'm thinking f/11 or smaller.
  4. JDDavis thread starter macrumors 65816


    Jan 16, 2009
    The distance from the lens to the subject was practically the same for both shots but the backgrounds were different. The first shot had a green towel hanging maybe less than a foot behind the orchid and of course the second shot was basically a wide open background with several feet of depth in the image.

    So you are saying that the depth of the background has an affect on how the lens at that large of an aperture will focus? (as in if the second shot had a much shallower background I might have produce a sharper image?) In both images I was focusing on the center of the flower.

    After messing with them for a while I also noticed that though the background was exposed ok, the flower (in the second yellow one) was way overexposed. Even at 1/4000. Bringing down the exposure in post brought more detail back (but not enough). So I'm guessing there was too much light for that aperture even at 1/4000?

    I'm not really trying to compare the two pics. I'm just trying to figure out what I was doing wrong and get some sharp pics of these silly little flowers. Even the shots I took at f/5.6 weren't as sharp as I would've expected them to be.

    Thanks for the info.
  5. Digital Skunk macrumors 604

    Digital Skunk

    Dec 23, 2006
    In my imagination
    Where you hand holding or on a tripod?

    I know they are compressed, but neither look TACK sharp, and the 50mm while a great lens isn't the sharpest at that f-stop.
  6. toxic macrumors 68000

    Nov 9, 2008
    were these done on a tripod, or handheld? were you using AF or MF?

    the second image could be softer because you (or the flower if there was wind) swayed a little bit and moved it too much out of DoF.

    if you were using AF, it could have misfocused are not locked at all.

    it could be that your lens is noticeably softer or exhibits halation at f/1.8, but I think that would just be a contributing factor, not the cause.
  7. VirtualRain macrumors 603


    Aug 1, 2008
    Vancouver, BC
    I'm no expert, but I don't think it has anything to do with the background but how much or little of the flowers are actually in focus... correct? What I see is that there is a very narrow focal range in both images, especially the yellow flower. The difference is that because the white flowers are relatively flat, more of the petals are in focus whereas the yellow flower is more three-dimensional so less of it is sharply in focus. if you look at the white flowers more carefully, you will notice that it doesn't take much distance front or back from your focal point before they are out of focus as well.
  8. NathanCH macrumors 65816


    Oct 5, 2007
    Stockholm, Sweden
    Print off a piece of paper with some lines on it and conduct a similar test by laying it down on a table then taking a picture of it on an angle. This way you can tell if the lens is soft. I'd expect some point along the lines on the paper it would be sharp. Basically you're eliminating all other variables.

    If you do this, and no where along the piece of paper is sharp, then it has to be the lens. But I have a pretty good feeling it's just the flower moving a bit out of focus. DOF is very shallow at this aperture.
  9. JDDavis thread starter macrumors 65816


    Jan 16, 2009
    Thanks for all the replies.

    After reading the posts, reading on the internet, and taking a look at the Photocalc app on my iPhone that I never bother to look at...I think I was asking for something that the lens just can't do. I've taken pretty sharp pictures with that 50mm (just this weekend) so I'm confident there is nothing wrong with the lens (just the operator).

    According to the calculator on my phone at that focal length, aperture, and distance to subject (about 2ft) there is barely any DOF at all (less than 1"). I was hand holding but shutter speed was really high, but there was a slight breeze and I did have it on AF using the dynamic single point focus. In that environment there was probably no way to get it in focus. Also as someone mentioned above the orchid was in a static environment and "thinner" compared to the yellow flower so it fit in the shallow DOF better.

    I'll try again this afternoon but I'll have to get further back from the flowers and crop in later. I'm just compiling the evidence for why I need that 85mm micro.
  10. toxic macrumors 68000

    Nov 9, 2008
    a macro (micro) lens is not the solution to your problem. a new lens will not stop the wind, nor will it stop you from swaying back and forth. you need a tripod and preferably a focusing rail, and you need to stop down - there is little need for a wide aperture for shallow DoF or lots of background blur at macro distances. a short subject distance takes care of that.
  11. compuwar macrumors 601


    Oct 5, 2006
    Northern/Central VA
    Also consider Helicon Focus for macro work.

  12. GoCubsGo macrumors Nehalem


    Feb 19, 2005
    The above answers are real good and I haven't anything more to offer. However, may I use the orchid as my wallpaper?
  13. HarryPot macrumors 6502a

    Sep 5, 2009
    Getting a micro lens definitely improves the quality of macro shots, but it won't help with DoF. To the contrary, they give you less DoF.

    With my 105 micro, when focusing at 31cms (12.2in) and at f/2.8, the depth of field is just 0.01m (.04in). Going to f/32 gives me the same DoF.

    The benefit of a 105 micro, or 85 micro, is that you can step back and still get the same frame, while gaining precious DoF. And obviously all the other benefits of a dedicated macro lens, like 1:1 magnification.
  14. jampat macrumors 6502a

    Mar 17, 2008
    wth? Where do we get these lenses that don't obey the laws of physics?

    A 105 micro (on a crop body), at 2.8 gives you 0.03" dof, at f32 it is 0.3". Both are small, but there is a factor of 10 difference. Things get a little more complicated at macro distances, but it is still roughly a factor of 10 difference in DoF.

    Check out the following link for much more detailed info.

  15. toxic macrumors 68000

    Nov 9, 2008
    different macro lenses do not get you any more or less DoF in when the magnification is the same. all you gain is working distance.

    the main difference between a macro and non-macro lens is the macro has a max magnification of 1:1.
  16. HarryPot macrumors 6502a

    Sep 5, 2009
    I'm just copying what the lens manual says.

    Focused Distance: 0.314m
    Depth of Field: At f/2.8 it's 0.31-0.32, and in f/32 it also says 0.31-0.32.
    Reproduction Rate: 1:1
  17. HarryPot macrumors 6502a

    Sep 5, 2009
    I'm no expert in the physics part of lenses, but I was under the idea that a 1:1 magnification gives you a shallower DoF than a 1:2 magnification. Is that right? Or does it not has so much to do with the magnification but with the distance from the subject?

    Previously I was stating that a Micro lens would give you a shallower DoF than the 50mm prime lens. Is this correct?

    I've never been exactly sure how this works.:eek:
  18. schataut macrumors member

    Jan 13, 2010
    From my testing of Nikon 50mm/1.8 lens (using focus charts) at 1.8 this lens is not that sharp (may be just my copy). But at 2.8 it was very sharp, so I would suggest you to do few shots at 2.8 and make sure you use a tripod.
  19. toxic macrumors 68000

    Nov 9, 2008
    at 1:1, you will get less DoF, because you are closer to the subject than at 1:2.

    no. at if you are 10" away with a 50mm lens at f/8, DoF will be the same whether you use a macro or normal lens. using a longer lens and maintaining the framing yields the same DoF, but with a longer subject distance. the DoF decrease from the longer focal length is offset by the DoF increase from a larger subject distance.

    however, the amount of blur is higher with a longer lens than a shorter one, for the same f-stop and framing, but amount of blur (i.e. size of the blur disk) is not the same as DoF. the amount of blur depends only on aperture, the physical size of the diaphragm opening. aperture = focal length / f-stop.
  20. snberk103 macrumors 603

    Oct 22, 2007
    An Island in the Salish Sea
    I think VirtualRain has hit the nail on the hammer...

    The centre of the daffodil is pretty much as sharp as the orchid.... but most of the yellow daffodil sits behind and in-front of the plane of focus.... so it appears generally unsharp.

    The white orchid has a lot more it sitting on the plane of focus, so more of it appears sharp - plus the parts that aren't on the plane of focus are only slightly off the plane, so they are appear less unsharp than the daffodil where the unsharp bits are much more (relatively speaking) off of the plane of focus.

    IMHO, of course. Nice shots. I like the background on the daffodil.
  21. TheSVD macrumors 6502a


    Sep 3, 2008
    The Jolly Ol' Midlands, England
    sorry that this doesnt help...
    but how on earth did you shoot that first picture at iso 100 at 1/4000!? did you use an off camera flash? really bright sun?
  22. mrkgoo macrumors 65816

    Aug 18, 2005
    Also depends on how you are focusing. ARe you using one point and focus-recomposing? With such narrow DOF, using this technique can be very hit-or-miss.
  23. JDDavis thread starter macrumors 65816


    Jan 16, 2009
    Yeah, I know. The solution is learning more and increasing skill. That doesn't stop me from wanting a macro lens, an ultra wide, a long prime....:)

    I just have to learn to use them, if I can ever afford them.;)
  24. JDDavis thread starter macrumors 65816


    Jan 16, 2009
    I'd be very flattered if you did use it as a wallpaper. I personally like this one a bit better. If you'd like a larger file that's not compressed so much just PM me.:)

    Attached Files:

  25. JDDavis thread starter macrumors 65816


    Jan 16, 2009
    It was f/2, 1/4000, ISO 100 with the Nikkor 50mm 1.8D. It was on my front porch in direct, bright afternoon sun. The green background comes from a green bath towel that was held up behind it. Our house had white siding so that was providing a lot of reflected light as well. I'm not sure of all the physics, it was just working at the time.

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