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Olympus 7-14 F2.8 Pro field curvature ?

Discussion in 'Native Lenses' started by Sootchucker, Aug 23, 2016.

  1. Sootchucker

    Sootchucker Mu-43 Regular

    111
    Aug 9, 2012
    Had my Olympus 7-14 F2.8 Pro for about a year now, but this weekend I actually took it along with me for some serious landscape shooting.

    When I got back, I noticed that the edges of the frame were quite a bit less sharp than the centre (at 7mm), and that was at apertures of F5.6-F8

    When I did a little more testing at home, I found that if I set the focus point on something right at the edge of the frame (and nearest the camera), rather than a further off centre point, then the edges (and centre) were much sharper and more in line with what I'd expect. For such a wide angle rectinunlar lens, I obviously don't expect the edges to be as sharp as the centre, but my initial images were actually quite soft at the edges (not just a little bit worse).

    This leads me to believe (rightly or wrongly) that the 7-14 F2.8 whilst a very sharp lens, does suffer from field curvature much more than the Panasonic 7-14 F4 that this replaced. Are my assumptions true and if so, what method do people use to ensure maximum DOF and sharpness across the frame please ?
     
  2. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    I haven't noticed any field curvature issues but I also haven't looked for them.

    You said you were doing "serious landscape shooting". Was there a significant difference in the distance of whatever was at the edges of the frame to whatever the focus point was? You often need something strong in the foreground of an ultra wide shot in order to avoid having the foreground look like a large empty space with the interesting areas of the image looking like they are receding into the distance. If there is too much difference in the distances between whatever you're focussing on and whatever is at the edges of the frame, then DOF may not be great enough to ensure that both the edges and the subject look sharp at a given aperture. The best solution to that is to use a smaller aperture to increase DOF.

    Apart from stopping the lens down further, there really is only one way to increase DOF and that is to increase the distance between the camera and whatever you focus on. You can either move further away which is going to change the proportions of near and far things in the frame, or you can shoot from the same point but focus on something further away than the subject but closer than whatever is at the edges of the frame. If you try doing that, remember that DOF extends further behind the plane of focus than it does in front of the plane of focus and the further behind the subject you focus, the more chance you run of the subject starting to look not quite sharp enough.

    Also remember that you can start to lose sharpness due to diffraction if you stop the lens down too far. With M43, diffraction starts to decrease sharpness somewhere around f/8 to f/11 and once diffraction starts to become an issue the question is going to be whether the gain in sharpness at the edges from stopping down further is going to be more valuable to you than any loss of sharpness at the subject due to diffraction. Sharpness just doesn't disappear drastically as you stop down further, it reduces gradually. Stopping all the way down to the smallest aperture the lens offers may not be a problem for some images and be a problem for others. It's worth trying.

    When it comes to comparing the PRO lens to the Panasonic lens, you need to remember that the PRO lens is a stop faster. If DOF is important to the image and you're going to be shooting wide open because you're shooting in low light and you're concerned about keeping your shutter speed high because you're hand holding and your ISO setting low for picture quality reasons, you may be worse off with the PRO lens because you're shooting at a wider aperture and reducing your DOF. You may be able to hand hold the camera better and avoid camera shake, you may have a lower ISO setting and less noise in the image, but you're also going to have less DOF because you're shooting at f/2.8 when you'd be shooting at f/4 with the Panasonic lens and whatever you gain as a result isn't going to help you if what you really need is greater DOF. Image quality depends on a lot of things and which of those things is more important can vary from image to image. Shooting wide open with the PRO lens because of the advantages you get from being able to shoot 1 stop faster is not what you want to do if what the image demands is greater DOF.

    There are a couple of other things you can try besides stopping the lens down further or focussing on something between the subject and whatever is at the edges of the frame:

    - use a tripod. Things start to "spread" at the edges of the frame when using an ultra wide angle lens so any blurring due to camera shake is likely to be a little more noticeable at the edges and that may be part of your problem. Using a tripod will also let you use slower shutter speeds and stop the lens down further than you can if you were going to handhold the shot.

    - in processing you can try using more sharpening at the edges of the frame than on the subject by using an adjustment brush or radial filter in your processing application. You can also try darkening the edges slightly with a vignette to make the lack of sharpness there less obvious and to focus the viewer's attention more strongly on the subject so they pay less critical attention to the edges of the frame.

    That's about all I can offer.
     
    • Informative Informative x 1
  3. Phocal

    Phocal Mu-43 Hall of Famer

    Jan 3, 2014
    This makes no sense. You can always stop down the Pro lens to match the Panny and get the greater DoF but you can't open up the Panny to ƒ2.8 to say lower your ISO or use a faster shutter speed. There is no situation where I could see the Pro lens making someone worse off then the Panny other then maybe size/weight (that's with the understanding that they are of equal IQ, which I have no idea when it comes to that).
     
  4. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    My point was simple. If you're comparing the 2 lenses and you use f/4 with the Panasonic and f/2.8 with the Olympus in order to get the fastest shutter speed you can get at low ISO, then what you're doing is reducing the DOF you will have in the shot taken with the Olympus lens. If reducing your DOF by shooting wide open at f/2.8 results in you having out of focus edges with the Olympus lens when shooting at f/4 with the Panasonic lens does deliver sharp edges and what you want is sharp edges, then you are worse off.

    And yes, you can't open the Panasonic lens up to f/2.8 but that may just be the reason why you get sharp edges with the Panasonic lens, and opening up the Olympus lens to f/2.8 may be the reason that you don't get sharp edges which is what I was trying to say. The problem may not be the lens but it may be the way it is being used. It can be very handy to have a faster lens but taking advantage of that extra speed can work against you in some situations.
     
  5. Clint

    Clint Mu-43 All-Pro

    Apr 22, 2013
    San Diego area, CA
    Clint
    To get the best sharpness across the image - based on my experience with the Nikon 14-24mm, both Olympus's 7-14mm lenses (although I have very limited experience with the f/2.8 lens), and the Panasonic 7-14 f/4.0; it seems to me when shooting at the widest FOV you are better off focusing as close as you can while meeting your desired DOF. Which is often from very close to infinite, even wide open.
     
    • Agree Agree x 1
  6. pkent

    pkent New to Mu-43

    7
    Jan 29, 2016
    I find the 7-14 F2.8 PRO indeed has profound field curvature. It also has some inherent weakness toward the edges of the frame even stopped down. This was obvious in my initial test shots done in a kitchen. It is a disappointment for Olympus’ latest/best wide angle. However in real world shots I find the problems not as bad as testing might indicate - the inherent depth of many subjects helps hide the weakness. As Clint says, setting the focus a little closer than you normally would helps.

    I photograph fairly static subjects with hi-res mode. If I am particularly worried I manually focus bracket. In landscape the dangers are extreme near-far compositions. When aiming for the highest quality I often focus stack at a moderate aperture and I take a specific shot for near edges. Of course all this is very difficult with changing light or movement. For those shots I stop down and live with the quality. The portability of m43 more than compensates.

    I would definitely be a customer for a revamped 9-18 with better behaved edges, updated sharpness, and the filter capability the bright 7-14 lacks…