1. Reminder: Please use our affiliate links for holiday shopping!

Maximizing DOF with the 20mm/1.7

Discussion in 'Native Lenses' started by scott, Feb 1, 2011.

  1. scott

    scott Mu-43 Veteran

    332
    Nov 15, 2010
    We have a big trip coming up in April, and I've been trying to get a feel for how to get the maximum DOF reliably with a lens that has no scale focusing, and a camera that won't display focus distance. (On the last big trip, I didn't have a tripod with me, and lost a lot of good pictures where the light was too dim for small apertures.)

    I've been constantly on the verge of buying a manual-focus 20mm or 21mm lens so that I could scale focus, but given my recent experience with shimming adapters and guesstimating correct focus, that seems like an unattractive option. It never occurred to me that lens adapters would make lens focusing scales inaccurate; I didn't realize it until I was way too focused (heh) on the idea of scale focusing.

    I even bought a couple of old accessory rangefinders, but time will tell if I actually can manage to reliably pick a distance for max DOF, find a focus point at that distance with the rangefinder, focus on that point with the G1's focus spot, and get correct focus. (That's a lot for a klutz like me to manage.)

    So lately I've been going around with a DOF table taped to the back of a G1 and trying to get a feel for estimating distances that will give good DOF. So far it's not going too badly, but I still wish there was a more precise but not cumbersome way to do this. I guess I'm just stuck in my old ways from when I was using an FM2 or a Fuji GW690. :-/

    Anyway -- this post is more wondering out loud than a specific question, but I'd be interested to hear what other people do in similar situations.
     
  2. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    I think you are making this much more difficult than it really is. It is easy to judge where in a scene would be the best distance to set focus.
     
  3. I don't really understand how scale focusing works. I'd just focus on your main subject and let the autofocus do it's thing. A 20mm lens inherently has a large depth of field, especially when stopped down.
     
  4. drpump

    drpump Mu-43 Regular

    154
    Oct 28, 2010
    I'm with Scott on this one. It depends a bit on the camera, but setting aperture to get the right depth of field in dim lighting conditions is troublesome. An aperture/distance/depth-of-field chart is required, and you need to guess the focus distance because the camera/lens won't tell you.
     
  5. scott

    scott Mu-43 Veteran

    332
    Nov 15, 2010

    That's true when you have a clear subject with less-important surroundings. However, a lot of what I'll be doing on this upcoming trip will be forest-interior pictures where there's no single clear subject, and I'm trying to get as much as possible of a complicated scene in focus.
     
  6. ~tc~

    ~tc~ Mu-43 Hall of Famer

    Oct 22, 2010
    Houston, TX
    If the goal is purely maximum depth of field, you only need to worry about the hyper focal distance, and learn to estimate those particular distances:
    F/1.7 = 52.1 ft
    f/2 = 43.8 ft
    f/2.8 = 31 ft
    F/3.5 = 26 ft
    Etc
     
  7. drpump

    drpump Mu-43 Regular

    154
    Oct 28, 2010
    So if the definition of hyper-focal distance at Hyperfocal distance - Wikipedia, the free encyclopedia is what you mean, then the nearest in-focus items are half these distances when the focus is set to its maximum, correct?

    So if I convert roughly to metres (metric guy, I'm afraid), the nearest in-focus objects will be at:

    f/1.7: 8.5m (26ft)
    f/2: 7.2m (22ft)
    f/2.8: 5.1m (15.5ft)
    f/3.5: 4.3m (13ft)
     
  8. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    If you focus on the hyperfocal distance (H), the nearest point in focus will be half the hyperfocal distance. If you focus on infinity, the nearest acceptable sharp point will be the hyperfocal distance.
     
  9. penfan2010

    penfan2010 Mu-43 All-Pro

    Nov 12, 2010
    NJ, USA
    My two cents

    Two other points:

    - I had a similar back and forth on another thread bec. I was using a MF 15mm lens set to what I would normally use as the hyperfocal distance for 35mm full frame; a number of forum members noticed that some of the shots I posted were out of focus, and one of them pointed out that given that the :43: sensor is about half the size of a full frame 35mm negative, the DOF range for a given aperture is also half. Not sure if you have to vary the DOF chart you have taped to your camera based on this
    - one other option to help sort this out (though probably more cumbersome than the DOF chart you are using and only an option if you are an iPhone user) is a handy iPhone app called Photo buddy which, among other things, shows DOF charts for all focal lengths and most make of 35mm and DSLR camera and :43: (it has settings for the Oly and Panny :43:; it correctly identifies the effective FOV for every given focal length on these cameras).
     
  10. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    To calculate the change in a depth of field scale or chart from one format to another, just use the crop factor to re-calculate the "effective aperture. The crop factor is 2 from 35mm to m4/3 and so when shooting at f/11 with a 35mm lens, you would use the f/5.6 data when used on a m4/3 camera.
     
    • Like Like x 3
  11. akulya

    akulya Mu-43 Veteran

    249
    Jun 21, 2010
    Lots of good advice so far,
    Basically it is inescapable that a large DoF requires a high f number, the higher the f number, the greater the DoF.

    Focussing the lens at the Hyperfocal distance (already mentioned) gives you the greatest DoF for that f number

    Diffraction limits the sharpness of lenses at high f numbers, and avaialble light limits your f number too. So even with very good light, you might impose a maximum of f11.

    Based on the available light, decide on an f number, then focus the lens at this distance. In another thread on this topic Mr. Hahn suggested putting a tight broad rubber band around the focus ring (very good advice) to stop it moving. You should also ensure the camera is set to manual focus only - and not to reset the lens when the camera is turned off/on. And there you have it set up.

    Dofmaster.com has all the numbers if your curious
     
    • Like Like x 1
  12. soundimageplus

    soundimageplus Mu-43 Top Veteran

    782
    Feb 2, 2010
    Worcestershire
    I don't know if you've ever considered this, but there are a couple of Voigtlander M-mount lens, the 12mm and 15mm that are so good for DOF at the hyperfocal distance that they virtually need no focusing. Both are relatively slow at f/5.6 and f/4.5 but even wide open they keep everything from 4-5ft to infinity in focus. The distance scales on them are huge and when manually focusing via the magnification in the viewfinder its difficult to see anything thats out of focus.

    These lenses are very popular with Leica users for street photography, who usually set a hyperfocal distance and just shoot away.

    I've included a sample of what the 15mm will do at f/5.6.

    Obviously low light is more of a problem. With lenses with no distance or aperture scale I use the focus 1/3 into the picture technique for general views and with the 20mm f/1.7 would use AF for closer subjects. Again I would use the 1/3 into the subject technique if I have enough depth.
     

    Attached Files:

    • Like Like x 2
  13. scott

    scott Mu-43 Veteran

    332
    Nov 15, 2010
    Thanks, and very nice picture!

    I had a CV 15mm until yesterday, when I sold it. It's a very nice lens, but the smearing of details in the corners was really bothering me; I know it's not a problem for some, but my pictures made it more noticeable. (I'll post some examples in the 15mm image thread soon.) I also have a Tokina 17mm, and there's a Canon FD 17mm on the way; I'll keep whichever one is better. DOF is obviously greater on those than on the 20mm. If I can get the adapters shimmed properly, they should work well.

    But I really like the "wide-normal" perspective of the 20mm, so I want to make sure I can get the most DOF out of that one as possible.

    I'll give the "1/3" technique a try and see if it gets me close enough.
     
  14. soundimageplus

    soundimageplus Mu-43 Top Veteran

    782
    Feb 2, 2010
    Worcestershire
    I had the same problems with the 15mm + a G1 but later versions of Photoshop and Silkypix eliminated it. I know what you mean about the 20mm though, I use mine an awful lot. With a bit of practice the 1/3 idea does help. I still like lenses with aperture settings and distance scales and infinity being infinity. I realise that AF lenses like a bit of infinity+ to stop them damaging themselves but theres nothing to beat those old lenses and a bit of accurate measurement.
     
  15. scott

    scott Mu-43 Veteran

    332
    Nov 15, 2010
    Interesting--I have a really old version of Photoshop, but didn't realize that was relevant. Was there a new tool to fix the problem? I assumed the smear was an optical problem, not a software problem.

    I feel the same way about lenses; if the 20mm wasn't such a great lens, I'd probably go back to MF lenses entirely for normal and wide-angle focal lengths. I just wish it wasn't such a PITA to get adapted lenses to scale-focus properly.
     
  16. penfan2010

    penfan2010 Mu-43 All-Pro

    Nov 12, 2010
    NJ, USA
    Agree

    Agree with Soundimage - I use the Cosina Voigtlander 15mm and it has very good DOF. That said, initially still had a bit of a problem as stated above bec. I did not compensate for reduced DOF on :43: sensor
     
  17. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    Same with my 12mm CV. Once you realize that, these lenses are very nice to use.
     
  18. soundimageplus

    soundimageplus Mu-43 Top Veteran

    782
    Feb 2, 2010
    Worcestershire
    Its apparently a de-mosiacing problem. Images didn't show it if processed in Silkypix but did in Photoshop. There was an update to camera raw and then all of a sudden it disappeared. Its not strictly a lens problem, but the design of the Voigtlander is a bit odd, very wide, very small etc. There were also some Zeiss W\A's which also did the same. All has been sorted now with the Adobe updates.
     
  19. scott

    scott Mu-43 Veteran

    332
    Nov 15, 2010
    Thanks--sorry I didn't respond to this post before, but I accidentally jumped past it to the end of the thread.

    But yes, I did use a table based on the smaller circle-of-confusion limit for m4/3. I've been using this one:

    Depth of Field Calculator


    That's odd and interesting. In a way I wish I had known all that *before* I sold the 15mm, but honestly I think I prefer the 17mm focal length. And besides--with the retrofocus lenses, I won't have to process out this problem, and I can keep using my old/cheap/free software.
     
    • Like Like x 2
  20. penfan2010

    penfan2010 Mu-43 All-Pro

    Nov 12, 2010
    NJ, USA
    Thanks

    Scott thanks for the link to the DOF calculator always good to have another reference.