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Depth of field with AF ?

Discussion in 'Beginner's Corner' started by whiskerytorpedo, Mar 10, 2019.

  1. With my old 35mm SLR with manual lens, it was a simple task to focus and then read off the depth field from the lens barrel.
    However my new Olympus E-PL9 with 14-42 kit lens this now seems a bit tricky. I know the aperture and what focal length the lens is at...but how do I know how far away I am focused. What is the best solution for calculating DoF?
     
  2. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    That's a very good question. I don't think I've ever come across a distance display on a M43 camera and I have/had several. :confused:
     
  3. PeteRob

    PeteRob Well-Known Member

    there are some calculator apps you can get. The web site cambridge in colour also has an on-line calculator.
     
  4. I have downloaded an app ( hyper focal pro ) to my phone and it appears to work fine. The problem is that the information it gives is a bit difficult to use if I don't know what distance my lens is set at.
     
  5. PeteRob

    PeteRob Well-Known Member

    You have to estimate. It was never that precise using the lens barrel markings. With a 14-42 lens the hyperfocal distance at F8 (say) probably isn't that far. There's also depth of field preview, which on a mirrorless, may not suffer the same viewfinder darkening as on an SLR. I have never made much use of it.
     
  6. Terrywoodenpic

    Terrywoodenpic Well-Known Member

    The distance displayed in many digital cameras is extremely unreliable especially at shorter focal lengths.
    The repeatability of the readings at the same distance also seems to be extremely low.
    However many cameras choose not to display a distance at all, nor is it recorded in the exif data.

    Unless you measure the distance some other way, there is no practical way to estimate the depth of field.
     
  7. EightBitTony

    EightBitTony Well-Known Member

    It's not in the commonly displayed EXIF, but it's in the RAW file.

    upload_2019-3-11_21-18-27.png

    Reliability I can't comment on.

    Also, exiftool can extract it as well (different image file).

    upload_2019-3-11_21-27-32.png
     
    Last edited: Mar 11, 2019
  8. PeteRob

    PeteRob Well-Known Member

    The only time I look at focus distance is when pbotographing birds with a super-tele and it does rapidly transition between a sensible number at 100m or so and a meaningless stab at infinity.
     
  9. GeoffR

    GeoffR Well-Known Member

    Always assuming that the lens reports focused distance. I shall have a deeper delve into some exif data, thanks for the information.
     
  10. PeteRob

    PeteRob Well-Known Member

    It depends on the camera and lens. Some AF systems can use the information, presumably to reduce "hunting". For my Canon the information sometimes shows up in the EXIF sent to Flickr but I don't think DPP or LR will show it.
     
  11. Excellent advice guys. So from what I can gather I need to work out the DoF with an app or chart. Then focus on something at what I believe to be the correct distance. With the the touch screen focusing enabled this should prove fairly straight forward. Some experimentation is required.
     
    Last edited: Mar 12, 2019
  12. Terrywoodenpic

    Terrywoodenpic Well-Known Member

    Unfortunately that focus data is not that useful as it always gives it as a fairly wide margin. in this case showing the actual focus point to be anywhere between
    3.61m and 5.2m. You would also find that if you took a number of individual shots of the same subject the camera would report and focus on different points.
    Many cameras including Canon have a wide variation of focus that they consider within tolerance.
    Greater accuracy is usually given by cameras using contrast detection or Hybrid focusing.

    However I am unable to read Distances at all, on my Fuji cameras in the exif data.
    neither Exif tool nor KUSO Exif viewer show it for them.
     
  13. GeoffR

    GeoffR Well-Known Member

    Thanks for the information Tony, Apple Preview does indeed give the focused distance in the EXIF data from a Nikon ,NEF file, not necessarily in a helpful way as there are no units attached. I now need to look at a file from a newer camera in a later version of Preview and see if that is more helpful.
     
  14. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    Thanks to the above I've now found that the "Focus Distance" is shown in the JPEG EXIF data from the Olympus E-PL5 - so it is likely also available for the OP's E-PL9...

    20190312 Screenshot Distance EXIF.jpg
     
  15. Chester AP

    Chester AP Well-Known Member

    You must also consider the change in sensor size from 35 mm film to a digital 4/3 sensor.

    Look at the recent 'Noise' AP issue dated 16th of March, where they discuss aperture and depth if field differences for different sensor sizes on page 41. This is in an articles where they use digital cameras with 4 different sensor sizes to compare noise in the images. For example, for depth of field purposes, F 8 on 35 mm (or digital 'full frame') is the equivalent of about F 5 on an APS-C camera body and F 4 on a 4/3 sensor. This puzzled me when I went from 35 mm film to an APS-C DSLR because I was getting more depth of field than I expected.

    So the depth of field on a 4/3 sensor will be much greater than on a 35 mm for the same size aperture, but there is also the problem that the diffraction problem that worsens resolution at small apertures starts at larger apertures on 4/3 sensors than on 35 mm (so if F 22 on your 35 mm camera, it may be F 11 on your 4/3 digital camera).

    At least with a digital camera body you can check the shot, and enlarge parts of it, to check what is in focus, and take another shot at a smaller or larger aperture if required.
     
  16. PeteRob

    PeteRob Well-Known Member

    No it's the same. It is greater for the same F number and image framing because the focal length is less on the smaller sensor camera and hence the aperture physically smaller. It is about one stop equivalent 4/3 cf 35 mm.
     
  17. Chester AP

    Chester AP Well-Known Member

    I know that the F number is a figure calculated from the lens focal length and physical size of the aperture, but since we use F numbers to describe aperture 'sizes', and since it is impractical to physically measure the actual size when using the lens, surely the advice about F numbers and depth of field for different sized sensors is helpful?

    This is also part of the reason why it is often impossible to get a shallow depth of field on cameras with very small sensors, unless a long focal length is used. It's also relevant when users progress from a smartphone (with a minute sensor) to a 4/3 or APS-C camera body and then find out the importance of focusing and depth of field.

    There is scope for AP to do a detailed article about this, rather than just referring to it when writing about other things like the noise article in the recent issue.
     
  18. GeoffR

    GeoffR Well-Known Member

    What do you actually mean when you say "for the same size aperture"? Do you mean the same physical diameter or do you mean the same aperture value (f number)? I suspect you mean the latter, in which case I think you are correct as the focal length of the 4/3 lens for the same angle of view is half that of that of a lens on 35mm film/Full frame sensor.
     
  19. PeteRob

    PeteRob Well-Known Member

    I think they did so, couple of years ago. The most recent discussion I've seen was a review of the new 50 MP Fuji GX camera against the Canon 5Dsr and whichever Nikon has the high resolution 35mm Sony sensor. That review went to long lengths to ensure "equivalence" of the images. Unfortunately I can't remember where I read it.
     

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