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AP Focussing Test Chart

Discussion in 'AP Magazine Feedback & Suggestions' started by Bawbee, May 27, 2011.

  1. Bawbee

    Bawbee Well-Known Member

    Anybody got a spare scalpel, or sharp scissors, for the cutouts? A 'Blue Peter' moment is required :)
     
  2. Malcolm_Stewart

    Malcolm_Stewart Well-Known Member

    I thought it was being bundled with next week's AP?

    And, is it designed to allow the key focus point to be perpendicular to the lens axis?
     
  3. Bawbee

    Bawbee Well-Known Member

    It is, my copy arrived this morning.

    For that Malcolm, you will need to read the instructions in the magazine ;)
     
  4. Dave_Rosser

    Dave_Rosser Member

    I am p....d off - I did a long reply to this thread and lost it all because the web site decided to log me off. In summary I said the Focussing test chart given away with this weeks AP is a complete waste of time and such devices have been deprecated by both Nikon and Canon. Any such device must have a focusing target normal to the lens axis otherwise you cannot be sure where the focusing sensor is really aimed - it is a slit and extends outside the indicators in the viewfinder. Test devices that meet the criterior of a normal focusing target are expensive, see http://www.whibalhost.com/lensalign/ for instance. I also said that it is generally thought that 90% or more of focusing problems are not due to back or front focus but to "pilot error", people do not read the instructions with their camera. Here is Nikons advice on using autofocus https://nikoneurope-en.custhelp.com/app/answers/detail/a_id/4585/kw/autofocus
     
  5. Mark

    Mark Well-Known Member

    Dave, I think you're being a little unfair. The sandwich box can be no more than an indicator of focusing accuracy. Anyone wanting the 'real mccoy' will have to buy the uber-expensive target plus a proper collimator to get accurate results. This 'Blue Peter version' does a reasonable job, but professionally may be more at home in Pret a Manger than a pro lens workshop. ;)
     
  6. TimF

    TimF With as stony a stare as ever Lord Reith could hav

    I have some sympathy with what Dave has written regarding the shortcomings of the "sandwich box" as a stand alone device. Definitely some vertical target is required to achieve a proper focused plane. That said it shouldn't be much of a task to knock one up - all that is needed is something along the lines of a large bar code to be attached to one side of the AP box aligned accurately with the zero position.

    The LensAlign device is rather more complex in that there is a backwards part to the focusing target with red blobs on it which are meant to be visible through holes in the front target. This is to ensure the camera is accurately perpendicular to the target (and hence the back/front focus marks on the angled plane). Doing without such is entirely possible if somewhat more fiddly.

    On the second part...

    That's true so far as it goes. However, back and front focus do exist, even in manually focused cameras. I had a slight front focusing issue with my M9 which I used LensAlign to prove to my satisfaction before taking the camera back for it to be corrected, which it was, free of charge.
     
    Last edited: Jun 3, 2011
  7. Dave_Rosser

    Dave_Rosser Member

    Focusing errors with Leicas .. never!!! Actually the opposite is true, many years ago (about 40) I had a Leica M4 and one of my lenses, a Canadian built 35mm f/1.4, had a very obvious focusing error - it had to go back to Leica to have the focusing cam re-profiled.
     
  8. Malcolm_Stewart

    Malcolm_Stewart Well-Known Member

    Here's my Blue Peter aided target; knocked up a few years ago:

    [​IMG]

    The target scales are available on the web: see here and I've then modified it to have a vertical focus plane.

    It's printed on a sheet of A4, folds flat, and is held in place using rubber bands. It really could do with being quite a bit larger, and certainly a larger vertical section for the AF sensor to focus on without ambiguity.
    In use it's sensible to ensure that the chart is perpendicular to the lens' axis by getting the central vertical line in line with the sloping vertical line above the aperture.
    For my longer lenses, I normally do that outside using the printed label on the vertical side of a 5L container as my target and judging errors by how the grass or gravel goes out of focus - pretty similar to what I need when shooting water birds & similar.
    I use Canon's Zoombrowser to tell me from the EXIF what amount of AF MA correction has been used for each shot, and I often use a LiveView focused shot as the quality baseline for reference. Definitely time consuming, but better than spending hours in a hide and then finding that none of the shots of the rare visitor are adequately sharp!
     
  9. mark_jacobs

    mark_jacobs Retired

    In which case a simple/minimal amount of additional/improvised scalpel, and perhaps some tape, work would suffice regards the 'target'. No? :)
     
  10. Fen

    Fen Well-Known Member

    You could use a bit of grated carrot out of the sandwich that was inside the package to do that :D :D
     
  11. mark_jacobs

    mark_jacobs Retired

    :) Happy to see that the amateur spirit lives on :p
     
  12. daft_biker

    daft_biker Action Man!

    If you place a bottle of beer next to the sandwich so the label is on the same plane as 0.....;)

    ....now if we've got the vertival target large enough to cover at least one whole focus point do we need to account for the plane of focus not being flat? With the likes of the 85mm f/1.2 shown in the link to the expensive setup the focus could be out by the time it gets over to the distance scale:confused:
     
  13. swanseadave

    swanseadave Well-Known Member

    The test chart is all very well if you have a camera that does have a fine focus adjustment.Many cameras do not,my A100 included.:(
     
  14. TimF

    TimF With as stony a stare as ever Lord Reith could hav

    All autofocus cameras have fine focus adjustment. It's called turning the AF off and twisting the lens barrel yourself! ;) ;)
     
  15. RogerMac

    RogerMac Well-Known Member

    I tried that and using an f2 lens manual was just as good as AF, but using a zoom at f4 manual was not as good as the AF. Of course I was using a ground glass screen without all the focussing aids we had in the old days.
     
  16. swanseadave

    swanseadave Well-Known Member

    :D:D:p nice one Tim.Manual focusing however is not as easy as in film days without split screen etc.Not to me anyway.
     
    Last edited: Jun 4, 2011
  17. GeoffR

    GeoffR Well-Known Member


    Which negates the reason for buying an AF camera in the first place. Anyway, I don't have to turn AF off to get manual adjustment with the zoom lenses I use most often.
     
  18. P_Stoddart

    P_Stoddart Well-Known Member

    I thought the article was going to be about comparing AF between different model/makers. So bit let down really.
     
  19. Malcolm_Stewart

    Malcolm_Stewart Well-Known Member

    I vaguely recall asking Angela some years ago if something on these lines could be done in a way which would remove operator skill (e.g. repeatable target moving towards camera), but can't recall getting a reply.
     
  20. GeorgeIII

    GeorgeIII Well-Known Member

    The chart instructions make no mention of whether the chart is applicable to prime or zoom lenses or both, although illustration no. 4 on p. 47 depicting adjustment on a 18–270mm zoom suggests it’s applicable to both. However, given that the instructions stress the need to set up according to the lens focal length does this mean a separate adjustment has to be made for every focal length likely to be used on a zoom lens? Quite a time–consuming task if it does. Would appreciate advice on this, as it would appear to be vital for sensible use of the chart. Or am I clearly more of a newbie than I thought?
    George
     

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