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Lens Calibration Article 27th June edition

Discussion in 'AP Magazine Feedback & Suggestions' started by Jim Pascoe, Jun 24, 2020.

  1. Jim Pascoe

    Jim Pascoe New Member

    Hello, I’m new on the forum and don’t like to be critical. But there seems to be a fundamental flaw with the latest article on lens calibration. Point number 3 in the ‘how to’ section suggests using live view to ensure precision focus to help ‘avoid mistakes’. However I think this would completely negate the whole point of the exercise. The point of calibration is to check whether the optical focussing system is working. Live view by definition will show true focus accuracy at the sensor. Possibly you meant using live view to check the focus was targeted correctly, rather than focussed correctly.
    Also, as far as I can see it does not mention that the whole article only applies to DSLR cameras. Mirrorless cameras and lenses such as the majority now being sold and marketed do not need this calibration.

    I am a long time reader and subscriber of AP - an excellent magazine..

    Jim
     
  2. Craig20264

    Craig20264 Well-Known Member

    Welcome Jim. I'm not sure anyone from the mag ever dips into the forum anymore, so your points may go unnoticed. Better to e mail them direct I would think.
     
  3. PeteRob

    PeteRob Well-Known Member

    The same thoughts went through my mind. I found it a bit hard to credit the examples with the calibration of a 20 mm lens too, though I haven’t been motivated to see what the view of a ruler end on looks like through a 20 mm.
     
  4. Jim Pascoe

    Jim Pascoe New Member

    Thank you Craig - I have now done that.

    Jim
     
  5. swanseadave

    swanseadave Well-Known Member

    I read the article and ended up checking critical focus using the steel rule method described.
    The lenses I tried seemed ok,which I suppose is just as well since my camera doesn`t have the ability for lens adjustment.:(
     
  6. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    It's a pity that dSLRs no longer seem to have focussing aids built into the optical finder. I always felt I knew where I was with a split image or microprism spot. On the other hand, all the dSLRs that I've used have focussed correctly anyway
     
  7. swanseadave

    swanseadave Well-Known Member

    I agree with you Andrew.For critical shots these days I`ll use liveview on a tripod.The old days made manual focus so much easier.
     
  8. GeoffR

    GeoffR Well-Known Member

    Welcome

    Quite correct, with the mirror down you are using the focus module in the bottom of the mirror box, with Live view you are using the focusing capability of the sensor. Thus if the problem occurs when using the viewfinder, testing in live view won't help.
     
  9. Chester AP

    Chester AP Well-Known Member

    I read this too, and suspected that somebody didn't understand what 'Live View' does and where the displayed image comes from.
    The user manual for my Pentax K5 has an 'AF Fine Adjustment' section that explains the procedure much better than the article in AP, and clearly states that after making an adjustment the user should 'Take a test picture'. There is no mention of 'Live View', although he camera body allegedly has it for the benefit of users migrating from smartphones.
     
  10. PeteRob

    PeteRob Well-Known Member

    Live-view is there originally to enable video. True that people coming from phones expect to hold a camera at arms length in front of them. That's why some compacts don't have viewfinders, electronic or otherwise.
     
  11. Bazarchie

    Bazarchie Well-Known Member

    Some guides suggest taking a reference shot with live view, but then to turn it off for the rest of the testing. Tethering to a pc is another suggestion.

    Does anyone calibrate their lenses?
     
  12. PeteRob

    PeteRob Well-Known Member

    Not I. I’ve never seen any consistent lack of sharpness. If I did with a new lens I’d return it to the shop rather than mess around with micro-focus adjustment.
     
  13. EightBitTony

    EightBitTony Well-Known Member

    I have used micro adjustments on both the 7d2 and the 6d.
     
  14. IvorETower

    IvorETower Little Buttercup

    Agreed.
    As to the article on calibration..... I suppose it depends on what method of focus the camera uses and if you usually use live view or the optical view finder to frame and shoot a majority of your shots. If you usually use the optical viewfinder, and the camera uses a totally different method of focusing for live view, then it seems pretty pointless at best to use live view to calibrate the focus. I'm sure that these days, autofocus and the ability to "pixel peep" means that we are far more critical of minor focus issues than in the days of film. I know many, many years ago when we suspected my mum's old 110 film camera was not focusing accurately (3 or 4 position slider switch to adjust focus), I made up some test targets (circles of different colours drawn on cardboard), set them at various distances from the lens and took some test shots. These proved that something was seriously awry with the lens so she got a new camera. If I were to doubt the focus of any of my digital cameras, it would be very easy to repeat such a test, blow the results up to a huge order of magnitude on a computer screen etc etc - plus it would be "instant" instead of having to send a test film off for D&P
     

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