1. Forkbeard

    Forkbeard

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    Is there any reason I can't focus an 18 - 55 Nikon VR kit lens on a D90? It won't even focus manually. It's wrapped up to go back, just thought I'd ask if there was anything I hadn't thought of. The camera is set to AF and there isn't a switch on the lens.
     
  2. gremlin16

    gremlin16

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    Turn camera focus mode to ‘M’? Can you manually focus now?
     
  3. Forkbeard

    Forkbeard

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    Nope, it appears to be completely dead. The focus area lights up on M, but the lens doesn't focus. The camera is fine by the way, it works with my 35mm 1.8.
     
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  4. MatBin

    MatBin

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    Silly question but you are turning the focus ring on the lens aren't you?
     
  5. Forkbeard

    Forkbeard

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    Yep! I know you had to ask :D

    It's like the focus mechanism is just not connected.
     
    Last edited: Jun 11, 2018
  6. toohuge

    toohuge

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    Is this a new AF-P lens? If so, I do not think these are 100% compatible with the older bodies.
     
  7. Forkbeard

    Forkbeard

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    I think it might be actually, yes. It's back in the box and wrapped to go back so can't check.
     
  8. StewartR

    StewartR Efrem Zimbalist Jr Advertiser

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    I bet that's it. AF-P lenses are really only compatible with comparatively new bodies. Here's Thom Hogan explaining the messy compatibility issues:
    http://www.dslrbodies.com/lenses/lens-articles/general-nikon-lens-info/understanding-the-af-p.html
     
  9. Forkbeard

    Forkbeard

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    Messy is the word. That is a bit disappointing; I like kit lenses on the whole. Not the end of the world though, I'll look for something else. I only wanted it as a light travel lens for a holiday.

    So did the older AF-S types work? The ones with the af-m switch and no lock button?
     
    Last edited: Jun 12, 2018
  10. toohuge

    toohuge

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    Yes. Any af-s lens will work on the d90. The af-p are optimized for video - I believe they have a stepper motor inside.
     
  11. john.margetts

    john.margetts

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    My two newest Canon (yes, I know) lenses will only manually focus with the shutter button being half-depressed, otherwise there is no power to the lens.
     
  12. Forkbeard

    Forkbeard

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    That sounds awkward.
     
  13. MatBin

    MatBin

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    Why do they need power to manually focus, surely you just move the A/M lens switch to M and turn the focus ring, are these FF or EF-S lenses?
     
  14. toohuge

    toohuge

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    Some lenses now have no manual interaction for focusing, i.e. the focus ring is not attached to the element group physically. The focus ring is measured and then adjusts the lens accordingly.
     
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  15. ancient_mariner

    ancient_mariner

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    That's it - focus by wire. It's one of the reasons AF-P lenses aren't worth anything used.
     
  16. john.margetts

    john.margetts

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    One EF and one EF-S lens. The focus ring is just actuating a sensor which in turn drives the focus motor.
     
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  17. Mr Badger

    Mr Badger

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    That'll be the STM motor type canon lens, not to be confused with the USM motor type ones? The only one of those I have is the 40mm pancake lens, which I suppose was too small to wedge a USM motor in there. The other that springs to mind is the 50mm f/1.8 STM. Nothing wrong with the design or AF function, it's just they need the power on to focus even when using manual. Not that many people tend to use manual focus on AF lenses on a regular basis these days (unless it's a macro lens).
     
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  18. MatBin

    MatBin

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    Interesting, does back-button focus work, I'm thinking you wouldn't press the shutter release by accident. Thanks for the explanation.
     
    Last edited: Jun 12, 2018
  19. WD40

    WD40

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    I recently picked up the Nikkor 10-20mm AF-P lens. The FBW focus does feel a touch odd and there's a nagging doubt it won't be as reliable as mechanical focus lomg term. Mind you, it's so slow and so wide focus doesn't really matter. Who needs it - focus schmokus :)
     
  20. WD40

    WD40

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    NB - do the Canon and Nikon systems differ in their implementation? I'm guessing there is either a direct-printed optical encoder or magnetic position sensor. Am I warm?

    Can anyone think of a benefit to it aside from cheapness? By losing the traditional mechanics are there potential benefits in terms of optics to price / weight ratio?
     
    Last edited: Jun 12, 2018
  21. john.margetts

    john.margetts

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    Yes, focus accuracy. When lens designers design a lens with manual focus ability as well as autofocus, they need to choose one of two defects. In order to have fast autofocus, the total movement of the focusing element needs to be small. This makes accurate manual focus nearly impossible as there is a minimum amount you can move your fingers. In order to gave accurate manual focus, the total movement of the focusing element needs to be large. This makes autofocus very slow. When you are only moving an actuator and the motor moves the focusing element, it is possible to have large finger movements giving a small lens movement.

    An example from my older lenses: my 1983 Cosina 50 mm lens needs you to turn the focus ring through 300 degrees to move from 1 metre to infinity - allows very fine adjustments. My old 18-55 kit lens needed you to turn the focus ring through about 30 degrees to change the focus the same amount - only allowing coarse adjustments.
     
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  22. StewartR

    StewartR Efrem Zimbalist Jr Advertiser

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    Excellent explanation!
     
  23. HoppyUK

    HoppyUK

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    Yes, though it describes the different 'gearing' needs of manual focusing compared to AF, rather than focus-by-wire vs mechanical. TBH, manual focus considerations have been an afterthought pretty much since the introduction of autofocus and neither AF lenses nor AF cameras are optimised for manual focusing. A lot has changed since the days of manual-only focusing when basically the whole lens was shifted back and forth on a big mechanical helicoid screw, and SLR viewfinders clearly showed what was going on.

    Cost is probably a major factor in focus-by-wire, though I don't see any downsides in principle - only in implementation, where it's still considered low priority and often feels a bit woolly. But many/most mechanical AF overrides are equally imprecise and some are frankly horrible. Focus-by-wire can be very good in manual and has an advantage in that gearing can be electronically adjusted, such as twist it fast for big movements, turn slowly for fine adjustment (eg Olympus).
     
  24. john.margetts

    john.margetts

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