manual focus difficulty on dslr

Discussion in 'Pentax' started by djnathan, Feb 24, 2008.

  1. How accurate is the focus assist light with non-AF lenses? With some dismay I
    have noted that when using the focus assist on my K100 with several older
    manual lenses (K and M42), the critical focus is hit and miss. Even though the
    in-focus indicator light comes on, the results are generally not as good as
    when using an autofocus lens.
     
  2. The in-focus indicator light doesn't work for me with manual focus lenses on my k100d. It often indicates focus when focus is clearly off and is so unreliable I don't bother paying any attention to it.

    Your best bet is to replace your focusing screen so you have a split-image to work with... just like the olden days. The best is a Katz Eye, but they are expensive. A number of people have had success with the ones on ebay (from china)... I think they are old Minolta screens which have been modified to fit. Either way, you'll find that focusing should be waaaaaay easier. Without a screen I'm just not able to see the critical focus point in anything but really bright light.
     
  3. Is there a down-side to fitting a split image focusing screen? Any impact on how well the screen works for composing etc?
     
  4. My experience with the focusing aid (on K100D) is as below:<p>

    - I understand that the focusing aid has been designed to cover the central area of the viewfinder which is much larger than the size of the green square.<br>
    - The sensitivity of the "aid" for transverse, vertical and diagonal lines are not of the same level.<br>
    - The sensitivity of the "aid" (read "hit rate") is lower under tungsten light. <br>
    - The hit rate may change from lens to lens. I had good results with my Jupiter 85mm f/2 and poor results (under tungsten light) with my Vivitar Series 1 100mm f/2.5 Macro.<p>

    However, I like the aid and use it whenever the need arises. I just try to be on the safe side and take more pictures after moving the focus plane a little bit forward or backward. Narrowing the diaphragm will also help by increasing the DOF. <p>

    None of the above is a "scientifically valid" statement however; they are the experiences of a single person with his available equipment...
     
  5. If you revert to an old screen, you gain some manual focus ability at the expense of the nice bright image obtained with slow zooms and the bright auto focus screens.

    I certainly would not want to change screens and lenses.

    You will notice the screen does not get brighter with a 1.4 lens compared to a 2.8 with the modern bright screen. With an old screen, 2.8 will appear dim.

    The split is made for vertical lines. To use it with a horizontal or diagonal line, twist the camera to focus. That is partly why the microprism surround was added.

    Splits work fine in tungsten, just that there is less light and focus is harder.

    The way to use focus confirmation, is to start at infinity and turn the focus slowly until the light flickers, then stays on. Keep the active focus spot right on the subject or edge of the subject. Properly uses it is as accurate as auto focus.
     
  6. Be aware it is very likely "customized" screen will affect AE accuracy. In my case it required about +1/2EV compensation.
     
  7. In all modes? Even in matrix? I can understand this for spot metering, and less severe for center. But I expect matrix not be affected (so much...)
     
  8. The O-ME53 magnifying eye-piece might help with focus-by-eye (though it won't make your electronic focusing aid work any better).
     
  9. Don re your OP: How accurate is the focus assist light with non-AF lenses?

    All I can say is that it is less accurate than visual . And believe me, it is awfully slow for me doing bird in flight.

    You tell me how can I wait for focus confirmation in these two pictures (from A300mmF4):


    <img src="http://www.pbase.com/danieltong/image/86922496/original.jpg">



    <img src="http://www.pbase.com/danieltong/image/87052210/original.jpg">




    I do believe we should post more pict. Mine are just so-so. But they are more effective in conveying our thought


    Daniel, Toronto
     
  10. I have tried two different cut down screens from China. Daniel has my first screen, a very large split image. It was OK for macro but not very suitable otherwise. My second screen was a cut down Minolta X700 piece, not really very dark but poorly centred. It worked well but I was not using manual lenses enough to tolerate the distraction of the split image (which BTW looks huge in the viewfinder of an APS-C DSLR).
     

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