Manual Focus Distance Window On Lens

Discussion in 'Beyond the Basics' started by decado, Mar 24, 2010.

  1. decado

    decado TPF Noob!

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    So on higher end lenses (like my 10-22mm canon) there's a window that shows focus distance to help with manual focus. But I've noticed that all the way at infinity on this is a little out of focus, and I find it hard to focus perfectly by eye. So where exactly on this little scale would be a perfect infinity focus?
     
  2. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    Most lenses have a little play at the infinty point on the scale, this is to account for small changes in the lens due to things like temperature change (expansion and contraction of materials) and other factors. Often a tiny bit back from it will be infinity but its really something you have to play around with and see.
     
  3. decado

    decado TPF Noob!

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    Well that's too bad, I'm really bad at getting focus just right. Is it better then to just autofocus a third of the way into the scene for narrow aperture shots instead of trying to manual focus the lens at infinity?
     
  4. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    Is this for handheld or tripod based shots? If its tripod based you could use an angle finder - even the 3rd party ones (eg Hoodman or Seagull) work well and give a 2* magnification view to the image - that is if you don't have liveview on your camera which also (in most models) has image magnification.

    Failing that have you double checked that your diopter in the viewfinder is correctly set?
     
  5. decado

    decado TPF Noob!

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    It's tripod, I'll try the magnification thing but it's even harder to see on the screen than in the bright viewfinder, maybe I'll try the angle finder. The diopter is correctly set.
     
  6. Joves

    Joves No longer a newbie, moving up!

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  7. white

    white TPF Noob!

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    If your lens has a depth of field scale on the barrel, you could place one end of the aperture bracket at infinity, instead of actually placing the focus marker there. You'll get more depth of field. For example, at f/16 you might get a range of sharpness from 10 ft. to infinity, as opposed to 15 or 20 ft.
     
  8. decado

    decado TPF Noob!

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    I'm not really sure what you mean here.
    What exactly are these things?
     
  9. benhasajeep

    benhasajeep TPF Noob!

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    What some are suggesting to you is called hyperfocal focusing. This is a technique that can be used to increase the dof of a scene. Newer lenses this is harder to do since lens manufacturers have removed the scales from the lenses for some reason. But if its a technique you use often you can make your own scales with some tape and a little leg work.

    I could write forever trying to describe what I am talking about. So I will just say look up hyperfocal focusing. Many many sites on the net gives great information on how and why to use it.

    As for your situation I have the same issue with my mf 300 f/2.8 lens. It is actually at infinity when the focus line is in the middle of the left circle of the infinity symbol. All I did was put a piece of tape on my lens and mark new lines. I prefocus the lens all the time for hyperfocal focusing. So what I have done is a series of tests at each f-stop to find focus for the infinity symbol. On the piece of tape I made new reference lines for each f stop. So now I can just prefocus the lens and leave it alone. No focusing required since most of the time what ever I am taking a picture of is always a bit away from me.
     
  10. Garbz

    Garbz No longer a newbie, moving up!

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    Newer lenses which focus past infinity typically do so due to variances with the zoom scale along with other reasons posted above. I know with one of my lenses (can't remember which off hand now but I think the Nikkor 18-70mm f/3.5-4.5) at 70mm the zoom is much closer to the end of the scale when focusing on a distant object than at 18mm. Likewise if you focus zoom then click rather than zoom focus and click I would end up with a blurry pictures.

    On the flip side a misalignment issue in my 105mm macro has caused me to lose infinity focus. Doesn't worry me since I never use infinity on that lens, but this would be heartbreaking if it happened on my wide angle.
     
  11. Joves

    Joves No longer a newbie, moving up!

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    It is a good old fashioned focusing screen. Like you had in your old film Slrs. As you focus the center area becomes sharp when you are where you need to be, in the case of the Micro-prism. For the Split the two halves in the center line up.
     
  12. Vautrin

    Vautrin No longer a newbie, moving up!

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    The important thing to note here is modern DSLRs are not really designed for manual focusing. They can support manual focusing more as an afterthought then an actual design decision.

    Back in the days of film focusing was hard. So there were all sorts of aids to be able to focus correctly.

    Just go to the used dept of your local camera store (if they still have film cameras) and you'll see what I mean. Waist level finders with magnifying glasses to make sure things are in focus, focusing screens you can look through that tell you when an item is in focus (that's the katzeyeoptics page someone posted)

    But digital cameras don't have any of that because your digital camera is probably better at focusing in the majority of situations then you are. With top of the line cameras you can maintain focus on a fast moving object in the dark. And with facial recognition and all sorts of other technologies there's no reason for manufacturers to build in good manual focus.

    That's why if you take a lot of new DSLRs on manual focus mode, the pictures might look terrible. You'll have difficulty seeing if a shot is sharp on the viewfinder -- and a little bit of blurriness will ruin the shot on screen...

    I think part of this is due to the fact that smaller digital sensor size yields more depth of field. So when you look through the view finder with the iris of the lens wide open, you get more depth of field then with a film camera.

    I think the best thing is to understand your medium. Digital camera? Stick with autofocus except for unusual situations. Film camera? Play around with focus all you want..

    And don't knock film cameras -- they can be a lot of fun. With my mamiya (medium format, with something called a waistlevel viewfinder) there's a magnifier built into the viewfinder. You can see every little bit of the picture -- which parts are out of focus, which are in, and you can see every little detail.
     

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