IR focus w/70-200 VR

Discussion in 'Night, InfraRed, and UltraViolet Photography' started by triangular, Sep 12, 2005.

  1. I'm recently into IR and its difficult to find the right focus. The 70-200 VR is of course a great lens, but Nikon did not put any IR reference mark on this lens and apparently it focuses IR somewhat closer than the visible spectrum. I've experimented and caught somewhat of a focus occassionally, but it seems very difficult. Landscapes and long depths are no problem to focus for infinity, or a tight aperture when it works, but I'm trying to do portraiture! It is harder than I imagined to find the right mark. There seems to be a very small margin for error at about 10 feet away. Nikon has not even published any IR focus conversions for this lens. Does anyone else have this problem? Any suggestions?
     
  2. nfoto

    nfoto Guest


    Have you tried to do AF with an IR filter in front of the lens? This should work.
     
  3. Bjorn,

    Yes I had tried AF with the filter, but perhaps I spoke too soon. I have found a measure of success now, though not as much as I'd like. I only received my IR filter recently, and every time I had the opportunity to use it we were having overcast days. There was enough IR light for photography, but I guess it wasn't enough to focus well through the very dark 89B filter. Today is a little cloudy but with bright sunlight, and I'm able to AF much better.

    However, it's still not quite as good as I'd like. My test subject is a pile of sand on a wood bench. With no IR filter I can focus on the grain very sharply. With the 89B it will focus, but not as sharp. At 3 meters away, I was using a single focus sensor aimed directly at the grain, tripod mounted with center-weighted metering and a -1.0 exposure compensation, ISO 320, Aperture Priority at F11. This time the light was not an issue, and the camera histogram shows most of the data in the 2nd brightest field.

    If these conditions are not enough to give the AF a pinpoint focus, I don't know what more could do it. It is focused, but not tack sharp on the granules of sand as in the straight shot. Now this is probably the perfect focus for shooting people under IR, giving room for that soft quality of IR light that I love so much. But it's not a good enough focus for doing close-ups (or fully zoomed), such as the beautiful IR images you capture with your plants and flowers. But I suppose you are not using a 70-200 VR for that, are you? On the other hand, I suspect it is more about the cameras AF ability (D2H) than it is about which lens I'm using. Any words of wisdom about improving the focus here?
     
  4. Wilk

    Wilk

    246
    Jul 28, 2005
    I'm getting my D70/live pixels mod sometime this week, so I'll be facing the same problem. I've seen others suggest you set up a test for each lens with a known distance to the subject and carfully examine the results and mark your lens on the tack sharp shot. I know mine will not focus correctly because the focus sensor will be visible light and the low pass filter will be IR.

    Something to consider.
     
  5. Found it!

    I sent a message to Nikon technical support. The response I received is to focus normally with the filter off the 70-200, then move the focus ring 3mm to the right. Have not tested yet, but that is straight from Nikon.
     
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