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Photo Forum / Film Photography / 35 mm / May 2007Canon 1DMKIII Question
Q. At what aperture does the new 1DMKIII lose autofocus? For example, my 20D (as well as the 5D, apparently) loses autofocus past f/5.6, meaning that if you use the 400 f/5.6L with the 1.4x TC you must manually focus (since the TC causes an effective focal length of f.8). My Fabulous EOS-1V, however, retains autofocus up to f.8. Do any or all of the 1D series cameras share this feature? > Q. At what aperture does the new 1DMKIII lose autofocus? This article explains the answer to your question. It's kind of complicated. http://www.imaging-resource.com/PRODS/E1DMK3/E1DMK3A4.HTM As I read the article, the centre point sensor works as a full cross sensor at f/4 and wider and as a horizontal-only sensor down to f8. There are 18 other cross-type sensors and 26 "assist" sensors. The vertically sensitive arrays in the cross sensors work at f/2.8 and wider. The horizontally sensitive arrays in the cross sensors work at f/5.6 or wider. Read the article to see if you agree with my conclusion. > > Q. At what aperture does the new 1DMKIII lose autofocus? > [quoted text clipped - 8 lines] > f/5.6 or wider. Read the article to see if you agree with my > conclusion. Yes, I think you summed it up. The camera will focus at f/8 if the center focus point is used. > Q. At what aperture does the new 1DMKIII lose autofocus? > [quoted text clipped - 5 lines] > My Fabulous EOS-1V, however, retains autofocus up to f.8. > Do any or all of the 1D series cameras share this feature? All 1-Series Canons AF at f8...clear back to the 1V, plus the EOS 3. That includes both film and digital. Who drools??? :)  SignatureImages (Plus Snaps & Grabs) by Mark² at: www.pbase.com/markuson >> Q. At what aperture does the new 1DMKIII lose autofocus? >> [quoted text clipped - 9 lines] > That includes both film and digital. > Who drools??? :) I realize that I know nothing about how autofocus works, but it strikes me that the amount of light available would be important.....IOW, wouldn't f/8 or smaller be adequate if you were focusing on the sun? And wide open should be inadequate if you were trying to focus in the dark........ Just my rambling thoughts........ >>>Q. At what aperture does the new 1DMKIII lose autofocus? >>> [quoted text clipped - 15 lines] > be inadequate if you were trying to focus in the dark........ > Just my rambling thoughts........ My Nikon D200, I don't think is rated for AF at f/8 but if I stack teleconverters, an f/2.8 becomes 5.6 at 2x & I'm not sure where another 1.4x takes it but somewhere above f/8. Anyways the AF works fine in daylight but the camera doesn't know it has two teleconverters, I had to grid of some tabs preventing that because that's another thing which is 'not supposed to work'. SignaturePaul Furman Photography http://www.edgehill.net/1 Bay Natives Nursery http://www.baynatives.com > >> Q. At what aperture does the new 1DMKIII lose autofocus? > [quoted text clipped - 15 lines] > be inadequate if you were trying to focus in the dark........ > Just my rambling thoughts........ Ok I am not going to say this well but more or less this is the deal. With phase detection some light is taken from either the right and left side or the top and bottom of the lens. The further off center you can sample from the lens the more accurate and faster the focusing will be, but it does mean that the lens needs to be able to open up enough so sampling areas of the lens are covered. Think of a range finder but instead of two lenses set apart you use on lens but use two parts of the lens set apart, this is how phase detection auto-focus works. If the lens can't open enough you can get enough separation between the views. Scott On May 21, 8:13 am, "William Graham" <w...@comcast.net> wrote: > "Mark²" <mjmorgan(lowest even number here)@cox..net> wrote in > messagenews:JQe4i.128550$Fk2.121075@newsfe08.phx...> Annika1980 wrote: [quoted text clipped - 19 lines] > be inadequate if you were trying to focus in the dark........ > Just my rambling thoughts........ Ok I am not going to say this well but more or less this is the deal. With phase detection some light is taken from either the right and left side or the top and bottom of the lens. The further off center you can sample from the lens the more accurate and faster the focusing will be, but it does mean that the lens needs to be able to open up enough so sampling areas of the lens are covered. Think of a range finder but instead of two lenses set apart you use on lens but use two parts of the lens set apart, this is how phase detection auto-focus works. If the lens can't open enough you can get enough separation between the views. Scott Ah! - That makes sense....Thank you. |
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