I've got a question which I've searched all over for the answer and have gotten conflicting answers or vague ones, and it seems like a fairly simple question:

I am deciding between the EOS1, 1n, or 1v. It will primarily be used with the 28-135IS and 100-400IS. From what I've read, the *central* sensor (or the only sensor in the case of the EOS1) goes from a cross-type to a single-axis with lenses slower than 2.8 (1 and 1n) or 4 (1v). So far I understand perfectly. But what about the *other* sensors on the 1n and 1v? Do they not work at all with a 5.6 lens? Will therefore using the 100-400IS on a 1n or 1v basically reduce it to an EOS1 in terms of AF, i.e. just one single central sensor? Many thanks to anyone who can clear this up for me!

-- Jay (infinitydt@aol.com), January 15, 2002

Answers

Jay, to quote from the Canon booklet "EOS-1v for Professionals," page 19: "Each of the 45 focusing points within the Area AF is composed of horizontal line detection sensors. These sensors operate with EF lenses having a maximum apertue of f5.6 or greater."

The brochure goes on to say that in addition to the 45 horizontal line sensors, there are six vertical line sensors which work with lenses f2.8 or greater, and one (central) cross sensor which works with lenses f4 or greater.

So yes, you have 45 sensors when you use an f5.6 lens, but they are all horizontal. You must use a faster lens to have the benefit of the vertical and cross sensors.

As an aside, I own an EOS-1 and it is a fine camera, quite adequate for the things I use it for. But the price of the 1n is so low at this time that it makes little sense to pay $500 or $600 for a used EOS-1 when you can get a new 1n for $900 or less.

I have an EOS-1, but have not used the 1n or the 1v. However, to extrapolate from some things I do know from personal experience: My A2 has five focus points and I do not lose any of them when using a 75-300 f4.5-5.6 lens at full extension. So it does not seem likely that a more advanced model would be worse in this regard.

-- Dave Jenkins (djphoto@vol.com), January 15, 2002.

I used to own an 1N and it behaves as described in the above post: all 5 sensors work with F5.6 or faster lenses. However, without the benefit of a fully enabled center cross sensor, I found slow zooms nearly useless for my type of work. In other words, an EF 100-300 4.5-5.6 USM racked back 'n forth on my EOS 1N. In contrast, the same zoom could focus fine on my EOS A2.

-- Puppy Face (doggieface@aol.com), January 15, 2002.

The A2 is a very under-rated camera.

-- Dave Jenkins (djphoto@vol.com), January 15, 2002.

The A2 has an F5.6 cross-type sensor. Before you cry "Why not the 1N?!", it is only a normal precision sensor (it will focus to within 1/2 the DOF of the lens of perfect focus), whilst the EOS 1s and the EOS 3 are high-precision when cross-type, so they will focus to within 1/3rd DOF of perfect focus.

The EOS 1 acts in the following way: With an F2.8 or faster lens, it will cross-type (not sure about precision...perhaps someone can enlighten me?) focus, otherwise it will have a single-axis focus up to F5.6, where the AF cuts out.

The EOS 1N: All 5 sensors work to normal precision, single axis at F5.6 or faster. At F2.8 or faster, the central sensor switches to cross-type High-precision focus.

EOS 1V: At F8, the central sensor works in single-axis, normal precision mode. At F5.6 the other 44 sensors join in, single-axis, normal precision. At F4, the central sensor switches over to cross- type, high-precision. At F2.8 a number (11 I think...again, perhaps someone can enlighten me) of the other sensors, clustered around the middle of the viewfinder/image will switch to cross-type, high precision mode.

The EOS 5 (A2) has 5 sensors, all of which always operate in normal- precision. The central sensor is cross-type, the other 4 are single- axis.

Remember also that when using a zoom lens, only the SLOWER maximum aperture is taken into account. This means that on an EOS 1V, a 24- 85 F3.5-4.5 USM will NOT ever be able to use cross-type focus, even in the centre, because the slower end is F4.5, which is slower than F4. The camera will not switch at some point in the range of a zoom. This is one reason that the 28-80 F2.8-4 L USM was replaced with the 28-70 F2.8L USM, because the former could not use cross-type focus.

In answer to your question, none of the cameras will give cross-type focus with the lenses you mention. However, from my experience with EOS 5, EOS 3 and EOS 1V, the EOS 1V will be much faster and more accurate than the other two bodies. It will also give you the option of using a 1.4X TC on the 100-400, and maintain AF on the central point.

-- Isaac Sibson (isibson@hotmail.com), January 16, 2002.