Confused: Aperture reads 5.6 with 400 2.8 + 1.4x + 2x.

[Tobers]

Has anyone else tried this? Putting my 1.4x and 2x converters onto my 400 2.8 yields a rather interesting 1120mm f/8 lens (or 1456mm taking the 1.3x crop into account).

However, my camera, a 1DIV, still reads it as an f/5.6 800mm lens, ignoring the 1.4x converter. The exif also shows f/5.6 and 800mm.

Anyone else seen the same thing? I'd have thought the camera should know it's 1120mm and f/8.

Image quality was surprisingly acceptable.

 

[CT]

It's a pretty well known thing actually, only one converter communicates it's presence to the camera, and yes - results can be surprisingly good although not too consistent.

 

[I-S]

Yes, it's a known thing. However, none of the mk I or mk II TCs actually communicate anything - they have no electronics in. They simply have data passthrough between body and lens.

What they DO have is several extra contacts on the front, and there are extra contacts on the back of the lenses with which they are compatible also. These operate on a simple truth table of what combination of pins is shorted together. Those pins being shorted together tells the lens that either a 1.4X or 2X TC is attached (and the Life-Size Converter for the 50mm macro has a different ID in this system also). The lens itself then reports the lens + TC value back to the camera.

Since the back of the 2X II (the 2X I is not stackable without an extension tube) does not have the extra contacts, and the lenses don't contain info for stacked extenders, you simply get the result of the TC that is attached directly to the lens, ie the 2X. If you did it in the other order, with 2X on the back of the 1.4X (again, using an extension tube) you would find it would report as though only the 1.4X were there (since that would be what is attached to the lens).

If you were to put an extension tube on the back of the lens, followed by the TCs, the camera would not know that any of the TCs are actually there.

 

[Roy C]

As already explained, the Camera only sees the 2x. I sometimes use this to good advantage with the 300/2.8 and stacked converters on the 7D - the Camera reports f5.6 so attempts to AF and does so fairly well in good light and a reasonably contrasty target.
EDIT: I found out a while back that with stacked Kenco Pro tc's (1.4x and 2x) the Camera will report the correct aperture unlike stacking Canon's.

 

[Tobers]

Awesome - thanks! I might try my 1546mm lens at the rugby tomorrow just for a laugh. Following the action may be a tad tricky but I'll try anything once.

 

[alexw9]

Awesome - thanks! I might try my 1546mm lens at the rugby tomorrow just for a laugh. Following the action may be a tad tricky but I'll try anything once.

Make sure you post your results.