Fast auto focus

[britt777]

Does anyone know how much faster if any faster the auto focus is on the 400mm 5.6 than the 300mm. f.4 And if you tape the pins on the 400 is the auto focus still pretty fast?

Thanks Britt

[SolPics]

Here are a couple of good reviews of the two lens.

The 300 F4 L http://www.the-digital-picture.com/Reviews/Canon-EF-300mm-f-4.0-L-IS-USM-Lens-Review.aspx

The 400 F5.6 L http://www.the-digital-picture.com/Reviews/Canon-EF-400mm-f-5.6-L-USM-Lens-Review.aspx

[GyRob]

i have both and they are very fast,i think the 400 is just a bit quicker that coud be because i have it set to not focus closer than 8.5 mts the 300 set,s to 3 mts .so i think at these settings the 400 has less movement henc quicker focus, i use a 1dmk2 so dont know about pin tapeing i asume you mean with a canon 1.4 tc. .Note some on here say other tc's give autofocus using a Tamron 1.4.
Rob

[foxbat]

I have the 400 f/5.6 and have tried it with the pins taped on the 1.4x. It is still fast but it is not accurate. Seriously, don't buy the 400 f/5.6 expecting to get a fully functioning auto-focus 560mm lens. Unfortunately there are no cheap shortcuts to a quality 500mm prime.

[Cadwell]

Pin taping is at best, a dodgy practice, and it’s something I wouldn’t do with any of my lenses on a regular basis. I have tried it with a couple just to see. Without the pins taped, two things are communicated back to the camera. One is the change in max. aperture and the other is the fact that a TC is present. When the camera knows a TC is present it slows down the AF drive. This is to allow for improved accuracy with the smaller depth of field at a given f/stop that results from a longer lens. Taping the pins prevents both items of information being passed back to the camera. What results is often most unpleasant with the lens driving to a position past optimal focus, then driving to a position before, a position after, a position before… and eventually the lens judders into correct focus. It’s slow and it’s probably not doing the lens focus motor much good.

The second major issue with the tape trick is that you’re running the camera’s AF system out of specification. You cannot (and will not) get the same level of accuracy and low light performance with taped pins.

The latter point is also true for the TCs that don't pass the change in aperture back to the camera.