EF 40 STM - my 1st impressions (sweeet) ;-)

Started Jun 21, 2012 | Discussions thread
photonius Veteran Member • Posts: 6,833
Re: af speed

mmullen wrote:

Arn wrote:

"L" designation does not make lenses fast. Small and light (AF group) lens elements usually result in a fast focusing lens. For example, the 85/1.2L with it's huge front element is certainly one of the slowest focusing lenses available (easily bested by the 85/1.8). The 40/2.8 is fast enough, pretty much comparable to the 50/1.8II (which is definitely not slow) as I said previously.

Please, don't spread rumors simply because it seems to make sense on the surface.

The speed of the AF has little or nothing to do with the size of the elements. For proof, look at the absolutely huge 400mm f/2.8 IS and the 300mm f/2.8 IS. Both have very large elements yet they are some of the fastest focusing lenses available.

The statement was ""Small and light (AF group) lens elements"; he is talking about the elements that need moving for focusing, which is key for AF speed.

In the 85mm f1.2 it happens that the whole front element moves in and out, so you have to move this huge mass. Further, due to the minimal DOF of this lens, the focusing mechanism has a very long focus throw to allow adjusting distance in fine increments.

For the 400 and 300mm lenses you mention, they are internally focusing.

If you look at one of the new Olympus MFT lens designs, it was completely redesigned to have just one single small lens element moving for fast AF.
Can't find the link right now, but I posted it here once, I think.

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Mike Mullen

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Life is short, time to zoom in ©

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