Panasonic 20mm f/1.7 Auto Focus

Started Feb 14, 2013 | Discussions thread
micksh6
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Re: Slower, but not slow
In reply to Anders W, Feb 15, 2013

Anders W wrote:

micksh6 wrote:

Anders W wrote:

damondean wrote:

Anders W wrote:

damondean wrote:

In my experience, the Lumix 20 1.7 focuses fine on Panasonic bodies. I have a GF3 and had a GX1 for awhile, and the lens focuses great on both bodies. I now have an OM-D, and not only does the 20 focus slower on it, it also struggles to lock focus in low light. It's a bummer, but I still love the lens.

That's strange. I use the 20/1.7 on the E-M5 and focus speed is just fine (and faster than on my G1). See my tests here:

http://forums.dpreview.com/forums/post/50110471

As to difficulties to lock focus, the 20 has no greater trouble with that than other lenses. On the contrary. Ability to lock is just a matter of light intake and the 20 is a fast lens, the second fastest AF lens for mFT.

So if you have difficulties with that, you are doing something wrong or are shooting under conditions which are hopeless for any lens.

I have tested locking capacity too against other (slower) lenses, using exactly the same target under exactly the same light conditions. As expected, the 20 gives up later, not sooner, as the light level falls.

Well...I had the GX1 for a couple weeks, then bought the OMD to test which one I liked best. Conditions were a dim room (1600, 1/100th, f/2), and I used the 20 on each camera under the same conditions. The GX1 locked focus easily, the OMD could not. I found with the OMD I could switch to a different focus spot (a more defined facial feature a few inches from where I wanted to focus,) and it would then be able to lock focus. Same lens, different camera, same conditions, much different results. In terms of image quality, the OMD is much more impressive, and for me this was a bigger priority so I didn't keep the GX1.

Different bodies (the GX1 and the E-M5 in your case) may well differ in their ability to handle a given focus target. See here for example:

http://forums.dpreview.com/forums/post/42293633

The lens, by contrast, isn't even involved in the process of deciding whether and when to lock (that's up to the body) and obviously projects exactly the same image on the sensor of either camera (if you did things right).

You concluded that the lens worked less well on the E-M5 than on the GX1. I would rather conclude that the E-M5 and the GX1 have different AF abilities for the target and AF mode you decided to test.

Maybe. It is also possible that Panasonic implemented slightly different AF algorithm for this lens. To optimize number/distance of focusing element movements for 20mm lens AF motor, in exchange for some focusing accuracy, for example. I don't know the likelihood of this, though.

I consider that highly unlikely on a number of grounds. Further, I have seen nothing to suggest that the 20 is worse for focus accuracy than other lenses. If I recall correctly, the 20 has been used by optyczne.pl in some of their tests of body (not lens) AF accuracy, and as far as I remember, the results were very good.

I should have added that I meant optimizing AF algorithm for dim light, when lens is likely to start hunting. There is no reason to sacrifice focus accuracy in good light

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