Focus shift tests with the 35 lux pre asph

[ampguy]

Used an M8, and setup some targets at about 110 cm away, with extensive focus bracketing, and markers in 4cm increments to test for focus shift on this lens. I didn't find any. Details are on my blog page.

[tightsqueez]

Thanks for posting these. I have owned the Lux ASPH for about three years now and until recently, never heard of such issue. A few days ago I tested mine with Tech Pan 25 and with an M8. With film it was negligible as it was on the M8, albeit more pronounced. Like any lens, I think it may have to do with the copy which may or may not be perfectly on axis. Surprisingly, I also tested a 35 Cron IV and it too exhibited the same shift.

There are a lot of factors but these mean nothing when you are out shooting. So to say the least; I'll revert to the day when I was unaware of such petty issues and just concentrate on the images.

Cheers!

[tightsqueez]

Oops, just realized that you were talking about the "Pre" ASPH. Attention to detail! Well, regardless, my point remains the same.

[ampguy]

I've never been able to afford the lux asph 35, but have heard mostly great things about it - sharp to edges @ 1.4, and sharp (high resolution) at most any aperture.

I have heard that it can be fussy to initially get setup for focus at min. aperture, and min distance, and then not shift, but like you have experienced, I've also heard it's not a major issue once setup.

ASPH also has a tad of distortion, but I'd guess folks with these kinds of bux for lenses can hire a Photoshop asst. to dial it out ;)

Ideally I'd like both lenses, pre-asph for the glow and low contrast, asph lux for the DSLR type shots :D

Oops, just realized that you were talking about the "Pre" ASPH. Attention to detail! Well, regardless, my point remains the same.

[Turtle]

the asph version shifts as a fact of life and no amount of setting up will change this. Its a product of the design and Leica acknowledges this. Whether it matters to you, or is noticeable to you, is another issue. You can have it optimised for 1.4 or any other aperture which might change the impact on your own work but it will always shift. Some say less os on film due to the thickness of the emulsion.

[ampguy]

I see 2 major issues with focus shift, although those who know their lenses well can simply work around the issues:

1. loss of resolution when non optimal aperture is used. Many folks feel "DOF covers it" but in reality, there is only one single point of focus, anything else that appears to be sharp in front of, or behind the single point of focus, is an illusion.

and

2. The shifted focal point is so close to the optimal (wide open, for me and my lenses) aperture, resolution loss is not a concern at the shifted focal point, but the DOF window has moved (usually rearword) giving an illusion of more rear DOF and possibly a more cluttered background than pre-visualized.

From images I see, the 35 asph lux is more #2. The images are usually sharp enough resolution wise for me, but the DOF windows from shifted focal points is all over the place.

Main reason I'm not big on Sonnars, unless strictly used wide open.

the asph version shifts as a fact of life and no amount of setting up will change this. Its a product of the design and Leica acknowledges this. Whether it matters to you, or is noticeable to you, is another issue. You can have it optimised for 1.4 or any other aperture which might change the impact on your own work but it will always shift. Some say less os on film due to the thickness of the emulsion.