Focus Shift testing of the 35/1.4 pre asph lux

[ampguy]

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I used my M8 today and did some testing today to determine if the pre-asph 35/1.4 Summilux had any focus shift. I didn't find any. My results are on my blog. Would be interested in any comments or feedback.

[ashrafazlan]

I thought the asph version was the one with shifting problems?

[ampguy]

it is, as well as having a bit more distortion (< 2% and correctable), but the issue of focus shift with the pre asph has been mentioned a few times, so I thought I'd do my own test.

 

I thought the asph version was the one with shifting problems?

[jaapv]

Yes- well, but is the focus spot-on at all apertures, because that is what focus shift is about.

[dpattinson]

I would retry the test with a smaller gap between the targets. At 110cm the effect of the focus shirt will be less than 4cm (if my 35lux asph is any indication). You might see an appreciable effect with the boxes at 1cm gaps. Also - it looks to me that the first shot (1.4) is less sharp on the target box than the subsequent (2.0) one - indicating perhaps that it was a little front focused to begin with. (Could also just be the lens is less sharp at 1.4)

[ampguy]

Thanks David,

 

You're probably right in that I should have used smaller steps, and I'm looking at putting together a 3d angled ruler that can be set at a preset angle, but give proper readings and be viewable from the front.

 

My previous test for focus shift test was with a Nokton CV 40/1.4 where I tested at 100cm and used 1.50cm steps, in front of, and behind main subject at 100cm and from 1.4 to f8, I only could resolve differences at about every 3 indexes (4.50cm), but random items ~15% in front of, and behind were of interest.

 

In any case, I agree, smaller steps would be better. Thanks.

 

I would retry the test with a smaller gap between the targets. At 110cm the effect of the focus shirt will be less than 4cm (if my 35lux asph is any indication). You might see an appreciable effect with the boxes at 1cm gaps. Also - it looks to me that the first shot (1.4) is less sharp on the target box than the subsequent (2.0) one - indicating perhaps that it was a little front focused to begin with. (Could also just be the lens is less sharp at 1.4)

[Guest mc_k]

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As you said, the intervals can be too small as well as too big. I think the test is a little problematic because you didn't use identical objects at the intervals.

[ampguy]

Thanks, that's a good point. For me personally, I was using the "XX cm" markings at 100-200% crops to examine, but do wish I had setup with 2cm intervals.

 

Good point though, the boxes were all uneven, and the distance indicators also weren't necessarily aligned either.

 

Great feedback for future tests. Thanks.

 

As you said, the intervals can be too small as well as too big. I think the test is a little problematic because you didn't use identical objects at the intervals.