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the last word

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You are here: Home / The Last Word / Focus shift and LoCA in Sony 90/2.8 FE Macro

Focus shift and LoCA in Sony 90/2.8 FE Macro

April 26, 2016 JimK 9 Comments

This is a continuation of testing of  the following macro lenses :

  • Sony 90mm f/2.8 FE Macro
  • Leica 100mm f/2.8 Apo Macro-Elmarit-R
  • Zeiss 100mm f/2 Makro-Planar ZF
  • Nikon 105mm f/2.8 Micro-Nikkor G VR

The test starts here:

Focus shift and LoCA in the Leica-R 100/2.8 Apo Macro

The first series of tests is aimed at determining focus shift and longitudinal chromatic aberration (LoCA) at 1:2 (half size on the sensor), See this page for the test protocol:

Towards a macro MTF test protocol

The Sony 90mm  f/2.8 FE macro debuted last year to rave reviews. It uses internal focusing, and had a focusing ring that is slid back and forth to invoke autofocus or manual focusing. It has a 270-degree focusing ring throw, which is marginal for accurate manual focusing. It has optical stabilization, and a handy focus lock button on the front of the barrel.

Let’s look at LoCA first. At f/2.8:

sony loca 28

The vertical axis is MTF50, measured in cycles per picture height (cy/ph). The horizontal axis is camera position shift in mm. The points on the left side of the graph are with the camera farther away from the subject than the points on the right. I used a 50 um (0.05 mm) step size. The three raw channels are plotted. Three things are apparent:

The blue and green channel peaks occur at identical distances.

The red channel peak occurs farther away from the subject — the very definition of LoCA —  but the difference is well under 1 mm.

The sharpness obtainable, as measured by the height of the peaks, in outstanding.

At f/4:

sony loca 40

The lens get sharper, but little else changes.

At f/5.6:

sony loca 56

Not quite as sharp. The LoCA remains low.

At f/8:

sony loca 8

The depth of field is starting to swamp out the LoCA.

At f/11:

sony loca 11

The LoCA is inconsequential.

Now we’ll regraph the same data in order to show focus shift.

In the red channel:

sony red focus shift

This is astounding. Focus shift is essentially nonexistent.

In the green channel:

sony green focus shift

Same idea.

In the blue channel:

sony vlue focus shift

Now we can see a tiny bit more focus shift.

I am very impressed.

The Last Word

← FOCUS SHIFT AND LOCA IN THE Zeiss 100/2 Makro-Planar Focus Shift and LoCA in the Nikon 105/2.8 macro →

Comments

  1. Andrea Blum says

    April 27, 2016 at 7:03 am

    Jim, where might I find out more about the software and gear (if any) required for making a test such as you have shown here? Thanks you.

    Reply
    • Jim says

      April 27, 2016 at 8:34 am

      Here’s the company that made the rail and the controller:

      https://www.cognisys-inc.com/

      For analysis software, I’m using MTF Mapper, DCRAW, and a Matlab script that Jack Hogan wrote — and that I’ve heavily modified — to drive both of them I use Excel for the final calculations and the graphing.

      Jim

      Reply
  2. N/A says

    April 27, 2016 at 7:33 am

    so AF-precision-wise among the native lenses witin 80-90mm range FE90/2.8 beats both Batis 85/1.8 and FE85/1.4GM in a focus wide open/shot stopped down scenarios…

    Reply
    • Jim says

      April 27, 2016 at 8:31 am

      This test does not measure autofocusing performance. Note also that the test was done at 1:2 magnification. Neither of the other lenses you mention can focus that close.

      Reply
  3. CarVac says

    April 27, 2016 at 10:06 am

    I notice that the f/11 DOF is very different…picking the blue channel and 600 LP/PH thresholds, the Sony has ~4.5mm, the Zeiss ~3.8mm, and the Leica ~3.5mm.

    Is this the focal lengths of the lenses changing relative to one another at close focus?

    Reply
    • Jim says

      April 27, 2016 at 10:21 am

      In the case of the Sony, certainly.

      Reply
  4. Erik Kaffehr says

    April 27, 2016 at 1:20 pm

    Hi Jim,

    You write:

    “The peaks are a bit broader, indicating that there is more depth of field at f/4 than f/2.8; no surprise there. There is slightly more LoCA than at f/2.8, as measured by the spread. This is in contrast to the conventional wisdom that LoCA decreases upon stopping down, but is consistent with what I have measured in the past, albeit at greater camera/subject distances.”

    What I think we see is that LoCA is relatively independent of aperture. But, stopping down increases DoF and also reduces peak sharpness. So, the visible effect of LoCA is reduced stopping down. So, your observations and conventional wisdom don’t actually contradict but just represent different points of view on the same issue.

    Best regards
    Erik

    Reply
    • Jim says

      April 27, 2016 at 1:46 pm

      Erik, we agree on the facts, and the reason why you can’t see LoCA if you stop down far enough. However, I have encountered people time after time who say that the effect itself diminishes when you stop down. That may be true in some cases — we’ve seen it in this testing — but it is the exception rather than the rule.

      Reply
  5. Christoph Breitkopf says

    April 27, 2016 at 11:38 pm

    Looks much better than the longer distance results from your medium tele test. Seems to be a macro lens optimized for macro – not a given these days, especially in this focal length range where the macro lenses are often used for portrait and general photography.

    Reply

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