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You are here: Home / The Last Word / MTF testing of 70-200mm lenses — fundamental effects, part 1

MTF testing of 70-200mm lenses — fundamental effects, part 1

October 17, 2015 JimK 2 Comments

In the past few posts on MTF testing, we’ve seen so many things that affect the Imatest MTF50 results that it’s reasonable to look at tests that change very little to find out how much instability there is in the baseline test protocol and the image analysis tools.

I made 128 exposures at f/4 with the Nikon 70-200/2.8 on a D810, focusing manually (once, wide open), and plotted the central (on-axis) horizontal edge MTF50 in cycles per picture height for the entire series. The time between exposures was 8 seconds for the Nikon gear (4 seconds to focus, then 4 seconds with the mirror up), and 5 seconds with the Sony equipment.

nikon mf vs time

Then I did the same thing with the Sony a7RII and the Sony 70/200/4, this time with the lens at f/5.6, which is sharper for that lens than f/4.

sony mf vs time

The amount of variation appears to be about the same, although it looks like the Sony gets a bit worse as the series wears on.

Looking at the two sets of data normalized to the average MTF50 for the entire series:

nikon mf vs time norm

sony mf vs time norm 1

Now, with a more apples/apples comparison, the Sony looks worse. We’ll be looking at standard deviations in a subsequent post.

Now let’s look at what happens when we turn autofocus (AF-S, focus priority) on. First, the Nikon plot:

nikon af vs time

And now the Sony one:

sony af vs time

Note the difference in the vertical axes. The Sony is more consistent. We’ve seen this before.

Plotting the normalized results makes things even clearer. The Nikon ones:

nikon af vs time norm

And for the Sony:

sony af vs time norm 1

That certainly makes the point.

Next up: how the above affects our standard statistics.

 

The Last Word

← MTF testing of 70-200mm lenses — more exposure effects MTF testing of 70-200mm lenses — fundamental effects, part 2 →

Comments

  1. Jack Hogan says

    October 18, 2015 at 5:06 am

    Now we are talking, +/- a couple of percentage points is what I understand is to be expected with good technique. Wow, the Sony’s focusing is really consistent.

    Reply

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  1. MTF testing of 70-200mm lenses — fundamental effects, part 2 | The Last Word says:
    October 17, 2015 at 3:57 pm

    […] the exact same data from the previous post and putting into the 16-exposure packets that we’ve been using for MTF testing, we get the […]

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