This is a continuation of a test of the following lenses on the Sony a7RII:
- Zeiss 85mm f/1.8 Batis.
- Zeiss 85mm f/1.4 Otus.
- Leica 90mm f/2 Apo Summicron-M ASPH.
- AF-S Nikkor 85mm f/1.4 G.
- Sony 90mm f/2.8 FE Macro.
The test starts here.
When John Henry was a little baby sittin’ on his daddy’s knee
He picked up a hammer and a little piece of steel
Said “Hammer’s gonna be death of me, Lord, Lord
Hammer’s gonna be the death of me”
Jack Hogan asked today for a comparison of manual focusing of the Zeiss Batis 85/1.8 to autofocusing. I was a bit concerned about putting my focusing skills up against a machine, particularly one like the a7RII that has been turning in spectacular results with the Sony AF lenses I’ve been testing it with.
I swallowed hard, and set up a test.
Now the captain he said to John Henry
“I’m gonna bring that steam drill around
I’m gonna bring that steam drill out on the job
I’m gonna knock that steel on down, Lord, Lord
I’m gonna drive that steel on down”
I mounted a Sony a7RII with the Batis 85/1.8 attached to the Cognisys computer-driven focusing rail,just as before, but I didn’t turn the rail on. I set the assembly 8 feet from the on-axis target, mounted the lens, focused on the Siemens star using manual focusing (more about that momentarily).
John Henry told his captain “Lord a man ain’t nothin’ but a man
But before I let that steam drill beat me down
I’m gonna die with my hammer in my hand, Lord, Lord
I’ll die with my hammer in my hand”
I used two other targets for the AF part of the testing:
When I used AF, I focused using AF-S with flexible spot, AF priority, small and medium spot sizes. I exposed 16-shot series with the lens wide open. I used Jack Hogan’s Matlab program, MTF Mapper, and DCRAW to pick the horizontal edges and calculate the MTF50s for the raw color planes, imported the data into Excel, and plotted the statistics of the results in cycles per picture height.
John Henry was driving on the right side
That steam drill driving on the left
Says, “Before I let your steam drill beat me down
I’m gonna hammer myself to death, Lord, Lord,
I’ll hammer my fool self to death”
The average results for horizontal edges:
The top set of bars, one for each raw channel, is for the images made with manual focusing at the high magnification with peaking turned off. I looked for aliasing as an indication of best focus.
The next set down is also for manual focusing, but with peaking turned on at minimum setting. As is usual with high contrast subjects and sharp lenses, the lowest peaking setting, even at maximum magnification, is more sensitive than would be optimum. Even so, peaking produced better results than the no-peaking test.
Notice that the manual focusing cases correctly and expectedly optimized the green channel at the expense of the red.
John Henry he hammered on the mountain
His hammer was striking fire
But he hammered so hard it broke his heart
And he laid down his hammer and he died, Lord, Lord
He laid down his hammer and he died, Lord, Lord
Here are the averages for the vertical edges:
Pretty much the same except for the four lower groups, which have higher blue and green values than for the horizontal edges.
Let me draw your attention to the third group of bars. They are for AF on the zone plate target. On this target, unlike the others I’ve used, the camera and the lens were able to cooperate enough to properly optimize the green channel, essentially as well as your faithful scribe.
The next four bars are for AF with both spot sizes using the Siemens star and Horshack grid focusing targets. As before, when faced with those targets the camera and lens collectively give more weight to the raw channels than they should, by a small amount for the vertical edges and by a larger amount for the horizontal ones.
John Henry had him a woman
Her name was Polly Ann
She walked out to those tracks
Picked up John Henry’s hammer
Polly Ann drove steel like a man, Lord, Lord
Polly Ann drove that steel like a man
Now I’m going to show you where the machine excels. Here are the standard deviations for both sets of edges:
In the no-peaking manual focus case, I wasn’t very consistent; the machine beat me there. With peaking, I was pretty solid, but not as solid as AF with the Horshack grid and a medium spot, or the Siemens star and a small spot, or the zone plate with the medium spot.
I can’t make much sense of the variations among the AF standard deviations.
Now every Monday morning
When a blue bird begins to sing
You can hear John Henry from a mile or more
You can hear John Henry’s hammer ring, Lord, Lord
You can hear John Henry’s hammer ring