A further drill down on field curvature and f-stop
I shot a center, edge, and corner series at multiple stops and at three focus settings, ∞, ∞ + 1.5mm, ∞ + 3mm. The results vary with f-stop, but understanding them helps figure out what the lens (this copy anyway) can and can't do.
In all these triptychs, the three focus points are, left to right, ∞, ∞ + 1.5mm, ∞ + 3mm. The Center and Corner crops are from the same images (taken on the diagonal). The Edge crops are from a second set of horizontal shots.
f/2.5 Center
f/2.5 Edge
f/2.5 Corner
f/2.5 summary: The center is sharp at ∞, the edge is very good at ∞ + 1.5mm , and the corner is ... least bad at ∞ + 1.5mm.
f/4 Center
f/4 Edge
f/4 Corner
Look at that! ∞ + 1.5mm (the center shot in each row) is sharp. All you need (on my copy, I repeat) is to focus 1.5mm past ∞, and that's why a mechanical focus scale is so important. If this were a tech camera, I would just shim the lens.
Does it continue? Let's look at f/5.6
Center
Edge
Corner
Yup
Let's just look at the ∞ + 1.5mm series for f/8 and f/11.
f/8
f/11
Some CA effects on the right edge of Mt. Sinai (the black monolith), but these were processed in LR and it doesn't have XCD 25 profiles yet. Indeed, CA seems the least controlled thing here. Running Adaptive CA Correction in Phocus usually gets rid of it, but that's not the standard setting, so you'd think something isn't quite right.
Well, I'd still like to know this compares to other copies.
Matt (who will post real pictures next time - promise!)