This is the fourth in a series of posts on the Hasselblad X2D 100C camera and the XCD lenses. You will be able to find all the posts in this series by looking at the righthand column on this page and finding the Category “X2D”.
And now, what some of you have been waiting for: modulation transfer function (MTF) numbers for the Hasselblad XCD 38 mm f/2.5 on the X2D 100C. If you’re not a numbers person, be patient, there are images coming up.
In the last year or so I’ve standardized lens test distance by field of view. Here’s the table I’ve been using, with the 38 mm distance added.
That means I need a distance of 11 feet for the 38.
Here’s what the setup looks like with the camera at that distance.
Feeds and speeds:
- AF-S (there isn’t any AF-C at present)
- Manual exposure
- f stops 2.5 and 2.8 through 11 in whole-stop steps
- Focus on Siemens star
- 20 images at each f-stop. Use Imatest to pick the sharpest.
- RRS legs
- Acra Swiss C1 head
- 2 sec self timer
- ISO 64
Here are full frame images at f/2.5 and f/11.
Lately, I have been using a complicated test for lenses. You’ll know about that if you’ve looked at the Fuji GF lens tests I’ve posted in the last year or so. That test requires that the camera have a focus bracketing feature. The X2D 100C has no such capability. It might be added in a future firmware release, but that doesn’t help me now. SO I was forced to fall back on cruder techniques.
I measured MTF50 of the sharpest image of the 20 images at each test condition for both slanted edges. When the target was positioned at the right edge, I found the sharpest image for each orientation. The sharpest image for the two directions were different, indicating some astigmatism. This is normal with short lenses; you’ll get a chance to look at astigmatism and other off-axis aberrations when I post the images in a subsequent post. I asked Imatest to look at the green raw channel.
Here’s the bottom line:
- The sharpest on-axis aperture is f/5.6.
- The sharpest edge aperture for a radial (horizontal) edge is f/8.
- The sharpest edge aperture for a tangential (vertical) edge is f/5.6.
- This lens should be capable of delivering sharp images over the frame from f/4 through f/8.
I hesitate to put this next chart up because it mixes apples and oranges, but people have asked how this lens compares to the 45mm f/2.8 GF. Take the graph with a grain of salt, since
- The GF test used white-balanced raw luminance as the metric, not green channel. That penalizes the GF lens because longitudinal chromatic aberration brings down white-balanced raw luminance.
- The GF test used complex processing to detect and eliminate outliers. The XCD test just took the sharpest image in each group. That should also penalize the GF lens.
- The fact that I only gave the ‘blad 20 tries to get the focus right under each condition should penalize it.
Enough caveats. Here’s the graph:
Overall, the 45 looks a little better, but remember those grains of salt. I”ll be doing direct comparisons later.
I like your standardized lens test distance chart. Very cool.
What does “on-axis” mean when you say the sharpest on-axis aperture? Is it just a fancy way for saying center?
Did you mean to write “35 side H” for the light blue? It says 45, but you already have a 45.
I have been quite impressed with my GF 45 edge sharpness. The only two native GF lenses I shoot with now are the 45 and 110, because those are my favs. Hoping the upcoming 55 1.7 delivers. Personally, I would have preferred a 55 f2, if it meant a smaller, lighter lens.