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 p.118 #13 · A7/A7r - performance with WA RF lenses | |
turnstyle wrote:
I've been specifically interested in purchasing both A7r and Lux 50 ASPH to use together, so your comments are of particular interest.
Are you using the ASPH?
Are you hitting infinity focus at the hard stop, or is the Metabones letting you focus a bit past infinity?
Can you possibly post any photos that show the problem with wide open focus toward the sides?
Thanks!
Blackout wrote:
Sure, let's go.
Yep, it's the ASPH (a brand new sample), and I'm hitting infinity at the hard stop.
Now two full-size samples, converted from RAW with slight exposure tweaks at the most, and noise reduction off.
Near MFD:
http://i.imgur.com/qEulCDX.jpg
At distance:
http://i.imgur.com/RGoGmpf.jpg
You can see how sharpness and contrast degrade rapidly over the plane of focus, from the center to the edges. I got much, much better results ie. with the Sigma 35mm f/1.4 wide open on the D800E. I have a picture from the same subject shot with that combo, and it's night and day.
It reminds me of how the Zeiss 50mm f/1.4 Planar rendered at close focusing distances, with low contrast and sharpness because it has no floating element, but the problem here obviously has other roots. And it was acceptable near infinity even wide open.
Steve Huff keeps telling me that it's normal, that it's a matter of DOF only, which is obviously wrong: it's sharp (but not jaw-dropping either) in the center but nowhere else, yet the plane of focus slices the cactus in the first scene and the trees in the second.
I'm on the verge of getting the Zeiss Otus in place of the Summilux. I'm willing to trade size and weight to get the most out of that sensor. Focus peaking is enough of a reason for me to shoot the A7R over a DSLR.
...Show more →
The Otus will give you a more consistent across-frame result. The FE55/1.8 will also be excellent. I think between the two, the FE's primary shortcoming will be LOCA or bokeh fringing. Compared to the 50 Lux ASPH, the FE has slightly less gaussian background blur.
The 50 Lux ASPH is a rather complex lens. As you've observed, it's sharp wide open in the center. In the mid zone area it gets softer. Then at the edges there is some recovery. In your image, you can see that at the top left edge, the distant trees appear to be in focus. It could be that the lens's field curvature is exaggerated by the a7R.
When I re-evaluated the infinity shots I did with this lens on the a7 (non-R) and the M9, the lens's overall characteristics remained pretty consistent between the two, however, there were differences. What I primarily noticed was that the mid zone drop in sharpness was more noticeable, changed character, and was over a somewhat wider band with the a7 than the M9. With both cameras, there was some recovery at the image edges. You'll also find that the drop in mid zone performance doesn't clear in a logical manner. One would expect that a stop or two down from wide open would improve the situation. But with the Lux ASPH (and some other fast Leica lenses), the opposite happens.
This pretty much mirrors Leica's MTF graphs. Whether or not results with the a7R are similar to, or worse than the a7, has yet to be conclusively determined by a controlled side by side test. That said, my opinion is that the 50 Lux ASPH does not reach optimum performance for farther scenes on the Sony cameras, especially at wider apertures. It's still usable, but may not satisfy technically demanding scenes and photographers. If you're planning to shoot a lot of landscapes with it at f/2.8-f/4, then I would advise against the Lux in favor of either the FE or Otus. If you're going to shoot a lot of wide open 3D scenes where you're picking out one detail to be in focus, then the Lux ASPH will work, and you'll be able to use its very smooth background blur character.
On a tangent, has anyone seen any a7/R results with the 50 Cron AA?
As for some of the other 50mm RF lenses suggested as a7/R alternatives to the Lux ASPH... I looked through my a7 series again (admittedly it's not the R), and of the lenses I tested, my ranking in terms of best wide open across-frame performance would be:
FE55
ZM50/2
50 Lux ASPH
CV50/1.5
Canon 50/1.4 LTM (RF lens from the 60s)
ZM50/1.5
I don't own a 50 Cron, therefore wasn't able to test one, but suspect it will be similar to the Zeiss 50/2.
The last three lenses in the list above are all pretty glowy wide open and the Voigtlander has the largest central sweet spot, with the Zeiss having the smallest and most 'lumpy' looking plane of focus. The Canon is more glowy/lower contrast than the Zeiss, but has a more gradual drop in sharpness moving away from the center.
The point here, I think, is there isn't really an easy, safe bet faster than f/2 50mm RF lens on the a7. I also have the Nikkor 5cm/1.4, Zeiss Opton 50/1.5 Sonnar and the old Summarit 50/1.5, but would be surprised if they're anywhere near the Canon wide open at infinity.
I had a quick look at the exit pupil of all these RF 50s just now (other than the ZM50/1.5 which was on loan), and the ZM50/2 has the farthest/largest exit pupil. Farther than the 50 Lux ASPH. The f/1.4-1.5 50s were all fairly similar, with the Nikkor seeming to have the nearest exit pupil.
Based on info from Zeiss's paper about this (pdf link), exit pupil size/distance and sensor topping thickness have a significant influence on how well a given lens performs.
From point 3 on pg. 12:
Lenses with a very large beam tilt react in a much more sensitive manner to a change of refractive index in the image space caused by filter plates in front of the sensor (such as low pass and IR-blocking filters). If the filter plate is not considered in the design of the lens, the edge definition will suffer. The effect of the additional path through the glass grows exponentially with the beam inclination. A Distagon which never achieves more than 20° beam tilt in the corner of the image reacts more tolerantly than a symmetrical wide- angle lens, which might reach a 45° tilt. This is why filters in digital Leicas are very thin – to remain compatible with older optics.
If the filter is significantly thicker, the contrast transfer for the image edge becomes worse for tangential structures. In the graph of the curves, this looks like the old retrofocus lenses but is caused by astigmatism rather than lateral chromatic aberration. The focus is shifted to greater distances for tangential structures by the additional path through the glass. If the best edge definition is to be achieved, then all that can be done is to stop down further.
Edited on Nov 25, 2013 at 04:28 PM · View previous versions
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