Samuli Vahonen Offline Upload & Sell: Off
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Bobu wrote:
Samuli, what's in your opinion the main difference between the ZF/ZF 1.4/50 Planar and the Loxia 50?
At the moment I have both lenses at home and plan to do some comparison myself, but I haven't bought the A7RII yet. My plan was to sell both the Otus 55 and the ZF 50 and use the Loxia 50 instead, expecting a similar performance and rendering to the ZF 50.
Wow what a question...this would need a book, but I try to answer short. These are my opinions and I'm not optics expert, just a photographer - if one is needed ask The Suede or Toothwalker to join discussion...
Notice: when talking boke, let's assume it's not "flower boke", any crappy lens will produce ultrasmooth boke in situation where subject very close and background very far away.
ZE/ZF1.4/50:
Wide open has various aberrations (e.g. spherical aberration) and rendering is pretty crappy until f/2.2 on large distances (until f/2.8 at MFD). I would call wide open focus plane rendering "dreamy" at best (some people prefer this for portraits). Spherical aberration causes lens to have focus shift, however this only happens close- and mid-distances, and at infinity focus shift is non-existent. Boke can be good wide open (specially at large/mid distances), but there are tendencies to form swirly boke (specially close-up) and boke highlight balls/rings tend to have bright edge. Zeiss would have avoided lots of forum crying by mediocre users if they would sell this as a f/2.8 lens instread of f/1.4 lens...
Nature of lens changes when it closed down to f/2.2 (large distances) - f/2.8 (close distances). Then aberrations are mostly gone and lens renders with very small amount of aberrations, as a results lens gives very good results in focus plane (good large object contrast, good microcontrast, good sharpness). Challenges are focus shift and field curvature. As you have ZF, just focus shooting aperture if <f/2.8 and at f/2.8 if shooting closed down, and you will never experience focus shift. Even it's "PLANAR" the field curvature is pretty bad, but at f/8 it's possible to shoot image which sharp from edge to edge. Good thing about field curvature is that the shape is round and smooth (e.g. no midzone dip). In practice when photographing 3D subjects, and not so much test targets, photographer can use the field curvature as to one's benefit. If you want to shoot planar subjects with wide aperture, please select some other tool for the job.
When operating apertures mentioned on previous chapter boke is really really good; contrast in boke is low compared to contrast in focal plane. In addition boke behaves nicely in almost every possibe situation. Also pay attention how on f/4 MTF sagittal and tangential lines are pretty close - this means that there is not much astigmatism and boke is not ruined by astigmatism. When reaching the optimal apertures (f/2.2-2.8 depending on distance) DOF is also uniform thickness over the whole frame.
Loxia 2/50:
Wide open performance is pretty good on focus plane, but microcontrast is missing. And we are talking here WAY BETTER than ZE/ZF 1.4 version wide open. Boke has tendency to draw harsh boke (hard edged boke highlight balls/circles). When closed down to f/2.8 lens improves considerably, micro contast is much better.
Lens doesn't suffer from major focus shift, but there is some sort of wave in the and in MTF zone B dips, not much it does. Focus shift is minimal and in practice does not need to be mitigated.
Boke quality improves a little also after f/2.8 unlike ZE/ZF series f/1.4 - maximum quality is reached by f/4. Even then I would describe Loxia boke character has more tendency to generate issues than ZE/ZF f/1.4 @ f/2.2-2.8 and smaller aperture. In order to reach same thickness of DOF all over the frame lens need to be close down to ~f/5.6 based on shooting experience (looking the vignetting graph, which clear only at f/8 the measurements support this). Boke contrast vs DOF contrast: boke contrast is lower than DOF contrast, but difference is not as clear than in ZE/ZF f/1.4.
At close shooting distances Loxia is slightly better at same aperture number until f/2.8, after which they seem to be about the same.
As can be seen from f/5.6 MTF chart sagittal and tangential lines separate in zone B. This indicates astigmatism and boke issues. Sometimes these can be seen, most of the times not visible - depends a lot of your scenes, if you need to lure this behaviour to visible I recommends evergreen forests and spruces with long needless.
Written in a hurry, hope I didn't forget anything essential about rendering style.
Focus plane sharpness can be seen and compared from MTF charts. Based on practical shooting I do not believe Loxia's good corner drawing with standard 2mm thick sensor cover glass, I hope it improves with Kolari thin sensor glass modification to be at level it's on the MTF chart by Zeiss:
What you didn't ask:
- Loxia is lots smaller and lighter (considering adapter). But if you have adapter with Arca-Swiss plate it makes tripod shooting better than trying to hang whole combination from camera.
- Loxia saves EXIF-information, this can be valuable when lens is new and one is learning the lens.
- Erconomics: Focus throw and feeling = same. Focusing is easier with Loxia as there is no adapter bringing the lens far away from camera body. But bad in Loxia is that it's sometimes hard to feel which is focus ring and which is aperture ring.
- Both lenses are pretty good against backlight, Sony sensor weird green reflections are bigger problem than either of the lenses. Both hoods protect as efficient.
- Loxia has weird 52mm filtersize, while ZE/ZF has 58mm.
These two lenses are very different. This is why I want to keep both "rendering style families" for various situations and shooting "moods".
Samuli
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