Like every camera system, the Sony FE cameras have their strengths and weaknesses when it comes to autofocus. For wide open shooting and face detect, at most apertures, the Sonys are, IMO, quite excellent. For shooting landscape stopped down, however, there are some issues. One of these is failure to correct for focus shift.
Many lenses shift the plane of focus as they stop down. In some cases, this is a mild effect, and it is largely covered up by increased depth of field. However, sometimes it is significant. In my experience, the effect is often visible at 100% and in large prints. I'm not satisfied with using a high resolution camera and settling for sub-optimal focus. Picky, I know. But why give away image quality because of inaccurate focus? I've often noticed slight front-focus with lenses I use a lot, including the 55/1.8 and the Batis 85mm, at f8 and f11.
Current Sony firmware, with some possible lens exceptions, focuses wide open in AF-S, even when the lens is stopped down. (The diaphragm opens briefly to focus, then stops down again.) Like with a DSLR, this does nothing to overcome focus shift. I know of no way to change this camera behavior right now.
For landscape, I often resort to magnified manual focus. When I do that, though, focusing at f8 or f11, it's hard to find the exact plane of focus (because of the relatively large depth of field). It's a pretty good method on a tripod; not so good hand-held.
In AF-C, the camera focuses stopped down after initial focus acquisition. But it isn't all that precise, as Jim Kasson has shown. For landscape, I find that I need to make three or four exposures in AF-C to be sure the camera has nailed focus. Focus accuracy does seem much better with faces and eyes, probably because of the additional focus tech at work.
Which FE lenses have minimal or no focus shift? Any suggestions on how to use camera controls to overcome focus shift during autofocus?
I find that I don’t need to focus at shooting aperture with any of my lenses for landscape. Some, I will close down some but no need to go to F8 in my experience. My CV 40/1.2 I focus at F2.8. The CV 50/1.2 seems to have less focus shift at infinity than the 40 and focusing at say F2 seems fine. My CV 65/2 I focus wide open. Same with Loxia 50 and 85 (the the 50 needs much more stopping down tha the 85). I would experiment if perhaps focusing at larger than shooting apertures but less than wide open might give you the accuracy of focus you need but a large enough aperture to assist in accurate focusing
DaveFP wrote:
At typical landscape apertures I don't see focus shift as having much of an impact.
Couple of feet one way or the other?
I have the opposite experience. At around 10 feet, I see a small but noticeable shift. For instance, if I shoot a storefront with my 55mm Zony at f8, focusing on the door frame, the sidewalk in front is more in focus than what's just inside the doorway.
At long distance, I also have focus shift problems with "normal" and telephoto focal lengths. For instance, if I focus on a particular building in the distance using AF-S, a nearer building will be in critical focus. My Batis 85mm gives this kind of results over and over. In these situations, I usually do better by using manual focus at taking aperture, or even by pre-focusing using the distance scale set at near-infinity. Here's some lab testing Jim Kasson did that I found interesting, because it explained what I was already experiencing: https://blog.kasson.com/a7riii/a7riii-af-accuracy-batis-85
It might be harder to see these effects using a wide angle lens at long distance. As it is, depth of field almost always gives me useable images. But my A7RIII's autofocus isn't giving me all the resolution the camera and lens are capable of at my chosen focus point.
By the way, Jim Kasson found that with the Batis, AF-C isn't affected by focus shift, since it eventually focuses at taking aperture. But he found that it's undependable for critical focus unless using face or eye recognition. https://blog.kasson.com/a7riii/a7riii-af-c-accuracy-with-batis-85-1-8 So, not too good for landscape.
Luvwine wrote:
I find that I don’t need to focus at shooting aperture with any of my lenses for landscape. Some, I will close down some but no need to go to F8 in my experience. My CV 40/1.2 I focus at F2.8. The CV 50/1.2 seems to have less focus shift at infinity than the 40 and focusing at say F2 seems fine. My CV 65/2 I focus wide open. Same with Loxia 50 and 85 (the the 50 needs much more stopping down tha the 85). I would experiment if perhaps focusing at larger than shooting apertures but less than wide open might give you the accuracy of focus you need but a large enough aperture to assist in accurate focusing ...Show more →
I'm not too surprised that the CV 65mm has minimal focus shift; thanks for confirming that. Interesting that the Loxia 50 needs to be stopped down more than the 85.
I do sometimes focus at in-between apertures, which can help when using manual focus. But it sure would be nice to use autofocus with my autofocus lenses. I wish Sony would allow stopped-down AF-S autofocus, even if it's just contrast-detect (which can be very accurate).
racetratr wrote:
I have the opposite experience. At around 10 feet, I see a small but noticeable shift. For instance, if I shoot a storefront with my 55mm Zony at f8, focusing on the door frame, the sidewalk in front is more in focus than what's just inside the doorway.
At long distance, I also have focus shift problems with "normal" and telephoto focal lengths. For instance, if I focus on a particular building in the distance using AF-S, a nearer building will be in critical focus. My Batis 85mm gives this kind of results over and over. In these situations, I usually do better by using manual focus at taking aperture, or even by pre-focusing using the distance scale set at near-infinity. Here's some lab testing Jim Kasson did that I found interesting, because it explained what I was already experiencing: https://blog.kasson.com/a7riii/a7riii-af-accuracy-batis-85
It might be harder to see these effects using a wide angle lens at long distance. As it is, depth of field almost always gives me useable images. But my A7RIII's autofocus isn't giving me all the resolution the camera and lens are capable of at my chosen focus point.
By the way, Jim Kasson found that with the Batis, AF-C isn't affected by focus shift, since it eventually focuses at taking aperture. But he found that it's undependable for critical focus unless using face or eye recognition. https://blog.kasson.com/a7riii/a7riii-af-c-accuracy-with-batis-85-1-8 So, not too good for landscape....Show more →
Yep; the Batis 85 is notorious for shift. I have one; had the same experience.
I either take multiple shots (one is always right) or MF.
If you’re looking to produce slow, high end work for prints shouldn’t you be using MF, hyperfocal distance and/or focus stacking regardless of camera body/brand?
derKoekje wrote:
If you’re looking to produce slow, high end work for prints shouldn’t you be using MF, hyperfocal distance and/or focus stacking regardless of camera body/brand?
Who says I want it to be slow? Some of my work is on a tripod, some is not. Wouldn't it be nice to be able to trust the AF of your camera to focus at the distance you ask it to, at various apertures? That's why I'm asking which FE lenses have little or no focus shift, and also whether I've missed some camera controls that would be helpful that I haven't considered.
As I mentioned already, I do often use MF. Not because I really want to, though. I am forced to use manual focus because of the limitations of the Sony autofocus system, which, in current firmware at least, is unable to deal with focus shift. And by the way, even when using manual focus, focus shift means you have to focus stopped down, which is not optimal.
I deal with it, though. I've focused manually for decades, on cameras ranging from large format to half-frame. But I believe that the stakes are higher with high-resolution sensors. It's easier to degrade critical sharpness with very minor focus errors.
In the situations where Sony autofocus works best--like with eye-af, or wide open shooting, or when a lens has little or no focus shift--autofocus is generally more accurate and more precise than manual focus, IMO. At some point, I would like to be able to take advantage of that accuracy for stopped-down landscapes, too.
I'm not sure why you bring up hyperfocal distance or focus stacking. I use those as needed. What's that got to do with focus shift?
Some of my work is on a tripod, some is not. Wouldn't it be nice to be able to trust the AF of your camera to focus at the distance you ask it to, at various apertures? That's why I'm asking which FE lenses have little or no focus shift, and also whether I've missed some camera controls that would be helpful that I haven't considered.