JVan_02 wrote:
Since there's some discussion of 40 CF and I think by and large I have a good amount of experience on the issue I'll say that it's got a lesser version of the 45 C's problems, excacerbated by Zeiss' software meddling. I use an α7 III.
To clarify: in good lighting (bright daylight, sufficient indoor lighting) I have practically no problems using the lens exactly how I wish too until the reproduction ratio/magnification becomes sufficiently high that DoF is under a CM... maybe 35cm, out. At this point, focus is only reliable on stationary objects. At a certain point, AF becomes less reliable in the 0.65-.24m range due to two factors. The first is uncorrected SA showing up in that range (almost certainly why Zeiss implemented their forced aperture behavior). The second is Zeiss' aperture behavior essentially interrupting the AF process. This becomes especially problematic in worse lighting, due to both lower contrast exacerbating SA based focus shift and the fact that lower light stresses mirrorless PDAF more than DSLR PDAF (I don't know why this is the issue, just something I've noticed).
This can be somewhat alleviated by stopping down to 2.5 as lighting gets worse. This aperture is where there are only the faintest amounts of SA and it stops Zeiss' software from interrupting the AF process. At this point, your biggest barriers become the same as any lens at 2.5: the -EV AF rating of your camera. At some point, contrast and lighting in the image are simply too poor to focus properly for your setup. The focus limiter actually comes in handy here: it's very unusual for a standard lens, and remembering to engage with it gives the opportunity to discard some AF calculations and make AF more efficient. In the same vein, spot focusing can eliminate a lot of AF calculations and further improve performance.
It's definitely not the almost completely brainless approach achieved by newer Sony lenses like the 20 G (and I imagine the 35 1.8 FE) and admittedly, it's probably not as hands off as say the Sigma 35mm f2. But the 40 gets a bit worse reputation than it deserves, imo. As a last point of info, I'd say the AF motor is exceptionally speedy: cameralabs clocked the average focusing time at 0.35 seconds. For reference, the 24 GM in the same test clocked 0.5 seconds.
So, is that to simply suggest that for both the Sigma and the Zeiss ... the design choice for the close focusing capability comes with the attributes of uncorrected SA, thus the root of problems for AF-C on PDAF? It does sound like a familiar story with my Tammy 45/1.8 (also CF). And, is that what is to be expected from such CF / SA designs for PDAF (vs. CDAF)?
JVan_02 wrote:
Since there's some discussion of 40 CF and I think by and large I have a good amount of experience on the issue I'll say that it's got a lesser version of the 45 C's problems, excacerbated by Zeiss' software meddling. I use an α7 III.
To clarify: in good lighting (bright daylight, sufficient indoor lighting) I have practically no problems using the lens exactly how I wish too until the reproduction ratio/magnification becomes sufficiently high that DoF is under a CM... maybe 35cm, out. At this point, focus is only reliable on stationary objects. At a certain point, AF becomes less reliable in the 0.65-.24m range due to two factors. The first is uncorrected SA showing up in that range (almost certainly why Zeiss implemented their forced aperture behavior). The second is Zeiss' aperture behavior essentially interrupting the AF process. This becomes especially problematic in worse lighting, due to both lower contrast exacerbating SA based focus shift and the fact that lower light stresses mirrorless PDAF more than DSLR PDAF (I don't know why this is the issue, just something I've noticed).
This can be somewhat alleviated by stopping down to 2.5 as lighting gets worse. This aperture is where there are only the faintest amounts of SA and it stops Zeiss' software from interrupting the AF process. At this point, your biggest barriers become the same as any lens at 2.5: the -EV AF rating of your camera. At some point, contrast and lighting in the image are simply too poor to focus properly for your setup. The focus limiter actually comes in handy here: it's very unusual for a standard lens, and remembering to engage with it gives the opportunity to discard some AF calculations and make AF more efficient. In the same vein, spot focusing can eliminate a lot of AF calculations and further improve performance.
It's definitely not the almost completely brainless approach achieved by newer Sony lenses like the 20 G (and I imagine the 35 1.8 FE) and admittedly, it's probably not as hands off as say the Sigma 35mm f2. But the 40 gets a bit worse reputation than it deserves, imo. As a last point of info, I'd say the AF motor is exceptionally speedy: cameralabs clocked the average focusing time at 0.35 seconds. For reference, the 24 GM in the same test clocked 0.5 seconds.
So, is that to simply suggest that for both the Sigma and the Zeiss ... the design choice for the close focusing capability comes with the attributes of uncorrected SA, thus the root of problems for AF-C on PDAF?
Dec 14, 2020 at 05:32 AM
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