Re: What's the deal with aperture stopping down during AF?
jhinkey wrote: AGeoJO wrote:
Guy, I don't think it is a major issue or actually any at all, with the GM lenses, at least. I consider this as a part of the lens design now. I am not selling any of my GM lenses, that's for sure. The few times I encountered this is mostly in the studio, especially the GM 85mm at f/8 or so and that's when the lighting was dim since only the modeling light was used. But this is not a studio lens, I reckon. The 24-70 shows the least of the 3, IMHO.
It just struck me as odd the other day when the Batis 25mm, an ultra wide angle lens, gave me fit with the AF at f/16. I don't know at what aperture it would do that and I don't used f/16 that often either and as you notice the lighting conditions were not that great. The ISO setting was 2000 to get f/16 and 1/125 sec.
Seems that at that focal length and f-stop EVERYTHING looks like it's in focus. I know that when I put my 15/4.5 Voigt to f/8 on my A7RII and then use 100% magnification to find best focus it's really really difficult because it takes a lot of focus ring turning to see a difference. At f/16 diffraction has taken a firm hold knocking off the sharpness that the AF system needs to find the best focus.
If found similar things with the 18-35G on my D800 - stop it down even in bright daylight and the AF system has trouble getting accurate focus.
John, the more I think about it the more inclined I am that it has to do with just the AF issues at smaller aperture settings and less with the focus shift at all. Furthermore one would indeed think that the DOF at f/16 using a 25mm lens would be sufficient to render quite a bit of zones in focus. But take a look at the images below. These are crops of 3 different images.
Image 1: I was using another lens at wide open previously and when I put the Batis 25mm on, I didn't think much about it and took this image at f/2. No problem with the focus but not enough DOF and the sunstar of the sun was not defined at all.
Image 2: Stopped down to f/16, and the AF issues struggled. I could see in the viewfinder/monitor that it flickered and the green button didn't turn on. I went ahead an took this shot since I really wanted to see the result. Well, nothing is in focus.
Image 3: I opened up the aperture to f/8, got AF right away. The green button is on and the EVF was not flickering at all. I stopped it down to f/16 and took the image. I am not worried about any diffraction issues at all. I just wanted to get the sunstar and in my experience, diffraction although maybe visible on charts but in real life shooting, a slight decrease in resolution turns out to be negligible. Again, these are all crops and you can see the full image of the 3rd image in the link I provided above.
Mar 21, 2017 at 10:25 AM
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