Z9 AF with heat distortion (and related focus racking question)

[nautiboy]

I think I've been noticing a trend/behavior and I'm curious if others have noticed it. On the days when I'm shooting with some amount of heat distortion, it seems to really give the Z9 fits - much more so than my D850. It often just keeps racking the lens all the way in and out. The D850 and D6 also have a little more trouble focusing, but they don't seem to rack the lens all the way like the Z9 is(*), it's mostly smaller movements around the target.

I'm wondering if the difference is largely contrast vs phase. With contrast focusing it's trying to find the highest contrast, which is often a bit muddled with heat distortion. With phase, it's trying to get two images to converge which I would think would be less prone to problems with heat-distorted-soft-edges. But I thought the Z9 used a combination of phase and contrast?

My question is largely academic, as the shots aren't likely good enough to be keepers in this scenario regardless. But I'm still trying to get a feel for the differences of the Z9/mirrorless system to better understand the effects in the field.

(*) Is it just me, or does the Z9 (and probably other mirrorless) tend to rack the lens much more? It's been driving me a bit batty because I might be relatively close to focus and it starts to get the focus but if it misses it (which could happen for a number of reasons) it just racks all the way to the end and back. Then trying to get focus back is really difficult because you often can't even see the subject to keep the lens on target and so it just keeps racking back and forth. I have to then stop and either try to manually get the focus close while also tracking the subject, or point away to some object/hill/whatever at roughly the distance and then try to re-acquire the target. I've been trying to get some BIF Peregrine shots and I've been finding it much harder than when I was shooting my D850. Of course once I do get a positive lock, it's typically pretty good about keeping it and then the shots get easier - but these guys move so fast and are fairly erratic, so always keeping the lens on target is really tough (at least for me) and I inevitably lose them for just long enough that the camera loses lock and then the racking begins and the frustration trying to re-acquire focus.

FWIW, the lenses I'm using right now are all F mount with FTZ in case that makes a difference (the 800f5.6, 600f4 and 100-300f2.8).

 

[abc123brian]

I think I've been noticing a trend/behavior and I'm curious if others have noticed it. On the days when I'm shooting with some amount of heat distortion, it seems to really give the Z9 fits - much more so than my D850. It often just keeps racking the lens all the way in and out. The D850 and D6 also have a little more trouble focusing, but they don't seem to rack the lens all the way like the Z9 is(*), it's mostly smaller movements around the target.

I'm wondering if the difference is largely contrast vs phase. With contrast focusing it's trying to find the highest contrast, which is often a bit muddled with heat distortion. With phase, it's trying to get two images to converge which I would think would be less prone to problems with heat-distorted-soft-edges. But I thought the Z9 used a combination of phase and contrast?

My question is largely academic, as the shots aren't likely good enough to be keepers in this scenario regardless. But I'm still trying to get a feel for the differences of the Z9/mirrorless system to better understand the effects in the field.

(*) Is it just me, or does the Z9 (and probably other mirrorless) tend to rack the lens much more? It's been driving me a bit batty because I might be relatively close to focus and it starts to get the focus but if it misses it (which could happen for a number of reasons) it just racks all the way to the end and back. Then trying to get focus back is really difficult because you often can't even see the subject to keep the lens on target and so it just keeps racking back and forth. I have to then stop and either try to manually get the focus close while also tracking the subject, or point away to some object/hill/whatever at roughly the distance and then try to re-acquire the target. I've been trying to get some BIF Peregrine shots and I've been finding it much harder than when I was shooting my D850. Of course once I do get a positive lock, it's typically pretty good about keeping it and then the shots get easier - but these guys move so fast and are fairly erratic, so always keeping the lens on target is really tough (at least for me) and I inevitably lose them for just long enough that the camera loses lock and then the racking begins and the frustration trying to re-acquire focus.

FWIW, the lenses I'm using right now are all F mount with FTZ in case that makes a difference (the 800f5.6, 600f4 and 100-300f2.8).

I haven’t done any testing, but since mirrorless cameras use the image on the sensor for focusing, if there was enough heat distortion to make the image not appear in focus, I could see it causing issues. I tend to not shoot in conditions where I can tell there is heat distortion because the images don’t turn out anyway.

 

[Rassie]

I think you've figured it out for yourself. The contrast detect AF has a problem with poor contrast on the target, so when the lens racked all the way in or out the focus is so far off that the camera cannot see the target, let alone the contrast in it, resulting in racking in and out continuously. Steve wrote about this in an earlier post. His advice is to manually focus near the target and then allow the AF to acquire the target from there. It can grab focus more easily if the target is not too much OOF to begin with.

I have the same issues with my Z6II with the 200-500mm F/5.6 lens mounted. I'm trying to train my hand to under those conditions, turn the focus ring all the way to one side, then bring it back halfway and then try to get the AF to acquire and lock again. I haven't tested this, but I suspect this problem becomes progressively worse the longer the focal length of the lens because the DOF keeps getting shallower the longer the focal length. Perhaps someone with more brains than me can comment on this.

 

[nautiboy]

I think you've figured it out for yourself. The contrast detect AF has a problem with poor contrast on the target, so when the lens racked all the way in or out the focus is so far off that the camera cannot see the target, let alone the contrast in it, resulting in racking in and out continuously. Steve wrote about this in an earlier post. His advice is to manually focus near the target and then allow the AF to acquire the target from there. It can grab focus more easily if the target is not too much OOF to begin with.

Yes, and I totally get that, and I do try and get the focus close. The problem is that even in that case the camera sometimes "misses" the focus - sometimes it's because the bird moved out of the box (if I'm using wide-area AF) while it was trying to focus, or sometimes it just plain misses it and in both cases it focuses all the way to the end making it difficult/impossible for it to reacquire and for me to keep the lens on the target. Then I have to try and get the focus close again either by manually focusing (which is difficult because I can't even see the target at this point because the AF threw the focus so far off) or I have to leave the subject and point at something else to get the focus "somewhat close" and then try and re-acquire the target - which takes some time and the bird may have gone way off by that point.

I dunno, I can play more with the AF focus settings - usually I use "erratic" for erratic birds, but maybe that's just exacerbating the problem (and it might've been nice if they kept the 1-5 method for steady/erratic instead of making it binary).

 

[Rassie]

I hear you. I'm in the same boat, and it's especially hard when the bird is close to me - too easy for it to move out of the viewfinder altogether and then to try and re-acquire it when the focus is that far off that it doesn't even show in the viewfinder.......

 

[Warren D]

I've noticed that myself. I was out in the fog last weekend and the Z9 had a lot of trouble finding focus. (Lens was 600 EFL with 1.4 tc) I ended up using single point AF which seemed better than 3D or Wide Area modes. I did not turn off subject detection, I don't like menu diving. After several minutes of this trouble, I switched to my D6 and the Group AF of the D6 did a noticably better job of finding and locking focus.
To be honest, I've had trouble with the D850 and D6 when it comes to trying to focus thru atmospherics, even when it isn't really obvious but the Z9 seems more sensitive to this than the dslrs.
This shot did get AF, fog was actually worse than what shows, post processing cleaned it up a bit.