Jamidu
New member
When planning to buy a Z8, I am looking for information on how AF behaves depending on the lens brightness. Eg. F/8 or F/11? Anyone know or where to find it. I appreciate any help
AF in Z8 against lens brightness
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By most accounts mirrorless camera AF capability is superior to dSLRs and using small apertures hardly or don't affect the AF.
If shooting at f8 or f11 or smaller, for example, the camera while focusing open up to allow more light in, not fully, but to a certain f number, 5.6 I believe, then closes down when you shoot. If shooting with an aperture larger than 5.6 it just stays at whatever f number you have set. Also, the z8 and z9 focuses better when the image in viewfinder is bright enough, but this comes from the whole combination of f number, shutter speed, and iso.
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If I understand correctly (and I think I do), autofocus is affected by the largest maximum aperture of the lens regardless of the actual aperture being used at the time. In other words, a 70-200 f2.8 will focus better (especially in low light) than a 100-400 f5.6 even if both are being shot at f8. It is not the aperture currently in use that matters (for autofocus), it is the maximum aperture that is available on the lens.
I believe the z cameras are unique. I know my Canon goes fully wide open to autofocus then stops down to whatever f number is set just while shooting. The z cameras only open up to 5.6 to focus if the f number set is smaller than 5.6.
I wonder if what the op is referring to is the dual stream on the z9/z8, where some of the AF depends on how bright the image is rendered by the livestream.
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I wonder if what the op is referring to is the dual stream on the z9/z8, where some of the AF depends on how bright the image is rendered by the livestream.
Z9 AF Operation Observations by Thom Hogan
OK, I just did my own test. I went into a small walk-in closet with a 60W-equivalent LED and pointed the camera at some low-contrast carpet and at a colored-striped notebook that I'd say is an "easy" target for an AF sensor. Exposure was 1/500 f/5.6 ISO1600. Cameras were in Single AF...
bcgforums.com
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Jamidu
New member
Thx but my question is not about setting the aperture to 8 or 11. What I'm talking about is the limitations of the lens. An F/5.6 lens together with TC-1.4 or 2.0 gives the resultant F/8 or F/11.
That's true for DSLRs but in Nikon's mirrorless implementations as Bill posted above the actual dialed in f/stop will be used for AF and EVF display until you exceed f/5.6 and then the view and AF will be performed at f/5.6 until the actual capture where the lens is stopped down the rest of the way. IOW, if you shoot an f/4 lens and f/2.8 lens, both with an f/5.6 or f/8 aperture dialed in they'll both perform AF and display the DoF in the viewfinder of an f/5.6 lens and then stop down the rest of the way just as the image is being captured. Of course if you shoot with a lens that's beyond f/5.6 wide open as in an f/8 or f/11 lens (or lens plus TC combo that gets you to that wide open aperture) then that will be the aperture used for AF and the DoF displayed prior to the capture regardless of what's actually dialed in for shooting aperture.
IOW, DSLRs (since around the 1970s) have used Open Aperture Metering which doesn't stop the lens down until the shutter is released. Prior to that cameras used Stop Down Metering where you'd focus and view the image (at least with a DSLR) at the actual dialed in aperture. Nikon's mirrorless cameras use what might be called 'semi stop down metering' in that they use the dialed in aperture up to f/5.6 and then stop down the rest of the way as the image is captured.
This is pretty easy to test and demonstrate. Look through your Nikon mirrorless camera at a scene where it's easy to see DoF changes using a fast lens. Stop down and watch the DoF change up till you hit f/5.6 and then see how you see no further DoF changes as you stop down further but if you capture images the DoF does continue to grow.
The AF systems in mirrorless cameras is not nearly as sensitive to wide open lens aperture like it was in DSLR days. You won't lose access to AF points across the frame nor see a huge reduction in AF performance as you use slower lenses or lenses with TC combos that yield a smaller wide open aperture. That said, even mirrorless AF systems like fairly bright light with conditions that provide good contrast so even mirrorless AF systems can struggle in low light or low contrast situations which can be made more difficult with relatively slow lenses. IOW, slow wide open apertures themselves don't create AF problems the way they did in DSLRs but there's still benefit to capturing a lot of light in low light situations.
Jamidu
New member
I fully agree, but I am asking about cases when the maximum aperture of the lens is 8 or 11. Will AF work fully or not. Do we know the limitation?
Okay you have just blown my mind (and thank you for that). My understanding was way off. As soon as I read your post I tested it as you suggest (I mean looking at depth of field in viewfinder). Luckily I had my 70-200 f2.8 lens already attached to my Z8 so I went to my living room and focused on my balcony railing with the condo across from me out of focus behind. Sure enough - when I go from f2.8 to f5.6 the condo behind gets somewhat sharper but when I stop down further it does not get any clearer in the viewfinder. I also assumed a larger aperture lens would focus better (going from SLR knowledge), but apparently that is not the case. A huge thank you for clarification. @Jamidu ignore my reply in post four because my understanding was wrong when it comes to mirrorless cameras.
Okay this one I do know. Yes autofocus will still work. I tested it just now by attaching Z 2x teleconverter to my Z 180-600 lens which gives a maximum aperture (when zoomed out) of only f13. Autofocus still works.
Sure, if the lens is not capable of opening up to 5.6 then the af has to use the widest it has. I'm sure f11 max aperture is still is fine for focusing the whole viewfinder, but smaller than that I don't know if it starts limiting to the center af points.
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Jamidu
New member
Jamidu
New member
Thx but I'm not talking about the aperture setting, but about the maximum brightness of the lens used.
I’ve noticed minor (sometimes unnoticeable) auto focus delay using the 1.4x TC with 70-200 f/2.8 and 400 f/4.5 lenses. A bit more using it with a 100-400 lens.
Using a 2x TC, the delay is quite noticeable no matter the lens. It’s one of the reasons I don’t use it often.
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Jamidu
New member
Thanks for info
Jamidu
New member
Great. Many thanks
Jamidu
New member
Great. At F/13 AF is still acceptable for BIF?
EricKlees
Well-known member
Yes. I know Nikon will AF up to f22 at least
Jamidu
New member
Thx. Great information. Where can I find such information?
EricKlees
Well-known member
I read that when the Z9 came out 2 years ago. I don't remember where
To be clear, it is my understanding that when you put a tc on a lens you reduce the maximum aperture on this lens. The autofocus system can only use the light available so it matters not for autofocus purposes what the maximum aperture was before you added the tc.
Taking the 600mm pf as an example, if you added the 2.0 tc to this lens to get 1200 mm you will be working with f/13. There is no way around that.
I have not tested autofocus at f13 and have no opinion on how it works.
Taking the 600mm pf as an example, if you added the 2.0 tc to this lens to get 1200 mm you will be working with f/13. There is no way around that.
I have not tested autofocus at f13 and have no opinion on how it works.
I don't do birds in flight often (mostly because I am no good at it). The 180-600 lens on its own is not great for that (though I have gotten a couple) and my intuition says with the 2x at f13 it is worse. I have not tried it for this, but I tested it once on some more static birds just to see if image quality was acceptable and it was not. I bought the 2x to use with my 70-200 and it works great with that (still very sharp), but with the 180-600 I think the combination is too much to work well.
On a minor detail a Z8 or 9 button can be set to show actual depth of field when shooting with combinations smaller than F5 .6 - in much the same way as a depth of field preview button on a DSLR can be used to check depth of field when shooting at wider than wide open.
Big difference with Mirrorless include
1/ for those thinking of a move to ML the viewfinder brightness particularly on a Z8 and Z9 starts several stops brighter than a DSLR.
2/ there is still a bright viewfinder in normal daylight with combinations of f11 to f13.
This is unlike a DSLR where viewfinder brightness is dim by f11 and possibly close to unusable at f16.
With f8 to f13 combinations there is reasonable Nikon ML AF performance.
Canon ML AF works with f16 combinations.
I assume Nikon can - though my smallest Z combination is a 2x on an f6.3 lens giving f13.
ajrmd
Well-known member
Sorry, Eric I'm going to call you on that. The 186 is great for BIF and I have thousands of images which demonstrate that from perigrines to pellicans to spoonbills... It doesn't take TC's well because of image degradation which is not unique to this style zoom lens. I felt the same about my Sony 200-600 and Canon 100-500 and the effects of TC's.