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Sony Aperture Drive in AF settings


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Lacking an ability to diving until this Fall I have been studying the manual for my new Sony A7R V. I am writing up what I learn so I can efficiently experiment with options once I start diving and, hopefully, to help others make sense of the myriad of menu functions, not all of which are well explained in the manual.

 

One example is the Focus > AF/MF > Aperture Drive in AF > Focus Priority | Standard | Silent Priority menu. The manual hints that it has to do with controlling sound volume. Other documents indicate that it affects multi-shot frames-per-second rate. The latter depending on which camera and lens combination you use. But in a series of experiments I believe it controls whether the camera keeps the aperture wide open or stops it down to the user's setting. This behavior is further coupled to whether or not you let the live view reflect your exposure settings.

 

Since I expect others have been stumped by this I am pasting the section on this topic below. It is complex enough that there may be aspects I have missed. If so please comment.

 

Aperture Drive in AF

The Focus > AF/MF menu has a somewhat poorly defined function named Aperture Drive in AF. This can be set to Focus Priority, Standard, or Silent Priority (the latter is not available for all lenses, including my 90mm F2.8 macro lens). The manual implies that this menu function controls a trade-off between focus performance and silence. For underwater stills photography we don’t care much about silence and we do care about autofocus performance so Focus Priority appears to be the obvious choice. But what does this setting really do?

 

Autofocus works best with the lens aperture wide open. This maximizes the amount of light to work with and it minimizes the depth of field (DOF), which helps to pinpoint the optimal focus position. On my Olympus cameras, live view is shown with the aperture wide open and you need to activate Aperture Preview, which stops down the aperture, to judge DOF under the aperture value set for the exposure.

 

Sony does this differently. By default, they show the live view with an aperture value matching the setting chosen by the user. As a result, live view shows the actual DOF, which is nice. However, the closed aperture limits light capture which has two drawbacks:

  1. when ambient light is substantially underexposed, as is common in strobe-dominated underwater photography, the viewfinder becomes very dark. You can boost the live view brightness by setting MENU → (Shooting) → [Shooting Display] → [Live View Display Set.] → [Live View Display] → [Setting Effect OFF] but a strong boost reduces live view image quality.

  2. if the aperture is kept close this would reduce autofocus performance

Impact on AF-S/DMF performance

Aperture Drive in AF = Standard (live Setting Effect ON)

In this mode the aperture is stopped down to the set value. You can see that by switching on Peaking in DMF mode. You see the Peaking pattern getting wider/narrower as you select higher/lower aperture values. The viewfinder simultaneously gets darker/lighter (you may need to boost ISO a bit if the view is too dark).

Initiating autofocus briefly narrows the Peaking pattern (narrower DOF). Once focus is locked, the Peaking broadens again (wider DOF), indicating that the camera opens the aperture transiently to assist with autofocus. Somewhat surprisingly, the viewfinder does not briefly brighten as the aperture opens.

Interestingly, this behavior is seen at F5.6 and higher but not at F4 and lower with my Sony A7R V and 90mm F2.8 macro lens. It appears that the aperture only opens when needed, with the F4 threshold dictated by either the camera body, lens, light level, or a combination thereof. (Edited: no longer sure this is the case)

Aperture Drive in AF = Focus Priority (live Setting Effect ON)

In this mode you see a narrow Peaking pattern that does not change as you select higher aperture values. This indicates that the aperture is kept wide open. Somewhat surprisingly, the live view brightness does respond to changes in aperture. Perhaps Sony electronically tunes the live view signal to match exposure settings, since that is what the user expects in Setting Effect On mode. This appears to be the case because if you activate AutoISO you get a much cleaner, less amplified, live view image with the Focus Priority than the Standard setting.

Initiating autofocus does not alter the Peaking pattern immediately but, once focus is locked, Peaking broadens while the shutter remains half-pressed. This indicates that the camera uses a wide open shutter for best autofocus performance but once focus is acquired it stops down to allow you to judge DOF.

Behavior with live Setting Effect OFF

When you set Setting Effect off, the camera is no longer expected to reflect exposure settings. Checking the Peaking pattern’s response to aperture changes and focusing shows that the Aperture Drive in AF no longer has any effect and both show the Focus Priority behavior described above.

My recommendation for AF-S/DMF mode

Based on the observed behavior I think using Focus Priority is the best option. This gives you the same behavior independent of the Aperture Drive in AF setting, which avoids confusion. You also get a cleaner live view image when ambient light is strongly underexposed and, with Setting Effect ON the camera can autofocus instantly without first having to open the aperture. The one disadvantage is the live view does not show DOF all the time. But you can get a DOF preview simply by half-pressing the shutter. You can also assign the Aperture Preview menu function to a custom button is you wish.

Finally, Sony documents indicate that Aperture Drive in AF also affects the shooting rate in multi-shot mode, but that doesn’t really affect underwater photography with strobe.

Impact on AF-C/AF-C+T performance (live Setting Effect ON)

In AF-C mode, optimal continuous focus requires that the aperture remains wide open and only close at the moment the image is taken. But showing exposure effects in live view requires that the aperture is stopped down to the set level. Comparing Focus Priority and Standard settings, the former could focus at F22 with shutter speeds down to 1/8000. The viewfinder was completely black but I suspect that the aperture was open. In the Standard setting, the camera showed a black screen with a shutter speed up to 1/1000 but it became bright at 1/1250 or less. Once focus is acquired it turns black again.


I suspect that up to 1/1000 the camera kept the aperture stopped down to the set value while remaining able to focus. At 1/1250 or less the ambient light must have fallen below a threshold and the aperture was opened briefly to allow AF-C to continue to work. The fact that the viewfinder remains black with Focus Priority but not Standard setting suggests to me that the former electronically darkens live view to mimic the aperture setting, whereas for the latter live view gets dark as the direct result of closing the aperture. When the aperture needs to be opened when it gets too dark, it shows up in the viewfinder. As expected, when Setting Effect OFF is used the camera starts to behave as in Focus Priority mode. Again I think using Focus Priority is the best option.

Edited by Biodives
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Sony cameras do not focus with the aperture wide open by standard they follow the setting dialled in

The focus priority aperture drive only matters when you use f values that are small which can happen in underwater photography and after the ISO has hit sanity values

When you use burst (unusual underwater) setting focus priority slows down the action because of the aperture variation

However souces show that only after f/8 or f/11 the camera starts keeping the aperture open to a minimum

To simplify imagine you shoot wide open to f/8 it makes no difference what mode you are on

Now you dial in f/16 the camera will focus at f/8 but meter at f/16 it won't go all the way down to f/2.8 even if the lens supports it in that is different to a DSLR

Considering when you are past f/8 is a more important consideration than light levels as the minimum stopped down value seems to be f/8

So for macro you want focus priority you will be shooting f/11 and smaller

For wide angle it depends what type of shooter you normally the camera focuses easily but if you are always at f/14 you should use focus priority

 

Topside different situation you shoot a long lens wide open it won't matter the aperture drive. You shoot bursts at f/8 and smaller you want to leave it to standard. Generally topside there is no major benefit to use focus priority. Even if you are in low light chances are you already opened the aperture so what the drives does does not matter

 

FYI the live view is an exposure simulation the camera runs the EVF and LCD refresh at a minimum shutter speed that does not always reflect the speed dialled in especially if slower

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The F/8 - F11 is what I had also read, though some suggested it depends on the camera/lens combination. Initially I had the feeling that the transition was between F4 and F5.6 for my 90mm macro lens but once you get close to F2.8 settings the difference becomes smaller to see by eye. It is rather clear though that Peaking signal in Focus Priority mode does not change as you change the aperture. I don't think they simulate that because if they did why not simulate the actual DOF? The improved live view image quality in Focus Priority also hints that the aperture is indeed open in that mode and not in the Standard setting. Perhaps the 90mm macro lens is an exception as focusing in macro photography can be more challenging?

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The whole mantra of live view is to work with standard aperture drive 

what you see is what you get 

when live view is off or aperture drive is in focus priority this is no longer possible 

if you are using peaking you are most likely using manual focus and you want the screen to reflect the depth of field as you dialled in

aperture drive in focus priority really is just for autofocus at very small apertures

 

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