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Front focussing on A7rII and certain lenses

Viramati

Member
A thread has been started on preview that at first I didn't take seriously
Returned A7R II because of severe frontfocus: Sony Alpha Full Frame E-mount Talk Forum: Digital Photography Review
But then I got to thinking and I notice that the A7rII opens up the aperture to focus which isn't the case on my A7s and I don't have the A7 or A7II anymore to check. On doing some testing with the FE24-70 at 50mm on a tripod etc I do in fact seem to be noticing a shift forwards and I can only presume that if the lens didn't open up to focus wouldn't be there. Now I only have the A7s to compare it with and it is only 12mp so I can't really get an accurate comparison ( when tested in the same way I can't see any shift) with something similar nor do I have a proper test chart that I can place at 45 degrees to see what is really going on. So it would be good if others could test this out. Thanks

P.S tested on the FE16-35, 55 and 28 and they are all fine with the focus point getting sharper as you stop down which certainly doesn't seem to be the case with the 24-70
 
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Vivek

Guest
Re: Front focussing on A7rII

Is it camera "front focusing" or lens having aperture dependent focus shifts that creates this problem?

Can you check with other lenses if this is the case?


PS: Just saw your PS. It is the 24-70 zoom, me thinks.
 

Viramati

Member
Re: Front focussing on A7rII

Is it camera "front focusing" or lens having aperture dependent focus shifts that creates this problem?

Can you check with other lenses if this is the case?


PS: Just saw your PS. It is the 24-70 zoom, me thinks.
I agree and would be interesting if someone could test the FE24-70 on an A7r or even A7. On the A7s it seems fine
 

Viramati

Member
I am glad the guy started that thread. After some initial bickering it now has some useful content.
I agree though I trust people her more to get to the bottom of it. Personally I am not that worried as I would probably never use the 24-70 on the A7rII as I really don't feel it is up to the 42mp sensor and have only kept it as it performs so well on the A7s and if I sell that the 24-70 will go as well.
 

Viramati

Member
I would request anyone testing the FE 24-70 on A7r or A7 to try turning 'Setting Effect' to OFF in the 'Live View Display' menu to see if this make s matters worse as I am not sure if in this mode the camera focuses first and then stops down. Thanks
 

tashley

Subscriber Member
If I get a chance I'll test it with a Spyder tomorrow. I wouldn't assume, though, that it is necessarily quite as simple as 'it opens up to focus'. On the RX1 it does different things depending on what aperture range you are in - that camera always focusses (and therefore previews) at the selected aperture for all apertures from F2 thru F8 BUT from F9 thru F22, it will open up to F8 for AF. So from F9-22, if you look at the preview while the camera is performing AF, you will get an inaccurate representation of DOF.

To compound the potential confusion, when I look into the lens barrel on the 24-70 f4 on the A7RII it looks as if the camera is opening up to focus, but there is also a hint that it does its first round of focus wide open, then stops down to maybe refine it even after the beep. This might be switching between PD and CD systems? It might also depend not only on whether you have settings effect on or off, and it might be affected by the balance between accuracy and speed you have set. Also, try pointing the camera at a featureless thing that it can't focus on and watch it's little aperture ring going in and out like a fish's mouth.

Of course what matters is that it works, which it should, so I will give it a go and report back. The last thing one wants to do is to have to remember how the camera is behaving in terms of focus according to several different combinations of settings but to some extent, as they open up all these choices, that's gonna happen...
 

tn1krr

New member
I would request anyone testing the FE 24-70 on A7r or A7 to try turning 'Setting Effect' to OFF in the 'Live View Display' menu to see if this make s matters worse as I am not sure if in this mode the camera focuses first and then stops down. Thanks
I have tested this on my A7R when I briefly had the 24-70/4 OSS. I tested Eye-AF with Elinchrom Skyport trigger with manual flash so it must have been with "Setting Effect off". I've reported this even here before but the AF accuracy was not good, I would not say massive focus errors, but enough to know that AF was a bit off. One of the main reasons my 24-70/4 OSS went back shop, only lens I've ever returned.

I actually still have the shots in my LR Catalog and I still can still super-easily pick the OOF 24-70/4 shots from FE 55 shots I shot for comparison and this was at F/5.6. The best shots I got with 24-70 were manually focused.
 

davidstock

New member
I'm interested in this issue, too.

I just started this thread on focus shift at DPReview:http://www.dpreview.com/forums/post/56363973

One of the things I like about my A7II is that it can easily focus with the lens stopped down to taking aperture. This avoids issues with focus shift that are somewhat common with SLRs. In fact, this is one of the reasons I transitioned to mirrorless cameras.

I am hearing from owners of A7RII cameras that the new camera's aperture opens up to focus, then stops back down to taking aperture, just like an SLR. This is a change from what the other A7 cameras do, AFAIK. I am wondering if this is causing any issues with focus shift.

Two things piqued my interest in this question recently. One is a review of the Batis 85mm lens on Luminous Landscape. In a series of photos of a truck, carefully focussed by Michael Reichmann using an A7RII on a tripod, there is clear evidence of front focus when the Batis is stopped down. Also, there have been at least four reports of zoom lenses front-focussing with the new camera. (example: http://www.dpreview.com/forums/post/56362175).

I wonder if others have experienced focus shift with any lenses on the A7RII, or are these reports just statistical outliers? Maybe just bad lenses?

I would be very curious to know if the A7RII opens the lens aperture part way or all the way in order to focus?

If it just opens up to f3.5 or so, this would probably eliminate most of the potential problems with focus shift. If it opens to f1.8 or f1.4 to focus, that seems to be inviting focus shift with lenses that are prone to it.

In that case, we would be back to where we were with SLRs--making sure our lenses have no focus shift, or else managing the shift as best we can.

Finally, I wonder what the A7RII's behavior is when back-button focus is used. Does the aperture still open up to focus when the camera is in this configuration?

Thanks for any information or insights.

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d


In thinking this over, I'm realizing that most focus shift is to the back, not the front. So maybe these reports are unrelated to aperture behavior.

Still, I'd love to know from A7RII users here if the aperture actually opens up all the way to focus, or just part way. And what happens when you use back button focus?

--d
 

Viramati

Member
I have tested this on my A7R when I briefly had the 24-70/4 OSS. I tested Eye-AF with Elinchrom Skyport trigger with manual flash so it must have been with "Setting Effect off". I've reported this even here before but the AF accuracy was not good, I would not say massive focus errors, but enough to know that AF was a bit off. One of the main reasons my 24-70/4 OSS went back shop, only lens I've ever returned.

I actually still have the shots in my LR Catalog and I still can still super-easily pick the OOF 24-70/4 shots from FE 55 shots I shot for comparison and this was at F/5.6. The best shots I got with 24-70 were manually focused.
What I am seeing is not AF inaccuracy because if I focus manually on an object take the shot wide open and then stop down I 'think' I am seeing the same shift. So I am concluding that when focussing with the lens stopped down on previous models this compensates for any focus shift. As I said I am unable to test anything on the A7s as the resolution would seem not to be enough to pick up any problems
 

sbay

New member
Still, I'd love to know from A7RII users here if the aperture actually opens up all the way to focus, or just part way. And what happens when you use back button focus?
I only have the 55 FE native lens (just got the camera), but as far as I can tell when you hit the back button AF the camera opens up to almost f/1.8 (but definitely not f1.8) and then gradually closes down the aperture as you achieve focus lock. The closing of the aperture does not occur instantly, and the camera may be pausing/slowing down as the aperture blades close (to recheck focus?).
 

tn1krr

New member
I only have the 55 FE native lens (just got the camera), but as far as I can tell when you hit the back button AF the camera opens up to almost f/1.8 (but definitely not f1.8) and then gradually closes down the aperture as you achieve focus lock. The closing of the aperture does not occur instantly, and the camera may be pausing/slowing down as the aperture blades close (to recheck focus?).
Yes, A7R II works this way, normal and back-button AF. My F/1.8 lenses (FE55 and Batis 85) open up to around F/2 or F/2.2 regardless of shooting aperture. My theory is that PDAF likes the wide open and then CDAF is used to confirm while stopping down. Although the lenses know their focus distance etc. so there could be focus-shift database in the camera and the gradual stopping down is just to avoid any sudden changes of brightness in the EVF. I tested this while looking at the aperture blades in think I heard focus confirm beef before aperture blades stopped down.
 

tashley

Subscriber Member
I only have the 55 FE native lens (just got the camera), but as far as I can tell when you hit the back button AF the camera opens up to almost f/1.8 (but definitely not f1.8) and then gradually closes down the aperture as you achieve focus lock. The closing of the aperture does not occur instantly, and the camera may be pausing/slowing down as the aperture blades close (to recheck focus?).
That's my current guess too, and tomorrow I'll have look at that happens when you change your focus preference settings in Cog>4 but I have to say that there are so many permutations that before we all start testing we need to think about what the possible variables are and then test around that knowledge.
 

Viramati

Member
So someone else on the dpreview thread has confirmed my suspicions and with the 'setting effect' set to OFF in the live view display on an older A7 he has replicated the issue with the 24-70. So if this is the case a solution would be to give us the option be able to disable the shutter from opening up during focusing. How to communicate these findings to Sony is another matter as I remember how difficult I found it trying to get through to anyone technical when I discovered the IBIS issue withe A7II and adopted lenses
 

davidstock

New member
That's my current guess too, and tomorrow I'll have look at that happens when you change your focus preference settings in Cog>4 but I have to say that there are so many permutations that before we all start testing we need to think about what the possible variables are test around that knowledge.
I agree. Another complication, mentioned by others, is that that Sony may encode the lens characteristics (including focus shift) to achieve better focus. If this encoding is not working, that might cause problems in limited cases. (If there is encoding, does it apply to Zeiss FE lenses, too? And what happens with adapted A-mount lenses....)

It might help to know which FE lenses are known to have focus shift. According to photozone, the 70-200 f4 does have some. On the other hand, based on its MTF chart, I doubt that the 55 Zony has any. With the 35mm f2.8, the shift looks minimal. Given what we've just heard about the 24-70 zoom on the A7, that lens does have noticeable shift. I wonder about the 85 Batis and the 35mm/1.4?

--d
 

Slingers

Active member
I had a similar problem on the A7S and the FE 35/2.8 right after I loaded the latest firmware. Every time I tried to focus i saw the green focus lock box but it looked like I was doing a bokeh test with nothing in focus. I had the camera on either wide or zone focus mode, I can't remember which, but to fix I had to swap to the center focus mode. Now that's the focus mode I will use on the FE 35/2.8.
 

Viramati

Member
Just to double check the issue again I have retested the FE24-70 on my A7s with 'display live view' 'setting effect' on and Off and with it off there is definite focus shift with the setting set to off so I am now convinced that this is an issue of the lens not being stopped down when focussing takes place.

I have also once again tried contacting Sony this morning and I can see that it will be a long and tedious process so if any of you reading this have some access to Sony that would be so helpful. I had thought of trying to contact Micheal at LuLa as he has just tested the camera and may have some Sony contacts
 

tashley

Subscriber Member
Just to double check the issue again I have retested the FE24-70 on my A7s with 'display live view' 'setting effect' on and Off and with it off there is definite focus shift with the setting set to off so I am now convinced that this is an issue of the lens not being stopped down when focussing takes place.

I have also once again tried contacting Sony this morning and I can see that it will be a long and tedious process so if any of you reading this have some access to Sony that would be so helpful. I had thought of trying to contact Micheal at LuLa as he has just tested the camera and may have some Sony contacts
I have tested it today with a Spyder Lens cal target, specially made for this sort of exercise.

Distance from focal plane to centre of target: 2.25 metres.

Tripod, delay, you name it.

Settings effects and so on all off
preferences in Cog>4 set to focus, rather than balanced priority.

First I tried with the camera set to MF and I focussed carefully at F4 at 50mm and 70mm and for each focal length I then stopped down to 5.6 and 8 without changing focus. This is intended to see if there is any significant focus shift inherent in the lens regardless of AF. IMHO though there probably is, it isn't significant enough to outstrip DOF at any of the tested focal lengths other than 70mm.

At 70mm it is clear that when focussed manually (I ran several series) the lens shifts focus forwards as it stops down, such that DOF is not enough to save it until F11. In other words, the POF is in less good focus at 5.6 and 8 than at F4.

Switching to AF (and again I ran several series) I had no problem at any focal length other than 70mm where I discovered two things: firstly, that exactly as with MF, the AF series saw focus shift forward such as to require F11 to achieve sufficient DOF to beat that shift and secondly, that the lens tends to front focus anyway, even at F4.

It certainly has the plane of focus within DOF but rather towards the back of that DOF, and therefore as the lens goes on to shift focus forward with smaller apertures, the effect of that focus shift is working with the natural front focus tendency to make focus just plain inaccurate at 70mm and F5.6 and F8 and barely satisfactory at F4 and F11.

I'd like to run these tests again now that I have a sense of what's going on but the light has gone now.

I think this should be easy to fix, assuming that anyone at Sony can be encouraged to pay attention. There's a whole lot of electronics governing where and how the lens focusses and a firmware update should deal with it.

But for now, at least at 70mm (and I want to test at 60 and 65mm) I think one has to shoot at F4 and put up with the limited DOF, or at F11 and put up with diffraction, or use DMF, or, more easily, just choose the furthest back part of the subject. Will eye AF work at 70mm and f5.6 or f8? I'll have to test that but I wouldn't bet on it.

EDIT: I have to add that the more cameras and lenses I own and test, the more I realise that one can only ever speak for a particular copy of a lens on a particular copy of a camera. YMMV.
 

Viramati

Member
Thanks Tim for your testing. I understand that there could well be lens variation involved here. I di the testing on mine at 70, 50 and 35mm all with similar results.
i have sent an email of my findings to Sony and will try to see if my dealer has some way of contacting them more directly.

P.S Tim if you have a previous version of the A7 try testing with the setting effect on and off in AF
 
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