Odd non focusing issues

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gfcphotography

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Hi - fairly new to Sony and today when out taking butterfly photos a few times the camera (with the Sony 100-400 lens) refused to focus. I use aperture priority, AF-C and medium rate. Use also the AF On button and have taken focus off the shutter button. It would focus in wide, zone, but none of the other focus modes. I wasn't too close to the subject but that wasn't the problem anyway as it wouldn't focus on anything unless it was in wide or zone. Will have to trawl through the settings and the manual as it was probably something I had done as I have found so far Sony kit is quite reliable.
 

Ziggy

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Small-subject AF isn't a strength of Sony full frames, at least of the A9 and A7R III. It's been talked about on Fred Miranda, Facebook and DPreview. I've documented my experience here: https://www.talkemount.com/threads/a9-focus-fails.19467/

When your AF area was wide or zone, was there any subject movement? This can help.
Otherwise people are getting a lock on something nearby and trying to move it across.
 

gfcphotography

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Thanks Ziggy - very interesting. Read all the posts and followed the links and I think you have hit the nail on the head! The strange thing is most of the day I used the expand flexible spot and it was fine when I got it on a butterfly / bee / flower - all of which were very small. The photo I took when I couldn't focus on anything was actually focussed on the background (I downloaded the exif programme and checked). Slightly disappointed that it is a weak spot with Sony full frame but will adapt and find a way around it! Thanks for your help - the advantages so far outweigh the disadvantages and it is all about getting to know your equipment!
 

Ziggy

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Glad to be of some help.

There's some inconsistency in it.

I recently was successfully shooting a black cormorant in bright sun that almost filled the frame. When I stepped back a bit the A9 wouldn't lock at all and there was nothing to transfer from.
To that point I'd been wondering whether it was a problem with monochrome subjects.
Hey ho.
 

jcastar

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Hi - fairly new to Sony and today when out taking butterfly photos a few times the camera (with the Sony 100-400 lens) refused to focus. I use aperture priority, AF-C and medium rate. Use also the AF On button and have taken focus off the shutter button. It would focus in wide, zone, but none of the other focus modes. I wasn't too close to the subject but that wasn't the problem anyway as it wouldn't focus on anything unless it was in wide or zone. Will have to trawl through the settings and the manual as it was probably something I had done as I have found so far Sony kit is quite reliable.

I've only had my 100-400 for a short time but I *have* noticed this behavior with the Sigma 50mm Art and the Rokinon 85mm when used with my a9. Both perform flawlessly on my a7riv but they get glitchy occasionally with the a9. Interestingly, no such problems ever noticed with go-to Sony 70-200/2.8.

When I get more time with the 100-400 I'll let you know.
 

AlphaWorld

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Glad to be of some help.

There's some inconsistency in it.

I recently was successfully shooting a black cormorant in bright sun that almost filled the frame. When I stepped back a bit the A9 wouldn't lock at all and there was nothing to transfer from.
To that point I'd been wondering whether it was a problem with monochrome subjects.
Hey ho.
Just a guess, but the AF system needs something with contrast to lock onto. Maybe a black cormorant that filled the frame was showing some details it could lock onto, but moving back meant it lost that detail and couldn't find something to lock onto?

It is frustrating when that happens. I have gotten better at switching to DMF and focussing manually, but only on static subjects. I am going to experiment with a custom button to do that.
 
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Ziggy

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Wayne of Camera Clinic in Melbourne says that the on-chip PD sensors are very small, line-type only of course, and can get confused.
I'm pretty sure in these cases that the AF doesn't get to CD.
 

Pharmer5

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I'm not sure if this a similar issue but when attempting to take a picture of a bird, my csmera will not focus if the bird is on a horizontal branch but will focus if the bird is the trunk of a tree (vertical). This occurs whether I'm using flexible spot or wide zone.
TIA
 

AlphaWorld

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I'm not sure if this a similar issue but when attempting to take a picture of a bird, my csmera will not focus if the bird is on a horizontal branch but will focus if the bird is the trunk of a tree (vertical). This occurs whether I'm using flexible spot or wide zone.
TIA

I believe that the PD AF sensors in the Sony sensors are good at detecting vertical lines, but not so much horizontal ones. Back in the days of DSLRs there was much made of “cross type“ AF points which could detect both horizontal and vertical lines; I wonder if they could be integrated into the sensor?

ooh, I wonder if you could get it to work by rotating the camera into portrait orientation?
 

Ziggy

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That's called canting.
I found no improvement with it 🙁
 

Ziggy

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I think there's 2 limitations with the on-sensor PDAF sensors : line-type only and they're small and can get confused. And I think it's the 2nd that gives us most grief with static subjects.
 

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