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Archive 2019 · What does the purple focus spot mean on the a7r iv?

saxguy
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p.1 #1 · p.1 #1 · What does the purple focus spot mean on the a7r iv?

My focus spot keeps turning purple when trying to focus in low light or with low contrast subjects. I can move the spot to an area of high contrast and get it to lock green. This often means focusing on the edge of my subject which is actually behind the focal plane I'm trying to achieve when using a wide open aperture. I'm wondering if this is something others are experiencing or if I need to send my a7r iv in to be checked out, as I know there were some issues with focus on preproduction/very early units.

Dec 07, 2019 at 10:40 PM

snapsy
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p.1 #2 · p.1 #2 · What does the purple focus spot mean on the a7r iv?

Purple means focus acquisition failure.

Dec 07, 2019 at 10:49 PM

saxguy
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p.1 #3 · p.1 #3 · What does the purple focus spot mean on the a7r iv?

snapsy wrote:
Purple means focus acquisition failure.

It seems to happen in AF-S and not AF-C. I still don't know if it's a problem with my particular camera or if other people are having some of the same issues.

Dec 07, 2019 at 10:58 PM

trogdon
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p.1 #4 · p.1 #4 · What does the purple focus spot mean on the a7r iv?

AF-S uses CDAF only. Purple means it can’t lock focus. It’s pretty normal to happen depending on the situation

Dec 08, 2019 at 01:18 AM

mcbroomf
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p.1 #5 · p.1 #5 · What does the purple focus spot mean on the a7r iv?

trogdon wrote:
AF-S uses CDAF only. ...

I wasn't aware of this and I use AF-S a fair amount as I don't typically shoot things that are moving. I do get the purple fail to focus occasionally, but usually as mentioned when the light is low or the area I'm focusing on is low contrast.

I couldn't find any mention of AF-S only using CDAF in the Help Guide.

Dec 08, 2019 at 05:22 AM

bobby350z
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p.1 #6 · p.1 #6 · What does the purple focus spot mean on the a7r iv?

When you say low light, how much low light we talking? And which lens? That way others can try if possible.

Dec 08, 2019 at 08:48 AM

snapsy
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p.1 #7 · p.1 #7 · What does the purple focus spot mean on the a7r iv?

mcbroomf wrote:
I wasn't aware of this and I use AF-S a fair amount as I don't typically shoot things that are moving. I do get the purple fail to focus occasionally, but usually as mentioned when the light is low or the area I'm focusing on is low contrast.

I couldn't find any mention of AF-S only using CDAF in the Help Guide.

AF-S actually uses a combination of PDAF and CDAF. It uses PDAF for the initial acquisition and then CDAF for extra accuracy. In low-light situations it may use only CDAF. AF-C uses only PDAF.

Dec 08, 2019 at 09:32 AM

mcbroomf
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p.1 #8 · p.1 #8 · What does the purple focus spot mean on the a7r iv?

snapsy wrote:
AF-S actually uses a combination of PDAF and CDAF. It uses PDAF for the initial acquisition and then CDAF for extra accuracy. In low-light situations it may use only CDAF. AF-C uses only PDAF.

Thanks Adam, so presumably the purple (if it shows up predominantly in low light) is indicating that the CDAF is not getting good focus after PDAF has done it's job.

Dec 08, 2019 at 10:15 AM

saxguy
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p.1 #9 · p.1 #9 · What does the purple focus spot mean on the a7r iv?

bobby350z wrote:
When you say low light, how much low light we talking? And which lens? That way others can try if possible.

Here's an example of where it happened with the Sigma 105 1.4.

ISO was set to 1250 with a 1/125 Shutter speed +1.0 EV - so not excessively low light. Metered for highlights. Couldn't lock on the faces of sculptures themselves, had to use an area where part of the sculpture was next to the sky to acquire focus lock. This is what the image looked like SOOC (just saved the RAW as a jpeg).

Edited on Dec 08, 2019 at 10:45 AM · View previous versions

Dec 08, 2019 at 10:33 AM

saxguy
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p.1 #10 · p.1 #10 · What does the purple focus spot mean on the a7r iv?

I just tried it in my home (fairly good light) with both the Sigma 105 1.4 and the Zeiss Sony 50 1.4 ZA. AF-C acquires focus lock pretty much every time and AF-S is hit or miss with these lenses, moreso with the Sigma. They're the only two lenses I have right now, perhaps the 135 GM and 24GM would give much different results.

Dec 08, 2019 at 10:44 AM

snapsy
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p.1 #11 · p.1 #11 · What does the purple focus spot mean on the a7r iv?

mcbroomf wrote:
Thanks Adam, so presumably the purple (if it shows up predominantly in low light) is indicating that the CDAF is not getting good focus after PDAF has done it's job.

I think the purple is a general focus acquisition failure, independent of whether the camera first attempted PDAF or not. I suspect the camera might forgo even attempting PDAF for AF-S in very low-light situations.

Dec 08, 2019 at 11:55 AM

kevphoto
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p.1 #12 · p.1 #12 · What does the purple focus spot mean on the a7r iv?

I'm having some issues with this with the Tamron 17-28 (which I've only had for a day). Using AF-S outdoors during the day but trying to focus on shadowed areas. Kind of frustrating.

Dec 08, 2019 at 12:03 PM

bobby350z
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p.1 #13 · p.1 #13 · What does the purple focus spot mean on the a7r iv?

Don't have my Sigma 105 yet. But I just did a test with Sony 85mm f1.8. It can lock focus in AF-S as well as AF-C at ISO128000, f1.8, 1/15 to 1/16 range. This is very low light compared to your case. For AF-S I even put my finger on the AF assist lamp. When it didn't focus (total dark area), I get green dot flashing or no green dot. No purple.

I am Fuji GFX50s shooter which had CDAF only. Focus on that is slow but never had issues not focussing. I mean ISO6400m f2, 1/60 range.

Dec 08, 2019 at 01:24 PM


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