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Can A99ii focus at f8?

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AkashRana

AkashRana

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I know A99ii doesn't do it currently, but when I look around lots of Canikon cameras are capable of autofocus with f8 aperture. This comes in handy when using tele-converters as they stop down lenses and render even the best of the lenses like 500 f4 crippled with 2x tele.

There is the obvious 500mm f8 lens which has AF capabilities since long, even though it was restricted to center point AF alone. But this restriction was built in ages ago and over the years AF sensitivity has grown better but the restriction was never lifted.

I believe the AF sensitivity on A99ii is good enough to handle theses chores, so Sony should be able to unlock this with firmware update. I don't assume that AF performance will be blazing fast but should be decent enough that other manufacturers allow this to happen. Even Sony allows AF at smaller apertures on E-mount cameras, so why not extend this to A-mount adding another feather to its cap.
 
Yes.

The 79-point AF module keeps working until about f/14 in my experience with the A68 and A77II. You have to give them a lot of contrast for them to work at such small apertures.

The on sensor points are rated to work at f/8 in the the A7RII.

Sony aggressively disables AF with their own A-mount teleconverters. Maybe no AF gets them less user complaints about AF performance. Minolta probably started this. Third-party A-mount 2x chipped teleconverters have always worked with f/4 lenses. All the Minolta cameras I've tried could AF at an effective f/11 too.

E-mount users can use their FE teleconverters at any effective aperture. Once past the aperture limit of the PDAF sensors the camera just uses contrast-detect. The on-sensor PDAF sensors on the A5100/A6x00, A9, and A7III are rated to f/11. A hybrid AF A77III if it ever comes out should focus better than A99II.
 
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AkashRana said:
I know A99ii doesn't do it currently, but when I look around lots of Canikon cameras are capable of autofocus with f8 aperture. This comes in handy when using tele-converters as they stop down lenses and render even the best of the lenses like 500 f4 crippled with 2x tele.
Click to expand...
Ever look at images from a 500mm f4 with a 2xTC....? Not worth bothering most of the time. So it's not a great loss, nor is it really crippled.

-Martin P

www.flickr.com

Martin Passchier

Explore Martin Passchier’s 973 photos on Flickr!
www.flickr.com www.flickr.com
 
Mike - said:
Don't understand what you are talking about..!

My a99 II focuses just fine set to f8.
Click to expand...
Your camera autofocuses with the lens wide open (or in some cases at f/3.5) before the diaphragm closes down to f/8, so there is no problem. The OP is talking about using an f/4 lens with a 2X teleconverter, meaning the effective wide open aperture is f/8. That's at or near the limit of reliable AF capability.
 
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sybersitizen said:
Mike - said:
Don't understand what you are talking about..!

My a99 II focuses just fine set to f8.
Click to expand...
Your camera autofocuses with the lens wide open (or in some cases at f/3.5) before the diaphragm closes down to f/8, so there is no problem. The OP is talking about using an f/4 lens with a 2X teleconverter, meaning the effective wide open aperture is f/8. That's at or near the limit of reliable AF capability.
Click to expand...
Thanks, I was wondering what it was all about too.
 
I say probably because they focus just fine with the Sony F8 500mm mirror lens. The F6.3 limit has something to do with the aperture opening diameter, not the amount of light, so because an F4 with 2x TC has the same aperture opening as it does without TC it should work. It would be best to hear from someone who has actually tried it however. That said 2x TCs often decrease IQ enough that many people find them unacceptable.

--
Tom
 
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tbcass said:
I say probably because they focus just fine with the Sony F8 500mm mirror lens.
Click to expand...
The Minolta/Sony 500 Reflex is a special case. Because of its design it appears as an f/6.7 lens to the AF system, and that's within limits for reliable AF.
 
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sybersitizen said:
tbcass said:
I say probably because they focus just fine with the Sony F8 500mm mirror lens.
Click to expand...
The Minolta/Sony 500 Reflex is a special case. Because of its design it appears as an f/6.7 lens to the AF system, and that's within limits for reliable AF.
Click to expand...
I thought about that. When using a 2x TC does the adapter double the aperture setting as seen by the camera? Does the camera read the F4 of the lens aperture or the 2 stops slower f8 resulting from using the TC?
 
tbcass said:
sybersitizen said:
tbcass said:
I say probably because they focus just fine with the Sony F8 500mm mirror lens.
Click to expand...
The Minolta/Sony 500 Reflex is a special case. Because of its design it appears as an f/6.7 lens to the AF system, and that's within limits for reliable AF.
Click to expand...
I thought about that. When using a 2x TC does the adapter double the aperture setting as seen by the camera? Does the camera read the F4 of the lens aperture or the 2 stops slower f8 resulting from using the TC?
Click to expand...
The Minolta and Sony teleconverters just identify themselves to the camera. The camera does all the work. That's why they don't work on the LA-EA adapters. Sony didn't add the logic needed into E-mount firmware. Same reason Xi lenses don't work on E-mount. Those also need logic in the camera to work beyond just current focal length and maximum aperture.

The Kenko chipped teleconverters actually change the focal lengths and apertures reported to the camera. Essentially they create a new A-mount lens as far as the camera is concerned. And that method works with pretty much every lens and every camera.
 
tbcass said:
sybersitizen said:
tbcass said:
I say probably because they focus just fine with the Sony F8 500mm mirror lens.
Click to expand...
The Minolta/Sony 500 Reflex is a special case. Because of its design it appears as an f/6.7 lens to the AF system, and that's within limits for reliable AF.
Click to expand...
I thought about that. When using a 2x TC does the adapter double the aperture setting as seen by the camera?
Click to expand...
A TC optically reduces the effective aperture, yes.
tbcass said:
Does the camera read the F4 of the lens aperture or the 2 stops slower f8 resulting from using the TC?
Click to expand...
That depends on what the particular TC tells the camera. Some alter the data coming from the lens, some don't.
 
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tbcass said:
I say probably because they focus just fine with the Sony F8 500mm mirror lens. The F6.3 limit has something to do with the aperture opening diameter, not the amount of light, so because an F4 with 2x TC has the same aperture opening as it does without TC it should work. It would be best to hear from someone who has actually tried it however. That said 2x TCs often decrease IQ enough that many people find them unacceptable.
Click to expand...
These are taken with a 2x TC on the 500mm f4 and you can see the softness even in good lighting conditions.

2x TC
2x TC

2x TC
2x TC

and these are taken with a 1.4x TC and look much better...

1.4x TC
1.4x TC

1.4x TC
1.4x TC

1.4x TC
1.4x TC

-Martin P

www.flickr.com

Martin Passchier

Explore Martin Passchier’s 973 photos on Flickr!
www.flickr.com www.flickr.com
 
sybersitizen said:
tbcass said:
sybersitizen said:
tbcass said:
I say probably because they focus just fine with the Sony F8 500mm mirror lens.
Click to expand...
The Minolta/Sony 500 Reflex is a special case. Because of its design it appears as an f/6.7 lens to the AF system, and that's within limits for reliable AF.
Click to expand...
I thought about that. When using a 2x TC does the adapter double the aperture setting as seen by the camera?
Click to expand...
A TC optically reduces the effective aperture, yes.
sybersitizen said:
Does the camera read the F4 of the lens aperture or the 2 stops slower f8 resulting from using the TC?
Click to expand...
That depends on what the particular TC tells the camera. Some alter the data coming from the lens, some don't.
Click to expand...
Then wouldn't the camera see the f4 lens as f4 with the ones that don't alter data allowing the camera to attempt to focus just like with the mirror lens whose true optical is f8 despite the camera seeing it as f6.7. The reason the mirror lens is f8 is because the mirror at the front, the one that bounces the light from the main mirror back to the camera, blocks some light. This effect should be similar to the light reduction due to the TC with the true f stop of the lens being f4. Is there some other technological limitation I'm missing?
 
Does the 500mm f4 with 2x TC autofocus? The loss of image quality is no surprise.
 
tbcass said:
sybersitizen said:
tbcass said:
sybersitizen said:
tbcass said:
I say probably because they focus just fine with the Sony F8 500mm mirror lens.
Click to expand...
The Minolta/Sony 500 Reflex is a special case. Because of its design it appears as an f/6.7 lens to the AF system, and that's within limits for reliable AF.
Click to expand...
I thought about that. When using a 2x TC does the adapter double the aperture setting as seen by the camera?
Click to expand...
A TC optically reduces the effective aperture, yes.
tbcass said:
Does the camera read the F4 of the lens aperture or the 2 stops slower f8 resulting from using the TC?
Click to expand...
That depends on what the particular TC tells the camera. Some alter the data coming from the lens, some don't.
Click to expand...
Then wouldn't the camera see the f4 lens as f4 with the ones that don't alter data allowing the camera to attempt to focus just like with the mirror lens whose true optical is f8 despite the camera seeing it as f6.7.
Click to expand...
Yes, the camera would attempt to focus, and it might succeed. The reliability of that attempt is the issue.
tbcass said:
The reason the mirror lens is f8 is because the mirror at the front, the one that bounces the light from the main mirror back to the camera, blocks some light. This effect should be similar to the light reduction due to the TC with the true f stop of the lens being f4. Is there some other technological limitation I'm missing?
Click to expand...
The reliability of the AF system depends on the apparent width of the aperture. That needs to be wide enough to allow good triangulation for comparing rays coming from opposite sides of the lens. At some point beyond f/6.7 the triangulation can become iffy even if the camera thinks the aperture is wider, though in some combinations of camera/lens or camera/lens/TC it will work okay.
 
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sybersitizen said:
tbcass said:
I say probably because they focus just fine with the Sony F8 500mm mirror lens.
Click to expand...
The Minolta/Sony 500 Reflex is a special case. Because of its design it appears as an f/6.7 lens to the AF system, and that's within limits for reliable AF.
Click to expand...
I think that's the case. It's also the case with 3x-1x/1.7-2.8 zoom which is effectively f/7.1 (well, f/6.9, but traditionally denoted f/7.1).

The design of 500/8 actually is f/8. DoF is for 500/8 while exposure value is lower (due to light loss from the secondary mirror).

Minolta was the first manufacturer that let its cameras focus at f/8, it took others years to match this capability.
 
sybersitizen said:
tbcass said:
sybersitizen said:
tbcass said:
I say probably because they focus just fine with the Sony F8 500mm mirror lens.
Click to expand...
The Minolta/Sony 500 Reflex is a special case. Because of its design it appears as an f/6.7 lens to the AF system, and that's within limits for reliable AF.
Click to expand...
I thought about that. When using a 2x TC does the adapter double the aperture setting as seen by the camera?
Click to expand...
A TC optically reduces the effective aperture, yes.
sybersitizen said:
Does the camera read the F4 of the lens aperture or the 2 stops slower f8 resulting from using the TC?
Click to expand...
That depends on what the particular TC tells the camera. Some alter the data coming from the lens, some don't.
Click to expand...
They all should according to the A mount communication protocol. Compare Nikon's F mount and Canon's EF mount. They both have two extra pins for teleconverters and extension tubes (in Canon, it's short one pin for 1.4x extension, both pins for 2x extension and second pin for extension tube, I think Nikon allowed 1.4x, 1.7x and 2x converters instead with the same bitwise scheme).

Minolta already solved that in 1985, while Canon couldn't do it in 1987 when releasing EF mount, Nikon didn't either when making AF F mount lenses, though it might have been covered by a patent. Both Canon and Nikon eventually resolved that.

The solution is actually very elegant in that the teleconverter is supposed to alter the values reported by the lens. I think it's also what allowed third parties to reverse engineer the protocol.
 
toughluck said:
sybersitizen said:
tbcass said:
sybersitizen said:
tbcass said:
I say probably because they focus just fine with the Sony F8 500mm mirror lens.
Click to expand...
The Minolta/Sony 500 Reflex is a special case. Because of its design it appears as an f/6.7 lens to the AF system, and that's within limits for reliable AF.
Click to expand...
I thought about that. When using a 2x TC does the adapter double the aperture setting as seen by the camera?
Click to expand...
A TC optically reduces the effective aperture, yes.
toughluck said:
Does the camera read the F4 of the lens aperture or the 2 stops slower f8 resulting from using the TC?
Click to expand...
That depends on what the particular TC tells the camera. Some alter the data coming from the lens, some don't.
Click to expand...
They all should according to the A mount communication protocol.
Click to expand...
Regardless of should, not all do.
toughluck said:
Compare Nikon's F mount and Canon's EF mount. They both have two extra pins for teleconverters and extension tubes (in Canon, it's short one pin for 1.4x extension, both pins for 2x extension and second pin for extension tube, I think Nikon allowed 1.4x, 1.7x and 2x converters instead with the same bitwise scheme).
Click to expand...
What about 3X TCs? They exist.
toughluck said:
Minolta already solved that in 1985, while Canon couldn't do it in 1987 when releasing EF mount, Nikon didn't either when making AF F mount lenses, though it might have been covered by a patent. Both Canon and Nikon eventually resolved that.

The solution is actually very elegant in that the teleconverter is supposed to alter the values reported by the lens. I think it's also what allowed third parties to reverse engineer the protocol.
Click to expand...
 
Last edited:
sybersitizen said:
The reliability of the AF system depends on the apparent width of the aperture. That needs to be wide enough to allow good triangulation for comparing rays coming from opposite sides of the lens. At some point beyond f/6.7 the triangulation can become iffy even if the camera thinks the aperture is wider, though in some combinations of camera/lens or camera/lens/TC it will work okay.
Click to expand...
That makes sense. The mirror lens triangulates like an f6.7 but allows only f8 worth of light to the sensor.
 
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