AF question about the GR....

[Ray Sachs]

I don't have my loaner GR anymore to check this out, but I'd appreciate if one of you could....

Does the GR open the aperture all the way up to focus? MOST modern cameras do - you have the aperture set to f7.1, half press to AF, and the aperture pops open to the maximum size, focus is locked, and the aperture close back down to shoot. I knew that the Sony RX1 does NOT do this - it lets the user-set aperture stay in place to AF up to f8. Beyond f8 it will open back up to f8, but it doesn't open all the way up to f2.0.

Much to my surprise, I just realized that the Nikon Coolpix A does this same thing. I'd never noticed it when comparing the "A" and the GR over most of the past month. It turns out I was notably under-estimating / under-reporting the Nikon "A"s ability to AF in low light because of this. You have to open the aperture up yourself (at least in Aperture Priority or Manual modes), but once you do, its actually much better than I'd realized in low light.

So, does the GR automatically open up the aperture to f2.8 to achieve AF? Or is it up to the user to open the aperture to achieve focus? I may have been under-estimating the GR's low light focus capability as well. Or it may be that the Nikon really does have an advantage in low light AF that I'd simply missed in my carelessness...

I wonder if more and more camera designers are opting to let/force the user to open the aperture to focus these days? Everything else I have available to check opens up automatically to focus, including the GXR-28. But the RX1 and now the Coolpix A leave it to the user to determine what aperture the camera will focus at...

-Ray
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Ray

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[Tapani Tarvainen]

Ray Sachs wrote:

So, does the GR automatically open up the aperture to f2.8 to achieve AF? Or is it up to the user to open the aperture to achieve focus?

Strange. As far as I can tell (looking at the shutter while focusing), it opens it up to f/4, not to f/2.8 -- indeed it seems that even when set to f/2.8-3.5, it closes down to f/4 to focus!

Why that would be, I've no idea.

 

[Ray Sachs]

Tapani Tarvainen wrote:

Ray Sachs wrote:

So, does the GR automatically open up the aperture to f2.8 to achieve AF? Or is it up to the user to open the aperture to achieve focus?

Strange. As far as I can tell (looking at the shutter while focusing), it opens it up to f/4, not to f/2.8 -- indeed it seems that even when set to f/2.8-3.5, it closes down to f/4 to focus!

Why that would be, I've no idea.

That's kind of interesting - thanks... Maybe there's some sort of sweet-spot between getting enough light into the sensor and yet having enough DOF to make it easier for the contrast detect system to find something to lock onto??? I've noticed with the RX1 that AF performance doesn't seem to get any worse between f2.0 and about f3.5 or 4.0, but it definitely starts to degrade in low light by f5.6. I'll have to play around with the Nikon and see where it does best. I'd guess that in the lowest light, f2.8 should still be the easiest, but with a bit more light, f4 might make some sense...

-Ray
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Ray

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[aleksanderpolo]

I took a quick look, the aperture vary depends on the current lighting condition, so it focus at that aperture rather than your shooting aperture. I don't think it makes any difference unless there is substantial focus shift, which I suspect the Sonnar lens in RX1 is susceptible to (if it is really a Sonnar lens, not in name only).

Ray Sachs wrote:

Tapani Tarvainen wrote:

Ray Sachs wrote:

So, does the GR automatically open up the aperture to f2.8 to achieve AF? Or is it up to the user to open the aperture to achieve focus?

Strange. As far as I can tell (looking at the shutter while focusing), it opens it up to f/4, not to f/2.8 -- indeed it seems that even when set to f/2.8-3.5, it closes down to f/4 to focus!

Why that would be, I've no idea.

That's kind of interesting - thanks... Maybe there's some sort of sweet-spot between getting enough light into the sensor and yet having enough DOF to make it easier for the contrast detect system to find something to lock onto??? I've noticed with the RX1 that AF performance doesn't seem to get any worse between f2.0 and about f3.5 or 4.0, but it definitely starts to degrade in low light by f5.6. I'll have to play around with the Nikon and see where it does best. I'd guess that in the lowest light, f2.8 should still be the easiest, but with a bit more light, f4 might make some sense...

-Ray
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[Ray Sachs]

aleksanderpolo wrote:

I took a quick look, the aperture vary depends on the current lighting condition, so it focus at that aperture rather than your shooting aperture. I don't think it makes any difference unless there is substantial focus shift, which I suspect the Sonnar lens in RX1 is susceptible to (if it is really a Sonnar lens, not in name only).

Interesting - thanks. So I presume its opening all the way up in the lowest light?
-Ray
--------------------------------------

Ray

Explore Ray’s 2,013 photos on Flickr!

www.flickr.com

 

[aleksanderpolo]

Ya in my observation. If it is brighter and you set it at f2.8, it will actually focus at the current aperture (f4 or even lower, depending on the light), and then open up.

 

[Tapani Tarvainen]

Ray Sachs wrote:

aleksanderpolo wrote:

I took a quick look, the aperture vary depends on the current lighting condition, so it focus at that aperture rather than your shooting aperture. I don't think it makes any difference unless there is substantial focus shift, which I suspect the Sonnar lens in RX1 is susceptible to (if it is really a Sonnar lens, not in name only).

Interesting - thanks. So I presume its opening all the way up in the lowest light?

I can confirm that, although there seem to be other factors involved as well (focusing distance, probably how contrasty the target is and whatnot). But in low light, at least sometimes, it does open up all the way.