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10-28-2014, 11:19 PM   #1
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Are all K-30s AF points -1EV?

I noticed that in low light the central focus point performs quite a bit better.

Is it just because of the lens vignetting, or some other physical variable, or are the other focus points less sensitive?

10-28-2014, 11:28 PM   #2
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Hi, there!

Normally the AF capabilities are valid for 50/1.4 lens, central focus point.
You are right - it's all physics

Take care!
10-28-2014, 11:30 PM   #3
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I can't find any data on the EV sensitivity distribution of the AF points on the K-30.

But with just about every other camera out there, including high end FF ones, the centre point (and sometimes the points immediately clustered around the centre point) are usually the most sensitive to both light and movement. So if that turns out to be the case with the K-30, it wouldn't surprise me.
10-28-2014, 11:55 PM   #4
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QuoteOriginally posted by rawr Quote
I can't find any data on the EV sensitivity distribution of the AF points on the K-30.

But with just about every other camera out there, including high end FF ones, the centre point (and sometimes the points immediately clustered around the centre point) are usually the most sensitive to both light and movement. So if that turns out to be the case with the K-30, it wouldn't surprise me.
I just heard on a youtube video that K-3 has three high sensitivity points (down to -3EV) and I am wondering if K-30 had a similar feature too.

10-29-2014, 12:09 AM   #5
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QuoteOriginally posted by rrstuff Quote
I just heard on a youtube video that K-3 has three high sensitivity points (down to -3EV) and I am wondering if K-30 had a similar feature too.
AFAIK, no- the K-30's AF system isn't quite as fancy. Also, that isn't fully accurate about the K-3. AFAIK, what the K-3 has are 3 points "sensitive to F2.8 luminance flux", which isn't saying anything about the minimum ambient light.

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10-29-2014, 12:26 AM   #6
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QuoteOriginally posted by Adam Quote
which isn't saying anything about the minimum ambient light.
The -3 EV sensitivity is certainly there in both the K-3 (and K-5II) specifications.

In the case of the K-3, it's probably a safe bet to say that the 3 central points 'sensitive to f2.8 luminance flux' are also the ones designed to work at -3 EV.

10-29-2014, 04:39 AM   #7
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Sorry to hijack the thread, but what exactly does "sensitive to F2.8 luminance flux sensor" mean?
10-29-2014, 06:10 AM   #8
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QuoteOriginally posted by AtitG Quote
Sorry to hijack the thread, but what exactly does "sensitive to F2.8 luminance flux sensor" mean?
it means the body can accurately focus a f2.8 lens or slower lens.

10-29-2014, 06:52 AM   #9
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Thanks.
10-29-2014, 07:52 AM - 1 Like   #10
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QuoteOriginally posted by AtitG Quote
Sorry to hijack the thread, but what exactly does "sensitive to F2.8 luminance flux sensor" mean?
QuoteOriginally posted by aurele Quote
it means the body can accurately focus a f2.8 lens or slower lens.
The term is somewhat misleading. The f/2.8 figure for the K-3 center column points is in comparison to the f/5.6 focus sensitivity of the remaining points. Focus sensitivity of a PDAF sensor is dependent on physical aperture of the taking lens and not the luminance flux (amount of light transmitted). The technical description is rather involved, but the easiest way to explain it is that the f/5.6 sensors have the same ability to detect an out-of-focus state at f/5.6 as at wider apertures.* The f/2.8 sensors are able to extend this ability to f/2.8 hence providing adequate focus sensitivity with fast lenses. Focus sensitivity is a property of the optical prism used by each PDAF sensor, not the light detector.

The low light sensitivity is a separate consideration and is a property of the photocells used for the actual measurement. The -1 EV value is essentially independent of aperture per se and applies equally at both f/1.0 and f/22 depending on shutter speed and ISO, though the convention is to assume ISO 100 if not explicitly stated otherwise. For ISO 100, -1 EV would be the amount of flux equivalent to 2 second exposure at f/1.0.

As for the presence of f/2.8 sensors on the K-30/K-50, it is my understanding that both cameras have f/5.6 sensors throughout.


Steve

* This essentially means that fine focus with faster lenses will be unacceptably imprecise with lenses faster than about f/3.5 maximum aperture. Sensors tuned to f/2.8 are acceptably sensitive for use with faster lenses.

Last edited by stevebrot; 10-29-2014 at 08:43 AM.
10-29-2014, 09:14 AM   #11
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Thank you, i guess that explains why my k-30 misfocus a lot with my da 50mm 1.8.
10-29-2014, 01:54 PM   #12
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QuoteOriginally posted by AtitG Quote
Thank you, i guess that explains why my k-30 misfocus a lot with my da 50mm 1.8.
ditto. That being said, it works ok with the central focus point.
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