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06-14-2012, 06:40 AM   #31
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QuoteOriginally posted by Ray Pulley Quote
Frankly, I have never understood why a simple offset could not be entered for use any time the user or AWB selected tungsten? This might not be a perfect solution, but it would probably satisfy most users. It could even be programmed to be triggered at certain light values as read by the meter, or to be applied in a gradual manner as the light is reduced.
Ray
Ray, interesting concept, but consider the following:
- this could only work for pentax lenses, because every lens has a different IR shift and I can;t see pentax programming for after market lenses. The other option of course is to allow a user adjustable IR shift in focusing.
- it will do nothing for manual focus lenses
- it would be very difficult to blend this in for absolute EV values, as you suggest since there is no way of knowing the blend of IR rich sources as absolute EV value goes down.

The real point is that while people moan and bitch about the performance of the cameras, they are performing infinitely better than we can perform ourselves, if people know there is an issue with certain types of light, they might wish to plan for it.

Now here is a thought, since we have settable by lens focus correction. then the more logical would be to allow a daylight balanced AF adjustment, and a custom AF adjustment for each lens, with a programmable button, that would let the user set it as they wish and toggle back and forth.

06-14-2012, 07:05 AM   #32
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The pic at the top is what happens inside the mirror box and the pic at the bottom is the actually AF itself, that's the whole unit where the second mirror directs the image/light to.
The optics in the AF module are the ones that are improved.


Interesting speculation that the mirror can cause CA as well, never thought about that.
Just shows how complicated the matter really is
06-14-2012, 07:25 AM   #33
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I would hesitate to call spectral effects a mirror, beamsplitter or coatings as chromatic aberration because it wouldn't behave quite the same as getting astigmatism in the blue, for example. However, in the final analysis, yes, it can have effects on different wavelengths, it is just not a dispersion effect per se.
06-14-2012, 08:26 AM   #34
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From what I can tell, the "diffraction lens" Pentax mentioned is probably a DO element of the sort Canon uses to make DO lenses. Such an element reverses chromatic aberration in the manner described in diagrams shown here on Canon's website. Pentax further states that (emphasis added):

QuoteQuote:
the new state-of-the-art SAFOX IXi+ AF sensor module....assures responsive, high-precision autofocus operation by incorporating a diffraction lens to minimize chromatic aberration in accordance to the characteristics of each individual lens.
This must mean the DO element is adjusted for the lens mounted. Thoughts?

--DragonLord

06-14-2012, 08:33 AM   #35
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Lets call it aberations then
06-14-2012, 08:35 AM   #36
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QuoteOriginally posted by DragonLord Quote

This must mean the DO element is adjusted for the lens mounted. Thoughts?

--DragonLord
How i read it, it's an adjustment for the AF module based on the lens you used.

Pentax know the CA of the lenses, since it uses them for the in camera lens correction so that information can be used to adjust the CA in the AF sensor to make it more accurate but that's just speculations from my part though.
06-14-2012, 05:41 PM   #37
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QuoteOriginally posted by Anvh Quote
That could indeed be but CA does always happen right or not?
CA means that different wavelengths are focused into different planes and/or receive different magnification, etc.

The lenses in the AF module, in combination, may work perfectly for "green" (you could say there is no CA for "green" but it doesn't make sense to talk about CA for monochromatic light) but will exhibit different optical properties for other wavelengths.

That's why the "colour temperature sensor" needs to evaluate the colour temperature so that the camera knows the error that the AF optics will introduce.

QuoteOriginally posted by Lowell Goudge Quote
Now here is a thought, since we have settable by lens focus correction. then the more logical would be to allow a daylight balanced AF adjustment, and a custom AF adjustment for each lens, with a programmable button, that would let the user set it as they wish and toggle back and forth.
I'm not saying this isn't a good idea, but ultimately it would be a workaround for a problem that shouldn't exist in the first place. Hopefully the new Pentax AF system will make us forget any FF sorrows we may have had.

QuoteOriginally posted by Anvh Quote
Pentax know the CA of the lenses, since it uses them for the in camera lens correction so that information can be used to adjust the CA in the AF sensor to make it more accurate but that's just speculations from my part though.
I have no inside knowledge, but I'd be very surprised if lens CA would be considered when obtaining focus. I do not believe that lens CA represents a problem due to the way the phase detection AF system works (as long as the lens CA is homogeneous).
06-14-2012, 06:30 PM   #38
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I would think that they don't really care about the CA of each individual lens since they can more easily create an algorithm to subtract the AF path response from the metering path response. Since both paths have input from the camera lens, the effect mathematically cancels out.

06-14-2012, 06:37 PM   #39
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But class A but during day-light all those lights are present and so is the CA as well, right?
06-14-2012, 07:08 PM   #40
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Anvh, I don't want to speak for Class A, but I think he already answered your question. "White Light" which is basically any typical lighting situation you'll run into (outdoors in the sun or indoors with artificial light) contains many "colors". So, while a system may be optimized for ONE of those colors (green was the example), then colors other than green within the white light spectrum will exhibit chromatic aberration in a refractive optical system.
06-14-2012, 07:42 PM   #41
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QuoteOriginally posted by Lowell Goudge Quote
Ray, interesting concept, but consider the following:
- this could only work for pentax lenses, because every lens has a different IR shift and I can;t see pentax programming for after market lenses.
This is not a not a lens issue, and it isn't IR related. Pentax lenses have a chip in them that transmits things like MTF and CA to the camera that is gathered in the factory tests for that lens. I would be surprised if there was not an IR cut filter in the AF module, as that is a common practice in these AF systems from what I have read.

The issue is CA in the AF optics, not the lens.

QuoteQuote:
The other option of course is to allow a user adjustable IR shift in focusing.
- it will do nothing for manual focus lenses
- it would be very difficult to blend this in for absolute EV values, as you suggest since there is no way of knowing the blend of IR rich sources as absolute EV value goes down.

I think a user setting tied to a manual selection of element tungsten WB would work, and the meter tells the camera the light level, so I see no reason why this would not allow for a sliding offset based upon light evel or at least a cut-in at a certaon low light level. The K5 has a color sensing element to combat this very problem (I believe the Nikon D7000 has a similar sensor), so it should just work

QuoteQuote:
The real point is that while people moan and bitch about the performance of the cameras, they are performing infinitely better than we can perform ourselves, if people know there is an issue with certain types of light, they might wish to plan for it.
Agreed. In addition, I suspect that if the image was analyzed with an EXIF reader as to the LV recorded by the metering segments in the camera, we would often see light levels below the lower limit specified for the AF system.

QuoteQuote:
Now here is a thought, since we have settable by lens focus correction. then the more logical would be to allow a daylight balanced AF adjustment, and a custom AF adjustment for each lens, with a programmable button, that would let the user set it as they wish and toggle back and forth.
This is exactly what I have been talking about, except I would allow for an offset based on selecting tungsten WB.
06-14-2012, 07:54 PM   #42
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QuoteOriginally posted by Class A Quote
CA means that different wavelengths are focused into different planes and/or receive different magnification, etc.

The lenses in the AF module, in combination, may work perfectly for "green" (you could say there is no CA for "green" but it doesn't make sense to talk about CA for monochromatic light) but will exhibit different optical properties for other wavelengths.

That's why the "colour temperature sensor" needs to evaluate the colour temperature so that the camera knows the error that the AF optics will introduce.
The FF issue is now most certainly confirmed by Pentax to be CA in the AF optics, as they introduced the color sensor in the K5 to try and offset the problem, and now have announced offsetting diffractive optics in the AF system of the K30.

Here is the PDAF of the K5 (credit to Falk Lumo who took the shot at Photokina in 2010):

http://falklumo.smugmug.com/Photography/Camera-Tests/Pentax-K-5/IMGP7387/1018266005_FvKA7-M.jpg

Ray
06-14-2012, 08:42 PM   #43
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Great photo...thanks Ray!
06-16-2012, 08:01 AM   #44
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QuoteOriginally posted by Asha Quote
Anvh, I don't want to speak for Class A, but I think he already answered your question. "White Light" which is basically any typical lighting situation you'll run into (outdoors in the sun or indoors with artificial light) contains many "colors". So, while a system may be optimized for ONE of those colors (green was the example), then colors other than green within the white light spectrum will exhibit chromatic aberration in a refractive optical system.
As far as i know the system is sensative for light not colours, but yeah it might be more sensative for certain colours...
06-16-2012, 11:51 AM   #45
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QuoteOriginally posted by Anvh Quote
As far as i know the system is sensative for light not colours, but yeah it might be more sensative for certain colours...
White light is a combination of many different "colors" of monochromatic light. The basic premise of chromatic aberration is that the dispersion of the glass or plastic will cause some components of white light to be refracted differently through the optical system. It is fundamentally the same thing as when you see a rainbow coming out of a prism.
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