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03-04-2015, 09:02 AM   #1
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Lens correction for manual focus lenses?

I'm in the processing of purchasing a used K5... I have been researching and trying to understand the focus correction on lenses.

My first question is how does this work... It seems like the auto focus sensor should see focus just like someone would with a split prism finder. It is either in focus or not regardless of what the distance scale says on the lens... Is it kind of like wearing glasses for a person? corrects things to be in focus?

Second, will this work on manual focus lenses? If not could it be that trap focus will be off just like an autofocus lens could need a correction?

Thanks in advance
Cory

03-04-2015, 09:15 AM   #2
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QuoteOriginally posted by soycory Quote
I'm in the processing of purchasing a used K5... I have been researching and trying to understand the focus correction on lenses.

My first question is how does this work... It seems like the auto focus sensor should see focus just like someone would with a split prism finder. It is either in focus or not regardless of what the distance scale says on the lens... Is it kind of like wearing glasses for a person? corrects things to be in focus?

Second, will this work on manual focus lenses? If not could it be that trap focus will be off just like an autofocus lens could need a correction?

Thanks in advance
Cory
In the AF fine adjustment, there are two types of corrections (+ or -) that you can check off, one affects all, the other affects individual lens. Only the one affects all applies to manual focus lens.
03-04-2015, 09:24 AM   #3
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QuoteOriginally posted by aleonx3 Quote
In the AF fine adjustment, there are two types of corrections (+ or -) that you can check off, one affects all, the other affects individual lens. Only the one affects all applies to manual focus lens.
Where is that documented? I assume it is for the same reason that lenses require focal length input - no cpu, no unique identifier, etc.
03-04-2015, 09:30 AM   #4
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QuoteOriginally posted by UncleVanya Quote
Where is that documented? I assume it is for the same reason that lenses require focal length input - no cpu, no unique identifier, etc.
No, the focal length of the manual lens is needed for SR only (AFAIK) since the camera has no way to telling what lens you have mounted on the camera. Also, if you want to use Catch-in-focus, you need to short the data pins using aluminum foil for anodised-metal base lenses for it to work properly.

The "affects all" option appears only when you mount a manual focus lens.

03-04-2015, 10:10 AM   #5
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QuoteOriginally posted by aleonx3 Quote
No, the focal length of the manual lens is needed for SR only (AFAIK) since the camera has no way to telling what lens you have mounted on the camera. Also, if you want to use Catch-in-focus, you need to short the data pins using aluminum foil for anodised-metal base lenses for it to work properly.

The "affects all" option appears only when you mount a manual focus lens.
Not sure what you mean. Affects all is available on my k50 and I tested it with my 18-135. I understood the specific adjustments could only be applied to lenses with unique Identifiers.
03-04-2015, 12:19 PM   #6
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Affects all, affects all lenses regardless of type. But, when you have something like an 18-135 lens the lens specific correction will apply in addition to the global correction that affects all.

With manual focus lenses, the camera can't identify the lens specifically, so the camera can't even try to make the lens specific correction. So, the only correction you can make is to change the global correction value. If that number needs to be different for multiple manual focus lenses, then you would need to adjust that in the settings each time you change the lens.

Keep in mind that if you have specific lens corrections already and you make adjustments to the global correction ("affects all") it will also affect the ones that have specific corrections, so in theory you'd have to readjust the values.

Alternatively, you could rely on a focusing screen to confirm focus and skip the adjustments all together. I've never really adjusted the focus for manual focus lenses because the green hexagon that indicates focus actually has some play in it anyway (i.e. there is actually a slight range of focus where it indicates focus) that makes reliance on it only approximate. I'm not sure that having the lens corrections will really help that much. If I was really concerned, I'd rely on a split prism focusing screen.
03-04-2015, 12:47 PM   #7
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QuoteOriginally posted by emalvick Quote
Affects all, affects all lenses regardless of type. But, when you have something like an 18-135 lens the lens specific correction will apply in addition to the global correction that affects all.
Thanks that is exactly what I thought - and my point earlier was that this was because the lenses - even A lenses don't have the data inside them (which is also why they don't communicate focal length) to allow the camera to identify them.

QuoteOriginally posted by emalvick Quote
Keep in mind that if you have specific lens corrections already and you make adjustments to the global correction ("affects all") it will also affect the ones that have specific corrections, so in theory you'd have to readjust the values.
My observations using the focus calibration showed me that the numbers for all and individual are not comparable. -5 (or +5) to all is not the same as -5 to a specific lens. Further -5 to all and +5 to a specific lens do not cancel. At least not when I tried calibrating my K50 and 18-135. This isn't different from what you have said above - just interesting.
03-04-2015, 12:51 PM   #8
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I could be wrong, my understanding is that the specific correction overrides the overall correction in case of auto-focus lenses, again, just my thoughts and at least that's how I experience with my DA* lenses; and that's how I would design/program it if I were writing the software.

03-04-2015, 12:55 PM   #9
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QuoteOriginally posted by aleonx3 Quote
I could be wrong, my understanding is that the specific correction overrides the overall correction in case of auto-focus lenses, again, just my thoughts and at least that's how I experience with my DA* lenses.
Well - I can't say I agree 100% - my testing showed that global adjustments did change the focus even if I had a specific adjustment locked in. It was clear some change happened, but the magnitude of that change wasn't the same as the magnitude of individual lens corrections.

I may have to break it out again but we are flowing off topic since this was initially about manual focus.
03-04-2015, 12:56 PM   #10
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QuoteOriginally posted by UncleVanya Quote
no cpu, no unique identifier, etc
You guessed it. The manual focus lenses don't have the seventh "data" pin on the mount and are unable to communicate a lens id.


Steve
03-04-2015, 01:38 PM   #11
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QuoteOriginally posted by UncleVanya Quote
Well - I can't say I agree 100% - my testing showed that global adjustments did change the focus even if I had a specific adjustment locked in. It was clear some change happened, but the magnitude of that change wasn't the same as the magnitude of individual lens corrections.

I may have to break it out again but we are flowing off topic since this was initially about manual focus.
This was my observation. And my finding was that it essentially did cancel out. When I entered a global adjustment, I was able to dial back a specific adjustment my the same or similar amount. I really think it is splitting hairs when you start getting down to the resolution of adjustments offered (perhaps I would notice more of a difference with a Macro lens at a shorter focus distance). I adjust using focus charts, and usually once that is taken care of, it all seems to work well in my real shooting conditions which are usually street or landscape photography.
03-05-2015, 10:49 AM   #12
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Hmmm... I think there is a misconception here.

AF lens correction is for AUTOFOCUS LENSES. It has no effect or influence on how manual lenses are focused (which is by the way, "by hand"). The AF adjustment affects how the camera treats a specific (single) lens or all of your arsenal (all).

The only moment the body asks for focal length when a manual focus lens is attached, is for calibrating the SR (shake reduction) according to such focal length. That's it. BTW, the camera has no memory neither the lens has the information to communicate with camera the "next time it is attached", so the camera will always ask for the focal length every time.
03-05-2015, 02:13 PM   #13
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QuoteOriginally posted by rburgoss Quote
Hmmm... I think there is a misconception here.

AF lens correction is for AUTOFOCUS LENSES. It has no effect or influence on how manual lenses are focused (which is by the way, "by hand"). The AF adjustment affects how the camera treats a specific (single) lens or all of your arsenal (all).
The OP was claiming that changing the AF adjustment impacted the PDAF focus confirmation accuracy. I've never tried it. My comments were around the ALL vs. Individual adjustments which I have done.
03-05-2015, 02:14 PM   #14
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QuoteOriginally posted by rburgoss Quote
It has no effect or influence on how manual lenses are focused
This should be the case, but there are a large number of users who depend on focus confirmation via the AF system when using manual focus lenses. As might imagine, the results are often a bit mixed with faster primes.


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03-05-2015, 05:05 PM   #15
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QuoteOriginally posted by UncleVanya Quote
The OP was claiming that changing the AF adjustment impacted the PDAF focus confirmation accuracy. I've never tried it. My comments were around the ALL vs. Individual adjustments which I have done.
QuoteOriginally posted by stevebrot Quote
This should be the case, but there are a large number of users who depend on focus confirmation via the AF system when using manual focus lenses. As might imagine, the results are often a bit mixed with faster primes.
Steve
I just checked both my K20D and K3 owners manual for the AF adjustment thing. In both cases, instructions and explanations are almost identical. None state specifically that this is for AF lenses only or in other words, says that this adjustment has no influence on manual focus lenses.

But this is where logic kicks in. In both cameras, it says it can store up to 20 different lenses with different AF adjustments. By logic, for the camera to "know" which lens is being used, it needs the lens info via electronics in lens mount, such as DA, DAF, F, FA, FAJ. Lenses from the K, M or A era DO NOT transmit lens information to body. That is why the camera cannot use certain features such as lens correction (K3) or certain flash modes.

Every time you mount one of this lenses, the camera asks for focal length, but only to adjust its SR system accordingly. The AF system does not play a role. Of course, there is still focus confirmation via PDAF or CDAF, but its bases on AF sensor positioning (PD) or actual CMOS image on sensor.

To my understanding, the AF adjustment affects on how long to move the AF drive (either screw or SDM) in order to achieve focus, but it does not actually change the AF adjustment (AF sensors or CMOS position) in relation to lens.

Can someone shed some light here?
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