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01-23-2014, 08:07 PM   #1
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Focus or Autofocus adjustment

Does the "AF Adjustment" setting in the menus actually adjust the physical positioning of the sensor back or forward, OR, does it just alter the AF behaviour of the lens by rotating the focus a bit more or less depending on the adjustment setting?

I use manual focus primarily, with mostly manual focus A and M series lenses. Using K20d's I am having trouble getting reliable critical focus, typically the viewfinder looks good but the actual focus is beyond the intended target in the actual capture. My K100DS is much more reliable in manual focus, like 95%+ of the time.

If the AF adjustment only alters AF behaviour then I assume its useless for adjusting for manual focus misalignment. However if it actually moves the sensor back and forth physically then it would also work for manual focus.

I ask because I saw a discussion about someone using a 5omm f1.4 manual lens, who claimed that he used the "AF Adjustment" setting at -8 to align his sensor and it did provide correct manual focus after that. I was surprised as I didn't think it actually moved the sensor, but maybe it does.

Anyone know?

And yes I have tried it, but its hard to judge because sometimes the focus comes out right anyway, so I can't tell if the adjustment is working or if I just happened to hit the point of focus that time.

01-23-2014, 08:25 PM   #2
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Af adjustments via the menu only affect the af sensor's measurements, so they'd have no effect on manual focusing. You might want to get a different focusing screen if you're having trouble with that, or use the live view zoom feature when precision is key (though I'm not sure if the k20 has that or not).

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01-23-2014, 08:29 PM   #3
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That's a good question and I don't know the answer. I've always assumed that the autofocus motor made adjustments to compensate and not the sensor.

Maybe you can use shims under your focusing screen to help calibrate your manual focus?
01-23-2014, 08:46 PM   #4
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Ideally, the distance from the lens to the autofocus sensor is equal to the distance from the lens to the sensor is also equal to the distance from the lens to the focussing screen. (See diagram below -- L1 = L2 = L3) Due to manufacturing tolerances, this is rarely the case without adjustment. Hence, the provision of AF Adjust and focus screen shims.

If you rely on the green octagon for focusing your manual focus lenses, then you can use AF adjust to get it as accurate as possible.

If you use the focusing screen, you'll probably need to adjust the shim.

I've needed to do both on my K5, and on the K20D I had before.



01-23-2014, 08:57 PM   #5
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The AF adjustment would affect the focus confirmation as well as catch-in-focus feature.

Personally, I don't use those features much because I don't find the experience quite the same as being able to eyeball it, like I could with my old film cameras and their better focusing screens. So while I do have some manual focus lenses, I would rather just use my AF lenses. One of these days I will get a better manual focus screen, maybe if I update to a new body so I have one that I'm not so afraid to screw up.

And yes, you can calibrate your existing screen via shims.

(Oops, looks like my post crossed with the previous one.)
01-23-2014, 09:14 PM   #6
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Thanks all, I thought that it would just alter the AF but not the sensor, so that seems to be the case. I have a Katzeye screen en route so I'll see what that does. I read that there is a mechanical adjustment screw in the base of the camera that may actually move the sensor, so if Katzeye fails I will try that I guess.

My goal is to be able to use the camera with the ease that my film SLRs have. So the focus confirmation hexagon and live-view, while they can help in some situations, aren't really practical in actual use most of the time for me. I miss being able to focus and frame with quick confidence.
01-24-2014, 12:49 AM   #7
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For manual focusing I find a split image with micro prism collar the most reliable. While I have been able to rely also on the focus indicator, you just can't rely on the stock focusing screens because they really seem (at least to me) to be really on,y useful for slow lenses, in the F5.6 range in terms of indicating focus. Fast lenses are not usually well represented by what appears "in focus" on the stock screen
01-24-2014, 09:52 AM   #8
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I had a Katzeye in my K20D when I owned it. I've just recently purchased a K5II and sent it to Katzeye to have them install a focusing screen for me. Part of their installation service is a manual focus calibration. It came back to me with perfect manual focus calibration. It is a joy to use with manual focus lenses now.

01-24-2014, 02:53 PM   #9
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One should mention that, if back or front focus is caused by changing the screen, a careful done adjustment of AF will automatically offer the needed difference in shim thickness for manual focussing.

That is, if the camera offers the adjustment values in micrometers (like with the K200D in debug mode).
Of course, this will be true only if AF and MF were both correct (or at least wrong by the same margin and direction) before changing the screen.

As this is true for the K200D, I would think it applies for the other Pentax bodies, too.
01-25-2014, 05:58 AM   #10
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So I have been able to compare now having received the Katzeye screen. In short, while the split prism and micro-prism ring do work accurately, the matte area of the screen is barely an improvement over the stock Pentax screen.

Unfortunately for me it was the matte area I really want to get back to how it was in my film SLRs, since the place I want to focus is not always right in the middle. For my film cameras that I used daily I have all-matte screens with no split/micro prisms at all (to me they just clutter the view and aren't necessary on a real focusing screen) and for snap manual focusing, focus and frame in one movement, these have always been great. Some later AF film cameras had all-matte screens as standard (with AF marks) that work just fine for manual focus. The prisms are useful if you have eyesight issues or for some specialized applications. But for the kind of shooting I enjoy, a real focussing screen should not rely on the prisms at the centre to be accurate or fast.

What I would like is an all-matte screen with the sharpness and clarity that the ones in my film cameras have.

In summary... The Katzeye is an improvement over the Pentax screen only if you specifically want the split and micro prism features, it works great.

If you want a sharp focusable matte area on par with a film SLR its barely any improvement and not worth $150.

Outcome, for the quality of viewfinder I am used to (from film SLRs) I will have to keep on using my film SLRs. Next experiment is a full frame body and a screen upgrade for that. Used FF bodies are getting very affordable so it's not a prohibitive experiment anymore.

I rattled on more about it at Photographen.co — Katzeye focusing screens; do they work?

Thanks everyone for your feedback. Hope my experience might help someone else down the road.
01-25-2014, 06:11 AM   #11
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I should just add that the focusing seems accurate using the split prism and micro-prism ring, so I believe the sensor is correctly aligned. The focusing problem I was having at the start of this thread appears to be entirely a result of poor sharpness and clarity of the focusing screens.
01-25-2014, 09:35 AM   #12
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QuoteOriginally posted by Matt Miller Quote
I had a Katzeye in my K20D when I owned it. I've just recently purchased a K5II and sent it to Katzeye to have them install a focusing screen for me. Part of their installation service is a manual focus calibration. It came back to me with perfect manual focus calibration. It is a joy to use with manual focus lenses now.
Hi Matt, do you know what they mean by manual focus calibration? What exactly are they adjusting, did they shim your screen?

The screw on the camera base seems only to adjust the AF sensor further than the menu or debug options can.

I can't find any way to actually shift the sensor back and forth, and maybe it can't be done. Someone once told me it could be shifted, but I don't know where they got that info. Thanks.
01-25-2014, 10:08 PM   #13
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Yes, they use shims if required to obtain perfect manual focus calibration. I believe they will ship your screen with shims if you require them. They do not touch the autofocus system or the sensor.
01-25-2014, 10:13 PM   #14
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Maybe look into the Canon S type (at least I think that's what it's called) focusing screen. It sounds like what you're looking for.

Focusing Screen
01-28-2014, 01:33 PM   #15
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QuoteOriginally posted by Matt Miller Quote
Maybe look into the Canon S type (at least I think that's what it's called) focusing screen. It sounds like what you're looking for.

Focusing Screen
Thanks Matt. I'm looking at the Canon 5d. I may try cutting down an old MX screen but it may not be possible to align it.
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