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04-10-2011, 05:26 AM   #1
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AF confirm innacurate (confusion)

And so I began doing some AF testing this week with my K-5 and I discovered something rather interesting. Which isn't particularly inherent to the K-5(per say), but... seems far more prevalent on the K-5 and so I thought I'd write about it here.

So here's the thing... Is anyone else under the impression that AF confirm was a completely separate thing from the AF module? For example.... when the AF confirm indicator is lit(hexagonal indicator in VF), then the camera is in focus right?

However... a few days ago, I realized that using the AF indicator with a MF lens proved to be off. Way off in fact... However... when I put an AF lens on the camera(same aperture and settings) focus was spot on! - How can this be(I thought), as I tied another MF lens for added testing. Same thing!

And so I'm now wondering if the focusing screen might not have something to do with AF confirm in MF mode? Or am I completely confused in my way of thinking?

Anyways, for what it's worth, the K-5 has a substantial FF issue when using AF confirm and a MF lens whereas the K20D does not.

Any suggestions?

04-10-2011, 07:36 AM   #2
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Hmmmm? I don't seem to have this problem and find the AF confirm to be spot on, same as my K20D.
On my K20D I had the Katz eye, but found it was no better than depending on the AF confirm light, so took it off and gave it to a friend. My K5 appears to be just as accurate. Works on AF or MF lenses just the same, so I have to assume your K5 needs an adjustment of some sort, although I would not know how that would be done?

I shot about a half dozen of these using the Kiron 105 MF lens and depended on the confirm light on every one...and every one was in focus or very near.

Do not think I am saying you don't have a problem, I'm not a Fanboy, although I love my K5 to death, but I realize all things are susceptible to problems. Some do, some don't....that is the reality in any brand.
Best Regards!

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04-10-2011, 07:45 AM   #3
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QuoteOriginally posted by JohnBee Quote
However... a few days ago, I realized that using the AF indicator with a MF lens proved to be off. Way off in fact... However... when I put an AF lens on the camera(same aperture and settings) focus was spot on! - How can this be(I thought), as I tied another MF lens for added testing. Same thing!

And so I'm now wondering if the focusing screen might not have something to do with AF confirm in MF mode? Or am I completely confused in my way of thinking?
I wasn't aware of that. Frankly, i have not tested my K5 with a manual lens yet but now its on my list Its important to know what you tested.

I assume you tested your K5 with a split lens focusing screen, and you have not tested your K5 on a MF lens without a split lens focusing screen - is that correct?
04-10-2011, 07:48 AM   #4
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An interesting observation. My first K5 had some intermittent AF issues so I spent most of the last couple of weeks I had it taking test shots with various AF lenses. I never got around to using the manual focus lenses I have with them. My replacement camera is fine as far as AF goes, so yesterday I wanted to shoot some macro/close-ups with my Viv S1 105 Macro and didn't have a problem with the focus indicator, whenever it lit up, the picture was properly focused. I did find that some of my subjects were such that it didn't "see" the focus at all, but that's not unusual - I've seen that with previous cameras. So I'm delighted as I've now been able to put the focus issue I was having to rest and go out and just enjoy my camera.

It would be very interesting to know if the indicator is separate from the AF, like you seem to be experiencing (perhaps that would mean there's a fault with your camera, since you are experiencing problems while at least two of us are not). Wonder if others are having the same issue?

04-10-2011, 08:00 AM   #5
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QuoteOriginally posted by philbaum Quote
I wasn't aware of that. Frankly, i have not tested my K5 with a manual lens yet but now its on my list Its important to know what you tested.

I assume you tested your K5 with a split lens focusing screen, and you have not tested your K5 on a MF lens without a split lens focusing screen - is that correct?
Hi, and thanks for the responses so far.
Allow me to expand on my initial experiment in hopes of clarifying things a bit better.

The first thing I did was put a manual lens on my camera. In this case, lets say the SMC-A 50/1.4 set at f/2

After this, I closed-in and used catch-in focus. Held down the shutter, beep and took the shot. After examining the image, it was severely front focused. So I though... okay, it was probably due to movement. So I tried again, except this time, without catch-in focus(manual shutter). Aim, focus, beep/confirmation indicator on, fire! - Same thing... severely FF image.

Okay I thought... I'll check with LV.
Focus... fire... spot on!

So now I was thinking.. well maybe I have a FF big after all?
So I grabbed an AF lens and tested with same conditions... and it was spot on!

So now I'm thinking... okay, maybe this is the AF module acting-up due to very wide aperture. So I grabbed my A/50/1.4 and adjusted it to f/3.5. Took a shot... and the same thing happened. Tried with smaller apertures and found it to be consistent. Though eventually, focus was achieved due to the broader DOF.

So now I'm wondering how it is possible for an AF lens to be spot on using AF while a MF lens is returning giving bad AF indicator data. My only resolve is that the MF indicator is somehow influenced by the focusing screen. But... that doesn't make sense to me as I was under the impression that the AF indicator was established by the AF same module...?!?

This is really confusing tbh,
In any case, I'm open to any tests/and or ideas that anyone might have to try and establish what is causing this strange behavior.

PS. I have 0 lens corrections in my camera. I shoot RAW and/with all setting off.

Last edited by JohnBee; 04-10-2011 at 08:20 AM.
04-10-2011, 08:36 AM   #6
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The AF sensor is the only source the AF indication can come from as long as the mirror is down. Maybe you have run into AF operation being specific to the lens, e.g. there are reports of the Tamron 17-50mm 1:2.8 consistently suffering from BF/FF, where a replacement copy has remedied the situation. (There are reports regarding other makes and models as well, but I have paid more attention to what I have myself )
04-10-2011, 08:39 AM   #7
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QuoteOriginally posted by jolepp Quote
The AF sensor is the only source the AF indication can come from as long as the mirror is down. Maybe you have run into AF operation being specific to the lens, e.g. there are reports of the Tamron 17-50mm 1:2.8 consistently suffering from BF/FF, where a replacement copy has remedied the situation. (There are reports regarding other makes and models as well, but I have paid more attention to what I have myself )

Okay thanks for the clarification.

I checked this phenomenon with several MF lenses and they all suffer from the same FF issue. So I'm thinking its likely not lens dependent per say. However, I certainly believe there is something very particular going on here since AF is spot on while MF is way off. Which is so very very strange.

On a plus side, I am still within my return policy, and so the only thing to figure out now is to try and figure out what could possibly cause such an issue.
04-10-2011, 09:05 AM   #8
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Your not alone.

I have had the exact same problems with my k5.
Im currently waiting for a replacement and i hope that one is ok.
One thing though.
FF has been quite different depending on what lens i use.
I have maybe 15 MF lenses that I regularly use and some of them are perfect while others FF. its more common that they FF though.
I wish I could turn of the focus indicator completely and not just the beep.
I have tried this with a katzeye and without. Problems the same no matter what.


QuoteOriginally posted by JohnBee Quote
Hi, and thanks for the responses so far.
Allow me to expand on my initial experiment in hopes of clarifying things a bit better.

The first thing I did was put a manual lens on my camera. In this case, lets say the SMC-A 50/1.4 set at f/2

After this, I closed-in and used catch-in focus. Held down the shutter, beep and took the shot. After examining the image, it was severely front focused. So I though... okay, it was probably due to movement. So I tried again, except this time, without catch-in focus(manual shutter). Aim, focus, beep/confirmation indicator on, fire! - Same thing... severely FF image.

Okay I thought... I'll check with LV.
Focus... fire... spot on!

So now I was thinking.. well maybe I have a FF big after all?
So I grabbed an AF lens and tested with same conditions... and it was spot on!

So now I'm thinking... okay, maybe this is the AF module acting-up due to very wide aperture. So I grabbed my A/50/1.4 and adjusted it to f/3.5. Took a shot... and the same thing happened. Tried with smaller apertures and found it to be consistent. Though eventually, focus was achieved due to the broader DOF.

So now I'm wondering how it is possible for an AF lens to be spot on using AF while a MF lens is returning giving bad AF indicator data. My only resolve is that the MF indicator is somehow influenced by the focusing screen. But... that doesn't make sense to me as I was under the impression that the AF indicator was established by the AF same module...?!?

This is really confusing tbh,
In any case, I'm open to any tests/and or ideas that anyone might have to try and establish what is causing this strange behavior.

PS. I have 0 lens corrections in my camera. I shoot RAW and/with all setting off.


04-10-2011, 09:10 AM   #9
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John, I have a similar situation (I think to a lesser degree) with my K20D. I do a lot of MF even with AF lenses and I've found the green hexagon to be only good for a certain degree of focus, I get the green hexagon and then tweek focus by eye. The green hexagon tells me I'm in the ballpark but a little bit off. Like you I'm FF but I think to a much lesser degree than what it sounds like you are. It's always been this way, I just thought it was "normal" just in the same sense that the AF sensors do not exactly correspond to the red squares in the VF. This is true whether I'm using my Katz eye screen or the one that came with the camera. (I change the two depending on whether or not I'll be using flash or not, the Katzeye doesn't play nice with flash metering).
One question, have you tried to manually focus ignoring the green hex?

NaCl(on my K20D the green hexagon isn't completely accurate)H2O
04-10-2011, 09:22 AM   #10
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I just thought of a new test that I think might shed a little more light on this.

I'm going to try after lunch and see if the issue appears on an AF lens in MF mode.
If so... then I guess there isn't much else that could be done.
Though something tells me that the issue if likely not so much a mechanical one as something that should be address with FW.

I've already contacted Pentax about the issue, but I doubt they will respond before my return period ends(Wednesday). Luckily, my camera dealer is very lenient with returns and so I'll likely get an extension to help figure this out first.

Either way, I'll post my results here shortly.
04-10-2011, 01:59 PM   #11
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I quickly shot off two shots using different MF (M42) lens. Narrow DoF used. Avoided using flash.
Catch in focus, poorish light. I did not experience any problem with flashing hexagon, but as I like using MF lens, I will now keep a close watch on this. I thought I would post these for your information.
Overall I was rather pleased with the outcome actually.

Super Tak 55/1.8 : 1/60/F11/isoF400. (incidentally on this one, I didn't set the focal length indicator that comes up on rear screen when using MF lens(did set on the 28mm shot. duh)



Super Tak 28/3.5 : 1/15th/F5.6/1so400.




Best of luck with yours, John
04-10-2011, 03:11 PM   #12
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Maybe I shouldn't comment, since I don't have a K-5, but how can this be considered a 'problem'?

We are talking MANUAL focus here - ie the camera setting where the photographer makes the decisions. Who cares what that little hexagon is saying - it plays no role in MF. I never pay any attention to it. With a MF lens the hexagon only responds to the centre spot anyhow.

Jeeze you guys are picky.
04-10-2011, 03:26 PM   #13
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QuoteOriginally posted by rawr Quote
Maybe I shouldn't comment, since I don't have a K-5, but how can this be considered a 'problem'?

We are talking MANUAL focus here - ie the camera setting where the photographer makes the decisions. Who cares what that little hexagon is saying - it plays no role in MF. I never pay any attention to it. With a MF lens the hexagon only responds to the centre spot anyhow.

Jeeze you guys are picky.
At the risk of sounding like a broken record, I think you're missing a few points in your criticism.

1. If other camera's do something properly and the K-5 doesn't then wouldn't that constitute a reason for concern?
2. Have you considered the implications of the AF indicator and Catch-in focus?
If you do, then you should have no problem understanding the value of a working AF Indicator and its use in the field.

thx
04-10-2011, 03:27 PM   #14
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Maybe this is a separate problem, but I have been shooting with A series lenses (particularly the A50/1.7) quite a fair bit recently, and I noticed that sometimes I get the AF confirmation even when I know the focus is off.

So I am not sure the AF confirmation is totally reliable for MF lenses. It seems to be mostly accurate, but since I have a focusing screen I pretty much ignore it and shoot when I think it's right.
04-10-2011, 03:30 PM   #15
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I had a bit of an issue here, but was able to dial it in pretty easily with AF fine tuning (which will have an impact on focus confirmation for an MF lens). This was typically with very low light.
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