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02-27-2007, 02:45 PM   #61
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QuoteOriginally posted by benjikan Quote
I was about 2 meters from the subject. I was lying on the floor of the studio shooting up at the model, focussing on her eyes. She is about 1m 80cm. Her feet were sharp and her eyes were out. That is why the kit has gone to Germany to be adjusted. Once I get the stuff back in about five days I'll share what I have re: diagnostic.
Ben,

I can't remember if you mentioned this earlier: what focusing method were you using? Spot focus?

Will

02-27-2007, 02:58 PM   #62
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QuoteOriginally posted by WMBP Quote
Ben,

I can't remember if you mentioned this earlier: what focusing method were you using? Spot focus?

Will
I was shooting vertically and used the upper led to focus with. Had I used the center led and re-framed, the parallax difference would have put the face out of focus. I would have had to focus on the eyes and move down about half of the whole frame shooting at a 45 degree angle. The face would have been way out at the distance I was shooting.
02-28-2007, 12:48 AM   #63
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QuoteOriginally posted by WMBP Quote
Have others found this, too? Someone else here in this forum (sorry, can't remember who or in what thread) recommended using spot focusing most of the time.

I have been using the Auto setting, I think. My pictures are not always tack sharp. I've been willing to take the blame myself so far. But I think I'll switch to spot focus and see if it makes a difference....

Will
As far as I know the auto setting will pick the focus point based on which of the nine reaches focus first. I don't think it is like some of the P&S and Bridge cameras that have face detect modes that try to make (what it thinks is) the face in focus.

However I may have underestimated the focus point selection algorithms in the K10D.

Barney
02-28-2007, 02:22 AM   #64
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The auto focus select function may well be confusing people about front/back focus. This is not what we are talking about here.

Ben and I are using manually selected focus points. You are correct, when in auto mode the camera will focus on the point that is closest to you.

When you are doing critical focus checks you need to select your focus point manually and examine the focus at that point in your image. Also, you should be doing any checks at maximum aperture. In the case of Ben where he has loss of sharpness when stopped down, there is something seriously out of whack.

Andy
Andy McInroy Photography - Landscape Photography of Great Britain and Ireland
Landscapes of Great Britain and Ireland


Last edited by amcinroy; 02-28-2007 at 03:47 AM.
02-28-2007, 02:40 AM   #65
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I'll Say

QuoteOriginally posted by amcinroy Quote
The auto focus select function may well be confusing people about front/back focus. This is not what we are talking about here.

Ben and I are using manually selected focus points. You are correct, when in auto mode the camera will focus on the point that is closest to you.

When you are doing critical focus checks you need to select your focus point manually and examine the focus at that point in your image. Also, you should be doing any checks at maximum aperture. In the case of Ben where he is stopping down, there is something seriously out of whack.

Andy
Andy McInroy Photography - Landscape Photography of Great Britain and Ireland
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Thanks for the clarification to others. Yes, all of the focus choices are manually employed and selected critically using the focus points available on the viewing screen. I knew that the extreme upper and lower vertical focus points are less accurate than the 9 others within the square area. I did however double and often quadruple my focus selection with the audio beep. The difficulty with manually focussing here, which I should have done, is that the face appears very tiny in the viewfinder when using the 21mm. The light was also very subdued.
I am sure that Pentax will find a solution with a suitable explanation.

Last edited by benjikan; 02-28-2007 at 06:25 AM.
02-28-2007, 03:16 AM   #66
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QuoteOriginally posted by amcinroy Quote
You are correct, when in auto mode the camera will focus on the point that is closest to you.
Glad to know that I wasn't spreading FUD.

QuoteOriginally posted by amcinroy Quote
When you are doing critical focus checks you need to select your focus point manually and examine the focus at that point in your image. Also, you should be doing any checks at maximum aperture. In the case of Ben where he is stopping down, there is something seriously out of whack.
I totaly agree.
Does the K10 have the same AF engine as the *ist Dx range and the K1x0D range ? If so I wonder what the problem is with the K10D, since I've not seen as many complaints about FF/BF for these cameras as I have for the K10D and the K10D has been available for less time.

Barney
02-28-2007, 03:33 AM   #67
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Barney,

I believe the 21mm focus problems were known about on the K100D/*ISTD series even before the release of the K10D, indeed many people hoped that the problem would not exhibit itself on the K10D. Sadly it has.

I did another test last night letting the autofocus do it's job with a subject distance of about 1m and aperture F3.2. The autofocus was off again but only a tiny amount of rotation was required to bring it in sharp. The problem as I see it is that that a tiny bit of rotation makes a HUGE difference to the focus on this lens. The autofocus only has to be out by a fraction at max aperture and the focus becomes unacceptable.

I agree with Ben that it is impossible to see this critical level of focus in the viewfinder.

Andy
02-28-2007, 04:01 AM   #68
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QuoteOriginally posted by amcinroy Quote
I believe the 21mm focus problems were known about on the K100D/*ISTD series even before the release of the K10D, indeed many people hoped that the problem would not exhibit itself on the K10D. Sadly it has.
Right ... though if the K10D uses the same AF system as the older cameras it is hardly likely to do a better job.

QuoteOriginally posted by amcinroy Quote
I agree with Ben that it is impossible to see this critical level of focus in the viewfinder.
So if it is impossible to see in the viewfinder ... you'd not be able to do a better job manually then ?

02-28-2007, 04:25 AM   #69
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QuoteOriginally posted by BarneyCG Quote
you'd not be able to do a better job manually then ?
That is correct, the degree of autofocus inaccuracy that I'm seeing is not detectable in the viewfinder. At least, not with my eyesight.

Andy
02-28-2007, 05:04 AM   #70
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QuoteOriginally posted by amcinroy Quote
That is correct, the degree of autofocus inaccuracy that I'm seeing is not detectable in the viewfinder. At least, not with my eyesight.
This may sound a little harsh ... but if you can't see the inaccuracy in the viewfinder how precicely do you expect the AF to do any better ?

AF is a wonderfull invention and all ... it definately makes life easier but it isn't a magic pill -- though I'm sure you're aware of this

Last edited by BarneyCG; 02-28-2007 at 05:25 AM.
02-28-2007, 06:29 AM   #71
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QuoteOriginally posted by BarneyCG Quote
This may sound a little harsh ... but if you can't see the inaccuracy in the viewfinder how precicely do you expect the AF to do any better ?
You make a fair point and I wouldn't disagree. I sometimes wonder that perhaps in this pixel peeping world in which we live, we may be asking too much from the autofocus at large aperture.

In bygone days of film, we perhaps wouldn't have been able to interrogate our cameras quite so aggressively. If we did get the odd soft enlargement then we would put it down to our technique rather than the autofocus accuracy. Conducting tests would have been both time consuming and expensive.

Still, there is certainly something different about that 21mm. At the end of the day, I am a landscaper, and I intend to use this lens stopped down for my commercial work. But I can fully understand the pain of Ben as a fashion photographer where sharpness at all apertures is paramount.

Andy

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Last edited by amcinroy; 02-28-2007 at 06:52 AM.
02-28-2007, 06:31 AM   #72
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f9.0 to 11.0

QuoteOriginally posted by BarneyCG Quote
This may sound a little harsh ... but if you can't see the inaccuracy in the viewfinder how precisely do you expect the AF to do any better ?

AF is a wonderful invention and all ... it definitely makes life easier but it isn't a magic pill -- though I'm sure you're aware of this

Normally at a distance of over 3 meters and parallel to the subject, this might be a non issue considering the aperture I was working at. However the reason I use a wide angle is to come in closer to the subject when wishing to use "that effect" of wide angle or if necessary in a very small working space. I have used other extreme wide angle lenses without this problem cropping up. It is the 21 Limited that has this anomaly.

Last edited by benjikan; 02-28-2007 at 04:44 PM.
02-28-2007, 07:45 AM   #73
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21 "issue"

is quite old in digital terms.. Sorry haven't seen an explanation or fix for this problem. It's not apparently camera related per se (appearing on a k100 and k10) but I could be wrong. I have not ran into a cause nor solution but my guess is a design conflict (somehow) between the lens and the AF system at specific conditions....... All speculation of course.
Old reference:
Question for the owners of the DA21/K100D: Pentax SLR Talk Forum: Digital Photography Review
On a DS:
Re: Adjusting focus of the Pentax *ist D: Pentax SLR Talk Forum: Digital Photography Review
And if you receive feedback from Pentax re: the 21, I'm sure there are a host of people that would be quite curious
Re: Now I'm (almost) lucky: Pentax SLR Talk Forum: Digital Photography Review

Last edited by jeffkrol; 02-28-2007 at 07:54 AM.
02-28-2007, 08:45 AM   #74
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QuoteOriginally posted by benjikan Quote
Normally at a distance of over 3 meters and parallel to the subject, this might be a non issue considering the aperture I was working at. However the reason I use a wide angle is to come in closer the subject when wishing to use "the effect" of wide angle or if necessary in a very small working space. I have used other extreme wide angle lenses without this problem cropping up. It is the 21 Limited that has this anomaly.
Gaaa ... I've spent ages trying to compose a reply and everything sounds rubbish I've got an engineering background and I look at things from that perspective rather than "just" as a user who wants to get good pictures and doesn't care about the physics and engineering limitations/bad design decissions ... but basically ..

I'm not trying to suggest that there is no AF issue, I was trying to put it into perspective. You are right that other lenses and AF systems don't appear to have this issue.

One day I'll actually produce a picture worthy of showing to people rather than just mouthing off

Last edited by BarneyCG; 02-28-2007 at 09:01 AM.
02-28-2007, 10:29 AM   #75
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Another thread of mine about the autofocus issue is seeing quite a bit of interest over on dpreview with a number of people seeing similar results to myself with other lenses.

21mm and K10D Autofocus: Pentax SLR Talk Forum: Digital Photography Review

Andy
Andy McInroy Photography - Landscape Photography of Great Britain and Ireland
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