Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
12-14-2006, 03:21 PM   #16
Veteran Member
joele's Avatar

Join Date: Sep 2006
Location: Melbourne, Australia
Photos: Gallery
Posts: 1,309
QuoteOriginally posted by RiceHigh Quote
I'm afraid that the case is not as simple as what Joele believes..

My experience with my original *ist DS is that Pentax have not much to do with AF errors and any misalignment in the AF system, in mechanical terms, within the DSLR body.

...

As told by my local Pentax service engineers, the focal plane position by no means can be adjusted *mechanically*.
I said CONSISTANT Back or front focus could be fixed mechanically and despite your expert hearsay opinion that focus plane cannot be manually adjusted.. it can... The link below explains how you can do it yourself... no software needed it is as simple as adjusting some screws...

I have fixed my front focus problem - how to: Pentax SLR Talk Forum: Digital Photography Review

This is ONLY for a consistant issue though as it is adjusting the body and will hence effect all lenses.. For a problem with just one lens I would suggest getting a lens replacement...

12-14-2006, 08:54 PM   #17
Veteran Member




Join Date: Nov 2006
Location: Hong Kong
Posts: 1,934
> I said CONSISTANT Back or front focus could be fixed mechanically and despite your expert hearsay opinion that focus plane cannot be manually adjusted.. it can...

I strongly disagree on your words of "hearsay opinion" used, which are totally untrue but just a pure speculation.

What I have told in my last reply is my first person experience with what Pentax service engineers told me as well as Pentax Japan's service engineers has indeed failed to rectify the problem in any mechanical way to the body except to adjust and change the "mirror angle" (I have a servicing report from Pentax Japan to prove it!). In the end, *nothing* is "hearsay" at all.

If you have read my provided link for the story in some more details, you will learn that my DS was unable to focus to infinity *mechanically* and actually the AF system of my DS was correctly showing that the focus cannot be reached and beyond the limit and physically and mechanically, the in-focus point has been fell out of range.

What I refer to in my last reply is that the body *focus collimation* of the *ist DS cannot be adjusted mechancially.

> The link below explains how you can do it yourself... no software needed it is as simple as adjusting some screws...
> I have fixed my front focus problem - how to: Pentax SLR Talk Forum: Digital Photography Review

The above mechanical adjustment is *probably* to move the AF detection module mechanically. Same effect can happen if the amount of FF and BF is input into the AF system in software means. I can't see the big difference here, that is, if the AF module is off-set by a certain amount, then this offset can be compensated by a software parameter in the AF calculation, if it is properly dialed in. Alternatively, the whole AF detection module can be moved, as it is described in your provided link.

Do note that the above AF system calibration has nothing to do with the focus collimation of the body. For anyone who are interested in what "focus collimation" is, just google the term.

> This is ONLY for a consistant issue though as it is adjusting the body and will hence effect all lenses.. For a problem with just one lens I would suggest getting a lens replacement...
>

Nope. Almost every Pentax lens has screws for true focus collimation fine adjustment. And it is fast and easy to do for a qualified techician with calibrated tester/simulator. FF and BF errors within a lens and for a particular lens model should be non-existent as the AF and MF is to be done Thro The Lens, so the remaining (only) alignment is on the focus collimation.

BTW, no matter how, any mis-alignment and incorrect calibration for a product out of the Pentax factory is the fault of Pentax. Indeed, all those calibration things we are discussing should be done in a precise and absolute way at the production line, but not at the Pentax service centres!
12-15-2006, 04:19 AM   #18
Veteran Member
joele's Avatar

Join Date: Sep 2006
Location: Melbourne, Australia
Photos: Gallery
Posts: 1,309
QuoteOriginally posted by RiceHigh Quote
I strongly disagree on your words of "hearsay opinion" used, which are totally untrue but just a pure speculation.
Hearsay means that you are saying that someone else said there is no mechanical focus adjustment.. not that you know from your own technical knowledge of the product, but you say you were told by someone else who apparently 'knows'... Thats is called hearsay, thats just what the word means..

QuoteQuote:
If you have read my provided link for the story in some more details, you will learn that my DS was unable to focus to infinity *mechanically* and actually the AF system of my DS was correctly showing that the focus cannot be reached and beyond the limit and physically and mechanically, the in-focus point has been fell out of range.
This thread wasn't about your long winded story.. I am sorry but it isn't, the OP had a problem with consistant FF and that can be adjusted mechanically in many cases (your particular case maybe not) but you told me I was WRONG and no Pentax DSLR focus can be adjusted manually.. I posted a link with instructions that explains how to do it... That may have helped in this particular case, maybe not yours but we are not dealing with your many Pentax camera issues here just Evolution's one...

His is now mostly solved due to a body exchange and I still think in his case it very well may have been a simple misalignement.. but we will never know for sure.. Case is closed...

QuoteQuote:
Nope. Almost every Pentax lens has screws for true focus collimation fine adjustment.
Yes every lens can be adjusted but if ALL your lenses FF or BF consistantly then maybe simple logic states that the problem more likely lies in the body and not every single lens??? All I was pointing out is you said there is no possibility of in-body adjustment but there is, and for some people who were unlucky enough to have this problem it helped them...

QuoteQuote:
BTW, no matter how, any mis-alignment and incorrect calibration for a product out of the Pentax factory is the fault of Pentax. Indeed, all those calibration things we are discussing should be done in a precise and absolute way at the production line, but not at the Pentax service centres!
YES EVERY product should always be perfect 0% fault rate across the board... Please WAKE UP, there is always a fault rate with EVERY product from EVERY brand.. It happens, some people have bad luck, other don't.. But all you can do is deal with it (like Evolution did by getting a replacement) and move on with your life and not turn every issue into a crusade..

And remember you hear on forums most about the problems as people always look for advice from fellow owners.. 99% of people who have no problems don't jump on the WWW to let us all know they had no problems..

Last edited by joele; 12-15-2006 at 07:07 AM.
12-15-2006, 05:59 AM   #19
Veteran Member




Join Date: Nov 2006
Location: Hong Kong
Posts: 1,934
Joele, from what you responded, it seems that you've forgot that I suggested in my first reply for a possible solution for Evolution's problem, that is, the amount of FF and BF can be set via Pentax's utility at their service centre.

It would be very unfair to me that you accused me of not helping the OP but telling my own story.

In my last reply, I just wish to clarify that what exactly I refer to for my statement of "mechanically not adjustable" and why I had told that.

You do have shown that the amount of BF and FF is mechanically adjustable in your last reply, but I would say this is no big difference for setting the *offset* as a programmable parameter in the firmware, again.

I don't "jump on the WWW" to tell others I saw the problems as you supposed, but there have already so many various K10D users reported their K10D FF and BF problems. This is a non-arguable fact. So, what does this mean?

If this is just an isolated case but not a poor QC or calibration inaccuracy, why there are have been so many reports just for less than one month's time??

12-15-2006, 06:54 AM   #20
Veteran Member
jeffkrol's Avatar

Join Date: Sep 2006
Location: Wisconsin USA
Photos: Gallery
Posts: 8,435
It seems that it would be best to first get the hardware right then to basically "hack" the software. Matter of fact I only consider software tweaks as "last chance efforts" to fix an inherent problem.....

Last edited by jeffkrol; 12-15-2006 at 07:06 AM.
12-15-2006, 07:06 AM   #21
Veteran Member
joele's Avatar

Join Date: Sep 2006
Location: Melbourne, Australia
Photos: Gallery
Posts: 1,309
QuoteOriginally posted by RiceHigh Quote
Joele, from what you responded, it seems that you've forgot that I suggested in my first reply for a possible solution for Evolution's problem, that is, the amount of FF and BF can be set via Pentax's utility at their service centre.
I remembered that you said it couldn't be done mechanically..

QuoteQuote:
You do have shown that the amount of BF and FF is mechanically adjustable in your last reply, but I would say this is no big difference for setting the *offset* as a programmable parameter in the firmware, again.
No doubt it can be done both ways, I never denied it can also be done in software.. I agree with Jeffkrol above though adjust the mechanical way first...

QuoteQuote:
there have already so many various K10D users reported their K10D FF and BF problems. This is a non-arguable fact. So, what does this mean?
And many, many people reporting no problems too, despite it being human nature to report problems but not to report a product working as it should..

Actually the vast majority of people I have seen reporting FF or BF issues have not been a consistant problem like we saw here but have been with one specific lens the FA50/1.4 (and under specific conditions)... This is being investigated by Pentax already, they have taken this issue seriously, but still the people with problems are a minority..

QuoteQuote:
If this is just an isolated case but not a poor QC or calibration inaccuracy, why there are have been so many reports just for less than one month's time??
Go look at the Nikon forum and the Canon forums, as soon as cameras are released people find issues.. Many of these issues are not noticed in real world shots, but in the digital age it is easy for people to search for very slight problems... You look hard enough you find something..
12-15-2006, 07:10 AM   #22
Veteran Member
joele's Avatar

Join Date: Sep 2006
Location: Melbourne, Australia
Photos: Gallery
Posts: 1,309
Maybe one day they (either Canon, nikon, oly or Pentax) may offer us a PERFECT camera and it will probably cost more than any of us can afford... LOL...
12-15-2006, 01:00 PM   #23
New Member




Join Date: Dec 2006
Location: San Diego, CA USA
Posts: 16
Anyone know what the 3 screws do exactly? The posts in the DP Review forum only speculate on them.

12-15-2006, 03:18 PM   #24
Veteran Member
joele's Avatar

Join Date: Sep 2006
Location: Melbourne, Australia
Photos: Gallery
Posts: 1,309
I think they actually move the sensor back or forward... I have no exact proof, only a Pentax tech would know for sure...
12-16-2006, 06:53 PM   #25
Inactive Account




Join Date: Dec 2006
Location: NSW
Posts: 6
Definite answer: body or lens?

Hi guys,

I can confirm that the 3 adjustement screws are used to adjust the plane of the autofocus sensor, by moving it up or down at the location of the screws, hence altering the points of autofocus. For example, and for illustration only, if the top AF points our out but the bottom ones are fine, you have a misaligned sensor plane. If all sensors AF points give you BF or FF, all 3 screws need to be adjusted by the same amount.

Now there have been contradictory answers on the topic of BF/FF: Can we confirm whether it is the body or the lens at fault please?

- To my best knowledge, af lenses have no AF adjustement in them, aside from the infinity stop, which only affects focusing at infinity (affects the focus ring rotation position in relation to the optical group and where it stops when the lens is at infinity). Aside from this, the AF assembly consists of a shaft, gears, and helocoidal, all mechanical with no place for collimation adjustment that I have seen. (I repair & clean lenses in my own time and I am familiar with their mechanics)

- Can someone describe the in-lens collimation adjustments mentioned by RiceHigh in this thread and how it would affect consistent BF or FF?

- AF detection and motor are in the camera, which suggest a BF or FF is always caused by the body interpreting the AF locations in the wrong spot, rather than the lens.


Can we confirm these please?

Another K10D shares his findings here (points to faulty body):

<http://forums.dpreview.com/forums/read.asp?forum=1036&message=20995715>


Thanks guys!
12-16-2006, 08:29 PM   #26
Veteran Member




Join Date: Dec 2006
Location: UK
Posts: 643
i read somewhere that the design parameters for auto focus is F3.5 to F5.6.. beyond those two point its not likely to be reliable..

the problem only occurs with fast lenses.. nobody ever complains that their kit lens dosnt focus correctly its also not just a problem with the k10.. i have experienced a pair of k100s one focused perfectly with a certain sigma F2.8 EX lens the other failed abysmally with the lens wide open..

trog
12-16-2006, 09:58 PM   #27
Veteran Member
joele's Avatar

Join Date: Sep 2006
Location: Melbourne, Australia
Photos: Gallery
Posts: 1,309
yep certainly not just K10d, head on the the Nikon and Canon forums at DPreview and search for BF or FF ;-)
12-16-2006, 11:24 PM   #28
Veteran Member




Join Date: Nov 2006
Location: Hong Kong
Posts: 1,934
QuoteOriginally posted by willc Quote
Now there have been contradictory answers on the topic of BF/FF: Can we confirm whether it is the body or the lens at fault please?
It's the body.

QuoteQuote:
- To my best knowledge, af lenses have no AF adjustement in them, aside from the infinity stop, which only affects focusing at infinity (affects the focus ring rotation position in relation to the optical group and where it stops when the lens is at infinity). Aside from this, the AF assembly consists of a shaft, gears, and helocoidal, all mechanical with no place for collimation adjustment that I have seen. (I repair & clean lenses in my own time and I am familiar with their mechanics)
Yes, I think you're right.

QuoteQuote:
- Can someone describe the in-lens collimation adjustments mentioned by RiceHigh in this thread and how it would affect consistent BF or FF?
See:-
Re: Alan, forget to ask you that..: Pentax SLR Talk Forum: Digital Photography Review

It cannot rectify BF/FF though, as you have suggested.

QuoteQuote:
- AF detection and motor are in the camera, which suggest a BF or FF is always caused by the body interpreting the AF locations in the wrong spot, rather than the lens.
Yep.

QuoteQuote:
Can we confirm these please?

Another K10D shares his findings here (points to faulty body):

<http://forums.dpreview.com/forums/read.asp?forum=1036&message=20995715>

Thanks guys!
Actually, you've got all the answers already!
12-16-2006, 11:56 PM   #29
Inactive Account




Join Date: Dec 2006
Location: NSW
Posts: 6
RiceHigh,

You're a star and I hope we've cleared a few myths here. My personal experience and findings while repairing the Pentax AF lenses are in alignment with your findings. Returning a wide aperture lens such as the Pentax-FA 50mm f1.4 for FF or BF errors will probably not solve your problem (unless you are experiencing consistently soft images throughout the aperture range, or find that you have a plannar misalignment in the optical groups causing part of the picture to be blury while others are sharp when taking a picture of a plannar subject).

As there is a lot of rubbish on the forums about these issues, let's work together to clear the misconceptions, here are my two cents from my experience and knowledge of the Pentax gear:

BF/FF is caused by the body, where the AF sensors are not calibrated correctly. AF occurs 'through the lens', which makes wide aperture lenses more vulnerable to focusing issues, as they have a shallower DOF, again explaining why smaller aperture lenses are not affected (f3.5 onwards). Small focus errors are simply more visible with wider aperture lenses.

I have not seen the existence of an in-lens focus adjustment with Pentax, aside from infinity collimation (unrelated to FF or BF).

Other thing to consider is lighting. Pentax AF system performs poorly indoors as reported by many users, and is prone to BF/FF issues in these situations. Make sure you test your gear outdoors.

To anyone experiencing FF or BF issues, I suggest trying a different body, maybe several!

What are your thoughts guys?

Cheers.

Last edited by willc; 12-17-2006 at 02:22 AM.
12-17-2006, 10:24 AM   #30
Senior Member




Join Date: Dec 2006
Location: USA
Posts: 135
Original Poster
Wow... this thread got sort of ugly... and sort of informative. I'm not certain everything that's been said is correct, but I'm not certain my thoughts are correct either... so here it goes.

Both bodies focus accurately over 90% of the time in good lighting with the Sigma 30/1.4, the Sigma 70-300 (tested in Macro mode), and the Pentax 18-55. Both bodies front focus everytime with the 50/1.4. For that reason I find it impossible to believe AF is a product of the body only. It may be that the body struggles with certain lenses, but the lens must have something to do with it. As evidence of this (perhaps), the Sigma 30/1.4 that I had for Minolta was focusing inaccurately before a trip back to the factory. Focus was much better when it came back recalibrated. Minolta also uses an in-body AF motor, so I'd assume the same principles apply.

Additionally, I've made adjustments to the "3 screws" before... with my Maxxum 5D. I needed to use the Sigma 30/1.4 on a vacation the weekend I received it, but because of the front-focus problem my only solution was to adjust the sensor alignment. I carefully marked the original positions and then spent a few hours shooting test shots while carefully turning each screw in 1/4 rotation increments. Eventually I had 2 sets of marks, one for the 30 to be in focus, and one for the rest of my lenses. I spent the weekend in Chicago with an allen wrench in my camera bag, making adjustements to the screws anytime I switched lenses. It worked, but obviously it's not the least bit ideal... nevermind the fact that I have reservations about my ability to properly reseal a weather-sealed body.

So I'm going to return the 50/1.4 to B&H and possibly try one more copy. If it has the same front focus issue, I may just keep it anyway because of the current rebate and just wait until the Holly Hills service center (an hour north of here) is checked out on the K10D. Then I can bring the body and all my lenses up there and let them figure out what's going on.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
amazon, body, camera, combo, dslr, k10d, lens, photography
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
K-5 Manual Lens Front Focus & Focus Beep woes fixed kneonx Pentax K-5 14 04-12-2014 03:47 PM
A-lens front focus but kit lens ok - Why and solution? LIJ Pentax K-r 7 05-25-2011 06:25 AM
So how can a lens affect front/back focus? klh Pentax SLR Lens Discussion 16 10-03-2010 05:18 AM
K-X front / back focus correction, lens tested ea77 Pentax DSLR Discussion 3 12-07-2009 06:56 PM
Front Focus - K10D BeerCur Pentax DSLR Discussion 13 01-27-2008 03:09 AM



All times are GMT -7. The time now is 04:26 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top