Will your K200d + Kit Mk 2 behave like this??

ckanthon · 07-09-2008, 07:32 PM

My K200d when shot at far objects at wide angles (i.e. 18mm and 24mm, and at Aperature F3.5 or F4), the lens file's "Focus Ring" will move to the end limit.....("AF" goes far beyond the infinite mark and hit the end)

See yellow arrow on attached picture.

Will your K200d + Kit lens behaves like this?
What could happen if I fit a F2.8 lens in!!?!!

babelphotos · 07-09-2008, 07:40 PM

Are the pics blurry?
Will it actually shoot?

I checked on my K20 and sometimes i will have that end limit too but only on a non Pentax lens!! But the pics are OK

ckanthon · 07-09-2008, 09:57 PM

Originally Posted by babelphotos

Are the pics blurry?
Will it actually shoot?

I checked on my K20 and sometimes i will have that end limit too but only on a non Pentax lens!! But the pics are OK

The AF sound triggered at higher level of light (feeling)

Whereas the IQ at wide angle ends at F3.5/F4 and shot at at distant objects seemed always a little bit soft (but the IQ in such wide angle is somehow softer anyway?)

I just fear of the AF hitting the limited end from time to time it could deteroiate the life of the Supersonic Motor

Or it could hit the limit more serviously if I buy the F2.8 lenses? (could be!)

I wondered why they dont make more margin for the motor to travel (forwards and backwards instead of just hitting a bombardment!!) at the "infinite" end position!?!

NB: same design of "infinite" position (right after "2m" mark) for DA17-70mm F4?!?

egordon99 · 07-10-2008, 05:01 AM

There is no supersonic motor (nor ANY motor) in the kit lens. Still not sure what you're trying to say; why would it be a problem if the focus ring moves to infinity? That's what it's there for!

And what does a f/2.8 lens have to do with anything?

bnishanth · 07-10-2008, 05:11 AM

Originally Posted by ckanthon

What could happen if I fit a F2.8 lens in!!?!!

How could your f stop affect focus

Can you post some pics that were shot with infinity ?

Sorry, I fail to understand the problem / issue here

Cheers
Nish

MRRiley · 07-10-2008, 05:37 AM

I believe the issue egordon99, that the OP is asking about is the fact that the lens appears to focus PAST infinity.

From what I understand this is a fairly common behaviour on modern AF lenses. I've heard it is intentional in order to insure that the AF motor does not run up against a hard stop when focusing to infinity.

I think the only people who notice this are folks who routinely focus manually. If you do so by feel and just 'turn it all the way to infinity" you will have over focussed and the pics will be a little soft. I've learned to focus to the stop then back off a tad with both my 16-45 and my Tamron 28-75. Seems the better the lens, the more likely you ae to see this "feature".

Jodokast96 · 07-10-2008, 05:55 AM

You could be right, but then he seems to worry about damaging the motor from hitting that hard stop. Bottom line, we can guess all day long and still not be right, so the OP really needs to clarify things.

ckanthon · 07-10-2008, 06:28 AM

Sorry for uncleared explanation of my story. (OK no SDM there)

1) at wide angle 24mm and 18mm. F/3.5 and F/4. shot at "distant" objects far away... The AF will stop beyond the infinite mark (see attached picture with yellow arrow) and it was possible to hit the end of the focus ring. AF stopped there and AF just takes action and pictures taken.

2) when Aperature decreases to F/8, the AF stop at around the infinite mark. no above issue.

3) Yes, for my kit lens, I noticed that the focus depended on the f-stop. When F/3.5, the focus is longer than at F/8. That was why the focus ring gone beyound the infinite mark when shot at F/3.5 or F/4. (I dont know why...)

RiceHigh · 07-10-2008, 06:47 AM

Originally Posted by ckanthon

My K200d when shot at far objects at wide angles (i.e. 18mm and 24mm, and at Aperature F3.5 or F4), the lens file's "Focus Ring" will move to the end limit.....(goes far beyond the infinite mark and hit the end)
See yellow arrow on attached picture.

Will your K200d + Kit lens behaves like this?
What could happen if I fit a F2.8 lens in!!?!!

It is a factory "focus collimation" error so that you cannot achieve focus for infinity objects especially on a clear bright day.

I have bought two DA 18-55 lens so far and the first one did have this problem. It is a factory QC problem afterall.

The infinity position is adjustable though. You can get it to the local Pentax service centre to fix it if it is still under the warranty. If not, the HK Pentax centre (Jebsen) will charge you for a few hundred dollar for this maybe simple job - even though it is a out of factory QC problem (only that the user may discover it too late!).

For more information on the in-depth technical knowledge for the lens and focus collimation, you can read my old article:-

RiceHigh's Pentax Blog: Focus Calibrations for (Pentax) (D)SLR Bodies and Lenses

ckanthon · 07-10-2008, 07:10 AM

Hi Rice,

It is nice to see you here in a "sunny" afternoon and better weather in the evening (nearly everyday is raining like cat&dog!!)

Oh! partially correct. In my case, when aperature is set at F3.5 or F4 (cloudy day), the AF goes beyond the infinite mark for shot at distant objects (and it hit the end limit). Whereas when aperature is set at F/8 (bright sunny day), the problem seemed disappeared.

Unfortunately however, this phenomena happened AFTER Jebsun fine-tuned the focus of my K200d Kit!!! Before that, the K200d was Front Focus with my kit lens.. Pictures were only sharp until F/8, F11 or higher. Besides, after the fine-tune they said the lens was OK.

I suspected, it is an error of positioning the optical element(s), the CCD plane could have been placed a little bit too backward, therefore the AF sensor unit was also adjusted too downward by Jebsan. (But I dont know exactly. I just a guess)

Thanks for the advises!

RiceHigh · 07-10-2008, 07:56 AM

Physical positions of the lens mount and CCD cannot be changed, according to what Jebsen told me.

Only that the AF module can be adjusted physically and most of the settings of the AF can be re-calibrated and re-programmed.

Pentax's AF system has been found to be adaptable to the aperture number selected, i.e., different f-number selected will change the behavior of the AF system, see this example:

RiceHigh's Pentax Blog: DA 21 Mis-Focusing - A Design Problem?

So, if the problem only occurred after adjustment at the Pentax service centre, got your unit back to them and ask them to rectify it. Asking here will help you to know more but will surely not get your problem fixed! :-)

Originally Posted by ckanthon

Hi Rice,

See you here in a "sunny" afternoon and better weather in the evening (nearly everyday is raining like cat&dog!!)

Oh! partially correct. In my case, when aperature is set at F3.5 or F4 (cloudy day), the AF goes beyond the infinite mark for shot at distant objects (and it hit the end limit). When aperature is set at F/8 (bright sunny day), the problem seemed disappeared.

Unfortunately however, this phenomena happened AFTER Jebsun fine-tuned the focus of my K200d Kit!!! Before that, the K200d was Front Focus. Pictures were only sharp until F/8, F11 or higher. Besides, after the fine-tune they said the lens was OK.

I suspected, it is an error of positioning the optical element(s), the CCD plane could have been placed a little bit too backward, therefore the AF sensor unit was also adjusted too downward by Jebsan. (But I dont know exactly. I just a guess)

Thanks for the advises!

ckanthon · 07-10-2008, 12:32 PM

Originally Posted by RiceHigh

Physical positions of the lens mount and CCD cannot be changed, according to what Jebsen told me.

Only that the AF module can be adjusted physically and most of the settings of the AF can be re-calibrated and re-programmed.

Pentax's AF system has been found to be adaptable to the aperture number selected, i.e., different f-number selected will change the behavior of the AF system, see this example:

RiceHigh's Pentax Blog: DA 21 Mis-Focusing - A Design Problem?

So, if the problem only occurred after adjustment at the Pentax service centre, got your unit back to them and ask them to rectify it. Asking here will help you to know more but will surely not get your problem fixed! :-)

Hi Gentlemen,

Thanks for your great advises as well as the linked information (which I quickly read thro').
Basically, I think what happened to Ben DA 21 also happened to my Kit Mk2. Except mine was Front Focus before the repair service

In fact, for very long time, I had decided to used DC "P&S" instead of using DSLR what's that I knew optics system(s) could be very tricky to deal with: Slightly mis-alignment with a little bit error could already ruin the system's performance because optics required accuracy in "one wave-lenght" levels. I learned this while I did laser projects in polyU time. Simple setup is better than system built with lens + mirror(s) etc....
I eventually switched to DSLR because I really started to feel not satisfact with my 7M pixels P&S whereas the latest P&S with higher M-pix seemed did not have real improvement on IQ (In fact, IQ of most of the Higher MegaPixels P&S really stepped backwards I realized). Obviously, now I get more after entering the "P" world but I still did not get what I supposed to....Ok....

Yes, I can confirm the "German guy's finding": focus (focal lenght of a piece of lens) depends on F-number. I can explain this phenomeon using my limited knowledge learnt in high school times.....It is caused by "lens imperfection". A real lens cannot be perfect in real life....In fact, when the Aperature is widely open, the focus at the centre of a piece of lens can NEVER be concidely overlapping with the focus point obtained at the "rim" of the same lens (not matter how high quality of the lens produced). This resulted that the "a real focus" of a bundle of parallel light from infinite, caught by a wide open lens, is in fact "an area" or in fact "a 3D oval region" rather than "a spacial spot". An "AL" or "ED" lens improved a little but not all.
But the "problem" here also caused by (or mixed complicately by) the characteristic of the AF sensor...how it responds to those images produced by non-ideal lenses.....

What I could say now is that I have a bit of BAD LUCK... that I already find a problem with my kit mk2.....not even before I buy a second piece of lens....In fact, the problem really not purely caused by the lens but by the "combined" error of the lens + the body when put them together..... List them: design error + illed tolerances + manufacturer QC + lack of final fine-tune + combined unceratinty when puttng them together + .. ..
I will cantact Jebsun again and decide whether I will buy more lenses to play with...!

Alfisti · 07-10-2008, 01:02 PM

Interestign thread. I have often wondered this too as virtually every lens I own will AF past the infinity mark if I focus at a distant object.

Odd.

ckanthon · 07-10-2008, 01:12 PM

To me.. AF passing the Infinite Mark is OK... but hitting the end limit of the focus ring (hard stop)everytime during AF at wide open Aperature is very annoying....

That was why I questioned why the focus ring was designed this way: "2m" than "inifite" than "stop at the end" so soon. I also insisted Pentax must allow K200d user to do focus correction on the manual (for different lenses) in order to cure the root cause (a little).

I think the phenomen not 100% fault of "Pen design" but it is really linked to design errors, factory QC, how to handle Uncertainty of each indivdual product produced....deviation from idealness of protool type....lack of degree of freedom for post production optical adjustments, finetune...

Fireball · 07-10-2008, 02:41 PM

All of my Pentax and non-Pentax lenses AF beyond the marked infinity point.