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Forum: Pentax SLR Lens Discussion 12-29-2018, 06:04 AM  
PENTAX-A 24mm F/2.8 infinity focus adjust (failed)
Posted By Kerusker
Replies: 6
Views: 552
Allen,
thanks for the hint. I didn't know.
iFixit Store Europe | Home is selling a set of JIS drivers.

I'm not optimistic though that this would solve 'my' problem because the driver must be very thin and it would hit the screw head aslant.

Happy New Year to all
Forum: Pentax SLR Lens Discussion 12-29-2018, 04:14 AM  
PENTAX-A 24mm F/2.8 infinity focus adjust (failed)
Posted By Kerusker
Replies: 6
Views: 552
In the following (old) post vizzy explains how to adjust oo-focus for the FA 50 (first part of FA50 disassembly and infinity focus adjustment - PentaxForums.com ).
I have acquired a P-A 24mm lately but noticed that I could not get oo-focus on my K-1. So I tried to adjust it in a similar way as vizzy has done with his FA 50.

1) I removed the lens ring inside the filter thread (it does not have the lens name on it as most lenses have)
2) After removal of the rubber grip of the focus ring, 3 small screws get visible - see image 1 (199)
3) After removal of the 3 screws the front end of the lens can be pulled out of the focus ring. Then you can identify 3 screws at the outer bottom inside the lens - see image 2 (201).

Now I would have liked to follow vizzy's advice to adjust oo-focus.
But a standard screw driver does not fit into the small gap between the outer focus ring and the inner lens (see img 2). :mad:

The front lens group can be removed easily but I don't think it's any good for oo-focus adjustment (right???).
SMC Pentax 24mm F/2.8 Disassembly - Page 2 - PentaxForums.com

So I gave up and I will use the P-A 24mm up to about 25m wide open and stopped down for longer distances (with my K-1).

Thanks to all members which supplied their knowledge and experiences on lens disassembly.:)
Forum: Pentax KP 07-04-2017, 06:18 AM  
Sticky: Pentax KP Review Posted!
Posted By Kerusker
Replies: 17
Views: 3,336
Adam,
thanks a lot for the review.
I received my KP about 4 hours ago.
My DA 18-135 DC should be able to focus continuously (AF.C) in movie mode - but the menu gives me a message that the lens can't do it.
I have tested a KP in a shop early this year and I still have a video on my PC with a KP + DA 18-85 DC which does refocus - what's going on here?
Forum: Pentax K-5 07-11-2013, 03:27 AM  
AF Fine Adjustment bug
Posted By Kerusker
Replies: 9
Views: 2,235
vanyagor,
when I posted this behavior in 2011 in the other forum, there wasn't much interest in it. It seems, over here it is about the same.
Wondering about it I thought: The internet fora are irrelevant regarding my PENTAX equipment. PENTAX is responsible for it's products and so I asked PENTAX to fix this fault of my K-5.
As we know, PENTAX didn't fix it (although I think it could be easily done by a FW fix).
Before warranty expired (2 years in Europe) I asked for a fix again or for a compensation. I got the latter - but I won't talk about the details.
Nevertheless I have just upgraded to the K-5 II because of a very good offer. Konowing about the fault before buying, I will not address it again for compensation. Hopefully PENTAX will fix it soon. But as there is only a minor interest by the users, I doubt it will come soon.
Thanks for picking it up. Let's see.
Enjoy
Forum: Pentax K-5 03-26-2013, 06:54 AM  
K-5 IIs focus consistency vs K-5
Posted By Kerusker
Replies: 64
Views: 14,547
Stan,
This is my current method to determine AF-Fine Adjust values:

My approach is a more practical than scientific one.
Starting point is Live View (LV using contrast detection on sensor = CD-AF) being more accurate than Phase Detect AF (PD-AF or AF for short). Using manual focus in LV (LVm) with up to 10 times magnification may be even more accurate than auto focus in LV (LVa). For simplicity, I use LVa for this description.
procedure A:
Auto focus in LV (LVa), turn off LV and observe the lens barrel when auto focussing (PD-AF).
The barrel may not move, turn towards 0 or turn towards infinity (v, ->0, ->oo)
v: the AF-FA value seems to be ok (at least close to best)
->0: PD-AF does FF i.e. move the AF-FA value to negative direction (f.ex. +5 ->+1 or +2->-4 or -1->-7)
->oo:PD-AF does BF i.e. move AF-FA value to positive direction (f.ex. -2->+3)
Repeat procedure A until the lens barrel does't move anymore.

In procedure A you will find that there may be several AF-FA values without barrel movement.
Therefore we will try to find the AF-FA limits where the barrel starts moving towards 0 (V->0) and towards infinity (V->oo). Usually we'll get a range V->oo,.....,V->0 in the AF-FA scale from -10 to +10, but sometimes V->oo or V->0 may be out of this range (and can't be determined).

procedure B:
B1) Auto focus in LV (LVa), turn off LV and observe the lens barrel when auto focussing (PD-AF).
R1) The barrel may not move, turn towards 0 or turn towards infinity (v, ->0, ->oo)
Repeat B1 with a different AF-FA value until the barrel does not move.

B2) Lower the AF-FA value and repeat B1 until the barrel starts to move towards infinity (V->oo)
B3) Increase the AF-FA value and repeat B1 until the barrel starts to move towards 0 (V->0)

B4) Pick an AF-FA value in the middle between V->oo and V->0 (if you prefer slight FF, take the one to the left of the middle value).

For a zoom lens you should do procedure B at least for the wide end and the long end of the zoom and then pick an AF-FA value which is approximately in the middle of both V->oo,....,V->0 ranges. In bad situations, there may not be a common AF-FA value at all in both ranges.

You can find a video for a similar procedure here:
'Dot-Tune'














You Tube




I've tried 'Dot-Tune' on my K-5 but since focus is set only once to determine the AF-FA range, it seems to depend a lot on the chosen focus setting. Also all mechanical variances are excluded since AF is turned off for the lens and only the AF indicator is used.

In procedure B above you should execute B1) several times for each AF-FA value to get good statistics with all AF elements included. (LVa does refocus each time!).

Procedure A and B can be executed without taking any picture (but you can of course).
Test setup is very similar to the one in the video. Additionally I use the following settings on my K-5::

2-sec timer (turns shake reduction off)
Enable AF on AF Button and disable AF on Shutter Button Half Press (Exposure Menu 5 'Button Customization')
Menu C1/4 'Meter Operating Time' = 3sec (minimum)
AF Center Point only
Lens aperture wide open (this is usually the case for auto focussing, but aperture may be closed for LV if target is very bright)
distance from cam to target should be about 50 times the focal length of the lens (or at least 25 times)

If the AF-FA ranges are often outside the -10,...,+10 scale (at one end), you should use Debug to control (and change) the AF -Correction value.

Thanks
Forum: Pentax K-5 03-25-2013, 02:45 AM  
K-5 IIs focus consistency vs K-5
Posted By Kerusker
Replies: 64
Views: 14,547
Stan,
thanks for your efforts. I was/am hesitant to get involved in AF as there are soooo many aspects which may come into play.
Did you find Enzo's 'Quantitative Method' from Jan. 2012?
https://sites.google.com/site/vincenzomiceli/quantitative-micro-focus-adjustment-for-dslrs
Please give more information on your test set up (as already requested by others).
Also, did you find a lens which needs more than a +10 or -10 adjustment?

I just had a K-5 II for one week and did some kind of focus adjust comparison to my K-5.
My finding (with my method) was that both need very similar adjustment values (which may be shifted along the adjustment scale).
The Best
Forum: Pentax K-5 12-28-2012, 01:59 PM  
Silent FW Upgrade for K-5
Posted By Kerusker
Replies: 10
Views: 2,194
On the Japanese Pentax site you'll find a silently updated K-5 FW:

Latest K-5 Firmware Update : Software Downloads | PENTAX RICOH IMAGING

It's a minor update since version goes from 1.13.23.23 to 1.13.23.25

The file attributes like date, time etc. stay the same, but content and checksum are different.

If you try and notice a difference, please report.

And a Happy New Year to you all. :)
Forum: Pentax K-5 10-29-2012, 11:39 AM  
Sticky: Pentax K-5 II / IIs Review Posted!
Posted By Kerusker
Replies: 99
Views: 100,760
Adam, thanks for your informative review.
One thing I'm missing badly is the SFOX X usability for apertures above f4 (f.ex. F2). You didn't mention this at all. Do you have any knowledge about it?
Thanks
Forum: Pentax K-5 01-13-2012, 11:07 AM  
K-5 Debug Mode now accessible
Posted By Kerusker
Replies: 26
Views: 22,491
JohnBee,
where's the focus after your service adjustment to -140 when you turn off micro adjustment in the menu?

Thanks
Forum: Pentax K-5 06-07-2011, 03:17 AM  
Just did AF Fine Adjustment - all my lenses are off?!
Posted By Kerusker
Replies: 30
Views: 8,129
Class A has set up a very good set of rules, but rules don't contribute much for understanding what's going on.


That's what I have observed also and there are some reasons for it.
Falk Lumo has set up a paper 'Low light focus accuracy with the Pentax K-5 camera' on his blog LumoLabs
Chapter 3 'General remarks regarding normal focus accuracy' does contain some of the reasons:
'In other words, focus tolerances df of up to 100 m are normal (for non professional cameras) even if this is probably shocking news for pixel peepers ;)'
I don't know what the adjustment value of one AF-FA increment is, but it seems to be less than the normal focus tolerance of the K-5.

' It is a pitty that Pentax didn't include at least an f/2.8 wide center AF sensor as it is needed really to exploit the K-5's high resolution. With its current phase AF accuracy, f-stop figures around f/8 to f/11 are required to bring b defocus down to about 1 px.'
Now this is an explanation why the K-5 is a pro-sumer camera and no pro-camera. It's optimized for slow consumer lenses like the kit lenses.

Till now I don't own expensive fast AF-glass and may be I never will. For me the K-5 is adequate but AF-FA is problematic.

Thanks
Forum: Pentax K-5 06-06-2011, 11:55 PM  
Just did AF Fine Adjustment - all my lenses are off?!
Posted By Kerusker
Replies: 30
Views: 8,129
My finding (which has been approved by PENTAX support) is simple:
Look at the 'AFAdjustment' value in EXIF data of the shot - that is what was actually applied to the shot.
Read the 'all' as 'all except the lenses with individual setting'.

Will post some more about the difficulties of 'AF Fine Tune' as experienced with my K-5 and lenses.
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