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Forum: Monthly Photo Contests 03-10-2019, 10:48 AM  
Biplane takeoff
Posted By mcewen
Replies: 32
Views: 544
I would like to nominate this photo
Forum: Troubleshooting and Beginner Help 03-26-2018, 03:20 AM  
DA 18-135mm ED AL IF DC WR Zoom Lens Focus problems
Posted By mcewen
Replies: 12
Views: 1,465
AGUARAV
I am sorry autofocus is not operating correctly with this lens. I am not sure from your description if the problem is the same as my own. I did describe in a number of earlier messages the exact detail of my own problem and attempt to strip down and repair.
At present I use this lens in autofocus up to 50mm, which is the range over which it operates correctly. At longer focal lengths I use manual. This really has not been a problem since most of my shots tend to be in the lower range anyway. This successful practice however made me lazy about pursuing the repair project therefore I did not make much progress beyond that already described in earlier messages. I did establish that the problem was not the spring contacts on the zoom ring, which were originally suspected. Probably the PCB and it's components are the areas worth checking next, if I ever get round to another repair attempt.
I cannot advise on repair cost since that has not been investigated.
As a general point I would not advise stripping the lens yourself unless you have some experience of this or similar types of repair but if you do have a go best of luck.
It would be helpful if you could feed back any progress with this problem.
Forum: Pentax SLR Lens Discussion 05-20-2017, 04:55 AM  
PENTAX DA 18-135mm ED AL IF DC WR Zoom Lens Focus problems
Posted By mcewen
Replies: 8
Views: 1,556
DrawsACircle. Thanks again for your last suggestion. Looking at this information it is possible that the 7th (digital) connector (which was added to allow digital communication of lens parameters to the body) is possibly being used to pass information from the body to the lens which would then allow the lens to know whether the body was set to Liveview or normal autofocus. I will do a further strip-down next week and check the optocoupler, ribbon cable and connectors since these seem the most likely source of trouble.
Forum: Pentax SLR Lens Discussion 05-19-2017, 02:13 AM  
PENTAX DA 18-135mm ED AL IF DC WR Zoom Lens Focus problems
Posted By mcewen
Replies: 8
Views: 1,556
DrawsACircle. Thanks again for your input. I will try to understand the whole system a bit better before trying a further strip down. In particular I still don't understand how the camera signals the lens that it is in Liveview mode (when it works correctly) and how the lens knows it is in normal autofocus mode (and has the fault). I suppose that sort of research it is all part of the challenge in taking on a repair project like this!
Forum: Pentax SLR Lens Discussion 05-17-2017, 02:05 AM  
PENTAX DA 18-135mm ED AL IF DC WR Zoom Lens Focus problems
Posted By mcewen
Replies: 8
Views: 1,556
Many thanks for the replies to my post.

DrawsACircle. Your suggestion was very helpful and perhaps I can provide some further information about the optocoupler. The disc on top of the optocoupler does not rotate when the manual focus ring is operated and while it is within the operational range of the manual focus ring. When the manual focus ring is moved beyond itís operational range at either end of that range the disc rotates. I assume it is part of the manual focus over-ride system and perhaps if itís signal is corrupted in some way it would affect the auto-focus function. Do you have a view on this? Do you have any advice on the best method of checking/cleaning the gap and can you advise what type of optocoupler this is (looking at component catalogues optocouplers all seem encapsulated items without a rotating disc) ?

Suraswami. Thanks for your helpful input. I will check continuity on the ribbon tracks and open the connector on the PCB and clean/re-seat the cable.

I am still puzzled that Liveview operates without problem while the view finder system does not. I appreciate it is a different system using different measuring components but both systems control the lens through the same two power contacts. As far as I can determine the other six contacts provide aperture and lens focal length information from the lens to the camera body.

Any further suggestions for identifying and resolving this problem would be much appreciated.
Forum: Pentax SLR Lens Discussion 05-16-2017, 08:53 AM  
PENTAX DA 18-135mm ED AL IF DC WR Zoom Lens Focus problems
Posted By mcewen
Replies: 8
Views: 1,556
I have seen comments in various forum about auto-focus problems with this lens at particular focal lengths.

My own one has a problem above 50mm focal length. The motor operates but not into focus. Beneath 50mm it operates correctly using auto-focus. It can however be focused manually over the full range of focal length and it does give a green LED when reaching focus. Interestingly in Liveview it does auto-focus correctly over the full Zoom range.

I have tried this lens on two different bodies with the same result so it does seem that the lens is the problem. I also have a second identical lens which does not have this problem when used on either of my camera bodies.

My lens was bought cheaply with this fault present and since it is still usable, albeit manually in the upper range or in Liveview, it would not make economic sense to send it to a repairer so I have decided to make a DIY attempt.

I have undertaken basic repairs and cleaning on Pentax lenses so was happy to partially dismantle it to see if anything obvious was amiss such as bad contacts etc., but nothing has been identified so far. I have attached some photographs in case anyone more knowledgeable on electronics can see any possible problems. (In order to relate the PCB photos to the lens mount the seven large round gold contact points sit against the lens contact springs and the two large rectangular ones are the DC power contacts).

My first thought was that the contacts in the lens barrel (sorry no photo) which feed back focal length position may have suffered damage but they seem OK. I have cleaned them and increased the spring pressure to ensure good contact in future. The ribbon cable connector connecting these contacts to the underside of the PCB was not checked because I was unsure how the locking system worked on this connector and did not wish to risk damage by forcing it. (shown in p5130077 beside my thumb). (Anyone actually know this particular connector and able to tell me how to unlock it? No guesses please.) The cable appears to be firmly attached but it remains an area that I wish to check, clean and re-fit to ensure good contact. The other ribbon cable between the manual focus ring and top side of the PCB (shown in P4240080a) was checked and contacts at both ends seem OK. After these checks the lens was re-assembled but the fault remains therefore I am about to have another go at it and would appreciate any advice.

In addition perhaps someone could explain (or provide a reference) concerning the technical operation of this auto-focus system. I assume the measurement of focus takes place in the camera body and it then feeds power through the two power contacts at the mount to drive the lens focus motor but some more detail would help to understand this process. In particular I am struggling to understand why the lens PCB is so complex with two IC modules etc., particularly since the auto-focus measurement is determined inside the camera.
Forum: Troubleshooting and Beginner Help 04-25-2017, 10:05 AM  
DA 18-135mm ED AL IF DC WR Zoom Lens Focus problems
Posted By mcewen
Replies: 12
Views: 1,465
Hi PLEO. I am trying to find a solution to the problem but so far have not found one but hope to do so. If I succeed I can provide some photos and instructions but I am certain it will involve a significant disassembly of the lens and you will need to be confident in your ability to do this. I have no idea how much a repairer would charge but it is unlikely to be cheap in view of the time involved and possibly component costs.
Forum: Troubleshooting and Beginner Help 04-25-2017, 01:46 AM  
DA 18-135mm ED AL IF DC WR Zoom Lens Focus problems
Posted By mcewen
Replies: 12
Views: 1,465
FilmORbitz and Jeff Lopez. Many thanks for your comments.
The various references to other web sites have been very helpful in particular the Rice High blog spot. His problem with the Pentax DA lens, which has many similarities to the DA 18-135, is almost a carbon copy of my own problem. In addition you will see from my previous reply that I am heading in the same direction ie to investigate the spring contacts on the zoom barrel. Unfortunately with my lens the spring contacts do not seem to be accessible from the outside hence my plan to remove the pcb etc to gain assess. One other difference between these lenses is that the pick-up tracks on mine are mounted in an axial direction on the barrel whereas his are circumferential on the zoom control ring. I assume however that the principle of operation is similar in that the zoom position is fed into the pcb electronics and it somehow influences the focusing motor control signal. If anyone can explain how/why I would be most grateful.
So far disassembly of this lens, in the absence of any service manual or breakdown instructions, has not been too difficult but I suspect the next bit will be more challenging so any hints or tips from people who understand this stage of the investigation would be appreciated.
Forum: Troubleshooting and Beginner Help 04-24-2017, 04:49 PM  
DA 18-135mm ED AL IF DC WR Zoom Lens Focus problems
Posted By mcewen
Replies: 12
Views: 1,465
Jeff Lopez. Thanks for your suggestion. I think the lens elements are OK but will try to check this further. The lens seems optically satisfactory with very sharp images and when operated in manual the focus system recognises a correctly focused image with the usual green LED. The problem is that in auto-focus the motor attempts to focus but drives the lens to an out of focus position. This only occurs above 50mm focal length. Beneath that it is usually OK.
I have now stripped the lens partially and the attached photo shows the pcb above the motor. There does not seem to be any obvious mechanical problem. Focus ring and zoom barrels move smoothly over the whole range. I intend removing the pcb and the casing ring on which it is mounted. This will allow access to the axially mounted "tracks" on the barrel and spring contacts which signal the zoom position back to the pcb. I need to check whether a bad contact in this system is causing my problem. Usually the electronic part of most mechanisms is reliable and it is the mechanical bits that fail so at this stage I do not suspect the pcb or it's components. The fact that this issue only occurs above 50mm also makes me suspect a zoom position feedback problem.
If anyone has had experience of a similar repair or some information about the principle of operation of the focus mechanics/electronics inside the lens their input would be welcome.
Forum: Troubleshooting and Beginner Help 04-23-2017, 02:50 AM  
DA 18-135mm ED AL IF DC WR Zoom Lens Focus problems
Posted By mcewen
Replies: 12
Views: 1,465
FilmORbitz many thanks for your very prompt and helpful reply.
The lens problem is present in good light conditions and with tripod support. The two power contacts have been cleaned and are on the same level and show witness marks from contact with the camera contacts.
I have two of these lenses and can compare the problem lens with the good one so I am fairly confident it is a lens issue.
At this stage I am trying to put together as much information as possible to understand how to dismantle the lens with minimum risk of damage and also understand the auto-focus mechanics so that I can identify the sections of the lens for investigation which are most likely to cause this problem.
My initial thoughts are that the camera body is receiving the necessary input to identify the correct focus point and it is sending the appropriate output to the lens. For some reason at longer focal lengths this output is not operating the focus motor to the correct position other than occasionally but it is operating the focus motor. I have attempted to find some pattern to this and to see if there is any correlation with other factors, for example short range v long range. So far the only thing that has been identified is that autofocus is more successful in liveview but not always successful and occasionally the camera freezes in liveview and can't be controlled with any controls or even turned off! One possible sources of problem is some kind of poor contact or earthing caused by the physical movement at longer focus but I have tested for continuity between each of the two power contacts and the lens mount ring. Continuity response is the same for the good lens and the problem one but I realise this does not rule out completely some issue within the lens electrical/electronic systems.
If anyone can offer further advice on dismantling or problem investigation this would be most welcome.
Forum: Troubleshooting and Beginner Help 04-22-2017, 03:14 PM  
DA 18-135mm ED AL IF DC WR Zoom Lens Focus problems
Posted By mcewen
Replies: 12
Views: 1,465
Hi
I have been reading about this lens on the forum and learned a great deal from the many contributions however I have seen very few comments about auto-focus problems with this lens.
This is perhaps a tribute to the quality of this versatile lens however my own one has a problem but only above 50mm focal length. It occasionally does auto focus OK but mainly the motor drives it well off focus then stops. It can be focused manually over the full range of focal length and it does beep and give a green LED when focused. Beneath 50mm it operates correctly using auto-focus. I have tried it on two different bodies with the same result so it does seem that the lens is the problem.
There is a short thread referring to this problem a couple of years ago but no clear solution was identified although one contributor did cure the problem by dismantling the lens and tightening some screws. Does anyone have any suggestions?
My lens is a second hand one without any repair guarantee and since it is still usable, albeit manually in the upper range, it would not make economic sense to send it to a repairer. I am quite happy to accept the risk of a DIY attempt to fix it but would welcome some advice on this, in particular dismantling guidance. I have stripped and cleaned lenses previously but not a DC motor version.
In addition perhaps some knowledgeable person could explain the basic operation of this auto-focus system. I assume the measurement of focus takes place in the camera body and it then feeds power through the two power contacts to the lens to focus in one direction and if that starts to make it worse it then reverses polarity to change focus direction until good focus is achieved. Is that the way it works? Is there any focus inputs through the lens contacts in particular the seventh one introduced with KAF3?
Many thanks for any help and I will of course feedback details of the outcome of my attempt to overcome this problem.
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