Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
10-29-2015, 03:53 PM   #1
Pentaxian




Join Date: May 2010
Posts: 6,707
16-50mm won't focus at infinity?

Have you ever heard of this lens or any of the DA zooms not focusing at infinity?

Mine doesn't seem to focus even when the distance chart states it is.. I've tried manually focusing too and it just doesn't seem to achieve focus.. as if there isn't enough travel in the focus ring to get there... even though I can go slightly past the infinity logo on the distance chart... it needs more

It is sharp everywhere else but infinity.. I'm confused.

No, AF microadjustments don't help.. tried that first. Also tried it on a second pentax body and it does the same thing there too.

10-29-2015, 04:03 PM   #2
Pentaxian




Join Date: Jan 2011
Location: New York
Posts: 4,217
It sounds like a lens problem if it's happening with 2 cameras. Something in the focusing mechanism may have slipped or an optical element is misaligned.

Make sure it's not focusing beyond infinity. You may have already tried this, but start with the focusing ring past infinity then use manual focus to see if it reaches focus as you focus closer.

Is this a lens you've had a while? It used to focus okay?
10-29-2015, 04:10 PM   #3
mee
Pentaxian




Join Date: May 2010
Posts: 6,707
Original Poster
It is severely front focusing at infinity.. that is the best way I can put it. it isn't a simple minor front focus adjustment though. But only occurs at infinity.

It seem if I let the camera AF at any other object between infinity and myself it hits it perfectly... just not anything at infinity. But even manually attempting to focus to infinity leads to not enough travel in the ring to achieve sharpness/focus.. even after I've hit infinity on the distance scale.. and then some. Strange.

It seems to be worse at 16mm than at 50mm but is way off on both ends.

Last edited by mee; 10-29-2015 at 04:30 PM.
10-29-2015, 04:32 PM   #4
Senior Member




Join Date: Mar 2013
Location: So-central, MI / Central, IN
Posts: 174
I experienced this with a then new DA* 50-135mm and new K-5 body. I'm quite certain the lens and camera body were near the limits of their AF fine adjustment tolerance ranges but at opposite ends. My original action was to swap the lens with another sample via B&H. The second sample was improved, but still could not focus to infinity. Since B&H (and Adorama) are my favorite retailers- I decided not to swap again for a fault that belonged to Pentax.

Since the lens and body were both sill under warranty Pentax service had me ship both items to them. They reported to have first calibrated the camera body using a master lens, then they calibrated my lens (most likely using my freshly calibrated K-5). I suspect the greatest tolerance discrepancy was with my camera body since two lenses varied but couldn't focus infinity.

Then net outcome of the warranty work has been great. My K-5 has been amazingly precise and repeatable in its AF. The DA* 50-135mm lens improved in AF precision and repeatability in most conditions- but not surprisingly still has a challenging time in low light.

As a side note: I've been convinced that the ability of the K-5 generation to focus accurately and repeatably is highly dependent on being quite accurately adjusted. In other words a certain amount of softness at the sensor (e.g. somewhat minor) can create havoc with the logic, but good definition / resolution at the sensor enables the AF logic to perform much more confidently.

Kevin

10-29-2015, 04:33 PM   #5
mee
Pentaxian




Join Date: May 2010
Posts: 6,707
Original Poster
btw I'm NOT afraid to take the lens apart should there be any way to adjust for this issue.. I would only need the instruction on what to adjust!

This is an old lens.. no warranty here! But it is nice to know it can be resolved at the repair center. I think that might be what I have to do. Ugh. I did NOT want to deal with Precision camera.

---------- Post added 10-29-15 at 06:37 PM ----------

QuoteOriginally posted by One3rdEV Quote
The DA* 50-135mm lens improved in AF precision and repeatability in most conditions- but not surprisingly still has a challenging time in low light.

As a side note: I've been convinced that the ability of the K-5 generation to focus accurately and repeatably is highly dependent on being quite accurately adjusted. In other words a certain amount of softness at the sensor (e.g. somewhat minor) can create havoc with the logic, but good definition / resolution at the sensor enables the AF logic to perform much more confidently.
As an aside.. Does your 50-135mm lens hunt back and forth (over the accurate point of focus) in low light ?

Oh and did Precision perform the adjustments?
10-29-2015, 05:06 PM   #6
Senior Member




Join Date: Mar 2013
Location: So-central, MI / Central, IN
Posts: 174
Hi Mee, It was 2012 and the warranty shop in Chandler, Arizona (CRIS as I recall, I've forgotten the differentiation between CRIS and Precision).

In general my 50-135mm rarely hunts to the point that I often forget that I ever had a problem with. Surprisingly so even in relatively low light conditions. However occasionally in very low light it will catch me by surprise and hunt significantly. Since I don't use that lens very often, I may have to get it out again and test it in order to help quantify its performance a little better or to at least ensure that I am not misleading.
10-29-2015, 05:30 PM   #7
mee
Pentaxian




Join Date: May 2010
Posts: 6,707
Original Poster
Thanks for the info, One3rdEV. Too bad that was with CRIS.. I doubt Precision would be that thorough...
10-29-2015, 06:50 PM   #8
mee
Pentaxian




Join Date: May 2010
Posts: 6,707
Original Poster
BTW if anyone has any other ideas.. please feel free to post here!

10-29-2015, 07:17 PM   #9
Senior Member




Join Date: Jun 2015
Photos: Albums
Posts: 235
KEH might be able to fix it. I think they do flat rate repairs on just about anything. I think.
10-30-2015, 06:02 AM   #10
mee
Pentaxian




Join Date: May 2010
Posts: 6,707
Original Poster
That is only if they can get parts.. I doubt they can. In any case, I emailed them a couple of days before posting my OP here. Still awaiting a response... the fact that we're on day 3 doesn't look good.

So I'm out for other options. Particularly self repair options should there be any.. as I said I'm not afraid to take the lens apart, I'd simply need to know what to look for in repair.. was hoping it was as simple as a few screws adjustment or something.
10-30-2015, 07:39 AM   #11
csa
Loyal Site Supporter
Loyal Site Supporter
csa's Avatar

Join Date: Aug 2014
Location: Montana mountains
Posts: 9,313
QuoteOriginally posted by dcshooter Quote
It came back from Precision with the following problems: 1) Broken hood bayonet was still broken in two pieces 2) Metal outer collar holding the hood bayonet was still bent with no attempt to straighten 3) hood bayonet was now 120 degrees out of position 4) Front grouping, which is normally held on by three set screws, was instead glued back on with a non-standard shim messily placed between it and the barrel. Set screws were missing, and the glue couldn't respond to solvent, so basically any future repair from the front (focus, zoom, etc.) if necessary would no longer be possible. 5) screws that were still in place were not tightened down fully
How very sad to hear of such sloppy, incompetent work.
10-30-2015, 03:24 PM   #12
mee
Pentaxian




Join Date: May 2010
Posts: 6,707
Original Poster
QuoteOriginally posted by dcshooter Quote
It's likely just a slipped infinity stop or retaining screws and can be fixed rather easily.

I would NOT trust Precision. I just got and repaired a lens from another PF member who had sent it in to Precision for repair after a drop that cracked the hood bayonet. It came back from Precision with the following problems:

1) Broken hood bayonet was still broken in two pieces
2) Metal outer collar holding the hood bayonet was still bent with no attempt to straighten
3) hood bayonet was now 120 degrees out of position
4) Front grouping, which is normally held on by three set screws, was instead glued back on with a non-standard shim messily placed between it and the barrel. Set screws were missing, and the glue couldn't respond to solvent, so basically any future repair from the front (focus, zoom, etc.) if necessary would no longer be possible.
5) screws that were still in place were not tightened down fully

If the damage to your lens is what I expect it is, then I could probably fix it for you for WAY less than precision will charge you, and it likely will require no new parts. If you are interested, drop me a PM, and we can discuss the details.

That is awful of Precision.. yet another horror story!


Is it possible you can just tell me what needs to be done? I'm rather handy with a jewelers screwdriver set and my fancy tweezers

I'm attaching some full sized images of the lens today at infinity -- one shot at 16mm, one at 50mm (soft 'OOF.jpg'). Then another between min focus and infinity (sharp 'IF.jpg'). All shot at f/2.8 (the softest ap on the lens).

16mm OOF
50mm OOF

50mm IF

If you think the 50mm OOF looks in focus, please keep in mind I was aiming center point at the tall weeds in the background. The lens distance guide was resting on the infinity logo.

---------- Post added 10-30-15 at 05:39 PM ----------

btw.. I'm getting responses from various places I reached out to for help.

C.R.I.S.'s response:
QuoteQuote:
No, Pentax transported all the equipment, tools and parts to their new service center. I'm sorry we can no longer service any Pentax product. All Pentax repair now go to Precision Camera Repair in Enfield, CT.
KEH's response:
QuoteQuote:
I apologize for the delay in answering your inquiry, I was waiting on an answer from our technician for you. Unfortunately we would suggest that you send the lens directly to Precision Camera for servicing, as they currently perform all of Pentax's warranty work and have all of the calibration tools for the various lenses.
Ricoh/Pentax's response (I asked if they were considering a different provider in the USA and if they sell parts to individuals):
QuoteQuote:
We need to get some information from you: Have you been in contact with customer service? If not, please contact them for assistance. 800-234-0276. RICOH is a Business-to-Business (B2B) company only, and does not sell to consumers (end users). At this time, there has not been any indication regarding a different service provider. PCR has a toll-free number. 800-665-6515 Thanks, Ricoh Imaging
Precision's response:
QuoteQuote:
*imagine the sound of crickets chirping because they never responded back*
10-31-2015, 12:19 PM   #13
mee
Pentaxian




Join Date: May 2010
Posts: 6,707
Original Poster
I've noticed there are 3 screws under the rubber around the focus ring. What do those do?
10-31-2015, 01:31 PM   #14
mee
Pentaxian




Join Date: May 2010
Posts: 6,707
Original Poster
I took it apart down to the SDM but couldn't find a safe way of removing the circuit board and ultimately the zoom ring. Inside the zoom ring connects the metal feelers that touch the metal grooves that tell the lens what focal length it is at. Those feelers look very brittle so I didn't want to risk it.

Ended up putting it back together. Still haven't reconnected the 3 screws under the focus ring though as I'm attempting to determine if they do anything...

A guide or blowout diagram of the 16-50 or really any of the DA* zooms would be handy. Since this one focuses internally it isn't like the FA50 or other infinity focus guides. boo.
10-31-2015, 03:12 PM   #15
mee
Pentaxian




Join Date: May 2010
Posts: 6,707
Original Poster
QuoteOriginally posted by dcshooter Quote
Thee way that infinity is set on this lens looks like it involves either moving the stop against which the tab hits, or moving the position of the ring the tab is attached to (the inner focus ring). The three screws you see under the rubber - are they attached to the outer focus ring you actually grip, or are they inset in holes and screwed into the non-floating inner focus ring? If they are attached to the outer focus ring only, they won't have any effect on infinity focus, since it can float to any position due to the quick shift feature. However, if they are attached to the inner ring, loosening them, focusing on an object at infinity, and making sure the focus scale is at infinity before tightening them back down should solve your problem. If they are attached to the outer ring, by loosening them, you might be able to remove the outer ring entirely and then access the necessary screws/stop on the inner focus ring.
The screws are tiny.. very short thread. I took them out completely.. but see no difference to the performance of the lens. Still takes photos as it did yesterday... things far off are a blur... even though the lens is sitting on infinity.

I think one pretty much has to take this lens completely apart to adjust what you're saying to adjust...
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!
16-50mm won't focus, 50-135mm, 50mm, af, bayonet, chart, distance, focus, hood, infinity, k-mount, lens, light, logic, pentax lens, precision, repair, response, screws, sensor, service, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
SMC Pentax A 100mm f2.8 won't focus at infinity? SointulArt Pentax SLR Lens Discussion 3 05-09-2014 12:12 PM
35mm Flektogon f/2.4 Carl Zeiss - Lens Won't Focus at Infinity bigrex Troubleshooting and Beginner Help 2 03-07-2013 09:52 PM
Vivitar 50mm f1.7 won't focus to infinity ChopperCharles Pentax SLR Lens Discussion 2 05-21-2012 12:47 PM
A 50mm /1.2 won't focus to infinity RXrenesis8 Troubleshooting and Beginner Help 46 07-22-2011 10:11 AM
zentar 16 won't infinity focus?? milapse Pentax SLR Lens Discussion 5 09-26-2008 09:45 AM



All times are GMT -7. The time now is 12:25 AM. | 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