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01-02-2014, 12:44 PM   #1
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Focus issue (?) on a slightly used DA* 300

Hi all,

I bought a slightly used, but not so especially new, DA* 300 for my new K3. Still has four months of warranty left on it (out of two years). Cosmetically the lens is mint. And a few shots in the backyard suggest it is optically excellent.

No surprise, it is not great hand held--just too much reach combined with the smaller sensor, max f4 etc., but that reach will be appreciated in many tripod-mounted field circumstances. As is the case with the 18-135 kit lens, this lens has surprisingly good close focus even though Pentax does not claim "macro". From my perspective, both lenses deserve consideration from shooters that need some macro capacity from lenses that are primarily for other things. Stand-off distance is a huge deal when shooting small critters that spook when approached, so a 300mm macroish lens can be a very good thing.

Here's my question: Autofocus seems accurate, when it hits the target, but the lens chronically hunts back and forth in the immediate range of the final setting, so I hear four or five audible clicks back and forth before I get the beep. This does not happen every time, but more than half. And sometimes I get no confirmation, and the hexagon in the viewfinder flashes at me. Happens on a tripod with the SR turned off. Doesn't seem right to me.

I assume this is not the notorious SDM failure issue. It does autofocus. But the clicks are not silent, and the hunting is not like what one sees when the lens doesn't know what range to look in.

Any experiance with this lens, or this issue in another lens would be appreciated. Any possibility the clicks indicate screw-drive is operating?

Thanks,

Bret


Last edited by BretW; 01-31-2017 at 10:16 PM.
01-02-2014, 02:47 PM   #2
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This lens does tend to hunt a bit. Looking at your sample photos, it looks like the focus point is top right on the upper photo and bottom right on the lower one. What is the aperture? With a 300mm lens, the DoF is incredibly thin at low f numbers, especially if you are close to the subject. I try to keep it over 6.3 to get the right amount. But even then, at 10 ft away at f/4, you get 0.05 ft of DoF. You need to be further than 43 feet away to get 1 foot of DoF.

In other words, at small f, if you focus on the moss, the ferns behind will be out of focus unless you're really far away. But my experience with this lens suggests you're not more than 20 feet away or so in the lower photo.

I'm pretty sure the lens is not capable of using screw drive at all, at least not without modification. If it did, people wouldn't be so unhappy when the SDM fails (it could just be a considered a bonus as long as it lasts)--because once it goes, you can only use MF.

One trick I recommend is setting the focus point to center and recomposing. With the shallow DoF of long lenses, it's the best way to guarantee that what you want will be in focus. I just don't trust the autofocus to select the right point otherwise, and when it chooses wrong, the results won't be good. With shorter lenses, if a neighboring point is selected, there's still enough DoF to put the subject in focus. That's not always true at 300mm.
01-02-2014, 03:17 PM   #3
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What you say is true about the low depth of field and the apertures. I the case of these photos, I was not using auto-focus-point-selection. I selected a focus point and either 1) placed it on the thing I wanted the camera to find, or 2) used the center point, auto-focused, then recomposed with AF disabled. In the first shot, I'm less than two meters away. In the second (with the broken log) I'm quite far away (maybe 20m)

My click, click, click... autofocus hunting issue happens irrespective of the autofocus settings, though. And the camera auto-focuses wide open, so the aperture is irrelevant to the hunting behavior. The close up was f4. The log shot was f4.5.
01-02-2014, 03:29 PM   #4
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My DA*300 does the little click thing regularly, but AF is very good and I don't have SDM issues.

I do not get the blinking hexagon with this lens very often, if I do it is because the scene is difficult to AF.
In those cases I let it focus on something it likes then fix it with a manual override using the quickshift.
This is possibly what happened in the second shot.

Screw drive is not active in this lens, the clicks are the SDM working and changing directions.

The first shot at 1/125 is too low speed and could be part of the problem either due to hand movement, shake reduction not enough to compensate, or the breeze moving the leaves out of focus.
try to keep the shutter speed up if you are not on a tripod.

In general I use center spot and recompose if needed, so good advice from MadMathKing.

Personally I have found the sweet spot on this lens is f5.6, which helps in low light environments.
If the scene is bright I just up the shutter speed accordingly, but stay at f5.6.

You may just need some time to get used to the lens, but you can also try confirming that the AF does not need a micro adjustment using your preferred tool.
My lens did not need any adjustment on my K-3.

If you consistently get the blinking hexagon it is very possible your lens has a problem, which could mean a trip to the repair shop, or if you can still return it to the seller you may want to do that instead.

This shot is hand held, AF-S, center spot, f5.6, 1/2000, ISO 200

100%


01-02-2014, 03:37 PM   #5
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From the way you describe this, it sounds like the camera not the lens. The lens is doing what the camera tells it to do.

Since you are getting sharp images once it does lock focus, the camera can't decide what it wants to be in focus. This will happen at times with mine in either low light or low contrast situations.

As a test, try a higher contrast subject in good light at f5.6 as crewl1 suggest - it should lock on very reliably in that scenario.
01-02-2014, 03:48 PM   #6
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Thanks. To be clear, both these shots were tripod mounted, and I'm not saying there is any obvious problem with them. I would say they are both acceptable, though I should reshoot at f5.6 and see if others think this copy of the lens is optically up to snuff. My feeling is that the glass itself is good, and my technique is the only issue on that score. The SDM clicking and ultimate failure is the thing that has me worried.

I am impressed that you could get those buffelhead shots handheld, though. At this point, I can not hold this lens that steady, and in general I have been pretty good at hand holding. Or at least I was with my Canon gear, though I never had an effective 400+mm lens for my EOS...
01-02-2014, 04:07 PM   #7
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QuoteOriginally posted by stormtech Quote
From the way you describe this, it sounds like the camera not the lens. The lens is doing what the camera tells it to do.

Since you are getting sharp images once it does lock focus, the camera can't decide what it wants to be in focus. This will happen at times with mine in either low light or low contrast situations.

As a test, try a higher contrast subject in good light at f5.6 as crewl1 suggest - it should lock on very reliably in that scenario.
I will try that. Maybe right now...

My impression, though, based on lots of Canon experience, and one month of K3 with 18-135 WR kit lens is that the body should be able to interpret the levels of contrast and light I'm dealing with. The kit lens at 135mm is slower than the DA* 300, so the body has more light to work with. The amplification of my movement could cause trouble, but not on a tripod, and I am seeing the clicking problem on a tripod.

Not sure why folks are focused on the aperture setting, though. That affects the shot, clearly, but should have no implication at all for autofocus. Or have I missed something?
01-02-2014, 04:13 PM   #8
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Hmmm so both on a tripod?
Motion should not have been an issue unless you did not use delay or remote and turn off SR? Breeze at 1/125 could have been a factor.

QuoteOriginally posted by BretW Quote
I am impressed that you could get those buffelhead shots handheld, though. At this point, I can not hold this lens that steady, and in general I have been pretty good at hand holding. Or at least I was with my Canon gear, though I never had an effective 400+mm lens for my EOS...
For longer lenses higher shutter speeds help a lot, but also one has to be more conscious of keeping things steady.

I am not that steady but I am getting better.
When possible I will use a monopod or tripod.
For the bufflehead shots I was leaning on a railing but I think the 1/2000 speed was key as well.

Heie wrote a tutorial on long lens technique here: Making the Most of Long Exposure Handhelds - Introduction - PentaxForums.com

I have gone through a progression of long lenses, and now I think that the first few that I tried and felt were not good were really just me not knowing how to use them properly since all my experience was with shorter stuff.

01-02-2014, 04:16 PM   #9
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QuoteOriginally posted by BretW Quote
Not sure why folks are focused on the aperture setting, though. That affects the shot, clearly, but should have no implication at all for autofocus. Or have I missed something?
I was just thinking that shooting more open could let you use faster shutter speed if there were other factors than just bad AF such as motion blur.
On a tripod should not be a factor.
01-02-2014, 04:31 PM   #10
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QuoteOriginally posted by crewl1 Quote
Hmmm so both on a tripod?
Motion should not have been an issue unless you did not use delay or remote and turn off SR? Breeze at 1/125 could have been a factor.



For longer lenses higher shutter speeds help a lot, but also one has to be more conscious of keeping things steady.

I am not that steady but I am getting better.
When possible I will use a monopod or tripod.
For the bufflehead shots I was leaning on a railing but I think the 1/2000 speed was key as well.

Heie wrote a tutorial on long lens technique here: Making the Most of Long Exposure Handhelds - Introduction - PentaxForums.com

I have gone through a progression of long lenses, and now I think that the first few that I tried and felt were not good were really just me not knowing how to use them properly since all my experience was with shorter stuff.

Yes, both were on a tripod with 2sec delay, so SR off.

I'm a big fan of fast shutter speeds for long lenses. And I have used a monopod quite a bit in my rainforest work. But with low light something (ISO, shutter speed, tripod when there is time) has to give. I'm thinking that as much as possible I want to shoot this lens f5.6 or smaller, and if hand held, a 300th of a second is risky even with SR due to the extra reach created by the small sensor.

I have read Heie's tutorial. Great stuff. It takes a marksman to crystallize the matter

What I really want to know is if this lens is not functioning well, if the K3 is interpreting the focus poorly through this lens, or if this lens/body combo is less than optimal for moderate light shooting.
01-02-2014, 05:00 PM   #11
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Afc or afs? On my k3 if the light is existent it is quite positive. You could be running into low light uncertainty. With afc it will jitter a bit.

I got one new and couldn't get accurate focus. There were some focus mechanism parts that finally gave out, now it is right on and positive.
01-02-2014, 05:03 PM   #12
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I just tried shooting a hummingbird that was in some dense tree branches and saw the behaviour you describe.
The lens will focus in and out and give up with the hexagon blinking.
I had to switch the AF setting to back button only and used the quickshift to pin it down. (Button customization AF2)

I swapped to the DA18-135 on the camera and the AF was more confident, it would lock right away and did not give the blinky hexagon once. The tree branches did not cause any problem.

So it seems from that perspective my DA*300 behaves like yours.
01-02-2014, 05:23 PM   #13
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QuoteOriginally posted by derekkite Quote
Afc or afs? On my k3 if the light is existent it is quite positive. You could be running into low light uncertainty. With afc it will jitter a bit.
I was on AFS. AFC was near hopeless at this light level.

QuoteOriginally posted by derekkite Quote
I got one new and couldn't get accurate focus. There were some focus mechanism parts that finally gave out, now it is right on and positive.
So this is interesting. If I understand what you have said, a brand new one had symptoms from the start, then it failed, but the repair made it better than it was when it was new.

Do I have that right?
01-02-2014, 05:34 PM   #14
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QuoteOriginally posted by crewl1 Quote
I just tried shooting a hummingbird that was in some dense tree branches and saw the behaviour you describe.
The lens will focus in and out and give up with the hexagon blinking.
I had to switch the AF setting to back button only and used the quickshift to pin it down. (Button customization AF2)

I swapped to the DA18-135 on the camera and the AF was more confident, it would lock right away and did not give the blinky hexagon once. The tree branches did not cause any problem.

So it seems from that perspective my DA*300 behaves like yours.
That's very interesting. I can't figure out if it is good or bad news.

I have my K3 set so the AF button on the back suspends autofocus, which amounts to the same thing as I use it--compose with AF then get it to chill out. Nothing worse than having a shot composed, and then having the autofocus get distracted (as the opportunity inevitably evaporates).
01-02-2014, 06:57 PM   #15
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QuoteOriginally posted by BretW Quote
I was on AFS. AFC was near hopeless at this light level.



So this is interesting. If I understand what you have said, a brand new one had symptoms from the start, then it failed, but the repair made it better than it was when it was new.

Do I have that right?
Yes. I bought it late 2012 on black friday and used it with the K5. It worked, but focus was unreliable. I was with another pentax shooter who had the same setup, and his was much more positive than mine, even on the K5. Shortly afterwards it quit. After repair it is right on and works very well on the K3. Extremely well in fact.

I use AFC by default, and find it pretty good even at low light levels. Single point focus. It will jitter somewhat when the contrast is very low along with low light, and I use the back button to focus and let go when it is on.

I think you may have an issue with the lens. Try it in good light with good contrast, and it should lock focus reliably without hunting. On a tripod what I do is focus on something with live view, then switch to viewfinder and hit the half shutter or af button to focus using pdaf. If it moves, the focus needs adjustment. If it hunts in good light and contrast, something is wrong. If you can try another body, that may help eliminate the body as the source of the problem. I know this is a pain in the neck, but if you send it in, send the body in as well. When you say two year that may mean Canada, and the Pentax repair in Mississauga is quite good. Whenever I get my stuff back I'm amazed at how good it is when everything is dialed in. Since you are close to the end of warranty, I wouldn't hesitate to send it in. It is hard to figure sometimes if it is technique or something wrong with the equipment, but I would definitely assert that the K3 with the DA*300 is fast, accurate and positive when it comes to focus. If yours isn't, then something isn't right. Of course technique can ruin the best, and I have hundreds of shots to prove it, but I have been able to get great results with that combination.

A blame nuisance I know. I have kept my K5 as a backup body for when the seemingly inevitable repairs are needed on my K3.

I wrote of my AF experience with the K3 and DA*300 in this thread: https://www.pentaxforums.com/forums/172-pentax-k-3/241586-my-k-3-af-experiences.html

Last edited by derekkite; 01-02-2014 at 07:06 PM.
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