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05-02-2021, 02:01 PM   #1
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Focusing struggles with DA*300mm

Iím trying to figure out if the way my DA*300mm autofocus behaves is normal for the lens or if thereís something off with it. Seems there are lots of reports of its AF being underwhelming, but after a couple of outings with it on my K-3 iii now, Iím getting pretty frustrated.

The lens seems unable to really settle into a happy focus point more often than I would like. Even just trying to focus on a test grid for AF fine tuning, sometimes it will jitter back and forth really close to being in focus and then give me a blinking green hexagon and refuse to let me take a shot. When I first ran into this, I thought that maybe it was that with a long lens and f/4, I didnít have enough light in the basement. So today I put a bright constant light source on the test chart and it still gave me jittery behavior. Even focusing in live view, when I use focus peeking, I find that itís not focusing as sharply as it could.

Out in the field, both shooting baseball last Saturday and shooting birds (both BIF and just standing around or swimming on the lake) yesterday, this jittery behavior is what I experience with it most of the time. Even in AF.S, it often refuses to lock focus.

I bought the lens used in the fall and used it a couple of times on my K-70 and didnít notice as many issues. However, I have a sneaky suspicion that I had the body set to shutter priority and not focus priority, so I wasnít noticing the failure to focus as much. For static subjects, I find it reasonable to work with, since I can use quick shift to fine-tune on the fly when it doesnít lock. However, putting the lens on to shoot anything moving just stresses me out right now.

Anyone have any suggestions on if this is just normal behavior or if thereís something I should look into more carefully?

05-02-2021, 02:18 PM   #2
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Havenít had any issues with mine on the K-1.
Are you sure itís a lens issue?


05-02-2021, 03:14 PM   #3
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QuoteOriginally posted by mtkeller Quote
Iím trying to figure out if the way my DA*300mm autofocus behaves is normal for the lens or if thereís something off with it. Seems there are lots of reports of its AF being underwhelming, but after a couple of outings with it on my K-3 iii now, Iím getting pretty frustrated.

The lens seems unable to really settle into a happy focus point more often than I would like. Even just trying to focus on a test grid for AF fine tuning, sometimes it will jitter back and forth really close to being in focus and then give me a blinking green hexagon and refuse to let me take a shot. When I first ran into this, I thought that maybe it was that with a long lens and f/4, I didnít have enough light in the basement. So today I put a bright constant light source on the test chart and it still gave me jittery behavior. Even focusing in live view, when I use focus peeking, I find that itís not focusing as sharply as it could.

Out in the field, both shooting baseball last Saturday and shooting birds (both BIF and just standing around or swimming on the lake) yesterday, this jittery behavior is what I experience with it most of the time. Even in AF.S, it often refuses to lock focus.

I bought the lens used in the fall and used it a couple of times on my K-70 and didnít notice as many issues. However, I have a sneaky suspicion that I had the body set to shutter priority and not focus priority, so I wasnít noticing the failure to focus as much. For static subjects, I find it reasonable to work with, since I can use quick shift to fine-tune on the fly when it doesnít lock. However, putting the lens on to shoot anything moving just stresses me out right now.

Anyone have any suggestions on if this is just normal behavior or if thereís something I should look into more carefully?
To ascertain if you new K-3 III is faulty use it with focus priority on your K-70. If it works well then I suggest you return the K-3 III. If you get the same mal focusing effect, perhaps the lens needs to be repaired or contacts cleaned(?).
05-02-2021, 03:35 PM   #4
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QuoteOriginally posted by mtkeller Quote
Even just trying to focus on a test grid for AF fine tuning, sometimes it will jitter back and forth really close to being in focus and then give me a blinking green hexagon and refuse to let me take a shot. When I first ran into this, I thought that maybe it was that with a long lens and f/4, I didn’t have enough light in the basement. So today I put a bright constant light source on the test chart and it still gave me jittery behavior.
So far, the only experience I've had with this lens on my K-3 Mark III is to calibrate its AF Fine Adjustment.

I didn't experience any noticeable issue during the AFFA process. The lens locked focus confidently on all shots with a solid green hexagon, albeit out-of-focus on most shots except at or near the optimal AFFA settings, as expected. I don't recall any jittery behavior.

FYI, my methodology was similar to that described in my article: Achieving Better Manual Focus with the Green Hexagon - PentaxForums.com

For the DA* 300, my AFFA setup consisted of a uniformly illuminated planar test chart placed at D = 720 cm (24 x FL). Exposure settings: f/4, 1/100, ISO 100. Center SPOT focus point. I did 7 runs -- 4 from focus preset at infinity, and 3 pre-set at a 'near' distance. I got fairly consistent results across all runs, although my data points were not as tight as I've seen with several of my other lenses.

The only time that I've experienced the type of behavior you describe was with my DA* 50-135mm. Its SDM failed on four different occasions over a 14-month period. In a couple of those instances, the lens would not lock focus at focal lengths beyond ~120mm.

My lens also works solidly on my K-3 II.

Sorry I don't have any specific suggestions, other than a possible SDM failure. Such failures in this particular lens seem to be uncommon, but possible. You may have seen this recent thread: https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/424103-sdm...-concerns.html

- Craig


Last edited by c.a.m; 05-02-2021 at 03:52 PM.
05-02-2021, 03:59 PM   #5
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QuoteOriginally posted by AfterPentax Mark II Quote
To ascertain if you new K-3 III is faulty use it with focus priority on your K-70. If it works well then I suggest you return the K-3 III. If you get the same mal focusing effect, perhaps the lens needs to be repaired or contacts cleaned(?).
I would be shocked if it were the K-3 iii at fault, as I did AF fine tune on Sigma 10Ė20mm f/3.5, DFA 100mm macro, DA 20Ė40mm Ltd, Tamron 70Ė200mm f/2.8, and DA 55Ė300mm PLM at the same time I was doing battle with the DA*300mm. I had tried to do the AF fine tune on the K-70 a couple of weeks back and found it was a struggle with the DA*300mm.

Iíll check the contacts to see if I can spot anything there.

---------- Post added 05-02-21 at 18:06 ----------

QuoteOriginally posted by c.a.m Quote
The only time that I've experienced the type of behavior you describe was with my DA* 50-135mm. Its SDM failed on four different occasions over a 14-month period. In a couple of those instances, the lens would not lock focus at focal lengths beyond ~120mm.

My lens also works solidly on my K-3 II.

Sorry I don't have any specific suggestions, other than a possible SDM failure. Such failures in this particular lens seem to be uncommon, but possible. You may have seen this recent thread: SDM 300 f4 concerns? - PentaxForums.com
Iíve been following the
, which has worked reliably for me on my other lenses and doesnít require me to take a bunch of shots and analyze them on the computer. This is the only lens where I consistently am failing to get a green hexagon. The other ones I have focused in live view and then very quickly find the range of AF fine adjust values for which I get the green hexagon and then set to the median. (Mildly annoying when Ė10 has wound up in the range, but I think Iíve only got one lens where that happened so far.)

I did see the recent thread and thought about hijacking it, but since Iím dealing with an active issue, I figured it would be better to start a fresh thread to see if I was just being too picky about the AF on this lens or if something might be wrong. Honestly, Iím pretty happy with how my screwdrive Tamron 70Ė200mm f/2.8 handles with tracking on the K-3 iii, so converting the DA*300mm to screwdrive wouldnít be the end of the world. Might have to solicit the input of @UncleVanya to see if this sounds like SDM failure or something else.
05-02-2021, 05:28 PM   #6
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I haven't shot mine for a while but I don't recall it doing anything like that.

Have you tried manual focusing with catch in focus?
05-02-2021, 05:50 PM   #7
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QuoteOriginally posted by caliscouser Quote
I haven't shot mine for a while but I don't recall it doing anything like that.

Have you tried manual focusing with catch in focus?
I have not tried that. Might give it a go in some good natural light later this week. It definitely can lock on focus and give me something sharp, but it seems that three out of four times, it hunts a bit and then gives me a flashing green hexagon instead of deciding that focus has been achieved. In live view, it says it has focused, but with extract edge on for focus peeking, I am finding a very small turn of the focus ring gets even brighter lines. Thatís the part that makes me wonder if thereís something more going on here than a potential issue with the SDM. Before rendering a verdict on that, however, I should probably try something like using Image Sync or a cable release for focusing, since the tiniest of movements of the camera, lens, or tripod can mess up focus on that long of a lens in my testing environment.
05-02-2021, 05:56 PM   #8
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I do not think it could be the camera if not other lens acts this way. I have the lens but not the camera. My lens has never acted that way on the four different Pentax cameras I've used it on. It is not the fastest lens to focus, but mine is very accurate (when I am steady).

05-02-2021, 06:10 PM   #9
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QuoteOriginally posted by ramseybuckeye Quote
I do not think it could be the camera if not other lens acts this way. I have the lens but not the camera. My lens has never acted that way on the four different Pentax cameras I've used it on. It is not the fastest lens to focus, but mine is very accurate (when I am steady).
When I was in the field yesterday (and last Saturday), I was mostly chalking up issues to me handholding and not being sufficiently steady. But today I was in my basement with the camera and lens on a tripod and it kept deciding not to settle on being properly focused. It generally gets very close, but when I take a picture by taking my finger off the AF button and pushing the shutter button, the image is clearly not as sharp as it should be.
05-02-2021, 07:11 PM   #10
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Here’s a video of me using the wireless remote to try focusing. You’ll see that sometimes it works and sometimes it doesn’t.


I did check catch in focus, and it works just fine.

I also can confirm that the focus achieved by the AF in live view is not quite where it should be, as I also tested that using the wireless remote’s AF button.
05-02-2021, 08:48 PM   #11
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My lens was extremely slow, sometimes not engaging at all in autofocus before I converted to screw drive. Never saw jittery behavior.
05-03-2021, 12:41 AM   #12
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Well, I would not be shocked if the K-3 III were at fault. It is a new camera and chances are almost non-existent, but every now and again start-up problems may arise. It is a camera with a lot of new technology in it. It could be anything, but maybe it is a small problem with the firmware. First thing I would do is try it out on the K-70. It can of course be a problem with the lens itself. I hope not and then the best thing is that it is a K-3 III problem, that might be shocking, but of the items you mention, the camera and the lens, the camera is the one with the warranty, not the lens.
05-03-2021, 03:02 AM   #13
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You can try to convert the lens to screwdriver AF and check if the behavior is the same.
05-03-2021, 03:03 AM   #14
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I would guess the SDM is starting to get flaky. The only thing to do would be to send it in. SDM is slow, but when it is working right it shouldn't be giving that sort of behavior.
05-03-2021, 04:46 AM   #15
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QuoteOriginally posted by AfterPentax Mark II Quote
Well, I would not be shocked if the K-3 III were at fault. It is a new camera and chances are almost non-existent, but every now and again start-up problems may arise. It is a camera with a lot of new technology in it. It could be anything, but maybe it is a small problem with the firmware. First thing I would do is try it out on the K-70. It can of course be a problem with the lens itself. I hope not and then the best thing is that it is a K-3 III problem, that might be shocking, but of the items you mention, the camera and the lens, the camera is the one with the warranty, not the lens.
Itís definitely the lens and not the camera. As I noted, none of my other lenses act up on the K-3 iii. I also put the DA*300mm back on the K-70, and it exhibits the same behaviors.

---------- Post added 05-03-21 at 06:50 ----------

Of course I just sold the K-7 that came attached to the DA*300mm to MPB, so I no longer have a body on hand capable of doing the screwdrive conversion. Iím thinking that by the time I pay for shipping and @UncleVanyaís time, I might as well stake out a low cost older body to try the screwdrive conversion myself. I could sell the body on again if things get sorted. Of course, if the fact that the lens isnít focusing quite as precisely as it could in live view is a potential sign of something larger that might be wrong, then it may make the most sense to send the lens in to someplace that can properly look it over for repair.
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