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01-04-2018, 09:31 PM   #1
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PLM autofocusing, is it really that fast?

I have an HD DA 55-300mm f/4-5.8 and a DA* 50-135mm f/2.8, and I find myself missing focus on a lot of shots with either lens because the subject was small/low-contrast or it was moving and the autofocus took too long to acquire at first or couldn't keep up with the movement or a combination of both. Anyway, I've had a lot less success with either of these lenses for wildlife and sports than I would like to have.

I know the camera body is largely to blame for AF tracking failures, but people seem to really praise the new 55-300mm PLM lens for fast autofocus. I have experience with an HD DA 16-85mm lens, although I don't own one right now. The autofocus on that lens was certainly a little more decisive than other Pentax lenses I have experience with, but when I used it for action, I had mixed results.

Is the PLM focusing of the new 55-300 lens really that good, or do people just praise it because it's better (by comparison) than the screw drive of the previous HD DA 55-300mm lens? Has PLM been faster for you than your experiences with DC and SDM autofocusing? Is there another modern zoom lens for Pentax that I should look at in the medium telephoto range instead?

01-04-2018, 09:42 PM   #2
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Yes, it really is that much faster than any other Pentax AF lens, at least the ones that I have used.
01-04-2018, 11:26 PM   #3
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Yes, the PLM 55-300mm is much faster than the other versions, and also faster than any other DC, SDM, or screwdrive lens. It almost feels instant from the time the camera gives the command.

You can see a great example in the video on the AF page:

HD Pentax-DA 55-300mm F4.5-6.3 PLM WR RE Review - Introduction | PentaxForums.com Reviews

It seems that one drawback to PLM is that it is only suitable for "light" lenses, hence it cannot (yet) be deployed in the larger ones. The D FA* 50mm will debut a new type of ring motor, though, so we may be in for a treat there.

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01-04-2018, 11:45 PM   #4
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QuoteOriginally posted by Adam Quote
Yes, the PLM 55-300mm is much faster than the other versions, and also faster than any other DC, SDM, or screwdrive lens. It almost feels instant from the time the camera gives the command.

You can see a great example in the video on the AF page:

HD Pentax-DA 55-300mm F4.5-6.3 PLM WR RE Review - Introduction | PentaxForums.com Reviews

It seems that one drawback to PLM is that it is only suitable for "light" lenses, hence it cannot (yet) be deployed in the larger ones. The D FA* 50mm will debut a new type of ring motor, though, so we may be in for a treat there.
Another focus motor? So that'll be four by my count - SDM, DC, PLM and this new one. Pentax should concentrate on replacing old lens designs (such as the DA*s), especially the focus motors used, rather than bringing out new ones.

01-05-2018, 12:18 AM - 2 Likes   #5
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QuoteOriginally posted by Jonathan Mac Quote
Another focus motor? So that'll be four by my count - SDM, DC, PLM and this new one. Pentax should concentrate on replacing old lens designs (such as the DA*s), especially the focus motors used, rather than bringing out new ones.
It's not only the motor itself that matters. It's also the optical design that can make a lens faster to focus. The PLM lens focus by moving a small and light lens group in the rear of the lens, while traditional DSLR lens focus by moving a larger and heavier lens group in the front of the lens. It's this change in optical design that made it possible to use the PLM motor, which is fast but not strong enough for older lens design.

So it't not going to change much by just replacing a motor in an existing lens design.

I believe the main problem with the DA* focusing speed is because of the dual focusing system . With both screwdrive and focus motor they had to sacrifice AF speed for backward compatibility. It may be possible to remove screwdrive and redesign AF mechanism to make DA* lenses focus faster.

Last edited by Fogel70; 01-05-2018 at 12:35 AM.
01-05-2018, 12:29 AM   #6
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QuoteOriginally posted by Gimbeley Quote
I have an HD DA 55-300mm f/4-5.8 and a DA* 50-135mm f/2.8, and I find myself missing focus on a lot of shots with either lens because the subject was small/low-contrast or it was moving and the autofocus took too long to acquire at first or couldn't keep up with the movement or a combination of both. Anyway, I've had a lot less success with either of these lenses for wildlife and sports than I would like to have.

I know the camera body is largely to blame for AF tracking failures, but people seem to really praise the new 55-300mm PLM lens for fast autofocus. I have experience with an HD DA 16-85mm lens, although I don't own one right now. The autofocus on that lens was certainly a little more decisive than other Pentax lenses I have experience with, but when I used it for action, I had mixed results.

Is the PLM focusing of the new 55-300 lens really that good, or do people just praise it because it's better (by comparison) than the screw drive of the previous HD DA 55-300mm lens? Has PLM been faster for you than your experiences with DC and SDM autofocusing? Is there another modern zoom lens for Pentax that I should look at in the medium telephoto range instead?

For fast moving subjects like birds in flight , with the HD DA 55-300mm f/4-5.8, one little thing I do is prefocus, which is like a standard procedure among wildlife photographers as it reduces focusing time and eliminates hunting. Doing so reduces the amount of travel required of the lens to snap into focus. But you could also get by just by turning the focusing ring to about the 10m mark on the ring before shooting, or somewhere between 10m and infinity. I find that it really snaps into focus almost instantly after this.
01-05-2018, 12:56 AM   #7
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Yes the PLM version is faster, and I think, noticeably sharper also. I love mine, silent and accurate.
01-05-2018, 03:39 AM   #8
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It's really fast -- particularly in comparison to your current lenses. Both the DA *50-135 and the older 55-300 are quite slow to focus (but excellent lenses otherwise).

01-05-2018, 04:30 AM - 4 Likes   #9
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Check this:

I have used the K-70/PLM lens combo for shooting airplanes with a very high keepers rate (90%+), I don't know how the older lenses would have performed.
I'm very satisfied, some examples:







Cropped:
01-05-2018, 06:54 AM - 2 Likes   #10
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QuoteOriginally posted by SSGGeezer Quote
Yes the PLM version is faster, and I think, noticeably sharper also. I love mine, silent and accurate.
You have very eloquently summarized the down side of said lense for us "Old Guys". "Silent" who knows after her Majesties Naval Guns have fired 20' from your ears or after spending 8 hours a day 4000' underground listening to the scream of a 4 cylinder JV Diamond Drill. Back when Men where Men and didn't need ear protection ! I have a Bigma 150-500 DC and miss 115% of my shots because I'm always looking at the big end to see and make sure if its turning while trying to focus on that distant prize. I've even tried putting beach sand down the big end so I can hear it turning ; then it stops turning altogether. "Accurate" How do we know? We're looking through our good eye that's being adjusted by the broken end of a beer bottle at an image this big. "Faster" hardly f4.5 - 6.3 up against the Super Fast f4 - 5.8 of the 55-300 Screwd Drive


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01-05-2018, 07:25 AM   #11
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QuoteOriginally posted by Andy Fern Quote
For fast moving subjects like birds in flight , with the HD DA 55-300mm f/4-5.8, one little thing I do is prefocus, which is like a standard procedure among wildlife photographers as it reduces focusing time and eliminates hunting. Doing so reduces the amount of travel required of the lens to snap into focus. But you could also get by just by turning the focusing ring to about the 10m mark on the ring before shooting, or somewhere between 10m and infinity. I find that it really snaps into focus almost instantly after this.
This past december holiday I again tried some BIF shots with a first generation 55-300 (not sure how many generations currently exist) on a K100D. Put lens on infinity and try to autofocus and it always goes to minimal focus distance and next back to infinity; somewhere in between I have lost the bird

I will try the 10 meter trick the next time.

PS
I never understand why I end up attempting BIF when I carry the K100D and not the K5 which might give me (I guess) a better chance.
01-05-2018, 07:38 AM   #12
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It really is fast. I'm using it on a K3II, and it is near instant. AFC actually becomes viable, but I will say that when I use AFC on my dog running at me (German Shepherd that can cover a lot of ground quickly), it will track her, but it seems the back half of the dog will be in better focus, not as much her face, as she's running directly at me. Now, this is the fish riding a bicycle at you scenario that we all laugh about, but none of my other lenses would have any part of the dog in focus, and at least this one gets the back half sharp and the front half good enough when not pixel peeping. Again, this is running full speed right at me. Otherwise, it locks on to the birds etc. plenty fast. There is no way my earlier DA 55-300 would have done as well. It was worth the upgrade, and I believe it's still on a nice sale at B&H for $75 off the normal price - down to $371.95 - a good snag if you're in the market.
01-05-2018, 10:30 AM   #13
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QuoteOriginally posted by honey bo bo Quote
You have very eloquently summarized the down side of said lense for us "Old Guys". "Silent" who knows after her Majesties Naval Guns have fired 20' from your ears or after spending 8 hours a day 4000' underground listening to the scream of a 4 cylinder JV Diamond Drill. Back when Men where Men and didn't need ear protection ! I have a Bigma 150-500 DC and miss 115% of my shots because I'm always looking at the big end to see and make sure if its turning while trying to focus on that distant prize. I've even tried putting beach sand down the big end so I can hear it turning ; then it stops turning altogether. "Accurate" How do we know? We're looking through our good eye that's being adjusted by the broken end of a beer bottle at an image this big. "Faster" hardly f4.5 - 6.3 up against the Super Fast f4 - 5.8 of the 55-300 Screwd Drive


Sincerely
Some Old Guys
Another old guy wrote,
I understand, I meant that it focuses faster, not that it is a faster lens. As former infantry, then a guy with hundreds of hours sitting next to ( <1M ) turbine engines in a Black hawk, I understand the comment completely. "Huh," and "Say what?" are my standard replies to my spouse if I am not looking directly at her.
01-05-2018, 04:52 PM   #14
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I tried it out in the showroom of a local camera store on a K3-II. It's so fast I was just focusing on all sorts of things. If I didn't need the DA15 I would have bought the 55-300 right there just so I could enjoy it more. It's quiet too. I don't care much for the switch for the zooming feature but that is minor. PLM is great and by now if there were any inherit problems with it like SLM had, we would have heard already. If you can use that focal range and don't mine the rather small maximum aperture, it's a no brainer.
01-05-2018, 06:39 PM   #15
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It is really fast. I had mine for two years. Its immediately noticeably faster than my DA 16-85 (DC) and DA 15 and 21 Limiteds (Very fast screwdrive) lenses which were my fastest focusing lenses. That is until I got the PLM. It will get birds in flight better than any other Pentax lens I tried including HD DA 500-300 screwdrive and DA* 200 and 300. It is also truly silent.
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