50-135 2.8 SDM

Text lifted from SRS.

Innovative SDM System for smoother, quieter autofocusing operation

These two new SMC PENTAX-DA_ zoom lenses come equipped with a new SDM System, which assures smoother, quieter autofocusing operation using a built-in supersonic motor. When mounted on the PENTAX K10D digital SLR camera body, the focus mode is

automatically switched to SDM-assisted autofocusing. When mounted on other PENTAX digital SLR camera bodies, the conventional autofocus mode using a camera-mounted motor is selected.

Question.
Do the SDM lenses focus quicker than non SDM lensesl?
I shoot quite a few running events over the year by its nature I am shooting a moving target usually closing in on me. Therefore if a SDM could maintain continous focus that would be great.
Does anyone have any thoughts or experience in this field with this lens?
Jason

SDM lenses focus very quickly, and pretty much silently.

G

Thanks George.

The quietness aspect has never been an issue for me as usually surrounded by spectators shouting encouragement. A different story for the wildlife shooter no doubt.

Have lost shots in the past when the AF (istD/K10D) could not keep up with the changing distance. So if this lens helps then a trip to SRS in May will be in order.

Jason

I have found both the *ist D and the K10D to be able to track flying birds quite well (using non-SDM lenses - the F 300mm 1:4.5 in particular).

I would expect SDM lenses to perform rather better, but there is a certain knack required on the part of the photographer - you have to keep the subject in the centre of the viewfinder, and with birds that is not always easy.

My only SDM lens is a 16-50, which is not really a sporting or wildlife lens. Unless you count elephants at the zoo.

G

The 300mm DA* certainly feels faster and more accurate to me than other lenses I have at a similar length. I'm not 100% sure that it definitely is, or whether the fact that the focus is nearly silent makes it seem so, though.

As George says, tracking moving objects really is an art in itself. If you're already used to doing this, I don't know how much more benefit SDM would really give you.

I was using my 50-135 to photograph my son throwing snowballs yesterday evening and it performed very well on continious focus and multi shot drive mode.

I have been looking at the continious focusing and it seems very quick, however, I have not tested it against any of my other lenses. The bright 2.8 optic helps and I have heard that focusing is up to 10% faster. I have yet to put the images on the big monitor, but they looked sharp on the LCD.

I haven't evaluated it in any scientific way, but I get the strong impression that SDM is much faster than ordinary focussing, especially on longer lenses.

But I see no reason why it should be more accurate.

G

SDM lenses are focusing faster than non SDM lenses. For tracking a subject moving across the frame is no big deal, even for non SDM lenses. The problems arise when your subject is moving away/toward the camera. When you depress the shutter,even on AF-C, the camera will freeze the focus because the AF sensor "loses" the subject. So, in this situation, your focus will lag behind your subject. The faster the subject, the larger the focusing error. That's the reason everybody is trying to make a predictive focus. If a racecar is moving toward you at 200 km/h, the af won't keep track of it when you "clik" the shutter. If your depth of field is good enough, then it is a mitigating factor.

I've been doing a few shoots at courts recently, capturing naughty people going in and out, and I would say out of all the shots walking towards me 50% are out of focus, 30% are OK, 20% good.

On at least one occasion whilst on AFC whilst holding the trigger down, it went about 2 seconds between shots, as it just would not lock on to a moving target. Last week as an example, went down to Aylesbury Crown Court to shoot Olly Barclay (England rugby player), he came out of a taxi about 10m behind us, turned, hit the shutter and got..... nothing, wouldn't even fire, all the while the Canon 1D's were going like machine guns. On the way out of court, he stood at the door for a second or so, went to shoot, got him, but as he walked down the steps, focussing went.

My experience seems to be that it feels a lot faster because it is quiet, my other non SDM lenses do seem to focus at about the same speed. Not definitive I know, but not quick enough for 'point & shoot' at a moving target.

Technique seems to be the obvious answer here, just gotta learn it! I'm not going to sit here and complain that the Pentax AF system is poor at moving targets, because what I have is 4x cheaper than what my cousin was shooting with, and when I get the shot right, it's just as good as what he gets!

A couple of examples




literally 2-3 secs later




Although this is my favourite lens, I'm not sure wether it's my technique, or if my K10D needs calibrating with my SDM lenses, I've read of several people who have done this, seems to focus better afterwards. Even my comp entry last week, the owl was stationary, and it was commented that it could have been sharper, even though shot at f7.1.

So to put it in a nutshell, feels very impressive but the results should be better more often. Could be the lens, could be a front / back focus issue with the camera, more than likely my technique!

It looked absolutely spot on to me. It was one of Belinda's few comments I didn't agree with.

Dan

Someting interesting to test would be using a much faster shutter speed. A target moving towards you at f2.8 may be in focus when the camera locke on, once you have fired off a shot at, say, 160th depending on the spead of the object it will have moved out of the zone of sharpness.

re: owl pic

My guess is that the lens was focused slightly in front of the owl and the DOF was enough to make the beak and eye sharp.

EDIT: On second thoughts, the tuft of feathers in the front is slightly softer, therefore I now think the focus was spot on!

Some people might have liked some more dgital sharpening, but it would have looked less natural then.

You should have your camera checked. On AF-C, it should fire as soon as you press the shutter, it doesn't make a difference if the focus is locked or not. On AF-S, it should not fire if focus is off.

Does SDM focus faster than non-SDM? No it doesn't! It may give that impression but SDM doesn't work faster. How come I'm so sure? Because I tested! When I got the DA*50-135/2.8 I hadn't upgraded the firmware on my K10D yet, so I tried it with traditional AF comparing it to some other screw drive AF lenses. Then I upgraded my K10D for SDM and the AF speed remained pretty much the same!

So, even if there may be differences in speed between some SDM lenses and some non-SDM lenses, the difference is not because of the SDM.

Cannot do the same test on the K20D because that supports SDM from the start and will never use screw drive on the DA*s...

SDM does seem faster because it slides into focus and does so very quietly. Screw drive focus is more abrupt and noisy.

hth,

Wim

Could you post some times please?

A comparison between the time, in milliseconds, for a focus travel from infinity to a given point.
Then the time from minimum focus distance to that same point.
A measurement each for SDM and Non-SDM focussing should be enough.
Light measurements would help.
Finally, may we know what equipment you used to make these measurements?