[BigMackCam]

I've used several walk-around, general purpose zooms on my K-3 and never felt that any of them didn't match the camera for IQ. Tamron and Sigma 17-50s plus Pentax 16-85mm, of which I've found the Sigma to be the best overall (though colours and exposure are much better on the 16-85mm). I prefer a good prime for walk-around and they're generally even better than the zooms.

Desipte the fact that it doesn't have the most characterful rendering, I also favour the Sigma 17-50 f/2.8, and it's my regular wide-to-short-tele zoom. It's a sharp lens at any aperture (even wide open) and, aside from some fringing in the edges and corners in high contrast elements of a scene (which is easily resolvable in post), it's an extremely capable and reasonably priced bit of glass...

[Wheatfield]

Just for giggle. Which lenses have you owned and tried.

My experience does bit match yours. Focusing has improved since the k-5. You will find quite a few people who suggest the focusing continues to improve.

Focus throw must be short for autofocus.

Auto focus had to improve since the K5. It could hardly have gotten worse. The K5 AF was why I bought a Katz Eye focus screen.

[BigMackCam]

Auto focus had to improve since the K5. It could hardly have gotten worse. The K5 AF was why I bought a Katz Eye focus screen.

Did you do a lot of artificial / lower light photography with it, Bill?

Honestly, I still shoot my K-5 with AF glass from time to time and I've never had AF accuracy issues (though I don't doubt that those that experienced them). The K-3 and K-3II are better, no doubt, but going back through my K-5 shots I don't find anything significant. Then again, it seems most of them were taken in reasonably good natural light. It wasn't until later on - after I'd bought my K-3 - that I started to become more interested in indoor and lower light photography...

[ZombieArmy]

Full frame lenses should and do in my opinion produce outstanding images because you generally use the sweet spot.

Not always because it can exacerbate diffraction. The lens would need exceptional resolution.

[Wheatfield]

Did you do a lot of artificial / lower light photography with it, Bill?

Honestly, I still shoot my K-5 with AF glass from time to time and I've never had AF accuracy issues (though I don't doubt that those that experienced them). The K-3 and K-3II are better, no doubt, but going back through my K-5 shots I don't find anything significant. Then again, it seems most of them were taken in reasonably good natural light. It wasn't until later on - after I'd bought my K-3 - that I started to become more interested in indoor and lower light photography...

I was shooting in the studio a lot at that time and found the AF worse than useless under the 3K modelling lights. In daylight the AF was OK as long as what I was focussing on was fairly neutral, but throw a strong colour cast subject at it, especially one that had a hint or more of red in it, and it would fail. My understanding was that the K5 was all over the place regarding this issue. I happened to have a very bad one.

[Sandy Hancock]

Not always because it can exacerbate diffraction. The lens would need exceptional resolution.

Would you care to go into more detail about this? I always thought glass is glass, especially if both crop and FF lenses are designed for the same registration distance.

[ZombieArmy]

Would you care to go into more detail about this? I always thought glass is glass, especially if both crop and FF lenses are designed for the same registration distance.

It's most noticeable when you use glass on a system like micro 4/3 or the Q. Since it uses such a small part of the actual image circle it tests the resolution of the lens itself. It's why diffraction hits hard on any lens on the Q when even stopped down a little bit. This usually isn't a problem for APSC because it's not much smaller than FF, but even there a lens can and will diffract sooner.

To put it more simply, a 200mm lens doesn't just become a 1000~mm lens equivalent on a Q without any downsides.

[Sandy Hancock]

To put it more simply, a 200mm lens doesn't just become a 1000~mm lens equivalent on a Q without any downsides.

Yeah, but this thread is about APS-C, not the Q. Diffraction limits on a crop sensor are maybe one stop worse vs full frame, which for all intents and purposes is trivial. I think most of us are aware of that anyway.

[ZombieArmy]

Yeah, but this thread is about APS-C, not the Q. Diffraction limits on a crop sensor are maybe one stop worse vs full frame, which for all intents and purposes is trivial. I think most of us are aware of that anyway.

I don't have the links but there have been tests where certain FF lenses can diffract a lot sooner on APSC. I only used Q as an extreme example.

I'm not saying this is a huge deal, just something to consider.

[kh1234567890]

There are plenty of direct comparison images available around the web for anyone interested in seeing the differences made by leaving out the AA filter when Pentax made the K-5 IIs.

Links please. I've never found one beside unrealistic still life studio test shots. It is an Internet myth.

[BigMackCam]

I was shooting in the studio a lot at that time and found the AF worse than useless under the 3K modelling lights. In daylight the AF was OK as long as what I was focussing on was fairly neutral, but throw a strong colour cast subject at it, especially one that had a hint or more of red in it, and it would fail. My understanding was that the K5 was all over the place regarding this issue. I happened to have a very bad one.

That's why I've never noticed a problem with mine... Almost entirely natural light shooting for me, back then. And yes, I remember the K-5 having a reputation for AF trouble in certain man-made lighting. I don't recall the issue with with AF and red subjects, and I don't think it affected me - but I can't be certain.

That aside, my old K-5 isn't getting a great deal of use these days, though I still like it...

[reh321]

It's most noticeable when you use glass on a system like micro 4/3 or the Q. Since it uses such a small part of the actual image circle it tests the resolution of the lens itself. It's why diffraction hits hard on any lens on the Q when even stopped down a little bit. This usually isn't a problem for APSC because it's not much smaller than FF, but even there a lens can and will diffract sooner.

To put it more simply, a 200mm lens doesn't just become a 1000~mm lens equivalent on a Q without any downsides.

My experience was different.

Several years ago I tested my Q-7 with several lenses at 300mm using a paper target. The Pentax-DA was equally sharp at f/5.6, f/8, and f/11. The Sigma APO got sharper from f/5.6 to f/8, then stayed the same at f/11. I expected that using a better portion of the lens was offsetting diffraction.

But this thread isn't about the "Q".

[Wheatfield]

Yeah, but this thread is about APS-C, not the Q. Diffraction limits on a crop sensor are maybe one stop worse vs full frame, which for all intents and purposes is trivial. I think most of us are aware of that anyway.

Let’s not forget that diffraction limits are not a hard wall where the image is good at one stop and then mush one stop down from there.

[normhead]

My Tess is still shooting her K-5 with great results.

Her favourite lenses, Tamron 17-50, Tamron 90 macro, my DFA 28-105 for more reach in a walk around zoom, and my DA*200 ƒ2.8.
If you pick highly regarded lenses, sharpness and AF shouldn't be an issue. All these lenses produce sharp images on my k-3 which has 50% more pixels, so is much more capable of showing off lens imperfections, If they produce sharp images on my K-3 they are at least 50% out resolving a K-5. Yesterday she got razor sharp images of a Heron in flight, using her K-5 and 17-50 and AF.s,

So what I'm suggesting is, I have no experience with the 17-70, so it could be the lens. That would be great news because there are plenty of great lenses out there. WIth regards to film era lenses, we own at least 10, none of them get used much. You might be barking up a tree going that route. My suggestion would be look for DA* or limited lenses.

Or even lenses like the 35 ƒ2.4 of DA 50 1.8. Both are razor sharp and relatively cheap. If you get soft or out of focus images with those, your camera needs calibrating or a focus adjustment. That is something you might want to explore with your 17-70.

[Mountain Vision]

I've been an owner of a Pentax K-5 for several years now. I got the camera at a discount and at that time I thought it was a pretty good deal. However, throughout the years I've been trying to find a decent walk-around zoom lens for it, without much success.

What I found that literally all of the "digital" lenses don't provide enough quality the sensor otherwise would be capable of. Since I tried many film lenses, I know what the sensor can do, but the obvious caveat there is the lack of focal length on the wide end. Regarding "digital" lenses, another issue has surfaced and that is a ridiculously small focus throw. My Pentax 17-70 has ruined quite a few shots because of inaccurate AF and accurate MF is impossible with that short throw.

It seems to me that Pentax, including competitors essentially killed off APS-C quality by manufacturing lenses meant for full-frame sensors. For me those are prohibitively expensive, not to mention they don't represent a good value (ala I'm not getting a 5 times better camera for 5 times the price). Since I'm a hobbyist, I'm not making money on photography either.

At this point I don't think there is a way to salvage my camera, since there won't be any normal zoom lens for it ever, that matches its sensor. I understand that people will say I wanted too much for too little, but I just wanted to share my experience.

The 16-85 is an outstanding lens. Downsides are it's not 2.8. Upside it's sharp wide open and usable at all focal lengths. Flare and contrast are well controlled when shooting into the light. I'd say it's one of the very best zoom lenses I've ever used when you consider it's focal range, the fact it's WR, the optical quality through the range, the size and price. And I've got a few lenses to compare it to. Including most of the limiteds, DA*s, and FA* glass.

Biggest issue for me is the focus ring. Since there is no infinity focus on it, I have to always make sure I have an additional lens for anything that requires infinity focus, such as star trails.