[VictorDA]

If size/weight are a concern, I would suggest the FA 28-70 (constant F/4). It's really a nice little lens and goes wider than the 35-70. The rendering is more modern than in the F series. It also can be had quite cheap (€50 in EU, or sometimes even cheaper attached to MZ bodies). Downsides are some distortion and significant vignetting (on full frame; much less relevant on APS-C). Also be careful to the used condition, this lens has a reputation for element separation generating a very dense white fog in the back. Over time I got 1 defective and 2 perfectly fine copies.

Otherwise and if you don't need wider than your 21, probably the most qualitative "slow" option would be the D FA 28-105.

28-70 on K-1:

Attached Images

 

[nandystam]

If size/weight are a concern, I would suggest the FA 28-70 (constant F/4). It's really a nice little lens and goes wider than the 35-70. The rendering is more modern than in the F series. It also can be had quite cheap (€50 in EU, or sometimes even cheaper attached to MZ bodies). Downsides are some distortion and significant vignetting (on full frame; much less relevant on APS-C). Also be careful to the used condition, this lens has a reputation for element separation generating a very dense white fog in the back. Over time I got 1 defective and 2 perfectly fine copies.

Otherwise and if you don't need wider than your 21, probably the most qualitative "slow" option would be the D FA 28-105.

28-70 on K-1:

Thanks. I have looked at the 28-70, do you happen to know which country of manufacture your lenses were? From what I have read the made in Japan lenses seem to be optically 'better' but can have the lens separation you mention. However, the made in Vietnam models seem to be poor copies? I don't know if that is consistent behavior or someone was just unlucky.

[robgski]

Another vote for the DA 18-135 WR with the K-5. I travelled with this combo for 6 months and seldom felt the need for another lens.
Great lens often found here on PF marketplace at a very good price.

[photogem]

I think that for the intended use the HD DA 16-85mm would be a better fit

I agree and throw the old DA 16-45 as a super-wide-angle zoom in.
But only if in really excellent condition (or new, but difficult to find). If it has a wobble, forget it, doorstopper at the best.
The Sigma 17-70/2,8 Macro Contemporary is very good.


The extra 1 or 2 mm make it special for landscape but it seems that you prefer there the DA21 which is a wonderful lens, I have it and like it very much.
But if you haven't purchased it yet: The DA20-40 ltd is a really great zoom, light, fantstic built quality + WR.


If 21mm with the DA21 is enough for wideangle:


The F35-70 is a light and small and very good lens with a kind of 1:4 macro at 70mm.
Far superior to the terrible FA28-70/4, to me one of those F or FA zooms I'd never even consider anymore! I never came across a sparp good copy.


A good copy of the F35-105 is good as well, the F35-135 I never had.

Stay away from the FA28-105/3,2 (IF)! Sadly the AF kind of mechanically hits hard at both ends too fast and then is slightly out of alignment!
Maybe it was good with the motor of a MZ30 or MZ60 but not the strong motor of the K5!

Too bad because otherwise it would be very good, has the special ghostless coating as well.

[UncleVanya]

40-120 on full frame translates to around 26-80 on crop. Given that the 18-135 is close to perfect. Generally the border quality issues are not a problem until after 70 or 80mm. As a bonus the range of 18-28 would provide additional flexibility, and focal lengths longer than 80mm are very useable all the way to 135 (similar angle of view to 200 on FF) as long as a mostly centered subject is the primary aim. In essence you’d have a 26-80 with Extra length and width baked in for when you need it.

As for the 16-85, it absolutely seems to be a good match, but I’m not recommending it for a few reasons:

1) cost - it’s significantly more expensive than the 18-135.

2) lack of personal expertise with the lens.

3) to a small degree, weight and bulk. Your coming to us from m43 and I suspect lighter will work better.

[VictorDA]

Thanks. I have looked at the 28-70, do you happen to know which country of manufacture your lenses were? From what I have read the made in Japan lenses seem to be optically 'better' but can have the lens separation you mention. However, the made in Vietnam models seem to be poor copies? I don't know if that is consistent behavior or someone was just unlucky.

Nope, I got only Vietnam ones (including the lame one as well as the one I still have and that took the attached picture this summer)!
I read the same thread as you did some time ago, but my guess is just poor luck and extrapolation.
However, buying from someone who knows what they're selling (and have a minimum degree of honesty) should save you of this trouble (or buying locally if that's an option). I think most of the cases with problems happen when the buyer takes a gamble (ie buying from someone who clears out their parents' house, etc). In my case I bought a dirt cheap (think it was €10) MZ-6 + 28-70 "as is", and it turned out that it was junk.

Good luck

Edit: I can add that I also had, and liked the 18-135mm a lot with my K-5 and K-3II. It's rather cheap 2nd hand, a safer buy, and worthwile considering as an alternative indeed, even though its range is much larger than your request. Probably not as good as the 28-105 though. But you did not exactly indicate a budget?

[ChristianRock]

I agree and throw the old DA 16-45 as a super-wide-angle zoom in.
But only if in really excellent condition (or new, but difficult to find). If it has a wobble, forget it, doorstopper at the best.
The Sigma 17-70/2,8 Macro Contemporary is very good.


The extra 1 or 2 mm make it special for landscape but it seems that you prefer there the DA21 which is a wonderful lens, I have it and like it very much.
But if you haven't purchased it yet: The DA20-40 ltd is a really great zoom, light, fantstic built quality + WR.


If 21mm with the DA21 is enough for wideangle:


The F35-70 is a light and small and very good lens with a kind of 1:4 macro at 70mm.
Far superior to the terrible FA28-70/4, to me one of those F or FA zooms I'd never even consider anymore! I never came across a sparp good copy.


A good copy of the F35-105 is good as well, the F35-135 I never had.

Stay away from the FA28-105/3,2 (IF)! Sadly the AF kind of mechanically hits hard at both ends too fast and then is slightly out of alignment!
Maybe it was good with the motor of a MZ30 or MZ60 but not the strong motor of the K5!

Too bad because otherwise it would be very good, has the special ghostless coating as well.

Very good recommendations and very good points. I did not know that the FA 28-105 3.2 loses its focus alignment that easily, perhaps it was just your copy?

Regarding the DA 16-45mm, I think you are spot on in regards to image quality. But at tis point it's a budget option - excellent performance (IMHO) but a weak build means it will probably start to have its barrels come lose (known as the "lens wobble") and that brings decentering. Which is what happened to mine.

When that happened I bought the old SMC DA*16-50mm f/2.8 HSM. Mine was very cheap as it was converted to screw drive (HSM motor had failed). It's not a perfect lens - auto-focus is very hesitant and keeps making micro-adjustments until locking focus. But I would say that it might be one of the best lenses in the Pentax lineup for scenery and landscapes, at any focal length (provided you stop down at least to f4). Micro-contrast is fantastic - it really gives better results than, for example, the DA 21 Limited at the same focal length. While the DA 16-45 is really good, the 16-50 is a clear step up. The amount of detail that it captures, including the color definition, is fantastic. Not a small lens, especially for the OP coming from M4/3 but I think its quality is amazing for that application. But it also doesn't reach further than 75mm (FF-equiv). Which is why I ended up recommending having a look at the DA 16-85 - I don't have it but its users that do landscapes speak very highly of it and show great results from it.

[photogem]

Very good recommendations and very good points. I did not know that the FA 28-105 3.2 loses its focus alignment that easily, perhaps it was just your copy?

Sadly not, I could test it on 3 copies: It is known to produce that problem. It is built too light and focuses too quick but hard. The mechanism really hits with a noticable sound and the shock produces the misalignement. It hits the focus point (particular at the long end), you get confirmation and then it tries to focus again, often going right down to the other end and then up again. So one could say it overrides if that's the correct way of putting it.
If you have a Katzeye split-image and focus manually it is an excellent lens.

Regarding the DA 16-45mm, I think you are spot on in regards to image quality. But at this point it's a budget option - excellent performance (IMHO) but a weak build means it will probably start to have its barrels come lose (known as the "lens wobble") and that brings decentering. Which is what happened to mine.

I know very well about the problems. It was designed by one of the best lensdesigners. I had the chance to talk to one of the best (vintage) repairers who worked for Pentax in USA. I had contacted him because of the FA31 and some questions I had. He told me that the DA16-45 was designed on the same floating principle but being a zoom it was much more complex to align.

The wobble usually happens when the at 16mm and full out (reverse zoom) and then hits something.
I have two of them, one is pretty old and always with an unsellable K5 in my car (had rough treatments). And it still works fine. but I never hit anything (nor anybody) with this lens.


I think the DA*16-50 is good indeed, but:

When that happened I bought the old SMC DA*16-50mm f/2.8 HSM....

sadly it isn't HSM ... sure a typo... but SDM. HSM would be fantastic.

I had it for a time also screwdrive converted and agree, it is much underrated. But a bit large and heavy.
I don't like big lenses. That's why I was happy when the DA55-300PLM came, too bad it won't work on a K5 or K5IIs, a scrilege I won't forgive Ricoh
because I love the K5IIs.

[mikesbike]

and a K-5 series camera (which I'm still to purchase)

For the K-5 series, I highly recommend the last version- the K-5 IIs. The "s" means the AA filter has been omitted. I have that and the original K-5. The IIs has several other upgrades, including improved AF. It can deliver superior fine detail in images due to the absence of the filter. All subsequent Pentax DSLR designs no longer include this filter. I also have the KP and the K-1 II, yet I still have a high regard for this camera and still use it sometimes for its fine imaging and great controls and layout. With patience, you should be able to find one in fine condition and moderate usage.

---------- Post added 11-19-21 at 01:44 PM ----------

The range of 40-

I am looking for an AF zoom lens that would cover somewhere around 40-120 (35mm equivalent) range

The APS-C equivalent would be about 28-80mm. The new DFA 28-105mm lens, as clackers suggests, would be ideal and would offer yet more reach. It has been given very fine test reviews. It has excellent fast, quiet AF and WR construction to complement the K-5 construction, and its price is reasonable for what it is. Since it is made for FF use, it will be there for any Pentax FF DSLR body that might be in your future.

---------- Post added 11-19-21 at 02:05 PM ----------

I am building up a travel kit based on the DA 21mm limited

This is a very good lens in general. Small and light for portability and with a versatile WA, wide but not too wide. However, with your stated concern for edge and corner performance, this lens must be stopped down for decent edges, and even then not a result to write home about as far as the edges are concerned, though it can turn out overall fine imaging. The small all-around DA Ltd proving great edge-to-edge performance is the DA 40mm f/2.8 Ltd. It is also functional for FF use. The best partner for the DFA 28-105mm would be the DA 12-24mm, which does provide superior edge-to-edge performance and very low linear distortion as well, between about 15-20mm, in case of linear subject matter being included in your shot. Now that the DA* 11-18mm f/2.8 has come, there may be more of the DA 12-24mm f/4 appearing in the used market.

The DA 18-135mm is really not bad for edge performance between 28-80mm. The best way to judge it is to check out the images offered in the SLR lens section, in the thread "DA 18-135mm WR Show us what it can do" starting with the last page working backward. Pay more attention to shots taken with more recent cameras not having the AA filter. You will find some very impressive imaging. But in your case, I really think the DFA 28-105mm and the DA 12-24mm f/4 are the way to go to meet your criteria. I have those as well as the DA 18-135mm, which is the best for all-around single lens use.

[nandystam]

Lots of very helpful replies here and a lot of information to consume.

Thank you to everyone who has contributed so far

[AstroDave]

Are you (Why?) fixated on the K5 and siblings?

For not a whole lot more, you can go to the K3 series, which will handle all the latest lenses.

[nandystam]

Are you (Why?) fixated on the K5 and siblings?

For not a whole lot more, you can go to the K3 series, which will handle all the latest lenses.

I wouldn't say i'm 'fixated' on it. However the reasons are party sentimental (I used to have a silver one many years ago), and in the used market the prices seem very competitive in comparison to other models. Plus it's still a very good camera.

[Sandy Hancock]

Another big vote for new-ish DFA28-105

Although designed as a full frame lens, the focal length is right where you want it. I used it quite a bit on the KP in Antarctica (when I had the DFA15-30 on the K-1), and was very happy with the results.

[disconnekt]

Even though not Pentax branded, there is a Tamron 28-75mm f2.8 (on your K5 will give a 42-112mm fov) on mpb.com for ~$214usd. Good chance they'll have one (or more) lenses that have been suggested here for sale there for a good proce.

Search - mpb.com

[angerdan]

Out of interest, how do zooms like the F 35-70/100 or FA 28-105 f3.2 or 24-90 compare against the 18-135 at overlapping focal lengths? These were some of the lenses that I thought could also be applicable.

If you check the lens search, the user ratings vote for the D FA 28-105mm.
FA 24-90mm is on rank 14 and F 35-70mm on rank 5:
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