[Tony3d]

Hi all, What's the sharpest super zoom lens for my K3? I have the Pentax 18-135mm, but would like something with a bit more reach. I'm not particularly impressed with edge to edge sharpness of the 18-135mm at the widest setting.

[Adam]

You're probably not going to be able to do any better with a superzoom. I'd recommend a dedicated telephoto lens, like the DA 55-300mm or DA* 60-250mm.

[FantasticMrFox]

I have the Pentax 18-135mm, but would like something with a bit more reach. I'm not particularly impressed with edge to edge sharpness of the 18-135mm at the widest setting.

You're already unsatisfied with the optical performance of your lens but want something even longer?

[Alex645]

Tony,
Completely agree with Adam. Sharp and super zoom is a bit of an oxymoron. Super zooms offer convenience but the trade off is sharpness and other optical qualities. My recommendation would be to pick out your favorite 10-20 photos from your 18-135mm. What was the focal length of those shots? If you're rarely shooting under 55mm, then you don't really need the wide end. If you are shooting at the extremes, then you're best off with at least two zoom lenses or perhaps a couple primes.

[maxfield_photo]

Zoom lenses are de facto a compromise since the lens elements can only be truly "optimized" for a single focal length (don't get me wrong, the compromise can be negligible).

If you take the longest focal length of a zoom lens and divide it by the shortest, you will get a certain zoom factor. e.g. 200 ÷ 70 = 2.8. My general rule of thumb is a zoom lens must have a zoom factor of 2 or greater before it's worth the space and weight it takes up in my bag, but I find that image quality starts to take a nose dive when the zoom factor exceeds 4. There may be exceptions out there, but they are rare.

[Des]

I had the Tamron 18-250 (same as the Pentax DA 18-250) and now have DA 18-135 and DA-L 55-300. The Tamron was about a stop slower across the range than the other two. Centre sharpness was surprisingly good, especially at the wide end, and when stopped down, but you wouldn't choose it for edge or corner sharpness. (When I first tried my DA 35 f2.4, the edge-to-edge sharpness was breathtaking by comparison, even though the Tamron was near its best at 35mm.) At the long end, the 55-300 is much better, and has much more reach than the extra 50mm would suggest (because it doesn't have focus breathing).

It seems to me you are looking for two different things: (1) better edge to edge sharpness than the 18-135 at the widest setting; and (2) more reach. The Tamron/DA 18-250 is not the best option for either, and (as everyone has said) I doubt any superzoom would be.

For the first issue, I'd suggest a DA 12-24 f4 or a wide prime. One of the Sigma 10-20 lenses would be a cheaper alternative.

For the second, the 55-300 if you prioritise budget and light weight over speed and higher IQ, or the DA*300 or DA*60-250 f4 if you don't.

[VoiceOfReason]

I've heard decent things about the Sigma 18-300, but you're going to get better IQ on your long end with something like the DA*60-250.

[calsan]

......or just tumble down the limited prime lens rabbit hole......

[crewl1]

Zoom lenses are de facto a compromise since the lens elements can only be truly "optimized" for a single focal length (don't get me wrong, the compromise can be negligible).

If you take the longest focal length of a zoom lens and divide it by the shortest, you will get a certain zoom factor. e.g. 200 ÷ 70 = 2.8. My general rule of thumb is a zoom lens must have a zoom factor of 2 or greater before it's worth the space and weight it takes up in my bag, but I find that image quality starts to take a nose dive when the zoom factor exceeds 4. There may be exceptions out there, but they are rare.

With a zoom factor of 10 the Sigma 50-500 actually does really well keeping image quality throughout its zoom range.
I'm pretty sure this is not what the OP was looking for though.

[Tony3d]

I do have the 55-300, I may go for a for a wide limited. The 55-300 is much better on edge sharpness at 55mm, and is reasonably sharp at 300.
I really don't like to change lenses for fear of getting dust on the sensor. I am very careful when I do. Always change indoors, with the body facing down, and I cap the back of the free lens immediately. Still it's a hassle. Thought that maybe there was a miricle lens out there I didn't hear about LOL!

[Des]

I really don't like to change lenses for fear of getting dust on the sensor.

Even when my superzoom was my only lens I still somehow got dust on the sensor!

With all the tech innovations in MILCs, it's suprising no manufacturer has come up with a hardware solution to protect the chamber from dust. Other than this: Keeping Your Camera's Digital Sensor Clean - Photo Blog - Niebrugge Images

Thought that maybe there was a miricle lens out there I didn't hear about LOL!

It's worth asking. Superzooms have a bad name because the early 28-300 ones were pretty ordinary. The Tamron 18-250 (and the later 18-270, each subsequently re-badged by Pentax) were quite a leap in quality at the time (from about 2007). (Photozone said, "the resolution characteristic is fairly amazing regarding the extreme zoom range".) Like a lot of consumer zooms, superzooms sacrifice wide apertures and corner sharpness (and generally even some centre sharpness at the long end) on the basis that they are less of a priority for most regular photographers than centre sharpness and versatility. For a traveller who wants versatility and reach, and mainly shoots outdoors at f8, they are a good option.

The latest Tamron 16-300 (not in K-mount) and Sigma 18-300 seem to be pushing the limits. LensTip is generally scathing about superzooms but they were reasonably kind about the latest Sigma (tested on a Nikon): Sigma C 18-300 mm f/3.5-6.3 DC MACRO OS HSM review - Introduction - LensTip.com
Still the pattern of being weakest at the long end and soft in the corners (even when stopped down, at the long end) continues.

[tvdtvdtvd]

dedicated telephoto lens, like the DA 55-300mm or DA* 60-250mm.

I feel my logic circuits smoking......

[Sandy Hancock]

Keep the 55-300 and if you really want something better than the 18-135, replace it with the 16-85.
Invest in a Rocket Blower and relax about sensor dust. WR lenses help to keep dust out anyway.

But really, at the risk of sounding elitist, what is the point of having a high-end interchangeable lens DSLR if you want only one low quality superzoom?

[biz-engineer]

Depending on their designs, superzooms are optimized for sharpness on the wide to medium tele and as the focal length increases corners get softer with decent sharpness in the center (stopped down). This design trade-off makes sense as long as the long focal length is used for portraiture with a subject in the center, the softness of the edges being less of a problem for out of focus areas. The other use of the long focal length maybe for landscape, in this case, sharpness across the frame does matter, so I wouldn't recommend a super zoom. Instead, an approach that can help solve the problem of versatility and image quality is to add a small prime to a zoom. The zoom covering most use cases and the prime covering occasional shots. For example , I'd go to the future DFA 28-105 zoom and complement is with a 21ltd or a 15ltd (limited are small). Or, the other combo that I use is the 17-50 (f2.8) or 28-75 (f2.8) + 100 macro (f2.8), the 100 macro is relatively small so I can have 100mm or do marcro when needed, all of those lenses being tack sharp at f4 (covering most natural lighting conditions). Hope this helps.

[Tony3d]

Keep the 55-300 and if you really want something better than the 18-135, replace it with the 16-85.
Invest in a Rocket Blower and relax about sensor dust. WR lenses help to keep dust out anyway.

But really, at the risk of sounding elitist, what is the point of having a high-end interchangeable lens DSLR if you want only one low quality superzoom?

Yes, I have asked myself the same question. I do have a rocket blower. Guess I need to just do what I need to do to get the shot, and deal with dust later. Just the thought of someday having to swab the sensor freaks me out! The 55-300 is not a WR LENS CORRECT?