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05-25-2014, 07:01 AM   #1
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Agonizing Lens decision...

I have a limited budget of $500 for a new lens. I really would like improve over the sharpness and gain some range on the wide angle side of things over the kit 18-55 WR that came with my K5. The two lenses on my short list are the Sigma 10-20 f4-5.6 and the 17-70 f2.8-4 "Contemporary".

I could live with the limited wide angle gains of the 17-70 if this lens were sharper at 17mm than the 10-20mm. I'd love a super-wide but my real concern is sharpness.

The only other lens I currently use are a SMC-F 35-70 that I really really like.

I could use the super-wide but also really need to have a better lens in that normal zoom range. How does the sharpness of the 10-20 compare to the 17-7- specifically at 17mm?

You can view my portfolio at:

David Hill | 500px

I appreciate any insight into these two lenses you can give.

Thanks, Dave

05-25-2014, 07:34 AM   #2
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The 17-70 has a very nice range, with close focusing. It gains you not much wider than the kit, and you have 35-70, so the 10-20 it is.
05-25-2014, 08:23 AM - 1 Like   #3
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You have excellent photographs on your site, apparently many of which were made with your current equipment. It seems like you're mostly using smaller apertures - I only looked at some images, but they were mostly f16. If you have a good copy of the 18-55, you might not see a huge improvement moving from your lens to something like a 17-70, and even with the very best primes, you might encounter some diffraction limitations.

For a lot of my own pictures, I'm happier accepting what may be sub-optimal resolution at f13 or f16, in exchange for getting the entire image relatively sharp. I find a significant problem is motion (foliage, etc.), much more so than lens resolution, when using those settings. Sometimes you need more depth of field than you can get at a decent shutter speed and ISO, so you end up with (subject) motion blur. And you can't use techniques like focus stacking when there's motion involved. Obviously for your static subjects, you have other alternatives.

Overall my guess is you'd get more interesting photos from a 10-20mm than from replacing your current range zoom, assuming again that you have a good copy of the 18-55mm. With the 10-20, you'll still be using those small aperatures a lot, simply because your frame will include subjects that are both very close and very far, and you'll probably (often, but not always) want everything in focus.
05-25-2014, 08:38 AM   #4
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Since you like your 35-70, I'd suggest that you consider the Pentax 12-24mm. I don't own one, but it's what I'm seeking to compliment my 35-105 and 80-200 zooms.

05-25-2014, 08:45 AM - 1 Like   #5
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I have two similar lenses; the 10-20 f/3.5 and the version 1 of the 17-70. And even if the 10-20 is good, the 17-70 is very sharp, even at 17 and even wide open. They're two different beast and IMO have two very different uses. The 10-20 is a fun lens with a very wide field of view but it has a bit of a limited use in my case, the 17-70 is a very nice walk around zoom and has a useful range.

If I were to do it again, I would probably get a 14 or 15mm prime and a manual focus ultra wide fish eye... For about the same price of the 10-20 f/3.5.

The 17-70 is stellar, arguably the best zoom in this range for K mount but would be redundant in your kit. The 10-20 (even the more expensive constant f/3.5) in term of sharpness is not a class leader.

In your case, you "need" the 10-20 for the field of view, but you "want" the 17-70 for its IQ.

Have you considered the SMC Pentax-DA 14mm F2.8 ED [IF] or the SMC Pentax-DA 15mm F4 ED AL Limited (Non-HD) both are around your price range and you'd get very good IQ, better than the 10-20... but you'd lose some field of view.
05-25-2014, 10:29 AM   #6
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QuoteOriginally posted by daveyohill Quote
"but my real concern is sharpness"
That argues more for primes than zooms - many great zooms out there, but primes win except for convenience. I've been using 'vintage' manual primes to better fit within my budget (two Takumar, one SMC, one SMC-M, two SMC-A).

If zooms are best for you: I also owned the 17-70 early model and found it to be a sharp and versatile lens, so if zooms must happen that's a good one. Sharpness can be challenging at really wide angles, since many objects can fit on the AF sensor - but go wide at f/8 and you're pretty much covered!
05-25-2014, 10:40 AM   #7
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If sharpness is your main criteria the Sigma 8-16 wins hands down. They recently went out of production for K-mount, so you need to get one used. IIRC one went for $500 recently (KEH, Adorama, B&H or Amazon), but it could have been $600. It's sharper than any other wide zoom for Pentax. I don't think even the primes beat it in sharpness, though some may equal it (Pentax DA15; Samyang 16/2, 14/2.8, and 10/2.8). These primes may have other advantages, like compactness, wider apertures, or even different color rendering, but I don't think they have more sharpness.

I say this based on my experience (I own both the Sigma 8-16 and the DA15), but you can see it in the MTF charts as well. Although I prefer my DA15 when it's wide enough, I never worry about the sharpness on my Sigma 8-16. Here are some objective measurements:

http://www.photozone.de/pentax/463-pentax_15_4?start=1

http://www.photozone.de/nikon--nikkor-aps-c-lens-tests/625-sigma816f4556dx?start=1


While you can't compare the exact MTF numbers because they're different cameras, you can compare the bar graph categories (good, very good, excellent). While the DA15 may be slightly sharper in the center, it looses in the borders or extremes until well stopped down. Notice also that the Sigma is excellent in the center and very good in the borders at every single aperture and zoom level - something the DA15 can't even say at its fixed focal length. Even Photozone's overall rating is higher on the Sigma (4 stars vs. 3 1/2). For perspective, the Pentax 18-55 WR gets 3 stars while the best lenses ever get 4 1/2 stars:

http://www.photozone.de/pentax/641-pentax1855f3556wr?start=1




EDIT: Notice also that the latest Sigma 17-70 (which is better than the older Sigma 17-70s, I believe) can't beat the 8-16. Also, the 17-70, like most other "normal focal length" zooms, gets weaker at the wide end (17mm):

http://www.photozone.de/nikon--nikkor-aps-c-lens-tests/822-sigma1770284os?start=1

Why not get sharpness throughout the whole UltraWide range with the 8-16?

Last edited by DSims; 05-25-2014 at 11:27 AM.
05-25-2014, 11:05 AM - 1 Like   #8
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I have been acquiring my wide angle lenses for some time now - on the one (or half) a lens per year plan. That said, there are a few things that I have "re-discovered" (something like re-inventing the wheel).
  • The wider you go, the more you are able to pull into the frame - at the expense of pushing back the center.
  • The wider you go, the more area each pixel will need to represent. In terms of overall sharpness, it will still look good, but when compare to a longer focal length lens, then you will see the difference. You are essentially pushing more view into a fixed size frame of the sensor.
To get around some of these situations,
  • Use stitching. In this respect as you add viewing area to the scene, you are adding pixels. You are also able to use longer focal lengths, so you are able to maintain the relative sharpness of the pixels.
  • 20, 28, 31mm are the primes I use. Also, I stitch for the previous reason. Primes add quality, stitching adds pixels. Plus, these focal lengths minimize distortion.
But, I do have zooms - and I like them a lot for a wide variety of reasons.
  • For capturing movement, you minimize your problems (that stitching presents).
  • For capturing large difference in light, you have a single frame, rather than several frames that you might need to work with. It's just easier.
If I were to do over again, I would pretty much do the same.
  • Save for the 12-24 or the 10-20. My 12-24 is one of my most used and favorite go to lens.
  • Perhaps get a 20, 24 or 24 prime A lens to supplement in terms of sharpness.
  • I find that the 8-16 can really be too wide a lot of the times. The 12-24 is a very good compromise in terms of controlling distortion.
You have a very fine portfolio of images. I live in the desert, but I grew up and really miss the ocean, the coast lines and especially harbors. I am thinking that maybe the 15 ltd would be good for you. Its wider, small and its flare control could be useful to you. Then again the 10-20 would work well also. What ever you get will work well with you and your skills and talent.



05-25-2014, 01:12 PM   #9
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QuoteOriginally posted by jimr-pdx Quote
That argues more for primes than zooms - many great zooms out there, but primes win except for convenience. I've been using 'vintage' manual primes to better fit within my budget (two Takumar, one SMC, one SMC-M, two SMC-A).

If zooms are best for you: I also owned the 17-70 early model and found it to be a sharp and versatile lens, so if zooms must happen that's a good one. Sharpness can be challenging at really wide angles, since many objects can fit on the AF sensor - but go wide at f/8 and you're pretty much covered!
It's difficult to directly compare overall image quality, because you lose some something (noise, sharpness, etc.) to the greater cropping required with primes. Obviously if you look at a prime at, say, 28mm, vs. a zoom at 28mm, you're likely to find that a good quality prime is better (less distortion, probably more sharpness, etc.) But if you really needed 37mm and crop the prime image vs. relying on the zoom, it may become more of a tradeoff.
05-25-2014, 02:56 PM   #10
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Thanks for the replies all! I have to say that I believe I would take advantage of the range of the 10-20 but feel the kit lens is showing it's limits and need to replace it first. I'm really leaning towards that "contemporary" 17-70... I do believe that the 15mm ltd. might be my holy grail lens but I need to have more confidence in my general use lens first. As I spend a lot of time at the wide end of things sharpness @ the 17mm range is top priority.

On a side note I did pick up a 55mm f1.8 Super Tak and the Bower adapter. The adapter "munged" the hell out of the threads of the Super Tak and I frigged up the auto/man clutch pin getting it off my K5... I am keeping my eyes peeled for a K mount 28, 35 or 50 but those don't fit my wide angle needs on the K5.

In a former life I shot Rollei 35 gear and had "PHENOMINAL" glass. I am being kind of critical here. I do pre-press work for the day job and convert so many soft images I am placing a premium on sharpness for my personal work.
05-25-2014, 05:26 PM   #11
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I think the main question you need to answer is what focal length(s) you want to cover first.

If you are trying to straddle the wide-normal range with one lens, the DA 16-45 is worth considering. It rates very highly for sharpness:
Best zoom lenses for the Pentax K-5 II - DxOMark

The rendering seems to get a lot of praise from users.

At f4 it isn't fast, but as DSims points out, the Pentax constant f4 lenses generally don't need to be stopped down (or not much) for excellent performance.

The extra couple of mm in width (compared to 17-xx or 18-xx) makes a big difference. And the 16-45 is said to be just about at its best at the wide end.

It would also go nicely with your 35-70 without too much overlap.

Down the track you could complement it with a 14mm or 15mm prime. The 16-45 is such a bargain you would have plenty of change from your $500 budget.
05-25-2014, 06:56 PM   #12
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Another option for the kit replacement is the DA 16-45/f4. It is sharper than the kit, not quite as long, and the 2mm difference on the wide end translates to 6.4 degrees in Field of View. They run around $200 used since Pentax has discontinued them a couple of years ago.

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