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01-06-2014, 02:02 AM   #1
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DA 20-40mm Limited review posted

While the new HD 20-40mm Limited zoom probably won't ever get as much praise as the Limited primes, we found it to be a very fun lens and we think that many Pentax users will enjoy it. Here's our review of Pentax's first Limited zoom lens:

HD Pentax-DA 20-40mm Limited - Introduction - PentaxForums.com


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01-06-2014, 03:41 AM   #2
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Thanks for the detailed review!

Since the previous review of the SMC vs. HD limiteds on the K-3 review didn't focus on sharpness, are these the first sharpness tests to appear in a PF review based on the 24mp sensor? I think that should be clarified, because people will try to compare the 100% crops and try to make direct comparisons with lenses that were tested on a 16mp sensor. One good thing about Photozone is they are very clear about this.

I like the look of this lens. It seems to have the Limited DNA in both its strengths and weaknesses. It's not meant to be a DA* lens, so we shouldn't expect it to be. All the real-world shots look really good and as the review points out, the bokeh is very nice.
01-06-2014, 03:54 AM   #3
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Is this a case of damning with faint praise?
01-06-2014, 04:36 AM   #4
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I want to like this lens. I had a chance to see the lens at my local camera store. Build quality and design are amazing, but after reading the review of the image quality seems to be disappointing at this price point. I was hoping the image quality would be near the Sigma 18-35, looks like Sigma is a champ in this area. But, the size of the 18-35mm is the drawback for me. Looks like I may pick up the 21mm over the 20-40 since I have the 15 and 40.

01-06-2014, 06:26 AM - 1 Like   #5
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QuoteOriginally posted by EricBrown Quote
I was hoping the image quality would be near the Sigma 18-35, looks like Sigma is a champ in this area.
The Sigma 18-35/1.8 is indeed a champ. It is exceptional in terms of IQ and you had your hopes up way too high, given that the Pentax DA 20-40/2.8-4.0 is optimised for size rather than IQ.

QuoteOriginally posted by EricBrown Quote
But, the size of the 18-35mm is the drawback for me.
I can sympathise with anyone who wishes for smaller lenses, but the 18-35/1.8 is exceptionally fast (fastest APS-C zoom in the world) and does not show more vignetting than primes in this focal range. It simply has to be that big in order to reach its performance parameters.

On the one hand I like that Pentax issues a lens like the DA 20-40/2.8-4.0 with such nice build quality, but on the other hand I wonder whether it is really justified to produce such an exquisite housing for rather average optical performance. I personally don't see how the lens justifies its price tag, but I appreciate that other people have other priorities.
01-06-2014, 06:30 AM   #6
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Frankly, I cannot help but be disappointed. Regardless of the nice control of other aberrations (save vignetting), this is a variable aperture zoom that is only 2x and yet they could not even manage to get it to produce good corners at maximum zoom at any aperture. While it still may be a decent lens overall, as one who always wonders about future lenses, I must admit this one does not exactly inspire me to confidence about Pentax's current optical design ability. Then again, maybe I am overreacthing and its poor performace in sharpness was down to size/weight requirments (still, if they want to set themselves above other makers in having smaller, lighter lenses, they really still need to be able to hang in there in sharpness, even it it requires truly brilliant optical designs. The prime Limiteds generally suceeded in this respect.)
01-06-2014, 09:40 AM   #7
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Adam, thanks for getting this informative review out there for us.

However, I did find the review rather confusing in places. For example:

"the 20-40mm controls chromatic aberrations (also known as coma, or more commonly known as fringing) very well, even in areas with strong highlights. In the center of the frame, we weren't able to provoke any visible coma."

"Coma" usually refers to comet-shaped distortion of off-center highlights.

Chromatic aberrations come in two flavors, lateral and longitudinal.

Fringing is a generic term, but "purple fringing" is a third effect, still not properly understood.

The gist of the review seems to be that the lens is good at the wider end,
but poorer at the longer end. To this extent, the new lens follows the pattern
seen in its FA 20-35/2.8 predecessor.

The main criticism of the new lens seems to be corner sharpness at 40mm:

"Coma is prominent at apertures wider than F11, however, which reduces contrast and perceived image quality."

If the "coma" here means lateral chromatic aberrations, then that can be corrected in PP to some extent.
The test photos were "unedited 100% crops of the original JPEG file."
If they were taken without in-camera correction,
then there is scope for some improvement of the perceived weak 40mm corner performance.
01-06-2014, 11:29 AM - 1 Like   #8
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What is a good lens?

I've been reading the comments and reports on this lens, and can't help asking what criteria for a good lens is.

Many seem to compare it with the new Art 18-35 from Sigma concluding the Pentax offering is lower optical quality than the Sigma. Ok Sigma seem sharper, but look at the general rendering. Look at the bokeh. Not how much blur the lens makes, but the QUALITY of the blur.

By all means. If you need a super sharp lens, buy the Sigma. Or perhaps better, change system to Nikon ;-) But if you are looking for the pleasant Pentax rendering, it seem the 20-40 is a strong contender.

I should probably say the I havent tried any of them personally. I just speaking from my general impression from. The samples seen at the web. I should probably appologise for some typoes to, just in case ;-)

01-06-2014, 02:35 PM   #9
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Haha, this lens. Let me rephrase that review for you:

Cons:
  • Doesn't perform at 20mm until f/4
  • Doesn't perform at 40mm until f/8 (just lol)
  • Even then, strong vignetting
  • Low contrast at 40mm
  • With corners that never get sharp ever
  • All this over a very limited zoom range
  • With a very modest, non-constant aperture

Pros:
  • Nice build quality
  • Small

You realize that even ignoring real pro-quality first party zooms like the Canon 24-70 f/2.8 and the Canon 24-105 f/4L, which can be bought for roughly $880 and $650 used, you could outright buy new third-party zooms like the Sigma 18-35 f/1.8 or Sigma 24-70 f/2.8?

I get that the build quality is nice (so are its competitors), I get that it is one of the first Pentax-branded lenses to have USM-type focusing (all its competitors did long ago, even third parties), I get that it's compact (use a prime instead, it's not like the 40mm end is any good anyway), but none of that matters if it can't deliver optically. Frankly this sounds a lot like a kit lens in a lot of ways, and it just doesn't stand up to the competition in its price range.

"It's a difficult lens to summarize" is a copout, it's a limited-range zoom lens with only one length fully usable, and it's a mediocre performer even there, for the kind of money that should buy actual pro-quality glass. Buy a 21mm and crop your shot, I don't think you'll be missing anything.

Last edited by Paul MaudDib; 01-06-2014 at 02:48 PM.
01-06-2014, 02:53 PM   #10
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must be a difficult review to do, for anyone. :P

an under-performed + over-priced lens, unfortunately.
01-06-2014, 03:37 PM   #11
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QuoteOriginally posted by Adam Quote
While the new HD 20-40mm Limited zoom probably won't ever get as much praise as the Limited primes, we found it to be a very fun lens and we think that many Pentax users will enjoy it. Here's our review of Pentax's first Limited zoom lens:

HD Pentax-DA 20-40mm Limited - Introduction - PentaxForums.com
One question that i have that has not been addressed concerns manual focus.

With the new "silent" motor focus, is the focus only with the motor when powered or can the lens be mechanically focused with the ring?

Such an application would be with the Pentax Q with the k to Q adapter.

Last edited by GXRUser; 01-06-2014 at 04:43 PM.
01-06-2014, 04:31 PM   #12
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QuoteOriginally posted by GXRUser Quote
One question that i have that has not been addressed concerns manual focus.

With the new "silent" motor focus, is the focus only with the motor requriing power or can the lens be mechanically focused with the ring?

Such an application would be with the Pentax Q with the k to Q adapter.
why in God's name would there be a focus ring if you couldn't focus the lens manually?
01-06-2014, 04:40 PM   #13
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focus ring, mechanical vs electrical control

modern lenses have different designs when it comes to camera focus. All use a focus ring, but the ring may be an electrical control.

1) Motor to move the lens elements. The motor's position is controlled by the "focus ring", but it is really an electrical control. Rotation of the ring is translated to direction and distance of lens element movement If the lens is not powered, there is no movement of the lens elements even if the ring is turned. The Pentax 06 lens for the Q is an example.

2) Mechanical rotation of the focus ring moves the lens elements via a helical. A motor may also move the helical. AF control from the camera is via the motor.

3) Mechanical rotation of the focus ring moves the lens elements via a helical. A motor in the camera body turns a screw that also moves the focus helical. The DA 70mm f2.4 uses this design. I know this design is NOT used with the Limited 20-40 zoom.

My question is which design is used for this lens.
01-06-2014, 04:45 PM   #14
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I would expect this lens uses similar approach as the other DC lens, the DA18-135.
You can use that lens on the Q adapter, the focus ring moves the elements with no power applied.
01-06-2014, 05:28 PM   #15
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My copy was hopeless at 20mm until f/5.6, and only decent from f/8.0. It was pretty good all the way from f/4.0 (wide open!) at 40mm: significantly different from the review copy it seems.

I returned it for a refund.
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