Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
02-21-2014, 03:12 PM   #16
Loyal Site Supporter
Loyal Site Supporter
monochrome's Avatar

Join Date: Mar 2008
Location: Kirkwood (St. Louis) MO
Photos: Gallery | Albums
Posts: 20,608
Nothing about the special character of the DA15

QuoteOriginally posted by MJSfoto1956 Quote
I think DxO pisses people off because of this feature of their analysis -- they try very hard to avoid using "resolution" numbers precisely because of what you state. Instead, they add biases that they believe more closely aligns with how people see. Thus, fast lenses generally get higher DxOmark scores because noise is one of those things that detracts from perceived sharpness. (not that noise is bad per se, but when it comes to perceived sharpness is certainly is)

Michael
I try very hard never to shoot wider than f/5.6 with any lens on any camera so a lot of that wide aperture perceived resolution is wasted on me.

The biggest argument I have with DxOmark is their Standard* that resolution itself (or sharpness, if one prefers) is the central metric that defines a good lens. If that must be the case then sharpness must, by definition, be the central metric that defines a good photograph, and the sharper the better. I disagree with that Standard altogether.

But in fairness to DxOmark's methodology, they can measure their metrics, can claim to measure them objectively (theycan't due to camera and sensor differences, but they can claim to) and so they can make a case for a scientific evaluation, ranking and sorting of lenses one to another - a kind of ordered meritocracy, if you will.

None of which explains anything about the special character of the DA15/4 Limited - the 'worst' lens in this little contrasting chart.



* Hierarchy:

Standard = Good - we all have to agree what is Good or what comes after can never be agreeable
Comparative = Better - rank accordingly and scientifically
Superlative = Best - in an Ordered Meritocracy, all other variables being equal, there should be no other rational selection.

That is why there is Price (and Marketing).

02-21-2014, 03:19 PM   #17
Pentaxian




Join Date: Jun 2008
Location: Flyover America
Posts: 4,475
QuoteOriginally posted by MJSfoto1956 Quote
they add biases that they believe more closely aligns with how people see.
A laudable goal but If so they must have a very large Psychology department - trying to define human visual perceptions like "pixie dust" for instance. In my over 50 years of messing about with glass, to the best of my knowledge, I have never had a lens that exhibited that elusive quality of "pixie dust".

But I digress.
Interesting thread whatever it's trying to express.

Last edited by wildman; 02-21-2014 at 03:26 PM.
02-21-2014, 03:27 PM   #18
Pentaxian
aurele's Avatar

Join Date: Jan 2011
Location: Paris, France
Photos: Albums
Posts: 2,975
It's more interesting to see the "field map" for sharpness.
You'll se the DAL 35 and the DA40 perform equally on the whole image, whereas the DA*55 perform very well in the middle only, wide open.

Pentax lenses don't score very well on DxO due to this character : sharp in the middle, softer in the corner.
02-21-2014, 03:36 PM   #19
Pentaxian




Join Date: Jun 2009
Location: GMT +10
Photos: Albums
Posts: 10,893
While I do like the presentation of the data, I don't totally buy the results for the DA40. In my experience, it performs better than the chart suggests.

02-21-2014, 03:56 PM   #20
Veteran Member
MJSfoto1956's Avatar

Join Date: Dec 2013
Location: Boston
Posts: 1,287
Original Poster
Ok. What I *REALLY* was interested in was to see how different Pentax's MTF Program Line diverged from the DxO data. While I don't have all the above lenses, I *DO* have a good handful. What I now have compiled (see below) is a DELTA between how Pentax computes the optimal aperture and what the DxO data is hinting at. More importantly, for some time now I have had my doubts about the Pentax MTF suggestions, often scratching my head wondering "what are they thinking"? (for example: in good light Pentax was selecting f/4 for the 16mm setting of the 16-45mm lens whereas DxO is suggesting it should have been f/5.6) The good news is that the two data sets often align quite well. Anyway, if any of you have the missing lenses, simply put your K-3 (it has to be a K-3 btw) into MTF Program Line mode, put the camera into P mode, then walk around observing what the aperture chosen is for a variety of dark and well-lit subjects. I will add your observations to the diagram and repost.

Michael

---------- Post added 02-21-14 at 06:04 PM ----------

QuoteOriginally posted by rawr Quote
While I do like the presentation of the data, I don't totally buy the results for the DA40. In my experience, it performs better than the chart suggests.
It is entirely possible their web-posted data is completely wrong, When using others data, we should be looking at trends rather than any specific data point. For example, DxO's data for the DFA 100mm macro to my eye looks entirely bogus and I didn't post it because my own experience of macro lenses over the past 35 years from a variety of manufacturers (Leica, Canon, Mamiya, Nikon, Schneider) have demonstrated to me that they are all great performers without exception. I might very well remove the 40mm because it simply doesn't look "right" to me (i.e. I can't imagine that Pentax would ship a "Limited" lens that stood out like that).

Michael

---------- Post added 02-21-14 at 06:19 PM ----------

QuoteOriginally posted by monochrome Quote
The biggest argument I have with DxOmark is their Standard* that resolution itself (or sharpness, if one prefers) is the central metric that defines a good lens.
The published DxOmark scores are not about sharpness or resolution. If you are curious their published methodology to calculate their lens+body scores is available for your reading pleasure.
That being said, the chart I am publishing in this thread *IS NOT* about DxOmark Scores (which is very very different) but rather it *IS* about sharpness (or resolution if you will).

Michael
Attached Images
 

Last edited by MJSfoto1956; 02-21-2014 at 04:13 PM.
02-21-2014, 06:07 PM   #21
Veteran Member
causey's Avatar

Join Date: Feb 2009
Location: Arlington, VA
Photos: Albums
Posts: 3,758
I just can't believe the DA 40mm is less sharp than the DA 21mm. All other reviews I've seen say otherwise. Anyway, my copy of the DA 40mm is plenty sharp from f2.8.
02-21-2014, 06:22 PM   #22
Veteran Member
MJSfoto1956's Avatar

Join Date: Dec 2013
Location: Boston
Posts: 1,287
Original Poster
QuoteOriginally posted by causey Quote
I just can't believe the DA 40mm is less sharp than the DA 21mm. All other reviews I've seen say otherwise. Anyway, my copy of the DA 40mm is plenty sharp from f2.8.
It is entirely possible their web-posted data is completely wrong, When using others data, we should be looking at trends rather than any specific data point. For example, DxO's data for the DFA 100mm macro to my eye looks entirely bogus and I didn't post it because my own experience of macro lenses over the past 35 years from a variety of manufacturers (Leica, Canon, Mamiya, Nikon, Schneider) have demonstrated to me that they are all great performers without exception. I might very well remove the 40mm because it simply doesn't look "right" to me (i.e. I can't imagine that Pentax would ship a "Limited" lens that stood out like that).

Michael
02-21-2014, 06:53 PM   #23
CDW
Veteran Member




Join Date: May 2011
Location: Big Island, Hawaii & Utah
Posts: 382
I've personally always taken DXO lens ratings with a lot of grains of salt. Photozone.de findings regarding the DA40mm correlate with user comments who find it very sharp.

Pentax SMC DA 40mm f/2.8 Limited - Review / Lab Test - Analysis

02-21-2014, 07:13 PM - 1 Like   #24
Pentaxian




Join Date: Jan 2011
Location: New York
Posts: 3,376
Thank you for posting this. My takeaway from this is, when using a prime lens that I don't have much experience with, and sharpness is my main objective (instead of fast shutter or controlling dof), then shoot at f5.6.

The 16-45 graph is surprising. It's sharper wide open than stopped down at middle focal lengths.

Everyone, remember that sharpness isn't everything. It's vital for some subjects and for heavy cropping, but many other lens factors contribute to a photo. Aberrations, flare, color, contrast can be more important depending on the photo. The OP isn't saying that photos taken in the red zones of the graphs are bad.
02-21-2014, 07:57 PM   #25
Loyal Site Supporter
Loyal Site Supporter




Join Date: Nov 2013
Location: Alabama
Posts: 2,450
It's very difficult to quantify that artistic quality that makes an image "pretty". DxO's strength seems to lie in measuring the quantifiable aspects of a piece of hardware. That's about as useful to an artist as counting the bristles on a paintbrush.
02-21-2014, 08:05 PM   #26
Veteran Member
MJSfoto1956's Avatar

Join Date: Dec 2013
Location: Boston
Posts: 1,287
Original Poster
QuoteOriginally posted by dansamy Quote
That's about as useful to an artist as counting the bristles on a paintbrush.
I think this is too broad a generalization. I own the DA 16-45mm and not surprisingly my experience with this lens aligns well DxO's data. I was wondering why that lens didn't shoot like other zooms I have owned. Now I know why. Nobody gives you insight into the behavior of lens + body systems as insightful as DxO. The DxOmark site is worth digging around -- if you keep your mind open, you might be surprised what you learn!

YMMV

Michael
02-21-2014, 09:00 PM   #27
Loyal Site Supporter
Loyal Site Supporter




Join Date: Nov 2013
Location: Alabama
Posts: 2,450
QuoteOriginally posted by MJSfoto1956 Quote
I think this is too broad a generalization. I own the DA 16-45mm and not surprisingly my experience with this lens aligns well DxO's data. I was wondering why that lens didn't shoot like other zooms I have owned. Now I know why. Nobody gives you insight into the behavior of lens + body systems as insightful as DxO. The DxOmark site is worth digging around -- if you keep your mind open, you might be surprised what you learn!

YMMV

Michael
What I mean is that the quantifiable aspects of a particular lens or camera, which can be graphed, charted, etc aren't necessarily the only measures whereby an artist finds value in a tool. The lens is just a tool. Sure, knowing where the weak spot is allows one to exploit it for artistic advantage or avoid it as desired.
02-21-2014, 10:59 PM   #28
Pentaxian
audiobomber's Avatar

Join Date: May 2008
Location: Sudbury, Ontario
Photos: Albums
Posts: 6,726
MTF results are interesting, but do not correlate very well with user opinions. The only lens test I've seen that correlates with actual Pentax user opinions is PopPhoto's SQF (Subjective Quality Factor) score.
Imatest - SQF (Subjective Quality Factor) and Acutance

Last edited by audiobomber; 02-22-2014 at 05:51 AM.
02-21-2014, 11:35 PM - 1 Like   #29
Inactive Account




Join Date: Apr 2010
Location: New Orleans
Photos: Gallery
Posts: 3,053
QuoteOriginally posted by DeadJohn Quote
Thank you for posting this. My takeaway from this is, when using a prime lens that I don't have much experience with, and sharpness is my main objective (instead of fast shutter or controlling dof), then shoot at f5.6.

The 16-45 graph is surprising. It's sharper wide open than stopped down at middle focal lengths.

Everyone, remember that sharpness isn't everything. It's vital for some subjects and for heavy cropping, but many other lens factors contribute to a photo. Aberrations, flare, color, contrast can be more important depending on the photo. The OP isn't saying that photos taken in the red zones of the graphs are bad.
I totally agree with this, the more I learn and hone my skills the more I appreciate the non-sharpness aspects of a lens' optical characteristics.
02-22-2014, 08:55 AM - 1 Like   #30
Veteran Member
MJSfoto1956's Avatar

Join Date: Dec 2013
Location: Boston
Posts: 1,287
Original Poster
well, the 21mm limited is a damn fine little lens. Here is one @ f5.6 I printed 18"x27" and it is tack sharp:



Michael
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
35mm, 40mm, chart, concept, da, data, diffraction, dof, dslr, dxo, f/8, k-3, k3, lens, lenses, macro, michael, mode, mtf, pentax, pentax k-3, sharpness, sigma, variety
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
More interesting Topaz Denoise/Noiseware Comparison Workingdog Digital Processing, Software, and Printing 4 12-30-2010 08:59 AM
Sharpness comparison between Pentax 18-55 and Tamron 17-50mm Rafalas Pentax SLR Lens Discussion 93 02-08-2010 07:23 AM
Interesting lens comparison from an Oly shooter jsherman999 Pentax SLR Lens Discussion 12 05-25-2009 06:46 PM
Interesting comparison - DA lenses on 35MM straightshooter Pentax SLR Lens Discussion 7 08-12-2008 01:14 PM
Interesting K10d K20d comparison PentaxPoke Pentax DSLR Discussion 24 03-04-2008 11:37 AM



All times are GMT -7. The time now is 10:00 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top