Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-23-2012, 07:22 PM   #76
Senior Member




Join Date: Mar 2012
Photos: Albums
Posts: 100
QuoteOriginally posted by Class A Quote
Ideally, lens tests specifying results with the unit "lp/mm" (or based on "lp/mm") should yield the same results independently of the camera that was used.

This unit should refer to the lens resolution only and should hence be independent of the pixel pitch of the sensor. Only where a low pixel-pitch sensor is outresolved by the lens, a higher pixel pitch sensor should yield higher resolution numbers for the lens, but everywhere else (corners, higher f-ratios) the two measurements should ideally agree.
I looked up system MTF in one of my books to refresh my memory. There are several factors to system MTF, the contribution of the optics (ie, the lens) being one of them. The other major contributor to the system is the MTF of the detector (which has several MTF components that combine to create the detector MTF). I think the PZ MTF is actually the SYSTEM MTF (optics + detector), not the OPTICAL MTF. In some examples I've seen, the detector MTF is a significant limiting factor to system MTF. Conversely, high performance optics will most likely elevate the system MTF.

For the record: System MTF = (Lens MTF) x (Detector MTF)

This doesn't totally explain why a system would have worse performance with a great lens and a better detector, so I still am wondering about error induced due to the test itself, pixel diffraction, etc.

05-23-2012, 10:57 PM   #77
Veteran Member
selar's Avatar

Join Date: Jul 2007
Location: Sydney, Australia
Photos: Gallery | Albums
Posts: 2,035
QuoteOriginally posted by Asha Quote
This doesn't totally explain why a system would have worse performance
Maybe you should post this in the FA43 retest thread, I dont really understand what your disappointment with the FA31 retest is.
05-23-2012, 11:16 PM   #78
ogl
Pentaxian
ogl's Avatar

Join Date: Dec 2007
Location: Siberia
Photos: Gallery | Albums
Posts: 7,250
QuoteOriginally posted by selar Quote
Maybe you should post this in the FA43 retest thread, I dont really understand what your disappointment with the FA31 retest is.
Me too...FA31 is very good at K-5 at all apertures. One of the best lens even at K-5.
05-24-2012, 05:16 AM   #79
Pentaxian
Class A's Avatar

Join Date: Aug 2008
Location: Wellington, New Zealand
Posts: 9,193
QuoteOriginally posted by Blue Quote
The tone of this thread is odd. It got a review of 4.5/5 (optical quality), 4.5/5 (mechanical Quality), 3/5 (price/performance) and :bigthumbsup: ...
You were apparently looking at the old test.

In the new test the 31/1.8 has been downgraded to 4 stars out of 5 for optical quality.

It is still a bit of a mystery, why the peak for sharpness shifted from f/4 to f/2.8. Klaus apparently does not know either.

05-24-2012, 06:09 AM - 1 Like   #80
Pentaxian




Join Date: Nov 2011
Photos: Gallery | Albums
Posts: 3,735
QuoteOriginally posted by Class A Quote
It is still a bit of a mystery, why the peak for sharpness shifted from f/4 to f/2.8. Klaus apparently does not know either.
As pixel density increases, the effect of diffraction kicks in at wider apertures,
as the link in bossa's post https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/186504-photozo...ml#post1962688 shows.
Nevertheless, f/4 seems to be too wide for that effect on 16MP APS-C.
05-24-2012, 06:17 AM   #81
Senior Member




Join Date: Mar 2012
Photos: Albums
Posts: 100
QuoteOriginally posted by selar Quote
Maybe you should post this in the FA43 retest thread, I dont really understand what your disappointment with the FA31 retest is.
I'm not disappointed, far from it. I'm just responding to others in the thread. The MTF comments I am responding to started here.

Feel free to quote me in the other thread, as appropriate.

Last edited by Asha; 05-24-2012 at 06:44 AM.
05-24-2012, 07:09 AM   #82
Moderator
Site Supporter
Blue's Avatar

Join Date: Jun 2008
Location: Florida Hill Country
Photos: Gallery | Albums
Posts: 17,212
QuoteOriginally posted by Class A Quote
You were apparently looking at the old test.

In the new test the 31/1.8 has been downgraded to 4 stars out of 5 for optical quality.

It is still a bit of a mystery, why the peak for sharpness shifted from f/4 to f/2.8. Klaus apparently does not know either.
Actually, it lost half a star out of five on optical quality and still has a bigthumbsup recommended rating. It never had a 5 in any category in the K10d evaluation.

Last edited by Blue; 05-24-2012 at 07:16 AM.
05-24-2012, 10:15 AM   #83
ogl
Pentaxian
ogl's Avatar

Join Date: Dec 2007
Location: Siberia
Photos: Gallery | Albums
Posts: 7,250
QuoteOriginally posted by Class A Quote
You were apparently looking at the old test.

In the new test the 31/1.8 has been downgraded to 4 stars out of 5 for optical quality.

It is still a bit of a mystery, why the peak for sharpness shifted from f/4 to f/2.8. Klaus apparently does not know either.
Stars rating is just Klaus subjective opinion and nothing else.

05-25-2012, 04:57 AM   #84
Veteran Member
selar's Avatar

Join Date: Jul 2007
Location: Sydney, Australia
Photos: Gallery | Albums
Posts: 2,035
Can't believe Klaus thinks the FA31 does not deserve a bokeh test:
Attached Images
View Picture EXIF
PENTAX K-5  Photo 
05-25-2012, 08:15 AM   #85
Site Supporter




Join Date: Jul 2011
Posts: 1,039
QuoteOriginally posted by lytrytyr Quote
As pixel density increases, the effect of diffraction kicks in at wider apertures,
as the link in bossa's post https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/186504-photozo...ml#post1962688 shows.
Nevertheless, f/4 seems to be too wide for that effect on 16MP APS-C.
Correct, for the K5 diffraction should really kick in at around f/6.3 while other parameters improve, so a real degradation in quality may be visible at f/9.5-11 on.

For pixel peepers: K5 pixels pixel pitch is less than for K10. Why do we see the same amount (in pixels) of chromatic abberation or even less for the K5. Simple guessing would assume a larger value for the K5.

To be fair. The FA31 is not designed to be a five star rating normal angle lens on an APS-C camera.
The test is for camera and lens combined. The camera adds not only pixel pitch, but sensor flatness, demosaiking, firmware issues, ... into the equation.

Last edited by zapp; 05-25-2012 at 08:22 AM.
05-25-2012, 09:35 AM   #86
Pentaxian




Join Date: Nov 2011
Photos: Gallery | Albums
Posts: 3,735
QuoteOriginally posted by zapp Quote
Correct, for the K5 diffraction should really kick in at around f/6.3
One more thought, though.
If diffraction effects are considered to spread out over a cone of a fixed angle,
that cone will cover more pixels at the edge of the frame than it does in the center.
So the degradation, measured in pixels, will appear earlier at the edge of the frame.
05-26-2012, 07:31 AM   #87
Veteran Member
kent's Avatar

Join Date: May 2009
Location: Lithuania
Photos: Gallery
Posts: 344
today I tried 31mm lens on my K-5. Great to hold, well focusing and IQ even at f/1.8...Oh boy. Great lens..
05-26-2012, 07:42 AM   #88
Pentaxian
normhead's Avatar

Join Date: Jun 2007
Location: Near Algonquin Park
Photos: Gallery | Albums
Posts: 25,830
I got to handle a 31 yesterday, nothing I've read about it was wrong, I'm still planning to get one, but because I have a DA 35 2.4, I've moved the 15 ltd ahead of it in the purchase order. I was kind of surprised when the Pentax guy said 10-17 was not designed to be a landscape lens but more of a fun lens. The barrel distortion on the 15 was better than the 10-17 by a large margin. Comparable to the 16-50 @16mm. I have to look closer to make a final decision on those two. The build on the 31 was very very tight. And being a limited, the weight is a big plus, at least of me.
05-26-2012, 08:00 AM   #89
Moderator
Site Supporter
Blue's Avatar

Join Date: Jun 2008
Location: Florida Hill Country
Photos: Gallery | Albums
Posts: 17,212
QuoteOriginally posted by normhead Quote
I got to handle a 31 yesterday, nothing I've read about it was wrong, I'm still planning to get one, but because I have a DA 35 2.4, I've moved the 15 ltd ahead of it in the purchase order. I was kind of surprised when the Pentax guy said 10-17 was not designed to be a landscape lens but more of a fun lens. The barrel distortion on the 15 was better than the 10-17 by a large margin. Comparable to the 16-50 @16mm. I have to look closer to make a final decision on those two. The build on the 31 was very very tight. And being a limited, the weight is a big plus, at least of me.
The DA 10-17 is a fisheye lens so the barrel distortion shouldn't be surprising.
05-30-2012, 07:28 PM   #90
Senior Member




Join Date: Mar 2012
Photos: Albums
Posts: 100
QuoteOriginally posted by lytrytyr Quote
One more thought, though.
If diffraction effects are considered to spread out over a cone of a fixed angle,
that cone will cover more pixels at the edge of the frame than it does in the center.
So the degradation, measured in pixels, will appear earlier at the edge of the frame.
Finally getting back to this MTF sub-discussion.

I'm not sure this statement is totally correct, although I may also be misunderstanding what you're saying!

The lens diffraction shouldn't change very much if the lens is within spec. However, the nominal resolving capability of the lens (number of line pairs per mm) may not be as good as the resolving capability of the detector. When the point spread function of a fine detail (or more specifically, two overlapping airy disks that represent a fine detail) overfills a pixel, image degradation will result because the "peaks" of the two airy disks merge into a blob at the detector plane. Mathematically, when the two MTFs combine, there could be significant degradation, especially in the fine details, and especially at the edges of the frame.
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!
31mm, f/1.8, f1.8, fa, fa31mm, k-mount, lens, lenses, pentax, pentax lens, quality, review, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Photozone Reviews Tamron 70-200 2.8 HOT! HOT! HOT! JHD Pentax SLR Lens Discussion 31 02-03-2011 09:11 AM
For Sale - Sold: FA31mm/1.8 Limited (Worldwide) LuzArt Sold Items 2 09-27-2010 12:20 PM
should I trade in DA*16-50mm for a FA31mm ltd? mokey Pentax SLR Lens Discussion 11 09-24-2010 01:27 PM
People Portraiture via the FA31mm [9 imgs] A Modest Mouse Post Your Photos! 2 07-27-2010 03:24 PM
More Photozone reviews! feronovak Pentax SLR Lens Discussion 2 05-04-2007 05:26 PM



All times are GMT -7. The time now is 06:23 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