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02-26-2009, 10:54 AM   #1
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Has K20D's sensor out resolved Pentax lenses?

I've been reading some people having soft issue (even after adjustment) with their lens on K20D.

1. Does it mean that K20D's sensor has out resolved some of K-mount lenses?
2. If yes, then which lenses that have been out resolved?
3. How do you know when a sensor out resolve a lens? How do you measure it?

Thanks,

02-26-2009, 11:39 AM   #2
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yes. mostly zooms. you have to compare on a lower MPix camera.
Look at the Canon forums for 50D vs. 40D comparisons...same issue...
02-26-2009, 12:20 PM   #3
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QuoteOriginally posted by kenyee Quote
yes. mostly zooms. you have to compare on a lower MPix camera.
Look at the Canon forums for 50D vs. 40D comparisons...same issue...
Hi Kenyee,

Do you know which zoom?
02-26-2009, 12:59 PM   #4
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Pretty sure it's out-resolved my 18-250mm, and probably my Sigma 70-200mm. With the sharper prime lenses, I doubt it.

02-26-2009, 01:18 PM   #5
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QuoteOriginally posted by HermanLee Quote
Do you know which zoom?
You're better off asking which zooms are known to be good with it...note that I said most zooms are not

First on my list would be the DA*50-135 which seems loved in the Tokina variant on other systems as well. I've never been too impressed w/ the DA*16-50.
My Sigma 17-70 is noticeably softer on the K20D than the K10D...meaning it needs to be stopped down a bit more to be decently sharp. The 18-250 was just ok on the K10D, so it's no surprise it's out-resolved by the K20D

But if you have no basis for comparison, everything looks good, so it's best to ask what you're comparing it to?
02-26-2009, 01:41 PM   #6
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QuoteOriginally posted by kenyee Quote
You're better off asking which zooms are known to be good with it...note that I said most zooms are not

First on my list would be the DA*50-135 which seems loved in the Tokina variant on other systems as well. I've never been too impressed w/ the DA*16-50.
My Sigma 17-70 is noticeably softer on the K20D than the K10D...meaning it needs to be stopped down a bit more to be decently sharp. The 18-250 was just ok on the K10D, so it's no surprise it's out-resolved by the K20D

But if you have no basis for comparison, everything looks good, so it's best to ask what you're comparing it to?
How about with FA* 80-200mm/2.8?

I noticed the photo is a little bit softer at 2.8 compared to when I mounted it on K100D.

While with my FA 43 Ltd, I couldn't see that much difference.
02-26-2009, 02:28 PM   #7
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My Sigma 70-300 comes out way soft looking on the K20D compared to the Ist DL
02-26-2009, 03:53 PM   #8
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QuoteOriginally posted by HermanLee Quote
How about with FA* 80-200mm/2.8?
I noticed the photo is a little bit softer at 2.8 compared to when I mounted it on K100D.
That's a terrible lens on the K20D...you should sell it to me

In all seriousness, it's a somewhat old design. I think the Nikon 70-200 and Tamron 70-200 beat it in sharpness from what I've seen, so I'm not surprised. It has a nice rendering though. Just stop pixel peeping with it

02-26-2009, 04:05 PM   #9
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''My Sigma 17-70 is noticeably softer on the K20D than the K10D...meaning it needs to be stopped down a bit more to be decently sharp''


Just about all of my lenses were softer on my k20 than my k10 until I began checking for front/back focusing. I discovered that all but one or two were anywhere from -10 to + 7 out of focus. By adjusting in camera I was able to correct most, but unfortunatly, not all. My incredibly sharp DA40 and VL 125 were out of range and the camera has since been sent back to Pentax for calibration. As a point of reference, my Sig 17-70, which I was disappointed in on my K20, is now VERY sharp and one of my best lenses. You might want to give this a try. It takes a while, but is definatley worth it.

Tony
02-26-2009, 04:43 PM   #10
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QuoteOriginally posted by AV82GOLF Quote
'As a point of reference, my Sig 17-70, which I was disappointed in on my K20, is now VERY sharp and one of my best lenses.
Thanks, Tony. I'll check it to be sure, but from the photos I've taken, it's sharpest at the point of focus, so it seems to be focusing accurately. I haven't had any problems w/ focusing my primes either, but I should check to be sure
02-26-2009, 05:29 PM   #11
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QuoteOriginally posted by HermanLee Quote
I've been reading some people having soft issue (even after adjustment) with their lens on K20D.

1. Does it mean that K20D's sensor has out resolved some of K-mount lenses?
2. If yes, then which lenses that have been out resolved?
3. How do you know when a sensor out resolve a lens? How do you measure it?

Thanks,
Yes and no... actually. Even with a lower resolution sensor, the answer would still be yes and no. But to understand this, one needs to read a long explanation.

First, it really depends on a number of factors such as light (wavelengths, brightness, and other characteristics), the aperture used, the distance of the subject, and the type of lens used.

It is said that the K20D is roughly better than the resolution of 35mm film (e.g. ISO 100). What does this mean? Well in a hand held good photo, there are about 13-15 million good quality pixel/grains exposed equivalent. However, an excellent exposure, on a tripod and with ideal lighting, there might be 19-22 million good quality pixel/grains. But I warn, this is arbitrary and not that useful, in fact, you may read contradicting comparisons. To say the least, this is a controversial topic.

Despite knowing this subject relatively well (working with Dalsa cameras for about 15 years and understanding the fundamentals for astronomy work - diffraction limits should be well understood), I still have trouble simplifying the topic.

I've always stated that if one cannot simply a complex subject, easy enough for the layperson, then one does not know the subject well enough. I guess I don't know the subject well enough....

Until I work on my own simpler text, the absolute best explanation I know of, can be found at luminous-landscape.com:

Do Sensors “Outresolve” Lenses?

Slightly off the topic but still interesting further reading:
Digital SLR vs. Film Scans, a technical discussion & comparison images

If you simply want the best quality photo possible, get the best available Pentax * (or limited) lenses (there are some great Tamron and Sigma PK lenses too), shoot as close as possible to your subject, and shoot with the best lighting possible.
02-26-2009, 07:26 PM   #12
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My Answers

QuoteOriginally posted by HermanLee Quote
I've been reading some people having soft issue (even after adjustment) with their lens on K20D.

1. Does it mean that K20D's sensor has out resolved some of K-mount lenses?
Most of the full frame K lenses, I would say, since the DSLR has a cropped sensor.

First, good Pentax film lenses generally have a resolution of 40 linepairs/mm at an average MTF of around 50%, e.g.:

Pentax SMC FA 24mm f/2.0 AL (IF) MTF data

Pentax SMC-FA 20mm f/2.8 MTF data

K20D has resolution from 1500 to 2400 linewidths/picture height at a MTF of 50%. So, just say 2000 lw/ph in average. As the sensor is 16mm height, which means the resolution figure in lp/mm is thus 2000/2/16 = 62.5 lp/mm.

So, the K20D outresolves the film lenses, even for better ones.

For DA lenses, if the image circle is confined to the APS-C 1.5X cropped circle, the resolution should be designed to be 1.5X higher. So, 40 lp/mm x 1.5 = 60 lp/mm, which is matching with the resolution of the 14.6 MP K20D.

However, in reality, since the DA lenses are not strictly 1.5X but just something like 1.3X to 1X, the resolution should not be much higher than film ones. With the DA lenses using the old form factor as the 135 Pentax lenses, the performance of the lenses cannot be optimised at best.

QuoteQuote:
2. If yes, then which lenses that have been out resolved?
Almost all, as fully explained.

QuoteQuote:
3. How do you know when a sensor out resolve a lens? How do you measure it?

Thanks,
Even the sensor has higher resolution than the lens, it is always advantageous to use a better lens, as any inadequate resolution of the lens will show up, still.
02-26-2009, 07:51 PM   #13
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Complex subject

The Pentax sensor does not out resolve many current and a bunch of older lenses.
AA filters skew any "mathematical" guessitmations.
will get back to this..

Pentax K20D review Cameralabs resolution results
Re: AA filters: Open Talk Forum: Digital Photography Review

Best:
http://www.luminous-landscape.com/tutorials/resolution.shtml
Thoughts on MTF numbers:
http://web.archive.org/web/20080121044448/http://www.imx.nl/photo/technique/...igital_ne.html
A quote for thought.........
That's where Nirvana lies. There is a very strange-logic group of people, however, who theorize that it is better not to see everything a lens offers, and think it best to undersample a lens, to avoid the lens' imperfections. This type of thinking is a thought virus, IMO. What proponents of such thought fail to take into account is that lower pixel density IS ITSELF a major source of blur, even though poor image display methods may make images with low density look sharp through high-contrast pixelation, which causes aliasing. It's usually this same group of people that like aliased, pixelated images which also like low pixel density images.
http://forums.dpreview.com/forums/read.asp?forum=1018&message=28433816
http://forums.dpreview.com/forums/read.asp?forum=1018&message=28433996
The fact that a lens at a certain setting and at a certain pixel pitch shows less pixel contrast, does not mean that the pixels are oversampling the lens already; what it most likely means is that the optics are *STARTING* to enter the zone where they become a more limiting factor. And don't forget; with a Bayer CFA, the ability to resolve red and blue is at 1/2 the frequency of luminance.

Last edited by jeffkrol; 02-26-2009 at 08:31 PM.
02-26-2009, 08:56 PM   #14
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QuoteOriginally posted by RiceHigh Quote
Most of the full frame K lenses, I would say, since the DSLR has a cropped sensor.


K20D has resolution from 1500 to 2400 linewidths/picture height at a MTF of 50%. So, just say 2000 lw/ph in average. As the sensor is 16mm height, which means the resolution figure in lp/mm is thus 2000/2/16 = 62.5 lp/mm.
Garbage......... completely ignores AA filter, color spectrum ect.
http://www.foveon.com/files/FrequencyResponse.pdf
Q: Why not measure the MTFs of the sensors instead of the convaluted way
DxO is trying to parameterize the sensors.



A: The MTF would be interesting information, providing information about resolution; it would reveal the characteristics of the AA filter over the sensor. One could extract it from the sort of RAW test that John Sheehy did recently:
http://forums.dpreview.com/forums/read.asp?forum=1019&message=30001276

But I suspect that this information is not so important for the programming of DxO's raw converter, so they see no reason to make such a measurement. More important for them is the sort of noise and color resolution information that they exhibit on their website.

Emil Martinec
http://theory.uchicago.edu/~ejm/
Real world 50d results (15.1MP sensor):
The bottom line is that the 50D seems to have all the true resolution a sensor can have at the pixel level (monochrome, of course, with Bayer CFAs), and there are lenses that cost only US $400 which can outresolve the 50D pixels.
http://forums.dpreview.com/forums/read.asp?forum=1019&message=29958483

Last edited by jeffkrol; 02-26-2009 at 09:34 PM.
02-26-2009, 10:40 PM   #15
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QuoteOriginally posted by kenyee Quote
That's a terrible lens on the K20D...you should sell it to me

In all seriousness, it's a somewhat old design. I think the Nikon 70-200 and Tamron 70-200 beat it in sharpness from what I've seen, so I'm not surprised. It has a nice rendering though. Just stop pixel peeping with it
Hahaha...I know, my eyes hurt already from pixel peeping. I guess you're right, when I scale down to view in 1:2 ratio or enlarge photos from K100D to 2:1 ratio, the difference is almost nil.

QuoteOriginally posted by pentaxmz Quote
Yes and no... actually. Even with a lower resolution sensor, the answer would still be yes and no. But to understand this, one needs to read a long explanation.

... To say the least, this is a controversial topic.
...
If you simply want the best quality photo possible, get the best available Pentax * (or limited) lenses (there are some great Tamron and Sigma PK lenses too), shoot as close as possible to your subject, and shoot with the best lighting possible.
Fiuh...it is a controversial and long explanatory topic. But it's interesting to learn this since I'm also an engineer .

I have some pretty good lenses besides FA*80-200, ex: FA 43 Ltd, FA*24/2, FA 50/2.8 macro, etc.

So far I've only tried FA*80-200 and FA 43Ltd.
At f/4 the FA43 reach the peak sharpness and I think this lens out resolve the sensor.
I still pixel peep and see the sharpness. Amazing lens indeed.

QuoteOriginally posted by RiceHigh Quote
Most of the full frame K lenses, I would say, since the DSLR has a cropped sensor.

First, good Pentax film lenses generally have a resolution of 40 linepairs/mm at an average MTF of around 50%, ....
Rice High, your explanation is interesting and logical.
What does it mean with line pairs?
why the graph always stop at weighted MTF 40lp/mm: 0.5
Does it mean 0.5 is the limit for a lens to be considered acceptable?

QuoteOriginally posted by jeffkrol Quote
The Pentax sensor does not out resolve many current and a bunch of older lenses.
AA filters skew any "mathematical" guessitmations.
will get back to this..

Pentax K20D review Cameralabs resolution results
Re: AA filters: Open Talk Forum: Digital Photography Review

Best:
Do Sensors “Outresolve” Lenses?
I'm waiting..

Yes, I'm reading the article from luminous-landscape. It's a good reading but still doesn't give simple explanation and not so clear conclusion.
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