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01-22-2009, 03:35 PM   #16
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QuoteOriginally posted by newarts Quote
The final resolution of an image is determined by the weakest link in the lens/sensor/display chain. It is possible for a sensor to resolve better than the lens, but the sensor doesn't make the image worse.

If one is going to use only poor lenses, then maybe one shouldn't bother to buy a K20, but from a resolution standpoint the K20 should produce at least as good an image as the K10.

I couldn't find any MTF data for the SMC 500mm 1:4.5 to compare its resolution to that possible with the K20.


As I see it, the differences between older film lenses vs. the latest digital is optimization. Most of the film lenses 55mm and under are optimized for F8. Lenses with longer focal lengths are optimised ~ FL x .8 to 1. That is a 200 mm film lens's sharpest aperture is between F16 and 20.

Digital designs, especially with regards to APS-C sensors need to be optimized between F4 and F8 - regardless of focal length.

You can not compare lens resolution to sensor in the same way you considered lens to film resolution in the old days. MP/resolution has a lot to do with the AA filter. The K10, with a weak AA filter punches above its weight. That same resolution get in the way by introduced artifacts. The K20 gets rid of the artifacts with a weaker AA filter and, in a 10MP/14MP race appears to swing well.

I have read a few articles about the K20/D50 comparisons. In this case it appears that Canon is using a stronger AA filter that Pentax. It is horses for courses - much like lenses.

I have found, in older lenses, that the orignal Super Takumar 50mm F1.4 is sharper wide open that the later ST, SMC-T, SMC Pentax, M and A series lenses. Contrast is much lower - can be an advantage - than the modern optics with modern coatings.

Of the earlier lenses I own, my personal favorites are any pre M series 35mm f3.5, any 55mm F1.8 and the SMC Pentax 28mm f3.5.

In short, if considering older lenses, little matters if it is a Pentax lens and the focal lenght is less that 105mm. Longer lenses need to be considered on a case by case basis. My own opinion is that the early K mount lenses (SMC Pentax) were the best of Pentax's lens prior to the digital era and a special few A, F, and FA lenses.

Cheers,

01-22-2009, 04:10 PM   #17
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QuoteOriginally posted by bobrapp Quote
..
You can not compare lens resolution to sensor in the same way you considered lens to film resolution in the old days. MP/resolution has a lot to do with the AA filter. The K10, with a weak AA filter punches above its weight. That same resolution get in the way by introduced artifacts. The K20 gets rid of the artifacts with a weaker AA filter and, in a 10MP/14MP race appears to swing well.
Does this say including AA filters the K20D out-resolves the K10D?
01-22-2009, 05:01 PM   #18
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QuoteOriginally posted by newarts Quote
Does this say including AA filters the K20D out-resolves the K10D?
Yes, but not by as much as the difference between number of pixels.

Cheers,
01-22-2009, 06:41 PM   #19
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QuoteOriginally posted by k100d Quote
do you like physics? read this
Do Sensors “Outresolve” Lenses?

i couldn't make it past the first paragraph
Thanks for the link: it was like being back in University Physics lectures in 1965, for me! Some of the words were familiar, although the concepts required a bit more work. In summary, very illuminating, if you'll forgive the obvious…

It probably won't make anyone a better picture-maker (as distinct from photographer) but it just might make a few of us hesitate with our LBA or CBA, especially as new DSLR models with more pixels appear on the market!

01-23-2009, 07:11 AM   #20
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How do you self adjust focusing? :)

QuoteOriginally posted by blende8 Quote
Another weak spot is the focussing as such.
Only if the lens is really optimally focussed, you will get the optimal resolution.
But normally you focuss just once, sometimes even with AF, and get the image.
This will not give you the optimal focus, normally.
You need focus bracketing with very small steps, to get it perfect.

In my experience with lens testing, so far, all my Pentax lenses outperform the sensor, at least in the center, if focussed optimally.

How do you self adjust focusing?

thanks

ok; on page 106 on the k20 book there is AF adjustment

I am guessing that you can easily goo back to default; time to test

Last edited by rdrum76; 01-23-2009 at 07:13 AM. Reason: new stuff
01-24-2009, 10:47 AM   #21
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Steve / wtlwdwgn,
you have caught the holy pope duck there! No worries, the edge fringing is from the saints' halo :-)

Here's another duck, and yes there is an in-focus area, but the lens is underresolving,

Triplet lens Trioplan 2.8/100 on K100D

My experience so far with clear underresolvers is:
- you will get some kind of grain (well not really filmlike but not too bad)
- you will get some glow with open apertures (not necessarily the result of underresolvance)
- postprocess could be to apply some kind of gaussian blur first (my pp skills are lagging)
- cropping is limited much more than on 'tacksharp' lenses
- AFAIR such lenses look better on a K20D than on K100D (no idea why)

Best, Georg (the other)
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