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02-12-2010, 03:00 AM   #1
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M 50mm MTF charts

Does anyone have some testing experience of the M f2. Is it sharper than the f1.7?

02-12-2010, 03:11 AM   #2
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QuoteOriginally posted by hoojammyflip Quote
Just found this link on the web, which interested me greatly. It appears the f2 behaves better than the fast 50mm lenses.
Pentax K fit 50mm's Photo Gallery by steve flynn at pbase.com

Does anyone have some testing experience of the M f2. Is it really better than the more expensive lenses?
Who's the source of these charts? Some companies publish computer generated "ideal charts."

A non-flat line could imply a non-flat field of focus.

Here's a quote from luminous-landscapes.com:

"To get a really good idea of a lens's performance using MTF, you'd need a "family" of charts. For starters, every lens will perform differently at different apertures and at different distances. Just charting an F/16 lens for three different object distances say, infinity, close focus, and perhaps 20 x F, where F = focal length, would mean you'd need 21 different charts. Really, you should have charts for at least six (and ideally, thirty!) randomly-chosen production samples, too, to account for sample variation. There are a dozen or so other conditions you should measure at every aperture and taking distance. You can see how the volume of data would quickly get out of hand for enthusiasts. But do bear in mind that when manufacturers give you one chart, it only measures performance at one aperture and one distance. That doesn't really tell you much, except comparatively, and it may not tell you want you need to know." (Understanding Lens Contrast)
02-12-2010, 03:37 AM   #3
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QuoteOriginally posted by hoojammyflip Quote
Is it sharper than the f1.7?
To compare resolution of finer details, look at the curves with bigger L/mm and LP/mm number (the bottommost curves). According to those charts, at f/4, 50mm f/1.7 is sharper in the center than 50mm f/2 (although the sagital and meridonial measurement curves differ).
02-12-2010, 09:01 AM   #4
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QuoteOriginally posted by hoojammyflip Quote
Does anyone have some testing experience of the M f2. Is it sharper than the f1.7?
Evidence from owners (I own both) will tell you the 1.7 wins on the sharpnes stakes

02-12-2010, 09:07 AM   #5
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People often assume or outright claim that the M 50 f/2 is not very sharp, and that's always puzzled me - it is actually a very sharp lens. But the A/M/F/FA 50 1.7 is sharper in my experience.
02-12-2010, 09:14 AM   #6
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forum member carpents did a test / showdown of a bunch of 50's here:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/8318-lens-test...-any-good.html

The M50/2 didn't make it past the first round, but neither did the M50/1.7.

The M50/1.7 and all the 50/1.7's have a reputation for outstanding sharpness, beyond that of the f/1.4 versions, because for the 1.4 versions they wanted nicer bokeh. Carpents' test doesn't support that, but who knows?

There was another theory that the M50/2 and M50/1.7 were actually the same lens, just one was prevented from opening up (can't find the reference, but I didn't make it up--maybe somebody trying to sell a 50/2? :lol"). The 50/2 is lighter and has fewer elements, so that theory's probably out!
02-12-2010, 09:35 AM   #7
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Is the OP trying to justify a 50mm f2 purchase? There's no way really to know the difference without trying both lenses. Like most users, I suspect that you will be left wanting more (whether you need it or not).
02-12-2010, 09:40 AM   #8
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QuoteOriginally posted by farfisa Quote
There was another theory that the M50/2 and M50/1.7 were actually the same lens, just one was prevented from opening up (can't find the reference, but I didn't make it up--maybe somebody trying to sell a 50/2? :lol"). The 50/2 is lighter and has fewer elements, so that theory's probably out!
Funny thing is M 50 f/1.7 has 6 elements, while the M 50 f/2 has 5 elements.
If you believe in the theory of integers, you can probably dismiss the theory you mentioned.

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Last edited by asdf; 02-12-2010 at 10:02 AM.
02-12-2010, 10:30 AM   #9
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Yep, I am thinking about picking up a f2 just to see! They are so dirt cheap, why not? If the 1.7 is sharper though, I won't bother for the moment.

Its just the chart for the f2 version looked good at f4, better than the f2. Interestingly on that link, the Cosina f2 appears to have better MTF numbers than the other lenses full stop. Both wide open and at f4. Very suprising.

I edited the original link out, once I saw it had the chaps name in it, but someone got in there with a reply and so now its in the thread, so here it is again for anyone who missed it.
Pentax K fit 50mm's Photo Gallery by steve flynn at pbase.com

Here is a link on MTF charts from Zeiss
http://www.zeiss.de/C12567A8003B8B6F/EmbedTitelIntern/CLN_30_MTF_en/$File/CLN_MTF_Kurven_EN.pdf

It does seem that lenses are optimised for different object distances, and without that being specified in the MTF, it renders the MTF less useful.
02-12-2010, 10:39 AM   #10
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QuoteOriginally posted by hoojammyflip Quote
Here is a link on MTF charts from Zeiss
http://www.zeiss.de/C12567A8003B8B6F/EmbedTitelIntern/CLN_30_MTF_en/$File/CLN_MTF_Kurven_EN.pdf
Thanks for the link.

"The performance data of a lens, irrespective of whether it is calculated by computer or measured in the laboratory, fill a small file."

At least out of perverse curiosity, I'd like to have access to those files, sometimes.
02-12-2010, 10:40 AM   #11
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QuoteOriginally posted by farfisa Quote

There was another theory that the M50/2 and M50/1.7 were actually the same lens, just one was prevented from opening up (can't find the reference, but I didn't make it up--maybe somebody trying to sell a 50/2? :lol"). The 50/2 is lighter and has fewer elements, so that theory's probably out!
.

I think you might be remembering the Tak 50 f/2 and 50 1.8 - both are the exact same lens, one just with a 'crippled' diaphram , IIRC.
02-12-2010, 10:40 AM   #12
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QuoteOriginally posted by jsherman999 Quote
People often assume or outright claim that the M 50 f/2 is not very sharp, and that's always puzzled me - it is actually a very sharp lens. But the A/M/F/FA 50 1.7 is sharper in my experience.
I wonder whether people have considered resolution limits of a sensor. A 1.5 crop sensor with 10MP has 161 pixels per mm. I guess that this limits resolution to something like 80lp/mm. In turn, this means any lens resolving higher than 80lp/mm will be irrelevantly sharp...really the question is contrast and not sharpness.

I think the perception of sharpness is being confused with contrast in most cases. The MTF is all about the contrast for a given level of detail (10lp/mm and 20lp/mm being the most relevant detail). I think photodo suggests that a lens needs to be over 60% to be considered useful, at the 40lp/mm detail.

Last edited by whojammyflip; 02-12-2010 at 10:53 AM.
02-12-2010, 10:56 AM   #13
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QuoteOriginally posted by farfisa Quote
forum member carpents did a test / showdown of a bunch of 50's here:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/8318-lens-test...-any-good.html

The M50/2 didn't make it past the first round, but neither did the M50/1.7...
Unfortunately, useful as the contest is, Sean's shoot-out was single elimination. The final rankings and even the eliminations were based as much on his personal preference as anything. There are several lenses that might have ranked higher had they been given another chance in a second round.

Considering the M 50/1.7...its first round pairing was against the Micro-Nikkor and its elimination was not on the basis of comparison with its opponent, but in comparison to other lenses in the survey.

As for the M 50/2...it was matched with the FA 50/1.4, a clear favorite.

One of the more interesting things about the shoot-out is that none of the entries were clear "stinkers". All were capable and none had fatal deficiencies.

Steve
02-12-2010, 10:58 AM   #14
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QuoteOriginally posted by jsherman999 Quote
.

I think you might be remembering the Tak 50 f/2 and 50 1.8 - both are the exact same lens, one just with a 'crippled' diaphram , IIRC.
"Crippled diaphragm" and an internal baffle IIRC...

Steve

BTW...55/2 and 55/2.8...
02-12-2010, 11:24 AM   #15
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QuoteOriginally posted by stevebrot Quote
"Crippled diaphragm" and an internal baffle IIRC...

Steve

BTW...55/2 and 55/2.8...


Yes, 55 f/2 and 55 f/1.8, not 50. The K versions might have the same relationship.

link --> The Cheapest Takumar!


.
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