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02-04-2011, 09:50 AM   #1
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Which lenses reach the resolution of a K5?

Currently I am using a 16-45 DA. Have just ordered the 17-70.

I just wonder if anybody has ever worked out whether these sorts of lenses are good enough for a K5-level camera, or if they are in fact too good?

Most of my shooting (at least where I want max sharpness) can be done at say F8.


Last edited by peterh337; 02-04-2011 at 09:57 AM.
02-04-2011, 10:31 AM   #2
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You might go here:

https://www.pentaxforums.com/forums/pentax-k-5-forum/124684-old-lenses-adequate-k-5-a.html
02-04-2011, 11:13 AM   #3
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Interesting, but nobody actually delivers any hard data.

There is some data out there on the resolution of some lenses, but how does this map onto the megapixel spec of the camera sensor?
02-04-2011, 11:18 AM - 1 Like   #4
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In my very unscientific humble opinion:

Film has better resolution than digital. Therefore, any lens that is good enough for film has enough resolution for any DSLR.

Trust me, I own a chainsaw.

02-04-2011, 11:25 AM   #5
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Lol, that was by far the best answer I've read in some time.
Also wins the price for best equipment list.
02-04-2011, 01:23 PM - 1 Like   #6
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QuoteOriginally posted by ajoe Quote

Trust me, I own a chainsaw.
I tend to trust you
02-04-2011, 01:46 PM   #7
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If everything aligns perfectly with that sensor, you're looking at 210 pixels per mm of information...ie a maximum resolution of 105 lp/mm. Now if a 105lp/mm pattern sat exactly pi out of phase with that sensor you'd see grey mush, so more like 50lp/mm guaranteed resolution (thats a back of the envelope guesstimate). I think most primes should manage 50lp/mm, but not many will deliver 100lp/mm with reasonable contrast. I doubt zooms will show off the quality of the sensor.

If on a budget, I really like the M series of primes. Great metal housing and threads means the elements are held in alignment. This means on axis rays pass in a straight line. I dont understand how modern plastic stuff can offer consistent alignment. However, old wide angles don't offer aspherics (to avoid monochromatic aberation) and extreme telephotos require low dispersion glass (to avoid chromatic aberation), and as I understand it, modern optics are better in this respect. I'd say you couldn't go wrong with something like a selection of modern DA Ltds.
02-04-2011, 02:45 PM   #8
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QuoteQuote:
Film has better resolution than digital
I am not so sure.

A few years ago I scanned my ~ 5000 35mm slides with a Nikon ED5000 scanner.

The scanner, with a bulk feeder taking 50 at a time, cost me GBP 1500. (I later sold it for GBP 500). There was another Nikon scanner, costing GBP 5000 (can't recall the model). I tested both scanners at a shop, against several "difficult" slides I had, and both delivered a visually identical result, and both showed the film grain clearly.

The resolution-wise best film I ever used was Kodachrome 25, but I rarely used it because it was nearly useless without a tripod. I went through a period of using Ektachrome 64 (real crap material; grainy as h*ll - some U.S. forums delete posts with the "h" word ) and the last film I used was Fuji Provia 100 which I think is comparable to Kodachrome 25. Even on Provia, the ED5000 showed the grain clearly.

The scanner was 4800dpi which translates to very roughly about 20 megapixels of a full-frame DSLR sensor.

The 15MP K-5 doesn't show any grain, of course.

So I think that the old lenses I had probably exceeded the capability of a 20MP sensor.

A DSLR of less than full frame will need a smoother lens because the image is passing through a laterally smaller bit of glass, but lenses have probably improved since 20-30 years ago.

Anyway, ISTM that lenses are not the limiting factor on a 15MP camera.

QuoteQuote:
If everything aligns perfectly with that sensor, you're looking at 210 pixels per mm of information...ie a maximum resolution of 105 lp/mm. Now if a 105lp/mm pattern sat exactly pi out of phase with that sensor you'd see grey mush, so more like 50lp/mm guaranteed resolution (thats a back of the envelope guesstimate)
That's true but a real-world image is not made up of lines close together. The "lines" in the image will be much thicker, and any lack of resolution will be visible on the edges.

I also see a sharper image at 15MP (16MP?) than with the camera set to 10MP.

BTW, 210 lines/mm translates to 5250 dots per inch; that is about the top slide scanners, unless you go to drum scanners and they are no good for bulk scanning. Since the ED5000 showed clear grain, this close equivalence suggests that a 16MP DSLR well exceeds any film resolution.

02-04-2011, 03:25 PM   #9
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how is it about moiré? if I can get it in my picture is the lens sharp enough for the camera?
02-04-2011, 04:10 PM   #10
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Its interesting that my ist DS appears to produce very "sharp" images with its 6mp sensor. I feel the number of mp are only part of the story in image quality. Some of my pictures from my M50mm f4 just "pop" as I see people used to say in the past, even when shot on ISO 800 film...not exactly high resolution, but just great feel in the image, like the subject is coming out of the print.

Maybe lenses are more important than the camera. I'd love to try some of the DA ltds...when my budget allows, as a single one costs the equivalent of my entire M collection.

I believe the eye can detect only about 5lp/mm in a print, and most prints are 5x, so 25lp/mm is all thats needed. Maybe a bit more is required for enlargements from APS-C.

Maybe a tripod is more important than a lens?
02-04-2011, 04:58 PM   #11
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QuoteOriginally posted by hoojammyflip Quote
Maybe a tripod is more important than a lens?
Bingo!
02-05-2011, 12:27 AM   #12
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The K5 sensor implies diffraction-limiting of the lens beyond about f9, so I would look for lenses that seem to be diffraction limited at f8. You might be able to judge this at a glance when looking at resolution "curves": such a lens would show reolution falling rapidly beyond f8, and rising appreciably for f5.6.

I suspect most lenses which exhibit this kind of characteristic would probably be capable of doing the K-5 sensor justice. For some examples of resolution curves, you could look here:

ERPhotoReview
02-05-2011, 01:13 AM   #13
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That review site has very little Pentax zoom data so it's hard to know what to make of it for e.g. a 17-70.

But it appears clear that if you want max sharpness you need to be using F5.6 or F8.
02-05-2011, 01:36 AM   #14
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QuoteOriginally posted by peterh337 Quote
That review site has very little Pentax zoom data so it's hard to know what to make of it for e.g. a 17-70.

But it appears clear that if you want max sharpness you need to be using F5.6 or F8.
True, but I was only suggesting a look at the site to get a "feel" for the sort of resolution curves to expect.

My main point was that a lens which is suitable for the K-5 could be identified by a falling-off of resolution from f5.6, with a very definite drop from f8 to f11.
02-05-2011, 01:41 AM   #15
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Just to amplify my point, I would say that, if a lens has a characteristic which is fairly flat around f5.6 to f11, then it probably ain't good enough!
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