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10-27-2010, 03:25 PM   #1
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Resolution Comparision

I've read various articles and comments all over the net and cannot seem to get a definitive answer to this question:

In terms of ultimate resolution (detail) what system would produce a better image? A 645 slide shot with a prime lens vs a 14-16MP APS-C image from say a K7 or K5?

I'd try it myself, but I lack one of the systems.

Thanks for any input, its appreciated.

10-27-2010, 05:56 PM   #2
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In my opinion, it is a matter of what kind of scanning one's affords. I scan 120 rolls at 16MP as jpegs at times (from a lab) but they are not all that clean. There are better options but they could be really pricey. I would argue that they are close enough. There are other things to balance as you probably are aware of.
10-27-2010, 06:19 PM   #3
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I know scanning is pretty much the deciding factor in the comparison, but I mean ultimate resolution in terms of the individual medium's nature. Meaning a slide on film not scanned, vs a digital file on a computer, which will resolve a more detailed image.
10-27-2010, 06:26 PM   #4
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QuoteOriginally posted by Halco Quote
I know scanning is pretty much the deciding factor in the comparison, but I mean ultimate resolution in terms of the individual medium's nature. Meaning a slide on film not scanned, vs a digital file on a computer, which will resolve a more detailed image.
Again my opinion: a slide can hold much more than 16MP, I believe. Taken full advantage of it becomes a different matter.

10-27-2010, 06:34 PM   #5
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If we can use math to make an answer that's definitive enough for you, the answer is the 645 wins. Here's how:

The K-5 has about 5000 horizontal pixels. The 645 has 56mm of horizontal image area. To record a line pair you need at least two pixels, so the K-5 has a maximum of 2500 horizontal line pairs. To beat this the 645 needs at least 2500/56 (45) line pairs per mm.

A quick look at the Velvia datasheet says 160 "lines per mm", which might well mean line pairs. But even if it doesn't, it would be 80 line pairs, which is a lot more than 45. (And I have no reason to believe Velvia is the highest resultion slide film.)

Looking at the diagonal or vertical size would give the 645 a slightly larger edge, since the format is closer to square.
10-27-2010, 06:42 PM   #6
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This topic is all over the Web and is a matter of endless discussion on the various large format and medium format film forums. The conclusions usually boil down to a few simple points:
  • It depends on the film/sensor
  • It depends on the taking optics
  • It depends on the display system (screen, digital printer, optical enlarger, scanner, etc.)
With one additional suggestion after all the arguments have been presented that resolution, by itself, is fairly meaningless. Truly!


Steve
10-27-2010, 06:50 PM   #7
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QuoteOriginally posted by Halco Quote
I've read various articles and comments all over the net and cannot seem to get a definitive answer to this question:

In terms of ultimate resolution (detail) what system would produce a better image? A 645 slide shot with a prime lens vs a 14-16MP APS-C image from say a K7 or K5?.

I have both a 645 and the K-7. The 645 has much more resolution. The 645D has about the resolution of the film 645 but better accutance.
10-27-2010, 06:54 PM   #8
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QuoteOriginally posted by drougge Quote
If we can use math to make an answer that's definitive enough for you, the answer is the 645 wins. Here's how:

The K-5 has about 5000 horizontal pixels. The 645 has 56mm of horizontal image area. To record a line pair you need at least two pixels, so the K-5 has a maximum of 2500 horizontal line pairs. To beat this the 645 needs at least 2500/56 (45) line pairs per mm.

A quick look at the Velvia datasheet says 160 "lines per mm", which might well mean line pairs. But even if it doesn't, it would be 80 line pairs, which is a lot more than 45. (And I have no reason to believe Velvia is the highest resultion slide film.)

Looking at the diagonal or vertical size would give the 645 a slightly larger edge, since the format is closer to square.
See this previous thread:

https://www.pentaxforums.com/forums/pentax-film-slr-discussion/117371-limits-...otography.html

This is for 35mm film, but the technical aspects are applicable to the larger formats. What is more important than the resolution (lp/mm) is the larger size media at that higher resolution. Even an APS-C size film image should be able to at least equal the K-5 given that 50 lp/mm is quite accessible with currently available films and lenses.


Steve

10-27-2010, 07:27 PM   #9
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QuoteOriginally posted by drougge Quote
If we can use math to make an answer that's definitive enough for you, the answer is the 645 wins. Here's how:

The K-5 has about 5000 horizontal pixels. The 645 has 56mm of horizontal image area. To record a line pair you need at least two pixels, so the K-5 has a maximum of 2500 horizontal line pairs. To beat this the 645 needs at least 2500/56 (45) line pairs per mm.

A quick look at the Velvia datasheet says 160 "lines per mm", which might well mean line pairs. But even if it doesn't, it would be 80 line pairs, which is a lot more than 45. (And I have no reason to believe Velvia is the highest resultion slide film.)

Looking at the diagonal or vertical size would give the 645 a slightly larger edge, since the format is closer to square.
Just like he said, that's the math. Slides, being an analogic media, have as high resolution as the chemicals allow, so it's naturally higher.

Another thing is scanning to put all that resolution to work, though.

At 160 lines per mm, this gives you 25,600 dots per mm, or 650,240 dots per inch. If you have a top quality scanner able to do 4800 dpi, then you can squeeze out of your slide an image that is 10,582 x 15,873 pixels, or about 167 megapixels.

I hope I didn't slip on the math somewhere, but I think it's it.
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