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01-19-2016, 12:06 AM   #241
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QuoteOriginally posted by zapp Quote
Pixel pitch in micron basically equals the f-stop number where diffraction becomes visible. Two f-stops later it becomes obvious.
Obvious how? In testing and pixel-peeking, or in actual photographs, full size and printed? I don't doubt what you are claiming for an instant (as I said above, my testing has absolutely proved that diffraction steals a lot of sharpness, in testing), but I would argue that, for many, many photographs, it wouldn't matter.

01-19-2016, 12:27 AM   #242
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QuoteOriginally posted by zapp Quote
That is exactly why large format lenses and digital world are not working together that well.
Actually the reason they don't work well together is that medium format digital backs have tiny sensors* compared to full 8X10 format. And that is why even at f/64 a 36X40 inch print from a 10,000 DPI wet drum scan from high resolution B&W 8X10 format film camera will rival, if not surpass anything currently on the market.

* a 36X40 inch print from 60X45mm format is roughly a 19X enlargement, a 36X40 inch print from a 203X254mm negative only needs about 4.6X enlargement. The biggest negative, always wins.

Last edited by Digitalis; 01-19-2016 at 12:33 AM.
01-19-2016, 01:32 AM   #243
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QuoteOriginally posted by asharpe Quote
You don't need bravery. If you want more depth of field, then stop all the way down and damn the torpedoes and diffraction
I agree (except for the damn part).
It is unfortunate that much of the photographic knowlegde from the film era seems to be lost.

In German language, there is a term "Förderliche Blende" (I am unaware of the appropriate translation).

It is the fstop which maximizes depth of field (further stopping down reduces DoF due to diffraction). And all of this terminology still applies, pixel sizes or digital play no role here.
01-19-2016, 03:16 AM   #244
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QuoteOriginally posted by falconeye Quote
I agree (except for the damn part).
It is unfortunate that much of the photographic knowlegde from the film era seems to be lost.

In German language, there is a term "Förderliche Blende" (I am unaware of the appropriate translation).

It is the fstop which maximizes depth of field (further stopping down reduces DoF due to diffraction). And all of this terminology still applies, pixel sizes or digital play no role here.
People often use 'sweet spot' in that sense, although it is not always clear wether they mean "kritische Blende" (maximizing sharpness irrespective of DOF) or "förderliche" Blende.

01-19-2016, 03:31 AM   #245
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QuoteOriginally posted by eyeswideshut Quote
People often use 'sweet spot' in that sense
Optimale blende? With DOF it is all within a bell curve, unless you are working with a lens that is diffraction limited.
01-19-2016, 03:05 PM   #246
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QuoteOriginally posted by asharpe Quote
You don't need bravery. If you want more depth of field, then stop all the way down and damn the torpedoes and diffraction. .
QuoteOriginally posted by falconeye Quote
I agree (except for the damn part).
It is unfortunate that much of the photographic knowlegde from the film era seems to be lost.

In German language, there is a term "Förderliche Blende" (I am unaware of the appropriate translation).

It is the fstop which maximizes depth of field (further stopping down reduces DoF due to diffraction). And all of this terminology still applies, pixel sizes or digital play no role here.
"Damn the torpedoes" is an Americanism from the American Civil War. A Union Admiral, told that mines (then called "torpedoes") blocked the path to their goal, included "damn the torpedoes" in a rousing shout which demanded that his men move forward, and ever since the phrase has meant charging forward regardless of obstacles.
01-19-2016, 03:09 PM   #247
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QuoteOriginally posted by Digitalis Quote
Optimale blende? With DOF it is all within a bell curve, unless you are working with a lens that is diffraction limited.
Sweet spot is pretty generic and "optimale Blende" is undefined (because generic), unlike "kritische Blende" and "förderliche Blende" which are mathematically defined and different from each other.

No, DoF is a bell curve even with a diffraction limited lens. Actually, the mathematical definition assumes a diffraction-limited lens. The "förderliche Blende" is about the fstop where CoC and Airy-disc radius become equal. Cf. Förderliche Blende anhand des Abbildungsmaßstabs berechnen lassen for an online calculator (German again, sorry about that -- but googling for "sweet spot" isn't really getting anywhere ).
01-19-2016, 03:09 PM   #248
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QuoteOriginally posted by Digitalis Quote
Optimale blende? With DOF it is all within a bell curve, unless you are working with a lens that is diffraction limited.
Lens? Isn't it an entire system that would be diffraction limited?

My understanding is that f/11 might be just fine if a particular lens is mounted on an APS-C camera, but would cause serious diffraction if the same lens were mounted on a Q.

01-19-2016, 03:14 PM - 1 Like   #249
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QuoteOriginally posted by reh321 Quote
Lens? Isn't it an entire system that would be diffraction limited?

My understanding is that f/11 might be just fine if a particular lens is mounted on an APS-C camera, but would cause serious diffraction if the same lens were mounted on a Q.
The diffraction for a given f-stop in absolute terms [µm] is the same for all cameras. However, the diffraction as percentage of image diagonal of course varies with sensor size.

This is why I prefer using 35mm-equivalent units (like 35mm-equivalent F16 rather than f/11 on APSC etc.) in all these discussions. Eliminates a redundant variable and should ease communication a day when these conversions lost their emotional property
01-19-2016, 05:38 PM - 1 Like   #250
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QuoteOriginally posted by falconeye Quote
DoF is a bell curve even with a diffraction limited lens. Actually, the mathematical definition assumes a diffraction-limited lens
Mathematicians have no idea how rare diffraction limited lenses are. And in any case DOF should be the same if the lens is diffraction limited or not, image resolution and the point where "kritische Blende" will be achieved will vary.

QuoteOriginally posted by falconeye Quote
The "förderliche Blende" is about the fstop where CoC and Airy-disc radius become equal.
An interesting concept, and it is just typical that Germans have a single word for it, that would require an entire sentence in English to get the concept across.

Last edited by Digitalis; 01-19-2016 at 06:45 PM.
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