"Sharpness" and resolution are closely tied together, so I will discuss them both.
Resolution is objective and quantifiable. It is a measure of the ability to separate two identical objects as they are brought close together. In photography, this is measured in lines per millimeter where the lines are black the spaces between the lines are white. Typically, the lines and spaces are the same width. The maximum possible resolution for any lens can be calculated from it's f/stop. The larger the stop (smaller number) the higher the maximum possible resolution. Unfortunately, the larger the glass, the harder it is to grind it perfect, make all the corrections necessary to mitigate the effects of various aberrations and control various types of dispersions, and align the elements to take advantage of this potential. Contrast is essential for good resolution, else the black is already somewhat gray to begin with and the white to is somewhat gray. Unlike resolution which is quantifiable, sharpness is a perception of the eye and the mind. Without good (or at least reasonable) resolution there would be no sharpness, but the mind can be fooled. Sharpness therefore contains an element of the subjective. Three different examples: 1. A photo with poor resolution can be scanned into Photoshop where it looks not sharp. The operator can apply a spatial filter called an unsharp mask to bring up the sharpness but not resolution. In fact, though edges appear sharper, resolution is actually decreased. 2. A lens with acceptable resolution but poor bokeh will often generate a similar result. It's operating as a similar spatial filter. 3. The effects of diffraction rings in a pinhole camera produce a similar effect giving a pinhole photograph greater apparent sharpness than it's resolution would suggest. Again, though apparently sharper, the ability to resolve (distinguish between) two closely spaced objects is poor. Regards, Bob... -------------------- "Let us contemplate our forefathers, and posterity, and resolve to maintain the rights bequeathed to us from the former, for the sake of the latter. The necessity of the times, more than ever, calls for our utmost circumspection, deliberation, fortitude, and perseverance. Let us remember that 'if we suffer tamely a lawless attack upon our liberty, we encourage it, and involve others in our doom.' It is a very serious consideration that millions yet unborn may be the miserable sharers of the event." - Samuel Adams, 1771 ----- Original Message ----- From: "William Robb" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Tuesday, January 15, 2002 2:42 PM Subject: Re: And did I mention wrong > ----- Original Message ----- > From: "Mike Johnston" > Subject: And did I mention wrong > > > > > There is no such thing as apparent sharpness. Sharpness is > an > > > absolute and quantifiable value. > > > > > > Wrong, wrong, wrong. > > Please elaborate. > > William Robb > - > This message is from the Pentax-Discuss Mail List. To unsubscribe, > go to http://www.pdml.net and follow the directions. Don't forget to > visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
