That's goes along with what I say about lens ratings in MTF and resolution. Lenses with ratings in the 3.2 range are hard to tell from lenses in the 4.0 range on film. That's why some brand loyal guy can say his lens is better than the other guys when in actuality it might be worse in testing but undetectable in film. Good example is the Pentax 80-200/2.8 which doesn't fare that well in Photodo's MTF resolution tests. And I seem to remember they have tested more than one of those with the same results (around 3.2 I think while my Sigma 70-200 EX gets a 3.9). But in reality on film you can't see any of that and it produces superb images. The only testing parameter you can actually see results in is the distortion value. Kent Gittings
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Bob Rapp Sent: Friday, October 26, 2001 7:41 AM To: [EMAIL PROTECTED] Subject: RE: DOF and format size Anthony wrote: "What you missed is that as film formats get larger the lens needed to get a certain angle of view also lengthens, so the amount of DOF getting onto the film in the first place is less." With very minor variations, the depth of field is a function of "angle of view" rather than focal length. Thus a suitable lens selected for 4X5, or 8X10 for that matter, will have the same depth of field - aperture for aperture as the 35mm counterpart. This applies as long as the reproduced images are the same size and not enlarged the same degree. In addition, a large format lens such as the 65mm Rodenstock Grandagon N offers its highest resolution at apertures between 22 and 32. The depth of field will be enormous although one would argue that diffraction will cause degradation. True, however the negative is almost 4 times the size that of a 24x36 35mm frame. What is also missed is that current 35mm films cannot capture the resolution of some of our higher quality lenses. In 4X5 photography the lens need to only be 1/4 as sharp (which is not the case) as lens for 35 mm to deliver the same amount of sharpness. Bob - 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 . ********************************************************************** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This footnote also confirms that this email message has been swept by MIMEsweeper for the presence of computer viruses. www.mimesweeper.com ********************************************************************** - 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 .
