Re: 28/2-class lens specs: Seven Third-Party Lenses vs. Three Pentax 28/2s(was: Re: fast kiron on ebay)
Rob, A longer barrel--such as that used on the SMC 28/2, which was designed with Zeiss--can bend the rays more "gently." Isn't extra barrel distortion one of the compromises usually introduced by a shorter lens (unless, perhaps, an aspherical element is used)? Isn't that why "no compromise" lenses are typically longer, and use more elements? Or do I need to brush up on my limited understanding of Cartesian optics? PS: Of course, every lens design is a compromise. By no-compromise, I mean to suggest "the best a lens maker has to offer." "Rob Studdert" [EMAIL PROTECTED] wrote: Subject: Re: 28/2-class lens specs: Seven Third-Party Lenses vs. Three Pentax 28/2s (was: Re: fast kiron on ebay) On 10 Mar 2001, at 19:20, [EMAIL PROTECTED] wrote: To my eye, 28mm is the widest practical focal length for "people-shooting," which is what I do. True, it makes people at the edges of the frame look fat. But this problem is minimized by selecting a well-corrected prime. Hi Paul, Please explain, to my mind there should be a similar degree of perspective distortion present (ie elongation of close objects at the edge of the frame) in any well corrected optic. The only way that I can imagine that there would be differences is if the lens that looks more normal has a semi-spherical plane of focus? Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 Fax +61-2-9554-9259 UTC(GMT) +10 Hours [EMAIL PROTECTED] - 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 .
Re: 28/2-class lens specs: Seven Third-Party Lenses vs. Three Pentax 28/2s(was: Re: fast kiron on ebay)
Hi, I am not Rob but I think he's right. I my (also limited) understanding the elongation of objects near the edge of the image produced by rectilinear super wide angle lenses is not related to optical aberrations of these lenses. It is inherent in how the image is projected on the film by these lenses. To avoid this you need a "cylindrical projection" (with the viewer in the center of the cylinder) as is provided e.g. by the Seitz roundshot camera. Also fish-eye lenses do not show such kind of elongations of close subjects near the edge. Alexander Mike Johnston wrote: Rob, A longer barrel--such as that used on the SMC 28/2, which was designed with Zeiss--can bend the rays more "gently." Isn't extra barrel distortion one of the compromises usually introduced by a shorter lens (unless, perhaps, an aspherical element is used)? Isn't that why "no compromise" lenses are typically longer, and use more elements? Or do I need to brush up on my limited understanding of Cartesian optics? PS: Of course, every lens design is a compromise. By no-compromise, I mean to suggest "the best a lens maker has to offer." "Rob Studdert" [EMAIL PROTECTED] wrote: Subject: Re: 28/2-class lens specs: Seven Third-Party Lenses vs. Three Pentax 28/2s (was: Re: fast kiron on ebay) On 10 Mar 2001, at 19:20, [EMAIL PROTECTED] wrote: To my eye, 28mm is the widest practical focal length for "people-shooting," which is what I do. True, it makes people at the edges of the frame look fat. But this problem is minimized by selecting a well-corrected prime. Hi Paul, Please explain, to my mind there should be a similar degree of perspective distortion present (ie elongation of close objects at the edge of the frame) in any well corrected optic. The only way that I can imagine that there would be differences is if the lens that looks more normal has a semi-spherical plane of focus? Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 Fax +61-2-9554-9259 UTC(GMT) +10 Hours [EMAIL PROTECTED] __ Do You Yahoo!? Yahoo! Auctions - Buy the things you want at great prices. http://auctions.yahoo.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 .
Re: 28/2-class lens specs: Seven Third-Party Lenses vs. Three Pentax 28/2s (was: Re: fast kiron on ebay)
On 11 Mar 2001, at 10:10, [EMAIL PROTECTED] wrote: Rob, A longer barrel--such as that used on the SMC 28/2, which was designed with Zeiss--can bend the rays more "gently." Isn't extra barrel distortion one of the compromises usually introduced by a shorter lens (unless, perhaps, an aspherical element is used)? Isn't that why "no compromise" lenses are typically longer, and use more elements? Or do I need to brush up on my limited understanding of Cartesian optics? PS: Of course, every lens design is a compromise. By no-compromise, I mean to suggest "the best a lens maker has to offer." Hi Paul, Rectilinear lenses should all provide the same projection on the film plane, it they did not then straight objects placed at the edge of the frame would be rendered curved. Therefore all well corrected rectilinear lenses should provide the same degree of subject elongation. The fact that the better SLR wide angle lenses (particularly pre-aspheric) tend to be long is due to their retrofocus design which is by all means a compromise designed to make available space in front of the film plane for the SLR mirror to swing. Don't kid yourself about SLR wide angle lenses, for real no compromise designs check out the Leica-M, Contax-G and Mamiya RF designs, most are virtually symmetrical designs and have a magnitude lower distortion than the best retrofocus wides, many are designed such that their rear elements are merely mm from the film plane. :-) Cheers, Rob Studdert (eBay ID: distudio) PO Box 701 HURSTVILLE BC NSW 1481 AUSTRALIA Tel +61-2-9554-4110 Fax +61-2-9554-9259 UTC(GMT) +10 Hours [EMAIL PROTECTED] Please check my current eBay auctions: http://www.ozemail.com.au/~distudio/ebay/ - 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 .
Re: 28/2-class lens specs: Seven Third-Party Lenses vs. Three Pentax 28/2s (was: Re: fast kiron on ebay)
On 10 Mar 2001, at 19:20, [EMAIL PROTECTED] wrote: To my eye, 28mm is the widest practical focal length for "people-shooting," which is what I do. True, it makes people at the edges of the frame look fat. But this problem is minimized by selecting a well-corrected prime. Hi Paul, Please explain, to my mind there should be a similar degree of perspective distortion present (ie elongation of close objects at the edge of the frame) in any well corrected optic. The only way that I can imagine that there would be differences is if the lens that looks more normal has a semi-spherical plane of focus? Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 Fax +61-2-9554-9259 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://www.ozemail.com.au/~distudio/publications.html - 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 .
Re: 28/2-class lens specs: Seven Third-Party Lenses vs. Three Pentax 28/2s (was: Re: fast kiron on ebay)
Paul - Interesting table. Just to fill in a gap or two, I have a Vivitar 28 f2 (not the close focuing one) - minimum focusing distance is 1 meter, 6 aperture blades. I ran some test with it when I first got the lens - I'd have to say it is a so-so performer. I recently added a Rikenon 28 f2.8 to the bag, and it is a surprisingly good lens. -- MCC At 07:48 PM 3/9/01 -0500, you wrote: -- Dan, I don't own the Vivitar Close Focus 28/2; that's a different lens, more closely related to the Kiron than to the Series 1 1/9. However, here are the specs for seven fast third-party K-mount 28s, shown together with Pentax's 28/2 offerings: Vivitar 28/2 ? in. (? in.) (?) f/16 55mm 2 ?? 08 ?/? ? 79-?? No - - - - - - - - - - Mark Cassino Kalamazoo, MI [EMAIL PROTECTED] - - - - - - - - - - Photos: http://www.markcassino.com - - - - - - - - - -
