Thanks Rob. The spreadsheet is very usefull. It's seems my 1.4/50mm resolves no more than 20-30 lpm when used on the *ist D.
Jens Bladt mailto:[EMAIL PROTECTED] http://hjem.get2net.dk/bladt -----Oprindelig meddelelse----- Fra: Rob Studdert [mailto:[EMAIL PROTECTED] Sendt: 2. november 2004 00:30 Til: [EMAIL PROTECTED] Emne: Re: USAF target and resolution tests On 1 Nov 2004 at 17:44, Jens Bladt wrote: > I can't seem to figure out how to convert UASF target photographs to lpm. > All the different explanations rather confuse than help me. Perhaps Rob or > others can explain how the read and covert the results, P l e a s e ? > > Iknow this is digital and not film. I used 55 times distance. Perhaps this > shoul be multiplie by the crop factor 1.55? > Neverthe less, it seems to me the resolution is quite poor compared to negs. > According to tsts done by others this lens i able to resolve up to 98 lpm. If using the *ist D to test lenses via USAF chart you have to be aware of the system limitations. From my past testing I found that the camera/best lens combo can manage no more than about 46lppm absolute resolution. Many lenses (such as the A50/2.8M) are good enough that you can virtually achieve maximum resolution from wide open to fully closed (and is virtually consistent across the entire image area). So the lens must have greater resolution than 46lppm to achieve the system maximum resolution. Testing lenses on the *ist D is relevant but mainly for determining charcteristics other than absolute resolution. My spread sheet can be used to automatically produce lens resolution for any combination of FL and shooting distance, as its not always convenient to use the standard distance multipliers at home. http://home.swiftdsl.com.au/~distudio/lenstesting/#LensTestingResources > Is there a better way to test lenses using a digtal camera. I could of > course test the lens on film...:-( But I still haave to get it - how to read and > convert the groups and elements. The fact is that there are now test suites which when coupled with specialized test targets can provide very detailed reporting of lens distortions and other factors which were difficult to achieve using film testing. Some of these package can even build digital profiles which can be used to correct many of the aberrations of the lens under test so there has really been more gains than losses IMHO. See: http://www.imaging-resource.com/NEWS/1077065799.html Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://members.ozemail.com.au/~distudio/publications/ Pentax user since 1986, PDMLer since 1998
