Usually if not specified otherwise lpmm of a lens (Arial) is 50% MTF. my chart figures: ----------------------------------------- lens % more TOTAL RESOLUTION lp/mm of 6 Mp FF Sensor vs. 6Mp APS Sensor
200 4.877246795 190 5.413011111 180 6.034483302 170 6.76054889 160 7.61545148 150 8.630661446 140 9.847515377 130 11.32098694 120 13.12512934 110 15.36099027 100 18.16814884 90 21.74139353 80 26.35410579 70 32.38840375 60 40.36516268 50 50.94376158 40 64.79643351 30 82.12404598 20 101.4719616 10 118.1540215 ----------------------------------------- is based on aerial lenslpmm and sensorlpmm using the equation: Total Resolution = Area * systemresolution^2 where 1/(systemresolution)^2 = 1/lenslpmm^2 + 1/sensorresolution^2 hence when lenslpmm is fixed and less than infinity, the total resolution is always greater with FF vs APS. As the lens gets worse or is stopped down, the FF gets even better. Only a perfect lens with no diffraction limits would allow a APS sensor to resolve as good as a FF and that lens does not exist. Even then it would be as good, never better. Just the opposite with FF sensor. This isn't even taking into account the lower noise a FF sensor allows. Taking lower noise into account, you could possibly shoot FF at faster ISO speeds than APS which could improve lens performance and or camera shake factors. While there may well be no visible difference in resolution of FF vs. APS when using a superb lens at its ideal aperture, when using typical lenses and typical apertures the difference may become very visible indeed according to the numbers above. And what is most important to remember is these differences will become greater as the Mp of the sensors continue to get larger. JCO ---------------------------------------------------------------------------- J.C. O'Connell mailto:[EMAIL PROTECTED] http://jcoconnell.com ---------------------------------------------------------------------------- -----Original Message----- From: Mark Erickson [mailto:[EMAIL PROTECTED] Sent: Tuesday, March 09, 2004 8:54 PM To: pentax-discuss Subject: RE: *ist D sensor and 35mm lens resolution JC, Read Rob's and my messages again. Pay particular attention to words like "significant," "insigificant," and "negligable." A camera is a signal processing system. In such a system, many different components (e.g., lens, film or sensor, physical body, tripod) may significantly influence the quality of the final output. In my engineering experience, it is typical for the limitations of one or two components to dominate. That doesn't mean that performance limitations in the other elements have no effect, just that the effects are insignificant compared to the dominant effects. A negligable difference is not the same as zero difference. I think that Rob and I are both talking about qualitative estimates, possibly educated guesses, of which component limitations dominate and by how much. You seem to keep beating the "absolute" drum, which isn't what we're talking about at all. The statement "I'm right because 0.999 is smaller than 1.0" just isn't convincing. If you want to really make your case, you need to define what you mean by resolution. 50% MTF breakpoint in lpmm? Or something else? How do you define detail? And finally, what exactly do you mean by image? Areal image? Image recorded on film? What are the imaging properties of the film itself? etc. Maybe we should use modulation transfer function (MTF) as the measure instead. Are you comfortable with frequency domain analysis? How about linearity vs nonlinearity in signal processing systems? If you make certain special assumptions about the structure of an MTF (for example that it represents a linear filter with a first-order rolloff characteristic), then you can specify its MTF at all frequencies with a single number like the 50% breakpoint in lpmm. If the MTF is more complicated (and they usually are), then the MTF response at a spatial frequency of 100 lpmm doesn't always say very much about the MTF response at, say, 50 lpmm. Then there are issues of accutance vs resolution that I really don't understand very well at all. I would be really interested to find out if, in practice, the *ist D sensor is the limiting component with, say, a 50mm prime. Norman Koren's MTF measurement methods at http://www.normankoren.com/Tutorials/MTF.html look like a good way to make some measurements.... --Mark JCO wrote: >I dont understand why you guys cant see that with a given, >fixed, lpmm of resolution, even the very best primes, unless it >is infinity, the cropped APS image will be less detailed than >the FF image. Very simple. And as the sensor's Mp gets bigger, >the difference between FF and APS will get even greater. > >The other thing mentioned before is that for a given Mp of sensor, >FF will outperform APS based on larger pixel area and hence lower >noise, greater dynamic range. Bottom line is a FF is better than >APS sensor, both sharper and less noiser, assuming Mp and lens >resolution remains the same. > >JCO
