I don't follow your logic, the higher the overall sensor resolution and sensor pixel densities get with time, the more the overall system resolution depends on the lens' absolute resolution AND FORMAT SIZE. If you use two lenses with same across the board resolution ( say 60 lp/mm), the larger FF sensor will approach 50% higher linear resolution (2.25X total resolution) with infinitely good sensors. Conversely, with infinitely good sensors, a FF lens with only 66% percent of the APS lens would give same overall system resolution. Now of course the sensors are not infinite resolution, but the same logic applies, all else being equal, the larger format will give higher system resolution for a given lens resolution or for same system resolution a lower resolution lens on the larger FF format can give same system resolution. This sounds like talking in circles I guess.
Anyway, sure if you have FF lenss that in the corners are less than 66% of the APS lens minimum, then nothing is to be gained. And sure, I guess on some mediorce or really wide angle lenses not designed for digital that may be occuring, but there are also many great FF lenses than have corner to corner performance at some apertures that exceeds 66% of the APS lens counterpart's resolution, and with those lenses at those apertures the net result is higher overall system resolution with FF vs APS. -- J.C. O'Connell (mailto:hifis...@gate.net) Home Page - www.jchriso.com Join the Audio CD PLAYER DISCUSSION list - http://tech.groups.yahoo.com/group/cdplayers/ -----Original Message----- From: pdml-boun...@pdml.net [mailto:pdml-boun...@pdml.net] On Behalf Of Adam Maas Sent: Saturday, August 29, 2009 7:19 AM To: Pentax-Discuss Mail List Subject: Re: OT: Sony Releases A850 FF Camera for $2,000 On Sat, Aug 29, 2009 at 6:30 AM, J.C. O'Connell<hifis...@gate.net> wrote: > Adam wrote : "Unfortunately while that's a nice theory it is not born > out in practice....."edit, see full quote below. > > No, I don't agree. Are you trying to say that a FF lens has to have > the same resolution across the board as an APS lens across the board > to match the APS overall system resolution?? No it wouldn't, That > makes no sense. You are correct from a theoretical standpoint. The problem is that in general we aren't dealing with systems of similar resolution but rather with systems of similar pixel density. Given current pixel densities common to 35mm FF and to APS-C cameras on the market today, there is only a fairly small difference in the necessary lens resolution to be sufficient for good results from each format, but it's significantly more difficult to maintain that necessary resolution across the 35mm frame, particularly with wide-angle lenses. > > With the sensors at the overall resolution of today (6Mp and up) a FF > system will outperform an APS system of same total pixels with same > quality lens in absolute lp/mm by a large margin, so much so that like > I said, even with a LOWER quality lens in lp/mm it still can > outperform or match an APS system on resolution. Yes, pixel density > matters, but with todays overall sensor resolutions, pixel density is > already high enough such that lens quality significantly affects > overall resolution. If sensors had much lower overall pixels, lenses > wouldn't matter as much and sensor size wouldn't help things, but by > now, lenses to matter and sensor size help improve performance with > real world lens resolutions. First off, given the same quality of lens of sufficient performance, ie a lens which exceeds theperformance requirements of each system the performance difference between FF and APS-C is small, not large in the real world given identical pixel count. There's just not enough difference in the size of the formats (It's just about exactly a doubling in area, notably smaller than the jump from 35mm to even 645) The only real advantages of FF become better High ISO performance and slightly increased dynamic range. But even in the case where this holds true (Which is only with the Nikon 12MP FX bodies) getting sufficient corner performance out of the lenses on FF is becoming difficult, whereas we aren't hitting serious performance issues with mid-range lenses on even 15MP APS-C. 20+MP Full-frame, which accounts for the majority of the FF bodies on the market today has pixel densities in the 10-12MP APS-C equavalent range and therefore needs similar performance from lenses across the 35mm frame to not show visible degradation in the corners. This is MUCH harder to acheive than a lot of people expected. This is a case where theory and real-world performance part ways due to other factors. In fee simple, getting the necessary resolution for even 15MP APS-C across the APS-C frame is easier for lens designers than getting the edge performance on 35mm FF necessary to not show degraded corner performance on 12MP FF and that degraded corner performance can be seen on prints. So while your math is correct, what works in theory in this case doesn't in practice because of additional factors. > > Of course its harder to design a FF lens that has same resolution as > an APS lens at same focal length, but with the larger FF sensor, you > need to use longer focal length ( same AOV ) and it doesn't NEED to be > same resolution as the APS lens to still outperform APS system > overall. > > > J.C. O'Connell (mailto:hifis...@gate.net) The problem being that as a practical matter, the FF lens needs to closely approximate the APS-C lens's resolution across a wider image circle because the FF sensor has similar pixel density to the APS-C and thus will resolve similarly. It comes down to two things. FF simply doesn't have enough of a size advantage over APS-C to reap the advantages inherent in a larger format in a significant way and the much higher pixel count of most FF bodies means they need lens resolutions approaching that demanded by the highest-resolution APS-C sensors but across the larger frame which is significantly more difficult. As a practical matter, it's easier to design lenses which are up to the performance of APS-C sensors at current pixel densities than to do the same for current FF sensors. This means that there is a fairly large cost delta inherent to FF due to the demand for the highest performance lenses available, while APS-C can deliver its practical best with much cheaper glass. -- M. Adam Maas http://www.mawz.ca Explorations of the City Around Us. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
