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Photo Forum / Digital Photography / DSLR Cameras / August 2005Is there any graph that shows lenses versus sensors?
That is, is there anything that says at what point sensor resolution outstrips current lenses in terms of what they are capable of delivering? Lenses have theoretical limits to resolving power, but sensors don't, as far as I know. -Rich > That is, is there anything that says at what > point sensor resolution outstrips current lenses > in terms of what they are capable of delivering? > Lenses have theoretical limits to resolving power, > but sensors don't, as far as I know. The theoretical resolution limit is determined by the sensor array's sampling density or sensor pitch. A sensor array with a sensor pitch of e.g. 6.4 micron (like in an EOS-20D) takes samples every 6.4 microns. To reliably resolve a small feature, it takes 2 sensors (Nyquist limit). That means that this sensor can resolve 78.1 cycles or line-pairs per millimetre. The contrast towards that theoretical resolution is somewhat modified by the Anti-Aliasing filter that is used, but tests will show that in the case of the 20D the 78.1 cy/mm still holds, albeit with reduced modulation in order to reduce aliasing artifacts. Bart > That is, is there anything that says at what > point sensor resolution outstrips current lenses > in terms of what they are capable of delivering? > Lenses have theoretical limits to resolving power, > but sensors don't, as far as I know. > -Rich For Canon L series lenses, it's probably around 25 megapixels. This is based on Linepairs Per Milimeter (lp/mm) comparisons between the best film (slow speed slide film) which reolves around 75 lp/mm and extrapolating the resolution up from the Canon 1Ds Mark II which resolves aroung 60 lp/mm. It's certainly possible that some lenses are capable of resolving well beyond the 75 lp/mm of the best slide film, so the limit of sensor resolution could be even higher, but the lenses had no way of really being tested beyond the limits of the best film. One table that may be of interest to you can be found at: "http://www.katharos.org/david/index.php?option=com_content&task=view&id=19&Itemid=32" Lp/mm is one more reason why larger sensors make sense as resolutions increase. The Olympus E300 for sure, and probably the Nikon D2x, are already exceeding the resolving power of many of the lenses that work with those cameras, not because of the resolution, but because of the lp/mm that are a result of the small sensor size. This is an interesting subject, and I'll probably add lp/mm to the web site tables. Steve http://digitalslrinfo.com >> That is, is there anything that says at what >> point sensor resolution outstrips current lenses [quoted text clipped - 29 lines] >Steve >http://digitalslrinfo.com Doesn't this imply that resolution of some of the P&S cameras is around 200 lpmm? Compared to around 100 lpmm for DSLRs because of the much smaller sensor sizes of some high pixel count P&S sensors? "Bittorrents are REFUNDS for all the BAD movie products Hollywood never gave us refunds for in the past" [] > Doesn't this imply that resolution of some of the P&S cameras is > around 200 lpmm? Compared to around 100 lpmm for DSLRs because of the > much smaller sensor sizes of some high pixel count P&S sensors? Yes, in terms of linear resolving power, the lenses for some P&S cameras will far exceed the resolution of some DSLR lenses. Shock, horror? No. David "David J Taylor" <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid> wrote in message news:T3ZKe.87229$G8.50189@text.news.blueyonder.co.uk... SNIP > Yes, in terms of linear resolving power, the lenses for some P&S > cameras will far exceed the resolution of some DSLR lenses. > > Shock, horror? > > No. Indeed, although some will be shocked. Due to the tiny physical dimensions of the sensor array the image needs a huge magnification for output, which will reduce the resolution rapidly (and magnify the noise and lens aberrations). I use the same criterion as suggested in the <http://www.katharos.org/david/index.php?option=com_content&task=view&id=19&Itemid=32> table intro, sensor lp/mm divided by magnificaton (from sensor array size to output size) should not fall below a certain quality level (e.g. 8 lp/mm for close viewing), anything less is a compromise. Bart > "David J Taylor" > <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid> [quoted text clipped - 20 lines] > > Bart I think it would be more helpful to take sensor size out of the equation, and think of line pairs (or cycles) per picture width when trying to compare DSLRs and P&S, although I also find the idea of representing an MTF curve with a single value as too great a simplification. David "David J Taylor" <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid> wrote in message news:Du%Ke.87354$G8.66013@text.news.blueyonder.co.uk... SNIP > I think it would be more helpful to take sensor size out of the > equation, and think of line pairs (or cycles) per picture width when > trying to compare DSLRs and P&S, although I also find the idea of > representing an MTF curve with a single value as too great a > simplification. That's almost (I used LP/PH) exactly what I posted some time ago, <http://www.xs4all.nl/~bvdwolf/main/foto/Imatest/SFR_Graphs.png>, but that needs an understanding of how such a curve translates to real life images. Also, MTF doesn't tell the whole image quality story although it does describe 'resolution' and contrast better than a single number ever could. Bart > Doesn't this imply that resolution of some of the P&S cameras is > around 200 lpmm? Compared to around 100 lpmm for DSLRs because of the > much smaller sensor sizes of some high pixel count P&S sensors? Consumers love megapixels. Even many DSLR buyers look only at resolution, without looking at pixel size, and those that are smart enough to look at pixel size are usually doing so only from the perspective of noise versus ISO, and deciding that they don't need high ISO capability, they aren't looking at the lpmm. You can look at threads in this newsgroup regarding the noise issues of some DSLRs. I think that lpmm is probably one of the reasons that Canon ended up with three different size sensors for their DSLRs (which probably drives their marketing group crazy). It's not that engineering didn't understand the cost benefits of sticking with a smaller size, it's that it made no sense to have a high resolution digital SLR with a small sensor. Try explaining lpmm to a customer that understands only megapixels. [] > Try explaining lpmm to a customer that understands only megapixels. Cycles per mm are only a relavant measure if the sensor size is the same. Cycles per picture width are a more relevant system comparison. David > That is, is there anything that says at what > point sensor resolution outstrips current lenses > in terms of what they are capable of delivering? > Lenses have theoretical limits to resolving power, > but sensors don't, as far as I know. Sensors do. The limit of the sensor is imposed by Nyquist - an anti-alias filter is required to ensure that the response of the sensor is zero at half the element spatial frequency. In practice, some AA filters are better than others. David |
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