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Author Topic: How much sensor resolution do we need to match our lenses?  (Read 8033 times)
ErikKaffehr
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« Reply #60 on: May 24, 2014, 09:42:49 AM »
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Jim,

I have rechecked and you are right. When I compare all tests on D800E the Otus has still what may be a significant advantage at medium apertures. Sorry for jumping conclusions!

Best regards
Erik

Erik, it looks to me like the Otus tests were made on a D800 with its AA filter, and the other two lenses ere tested on a D800E with no (well, OK, a now-you-see-it-now-you-don't) AA filter.

Jim
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joneil
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« Reply #61 on: May 25, 2014, 10:28:18 AM »
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 Can I make a point off tangent a bit here.   

  I tried out a couple of Zeiss Otus lenses on my D800 this past week, and compared them too my "regular" Zeiss ZF2 lenses on my D800.   Came home, pulled them up on screen, looked at them closely.  No math or other technical points, just my  gut feeling reaction here:

1) Pros
- build quality is second to none;
- optically, yes, I think better then the "regular" Zeiss lenses;

2) Cons
- while optically better than "regular" Zeiss lenses, that is like saying brand A of sports car is better than brand B because brand A does the quarter mile a tenth of a second faster than brand B.   IMO, the regular Zeiss lenses are in most cases so far ahead of many other lenses, well, it depends on what you are looking for;
- while the build quality is better, they are huge and heavy lenses compared to the "regular" Zeiss lenses.   I mean, in real world use, if I am going for a 2 or 4 hour hike in the bush, hauling around a lens that is twice the weight (or more) of it's closest equivalent - I dunno.  I mean, it is not money alone, as there is a reason i now use carbon fibre tripods and monopods as opposed to aluminium ones, I am just saying, do people think about these situations outside the lab?
- cost.   I can almost buy three ZF lenses for the price of one Otus.  I just don't have those kind of dollars.

   so my apologies if I have offended anyone, especially those who own or plan to own an Otus.   Wonderful lens, I am very impressed by it.   All I am saying is no matter how good it is, think about real world use, not just charts and diagrams.

  One more weird thing.  i was testing these lenses at the big camera show in Toronto this past weekend, hosted and put on by Henrys.   The main "theme" of this years expo was improving your smart phone photography.  Even the local media was in on it.  New software for your iphone, new lens adaptors for both telephoto and macro shots on your iphone, etc, etc.   Everything was about how good, how high the quality of the iPhone and other smart phones were.

   The Zeiss both, where I was playing with the Otus lenses, was right beside the area promoting "the art of phonography" as they were calling it.

    Irony, eh?
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Jim Kasson
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« Reply #62 on: May 25, 2014, 10:58:01 AM »
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I ran a more complete Otus sim versus f-stop and pitch yesterday.

Here's a 3D look:



Here it is in two dimensions with f-stop as the horizontal axis:



Now we can see where improving sensor resolution stops helping; there's not much improvement as we go from a pitch of 2.4 um to one of 2 um.

And here it is in two dimensions with f-stop as the horizontal axis:



Making the pitch finer doesn’t help much at all at f/16.

There are curves for diffraction-limited lenses, both with and without a simulated 4-way beam-splitter AA filter, here.

Jim

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Jim Kasson
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« Reply #63 on: May 25, 2014, 11:16:33 AM »
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  I tried out a couple of Zeiss Otus lenses on my D800 this past week, and compared them too my "regular" Zeiss ZF2 lenses on my D800.   Came home, pulled them up on screen, looked at them closely.  No math or other technical points, just my  gut feeling reaction here:

1) Pros
- build quality is second to none;
- optically, yes, I think better then the "regular" Zeiss lenses;

2) Cons
- while optically better than "regular" Zeiss lenses, that is like saying brand A of sports car is better than brand B because brand A does the quarter mile a tenth of a second faster than brand B.   IMO, the regular Zeiss lenses are in most cases so far ahead of many other lenses, well, it depends on what you are looking for;
- while the build quality is better, they are huge and heavy lenses compared to the "regular" Zeiss lenses.   I mean, in real world use, if I am going for a 2 or 4 hour hike in the bush, hauling around a lens that is twice the weight (or more) of it's closest equivalent - I dunno.  I mean, it is not money alone, as there is a reason i now use carbon fibre tripods and monopods as opposed to aluminium ones, I am just saying, do people think about these situations outside the lab?
- cost.   I can almost buy three ZF lenses for the price of one Otus.  I just don't have those kind of dollars.

I know I'll get flamed for this, but I can't help myself. For me, the comparison is the Otus 55 with a 80 or 100 mm medium format lens. OK, it's an old MF camera, but when I use the Otus on the a7R or the D800E, I get sharper results in general than I do with the Hassy 80mm f/2.8 or the 120mm f/4 on a H2D-39. Essentially the same resolution. The Otus is heavier and bigger than the 80mm, and smaller and lighter than the 120. On the camera, the Hassy is bigger and heavier with the 80mm than with the Otus on either body. The Hassy 80 costs three-quarters of what B&H gets for the Otus, and the Otus is two stops faster.

Let's say that Zeiss comes out with an Otus 85mm and an Otus 35mm, and they both cost about $4K. Let's further say that Sony and/or Nikon introduce 56 MP cameras (full frame at NEX-7 sensel pitch) at about $7K. So now, for under $20K, you can buy a kit that will challenge cameras built around the Sony 33x44mm sensor, as well as the Hassy H5D-40 and H5D-50 and the Phase One equivalents. Yes, there are advantages to the larger sensors, but there are disadvantages to the larger cameras as well. With Pentax's recent announcement, there are signs of price erosion in the MF market, and a bigger line of Otus lenses could provide a different kind of price competition.

It's an exciting time to be a photographer.

Jim
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Fine_Art
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« Reply #64 on: May 25, 2014, 12:30:55 PM »
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Prices have to come down a lot further for most people to care. An Otus 50 shot will not beat a 4 shot stitch with a good 85 or a 100 macro. Pushing the engineering envelope is great. For a profitable commercial product you need winning value per dollar. At least from people that use the product rather than buy status symbols.
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Telecaster
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« Reply #65 on: May 25, 2014, 01:47:21 PM »
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I agree with Jim that the Otus + D800e/A7r makes for a medium format system competitor. If that's not what you want or need then IMO you're better off with the ZF 50/2 or (on the A7r) the Sony/Zeiss FE 55/1.8. Or maybe even the new Sigma 50/1.4. These are relatively affordable, compact & unobtrusive lenses. I love that the Otus 55mm exists, and I hope there are more of 'em coming, but that doesn't mean I feel obliged to own one.   Wink

-Dave-
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ErikKaffehr
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« Reply #66 on: May 25, 2014, 02:02:25 PM »
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Hi,

I would agree, mostly.

My guess is that 50+ MP 135 is around the corner.

Erik

I know I'll get flamed for this, but I can't help myself. For me, the comparison is the Otus 55 with a 80 or 100 mm medium format lens. OK, it's an old MF camera, but when I use the Otus on the a7R or the D800E, I get sharper results in general than I do with the Hassy 80mm f/2.8 or the 120mm f/4 on a H2D-39. Essentially the same resolution. The Otus is heavier and bigger than the 80mm, and smaller and lighter than the 120. On the camera, the Hassy is bigger and heavier with the 80mm than with the Otus on either body. The Hassy 80 costs three-quarters of what B&H gets for the Otus, and the Otus is two stops faster.

Let's say that Zeiss comes out with an Otus 85mm and an Otus 35mm, and they both cost about $4K. Let's further say that Sony and/or Nikon introduce 56 MP cameras (full frame at NEX-7 sensel pitch) at about $7K. So now, for under $20K, you can buy a kit that will challenge cameras built around the Sony 33x44mm sensor, as well as the Hassy H5D-40 and H5D-50 and the Phase One equivalents. Yes, there are advantages to the larger sensors, but there are disadvantages to the larger cameras as well. With Pentax's recent announcement, there are signs of price erosion in the MF market, and a bigger line of Otus lenses could provide a different kind of price competition.

It's an exciting time to be a photographer.

Jim
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Jim Kasson
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« Reply #67 on: May 25, 2014, 04:41:49 PM »
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Prices have to come down a lot further for most people to care.

I agree. I'll go even further. Most people won't care no matter how far down the prices come. Most people are satisfied with the images produced by their cellphones. Of the photographers (if you buy a violin, you own a violin; if you buy a camera, you are a photographer) remaining, most will make prints at 4x6 inches or smaller, or just be happy with screen res, so they won't care at any price, either. Of the photographers left, most won't care at any price because they demand autofocus. When you subtract out that group, you're left with a cohort that could easily be turned off by price/size/weight. Take them out of the mix, and there is a group whose members care  passionately about image quality, and are willing, under the right conditions, to dig deep into their wallets.

An Otus 50 [55?] shot will not beat a 4 shot stitch with a good 85 or a 100 macro.

Yep. Stitching is great if your subject and the lighting will hold still long enough. But sometimes you need a single capture. Or you've already committed to multiple captures for HDR or focus stacking, and adding stitching is just too complicated and error prone.


Pushing the engineering envelope is great. For a profitable commercial product you need winning value per dollar. At least from people that use the product rather than buy status symbols.

In photography, like so many other things (audio, video, musical instruments, automobiles, clothing, wine, etc), the amount of performance received for your money is higher at the lower end of the market than the higher. That doesn't mean that companies selling at the higher end of the market can't be commercial successes.

Jim
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Dave Ellis
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« Reply #68 on: May 25, 2014, 05:31:48 PM »
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Hello Jim

I'm a newcomer to this site but could I say that I really appreciate the technical posts that people like yourself, Erik and Bart provide.

I have a couple of questions relating to your model :


In general terms, how are you modeling the lens aberrations ?

I'm struggling to see how pixel pitch affects mtf. As I understand the basics of sampling theory, the pixel pitch determines the spatial sampling frequency and this must be at least twice the highest frequency component of the signal for accurate reproduction. If not, artefacts will be produced for those frequency components of the signal that are above the Nyquist frequency. But how does this affect the mtf of the lens/camera system ? I appreciate that pixel size and fill factor affects mtf as a result of non-point sampling and I assume that de-mosaicing affects mtf also. But are these the only factors or am I missing some basic concept here ?




Thanks
Dave
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Jim Kasson
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« Reply #69 on: May 25, 2014, 06:05:05 PM »
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In general terms, how are you modeling the lens aberrations ?

Welcome to Lula, Dave. The short answer to your question is, "Not very well." I'm modeling the Otus 55 mm f/1.4 on-axis performance with a double application of a pillbox (circular) kernel with radius equal to 0.5 um + 8.5 um / the f-stop to a target image that's already been blurred by diffraction. This yields a tolerable fit to the performance of the sample of the Otus that I'm testing against. However, there's a lot of uncontrolled moving parts. The real images are demosaiced by Lightroom, and the synthetic ones with bilinear interpolation, and it looks to me like Lr sharpens a bit, which kicks the MTF up. The real images are subject to focus errors and other unmodeled defects. I figure it's not all that important if the task is to get at general concepts relating sensor resolution to lens resolution.

I'm struggling to see how pixel pitch affects mtf. As I understand the basics of sampling theory, the pixel pitch determines the spatial sampling frequency and this must be at least twice the highest frequency component of the signal for accurate reproduction. If not, artifacts will be produced for those frequency components of the signal that are above the Nyquist frequency. But how does this affect the mtf of the lens/camera system ? I appreciate that pixel size and fill factor affects mtf as a result of non-point sampling and I assume that de-mosaicing affects mtf also. But are these the only factors or am I missing some basic concept here?

No, I think you've got it. One subtlety worth exploring is the way that the frequency part of MTF is reported. If you look at cycles/pixel, you'd say that making the sensor pitch lower makes the MTF worse. But I'm looking at a measure that I think is more relevant to photographers, cycles per picture height, which is cycles/pixel times the vertical dimension of the image in pixels. I'm assuming landscape orientation and a 24x36mm sensor.

If you look at my blog, you can see that I'm dancing around the aliasing issue a bit. I'm looking for a single number that I can derive from slanted edge MTF testing. Some people, including the well-respected Imatest folks, look at MTF at the Nyquist frequency (half the sampling frequency). I think that's better than nothing. I'm playing around with the sum of all the spatial frequency energy between the Nyquist frequency and the sapling frequency to see if that's a good metric. No conclusions yet, though.

That help?

Jim
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Dave Ellis
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« Reply #70 on: May 25, 2014, 06:51:34 PM »
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Thanks for the welcome and the comments Jim.

I figure it's not all that important if the task is to get at general concepts relating sensor resolution to lens resolution.

No, I think you've got it. One subtlety worth exploring is the way that the frequency part of MTF is reported. If you look at cycles/pixel, you'd say that making the sensor pitch lower makes the MTF worse. But I'm looking at a measure that I think is more relevant to photographers, cycles per picture height, which is cycles/pixel times the vertical dimension of the image in pixels. I'm assuming landscape orientation and a 24x36mm sensor.


I agree, the precise figures don't really matter, it's the demonstration of the concepts that is important with modeling like this (to improve our understanding of the significance of different factors).

I hadn't picked up on the point that you are using cycles per picture height with the definition cycles/pixel x vertical image height in pixels. I'll have another think about this but it probably answers my question.

Dave
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Dave Ellis
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« Reply #71 on: May 25, 2014, 11:35:09 PM »
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Jim

I've had a further think about this and come to the conclusion that the cycles/ph concept is not the issue. I think I have simply been under-estimating the mtf contribution from the non-point sampling and demosaicing. I had it in my mind that they were only small contributors but I've never looked at how their contributions vary with pixel size. Also, I guess they become more significant for higher quality lenses at their sharpest aperture.

Dave
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Jim Kasson
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« Reply #72 on: May 26, 2014, 12:50:58 PM »
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I think I have simply been under-estimating the mtf contribution from the non-point sampling and demosaicing. I had it in my mind that they were only small contributors but I've never looked at how their contributions vary with pixel size. Also, I guess they become more significant for higher quality lenses at

Right you are about non-point sampling. Here's an extreme example with 1% and 100% fill factors:





Jim
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Dave Ellis
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« Reply #73 on: May 26, 2014, 03:12:33 PM »
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Thanks for that Jim. If you take your figures for say f/2.8 and 0.4 cycles, for 100% fill factor the mtf is 0.45 and for 1% fill factor the mtf is 0.6. The ratio of these figures is 0.75 which I think should be the mtf contribution of the non-point sampling. This appears to be consistent with the sinc function calculations I've seen elsewhere.

Dave
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Jim Kasson
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« Reply #74 on: May 26, 2014, 04:35:25 PM »
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Thanks for that Jim. If you take your figures for say f/2.8 and 0.4 cycles, for 100% fill factor the mtf is 0.45 and for 1% fill factor the mtf is 0.6. The ratio of these figures is 0.75 which I think should be the mtf contribution of the non-point sampling. This appears to be consistent with the sinc function calculations I've seen elsewhere.

Dave

That's good to know, Dave. I'm not working in the frequency domain at all until the MTF numbers come out of the Burns slanted edge STF program; I'm doing everything up to then using convolution kernels. Jack Hogan has been doing similar work in the frewuency domain. We touch base from time to time, and for the most part our results are consonant.

Jim
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Jim Kasson
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« Reply #75 on: May 26, 2014, 05:29:17 PM »
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Here's the result of an attempt to run directly at the topic of this thread. It's a plot of the direction of most rapid improvement in MTF50 ("steepest ascent" is the mathematical jargon from the world of optimum seeking methods), with the length of the arrows proportional to the slope of the MTF50 curve in the direction of steepest ascent, all plotted for a diffraction-limited lens on a Bayer CFA camera with no AA filter for f-stops of f/2.8 to f/16 and sensel pitches of 2 um to 5.7 um:



Sensel pitch in micrometers (um) is the vertical axis. F-stop is the horizontal one. You can see that for pixel pitches of 4.7 um and up, except at f/16 the lines of steepest ascent all point in the direction of greater sensor resolution. As the sensor resolution goes up and we get lower on the graph, the direction of the arrows on the left side of the graph begin to point more and more to the left, indication that the easiest way to gain MTF50 is to open up the (perfect) lens.

The direction of the arrows is unfortunately a function of the scaling chosen, but at least it's a quantitative way to look at the sensor resolution vs lens resolution question.

More plots here.

Jim
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BartvanderWolf
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« Reply #76 on: May 27, 2014, 03:20:42 AM »
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Here's the result of an attempt to run directly at the topic of this thread. It's a plot of the direction of most rapid improvement in MTF50 ("steepest ascent" is the mathematical jargon from the world of optimum seeking methods), with the length of the arrows proportional to the slope of the MTF50 curve in the direction of steepest ascent, all plotted for a diffraction-limited lens on a Bayer CFA camera with no AA filter for f-stops of f/2.8 to f/16 and sensel pitches of 2 um to 5.7 um:


Hi Jim,

Nice way of looking at it. While I understand the MTF50 metric of a lens/sensor combination as a general indication of perceived contrast/resolution (although it depends on subsequent magnification), I do have a slight concern with the MTF50 only metric though. Since the ISO specify that limiting visual reolution corresponds reasonably well with the spatial frequencies at MTF10 (or at the Nyquist frequency, whichever is reached first), I do wonder if it would be instructive to also show that. Afterall, with deconvolution sharpening we are able to boost these lower MTF responses to higher levels, and I always sharpen my images, so MTF50 before sharpening becomes a bit arbitrary ...

I think the general conclusion will stay the same (see attachments), narrower sampling densities are more beneficial unless the image is dominated by diffraction blur, but beter lenses and narrower sensel pitch benefit even more. Adding MTF10 would allow to get a bit closer to real life where sharpening will always be involved.

Of course, modelling the effect of sharpening on MTF in advance is also not easy, I do know from experience, that's why I usually determine that by analyzing the end result after e.g. regularized Richardson-Lucy or Van Cittert deconvolution, or after FocusMagic did its magic. But knowing the MTF10 before restoration already gives an idea whether there is anything salvageable to begin with.

Cheers,
Bart
« Last Edit: May 27, 2014, 03:29:23 AM by BartvanderWolf » Logged
Jim Kasson
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« Reply #77 on: May 27, 2014, 05:28:23 PM »
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Nice way of looking at it. While I understand the MTF50 metric of a lens/sensor combination as a general indication of perceived contrast/resolution (although it depends on subsequent magnification), I do have a slight concern with the MTF50 only metric though. Since the ISO specify that limiting visual reolution corresponds reasonably well with the spatial frequencies at MTF10 (or at the Nyquist frequency, whichever is reached first), I do wonder if it would be instructive to also show that. Afterall, with deconvolution sharpening we are able to boost these lower MTF responses to higher levels, and I always sharpen my images, so MTF50 before sharpening becomes a bit arbitrary ...did its magic. But knowing the MTF10 before restoration already gives an idea whether there is anything salvageable to begin with.

That makes sense, Bart. However, with diffraction-limited lenses, and even with my simulated Otus, MTF10 occurs above the Nyquist frequency at some f-stops at today's full frame pixel pitches. I'll run some sims and post the results.

OBTW, the sims are taking longer as I do enough of them to get 2D gridded results. I'm doing all my convolutions sequentially. I see no reason why I can't just build one big kernel to use at the resolution of the target by centering and adding the kernels for diffraction, lens defects, focus error, AA filter, fill-factor, etc., and then just applying that kernel to the target before sampling. However, I think I saw, somewhere on the 'net, a warning that you shouldn't do that. I don't understand the warning. It's a linear system at the presampling calculations, isn't it?  Any advice on this point? It's going to be a fair amount of work to write the code to add all the kernels together, since they're all different sizes.

Thanks,

Jim
« Last Edit: May 27, 2014, 05:30:11 PM by Jim Kasson » Logged

BartvanderWolf
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« Reply #78 on: May 28, 2014, 04:17:55 AM »
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That makes sense, Bart. However, with diffraction-limited lenses, and even with my simulated Otus, MTF10 occurs above the Nyquist frequency at some f-stops at today's full frame pixel pitches. I'll run some sims and post the results.

In my SFR measurements a modulation of 10% is often achievable for the best apertures before reaching the Nyquist frequency. So one either uses MTF10 or Nyquist, whichever is reached first. Maybe the MTF10 sims will look pretty much the same as the MTF50's, only at higher spatial frequencies or LPPH.

Quote
OBTW, the sims are taking longer as I do enough of them to get 2D gridded results. I'm doing all my convolutions sequentially. I see no reason why I can't just build one big kernel to use at the resolution of the target by centering and adding the kernels for diffraction, lens defects, focus error, AA filter, fill-factor, etc., and then just applying that kernel to the target before sampling.

Sequential/cascaded convolutions can indeed be replaced by one compounded convolution, which pretty fast starts looking like a Gaussian (due to the Central limits theorem). Here's some more explanation in pretty simple words.

Quote
However, I think I saw, somewhere on the 'net, a warning that you shouldn't do that. I don't understand the warning. It's a linear system at the presampling calculations, isn't it?  Any advice on this point?

I think you might have remembered seeing the warning at David Jacobson's lens tutorial page, which warns against simple MTF multiplications where negative lobes are involved in the original (COC) signals.

Quote
It's going to be a fair amount of work to write the code to add all the kernels together, since they're all different sizes.

I understand. The cascaded kernel will also grow significantly with each additional convolution, but ultimately it should produce fewer multiplication+addition operations because you end up with a single convolution kernel for all image inputs. Also, given that the resulting kernel may turn out looking pretty simple, it would be possible to truncate or filter it to a smaller kernel support size which would also speed up things once the cascaded kernel is available in floating point precision. And once you indeed find that you can replace the compound result with a separable Gaussian, things can be sped up hugely.

But the difficulty is in finding the fastest way to cascade the kernels. Maybe a Symbolic solver like Mathematica can assist, although having to deal with discrete sampled sensel apertures instead of continuous point samples does make life more difficult.

Cheers,
Bart
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Jim Kasson
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« Reply #79 on: May 28, 2014, 11:47:52 AM »
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In my SFR measurements a modulation of 10% is often achievable for the best apertures before reaching the Nyquist frequency. So one either uses MTF10 or Nyquist, whichever is reached first. Maybe the MTF10 sims will look pretty much the same as the MTF50's, only at higher spatial frequencies or LPPH.

OK, here are some MTF10 (or MTFNyquist, whichever is higher) plots for a diffraction limited lens from f/2.8 through f/16 and sensel pitch 2 um through 5.7 um. The MTF units are cycles/picture height, assuming a 24x36mm sensor.

In 3D:



As a contour plot:



As a family of curves in 2D:



And as a quiver plot:



I'll do a run for the simulated Otus, which won't spend so much time with MTF10>MTFNyquist.

Jim
« Last Edit: May 28, 2014, 12:09:42 PM by Jim Kasson » Logged

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