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Rainer SLP

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« on: December 17, 2002, 06:13:57 pm »

[font color=\'#000000\']Hi Petru,

How do I explain it?

Why is a 12mm wide angle lens for 35mm full frame a 16mm for the let us say 3/4" chip?

because the distance from the chip plane is the same to the focal central point as the 35mm full frame chip to the 12mm wide angle lens.

Draw again your sketch for example simulating the lens as well as the chip OK?

Now put the 3/4" chip on the 35mm full frame chip OK now draw lines from the 3/4" chip to the central focusing point of your 12mm lens OK and what do you get. A leser steep angle but a 16mm wide lens.

So assume instead of being a 12mm wide angle 35mm full frame lens that it is a 16mm. Again the same you get a lesser steep angle on the 3/4" chip but the focal length is then let us say 24mm OK?

If you want to have a real 16mm focal length wide angle lens on the 3/4" chip you have to move the central focusing point towards the 3/4"  chip until you get the same angle as the 16mm on the 35mm full frame and  Voila! your angle is the same as on the 35mm full frame chip.

Everything clear?

If you have a lesser steep angle then you do not have the same focal length! Very easy!

The bigger your negative the bigger your focal length compared to other negative sizes. With negative I mean Film or chip, does not matter.

Take a look at my sketch:

http://www.rainerehlert.com/fotos/wideangle.jpg

Do not be confused because the green lines of the 16mm 3/4" do not meet the 16mm black lines of the 35mm chip, they do in infinity and there is where the focal length is calculated.

Or is somebody here than can tell me that I am wrong with my assumption?[/font]
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PDW

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« Reply #1 on: December 23, 2002, 08:51:05 pm »

[font color=\'#000000\']In that review there is vignetting, but what is the cause?  The lens or the lens mount? I can't see why a FF CCD or CMOS sensor would vignette any worse than a piece of film of the same size.[/font]
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Ray

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« Reply #2 on: January 06, 2003, 07:49:21 am »

Quote
digicam test results often show well over 120lp/mm while pro 35mm zoom lenses are typically back at 60lp/mm or less. Clearly 35mm designers are still pushing to improve, so it must be genuinely easier for the smaller image circle designs.
BJL,
I've never seen any test results of a digicam or P&S camera. 120 lp/mm is impressive by 35mm standards but not enough if the sensor is only 8mm x 6mm (or thereabouts).

There's confusion between 'system' resolution and lens resolution. 35mm zooms might typically produce a 'system' resolution limit of 60 lp/mm, but the lens itself must surely be capable of much higher than this. The D60 at 135 pixels (photosites) per mm has a maximum resolving power of 67 lp/mm. I think this is exaggerated on two counts. The Nyquist theory which suggests 2 pixels are required for each line pair is not perfect in practice. Somewhat more than 2 pixels are required (according to Norman Koren). Secondly, the D60 has an AA filter which, as we know, blurs the image slightly. Net effect is probably, a wild guess, 55 lp/mm. Doesn't matter how good your lens is, you're not going to get more than (55 lp/mm?) with the D60.

Now I'm going out on a limb here, and I stand to be corrected, but I suspect the opposite applies to P&S cameras. The sensors actually have higher resolving power than the lenses, hence no need for an AA filter. Any resolution test are therefore likely to apply to the lens itself. The sensor is probably capable of even higher resolution.

As I see it, from a very simple mathematical point of view, a 35mm standard lens which is truly diffraction limited at F2.8 could produce an image the same size, quality and DoF as a standard lens for an 8" x12" field camera, diffraction limited at F22, provided the 35mm sensor has sufficient resolving power. I can't see much point in pinning one's hopes on an even smaller format than 35mm.
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« Reply #3 on: January 13, 2003, 04:31:48 pm »

Some of us are also old enough to remember half frame. A great idea that never caught on.

I believe that the cost differential between APS sized sensors and full frame sensors is a brief historical anomaly. That's one of the reasons why I believe that if Nikon is taking a 4/3rds or similar route they are making a mistake. Canon has just completed a major investment in a new CMOS imaging chip fabrication plant. This will allow them to bring the price of these sensors down to the point that there will be little financial advantage to smaller chips.

Add the installed base of tens of millions of full frame lenses and the desire by pros and serious hobbiests to have the highest possible image quality and I can't see much of an advantage for reduced frame sensors after another couple of years.

Michael
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Ray

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« Reply #4 on: January 16, 2003, 11:51:43 pm »

Quote
A 4/3" sensor gets almost twice the milage out of a 400mm lens as a "Full Frame" sensor.  Glass for smaller sensor imagers is lighter, faster, cheaper.
Matthew,
But the bottom line for us enthusiasts is the final quality of the enlarged print. If technology advances to the extent that a 4/3rds format sensor can produce acceptably sharp Super A3 size prints with low noise and reasonably high dynamic range, then the same technology applied to the larger full frame 35mm sensor will allow for equally sharp but larger prints with perhaps even lower noise and higher dynamic range. The heavier lenses will have their purpose.
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Ray

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« Reply #5 on: January 17, 2003, 08:57:55 pm »

Quote
The bottom line is NOT the quality of the print.  Or we all would be using 8x10 view cameras, or even 16x20.
Matthew,
Okay! Perhaps I'm guilty of a bit of hyperbole there. The bottom line is a compromise between quality and convenience. The 8x10 field camera has a significant quality advantage over 35mm but an absolutely huge inconvenience disadvantage - hence its lack of popularity.

What concerns me about the smaller format with lighter lenses is, how much quality might I be sacrificing for the greater convenience? At this stage it's simply not clear. The fact is, most people do not use super telephoto lenses, nor has there been any comparison that I'm aware of between a Canon 500mm lens and a 4/3rds designed 500mm equivalent.

For example, Michaels 500mm lens is so good it can be used with a 1.4x converter to produce an effective 700mm lens.

I would suggest that the 4/3rds size sensor would have such high pixel density, designed to extract the most out of its lenses, there'd be no room (resolution to spare) for a converter. From a quality point of view, the comparison might be between an equivalent 700mm (or even a 1000mm) 4/3rds lens and a 500mm 35mm lens + converter.

Supposing one were to find that a good 35mm lens with converter ( and bearing in mind the superior noise and dynamic range of the larger photodetectors) still gave a higher quality result than any 4/3rds system.

As a general observation, it's my view that when you change whole systems which involve a lot of additional expenditure on infrastructure (in the case of cameras, on lenses and accessories) you have to make sure you're offering a substantial improvement in quality and/or convenience. There's no way that the 4/3rds format can compete quality wise with 35mm (I suspect, or am led to believe) and the greater convenience of the smaller format seems relatively marginal with the most commonly used lenses.

Nevertheless, I'm not against the introduction of a smaller format with different proportions. I'm all in favour of variety of choice.
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dbarthel

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« Reply #6 on: December 16, 2002, 09:14:44 am »

[font color=\'#000000\']Michael, I think you have your economics wrong on the cost of imaging chips. The cost/area remains constant. Moore's law says you can put more in a given area, thus the price of a functional unit decreases. The correct assumption is that a 22 megapixel chip will cost no more than an 11 megapixel chip in a couple of years, but also that a given sensor size will remain about the same.

Dan[/font]
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Rainer SLP

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« Reply #7 on: December 17, 2002, 06:37:39 pm »

[font color=\'#000000\']Hi,

Sorry I meant 4/3" and not 3/4", but anyhow this is not so important.

Afterwards it came to my mind why do we speak of a 80mm focal length in MF as normal when we all are used to say that 50mm on 35mm is normal.

Because of the angle of view.[/font]
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Paul Caldwell

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« Reply #8 on: December 21, 2002, 12:38:44 pm »

[font color=\'#000000\']Actually if you follow the costing models of the chips over the last  say 4 years, we are following Moore's law pretty close.  

The 460 Kodak was 35K, the 660 was 25K, then the huge drop was the 760, at 7K.  Of course it didn't have a larger chip than the 660 but all new electronics.  

Now Canon's 1ds is almost 2x the 6mp 760 and is less than 1K more than the 760 Kodak.  I use the 760 as my model since its body model is the Nikon F5 which is the base eqivalent to the Canon.  I realize that there are many differences, but as for overall body strength the two are very close.  

If you really read Moore's law and get into the theory, it also gives mention to the other piece of this puzzle, the basic law of supply and demand.  Canon has the only camera currently that can offer a high end body, and high end 11 mp chip.  They basically can set the price where they want it.  Any by picking a price right above the 760 I think that they did OK.  I have made many posts to the effect that I also believe that they could have made the price lower and sold more, but only Canon knows their internal costing model..  I will have to say that there is more profit in 1 1ds, than about 8 D60s.  

Until Nikon or Someone else brings their body out to equal Canon, there is not reason to change and this also effects Moores law, as it is looking at the industry in general.  In general there are always more than one of any product,  example PC's VCR's, you have to have more than one.

Someone also brought up the "sleeper" issue on the FF for Nikon.  The mount opening.  Nikon is smaller than Canon and if you look at Phil Askey's 1ds review, on some of the image you can see vignetting on the corners.  As much as I hate to admit it, I don't see how Nikon will get around this, or Kodak with the 14n.  It means that you won't be able to take advantage of the F2.8 speed of all your high end glass, instead having to start at around F4.0.  

Nikon is in a pickel unless some sort of software correction can be made and I feel thats where they are headed.  They have added the vignetting correction in Capture 3.5, but thats for current cameras.

Paul CAldwell[/font]
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BJL

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« Reply #9 on: January 06, 2003, 03:17:36 pm »

Quote
There's confusion between 'system' resolution and lens resolution. 35mm zooms might typically produce a 'system' resolution limit of 60 lp/mm, but the lens itself must surely be capable of much higher than this.
...
I can't see much point in pinning one's hopes on an even smaller format than 35mm.
I was talking about lens resolution only.

The figures I quote for 35mm pro lenses are for lens resolution, based on "MTF50", the lp/mm at which MTF is 50%, as recommended by Norman Koren and others. For example,
http://www.normankoren.com/Tutorials/MTF1A.html
gives an MTF50 of 61lp/mm for the Canon 28-70mm f/2.8L, one of the sharpest 35mm normal focal length zooms around.

I ignore the far higher lp/mm figures based on "extinction resolution" at which a very high contrast target is barely visible: those numbers correspond to resolving only 2-10% of true subject contrast, and so are of little relevance to human perception of a normal image.

Clearly the "one-piece digicam" test results are "system resolution", but  the lens resolution is at least as good, and as you say only slightly better, since lenses are probably the main limit there.
The figures I quote for them might be a bit optimistic as they are not rigourous "MTF50", but nor are they the maximal "extinction resolution" figures.

If anyone wants endless data on 35mm and medium format lens resolution, measured as MTF at various resolutions up to 40lp/mm, check out http://www.photodo.com/nav/prodindex.html


I pin my hopes on a somewhat smaller format than 35mm, probably no smaller than the Kodak/Olympus 4/3" format, because it could easily exceed the resolution needed by the overwhelming majority of photographers in a more convenient way: enough resolution for ANY SIZE of print so long as it is viewed "normally", meaning from a distance at least as great as the image size, so that most or all of the image fits into the field of view. Even with large murals and panoramas, the closest distance that makes sense to me for normal viewing is the short dimension of the print. About 3000 full colour pixels across a distance equal to ones viewing distance is all the eye can distinguish, pessimistically up to 4500 for Bayer pattern pixels. That is partly why 35mm lens MTF is typically measured only at up to 40lp/mm, which corresponds to just under 2000 lines by 3000 lines across the whole frame.

Thus I expect to eventually leave the bulky, more expensive lenses and other gear of larger formats (including 35mm format DSLR's) and their higher resolutions to the small minority of high end photographers who care about scutinizing small portions of the whole image, or who use primes and therefore more often have to crop significantly, or who need backward compatability with existing 35mm lenses.
 

P. S. I will also be happy to ditch the 2:3 aspect ratio of 35mm format.
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herb

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« Reply #10 on: January 13, 2003, 02:06:26 pm »

People seem to forget that 35mm film was not created as a still picture format. It's spectacular success has probably been due to the fact that the cameras are about optimum size for hand holding by most people; certainly by the males who previously were the main users. Those who have a great vision about the opportunity to throw off old restrictions from the past are deluded. There were no such restrictions. By the late 70's Pentax, with their M Series, out-miniaturised the Olympus OM Series. Yet big Nikons and Canons remained popular. Don't men like their big EOS 1V's and F5's? Really? Pentax MX's and Olympus OM's were beautiful cameras, ideal for portability AND had the same size sensor as their larger competitors. Now the suggestion is that folk will clamour for a sensor half the size of what's not broke! Kodak have a great track record on new small formats. It's a bit of an obsession; 110, Disk, APS, ...  Don't be surprised if 4:3 goes the same way. Suppose Canon announces a full frame D90 at a sensible priice. Who will want to sell their Canon gear to pick up an inferior 4:3 Kodak?
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Ray

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« Reply #11 on: January 16, 2003, 11:36:29 pm »

Quote
Why then is virtually every standard enlargement bigger than 4"x6" cropped to a squarer shape than the 2:3 (1.5) ratio of 35mm's 24mmx36mm frame?
BJL,
I'm sure there must be lots of reasons and sometimes perhaps no reason at all. Irrationality rules the day.

To satisfy my curiosity, I had a look at all the popular formats. Here are the ratios.

6cm x7cm - 1 : 1.17

Old fashioned TV - 1 : 1.33

A4 - 1 : 1.41

Super A3 - 1 : 1.46

35mm - 1 : 1.5

Widescreen TV - 1 : 1.78

Widescreen Cinema - 1 : 2.35

The Golden Mean is represented by the irrational number 1 : 1.618. This ratio appears to be present in the growth patterns of many, many things in nature. It had a mystical quality for the Greeks. There are many references on the net which suggest the Rule of Thirds originated from 'The Golden Section' (also known as the Golden Mean). I'm no authority on the origin of these terms, so if you have information on this, share it with us.

I find it significant that the two most popular formats that approximate most closely to this mystical Golden Mean are 35mm and Widescreen TV. Is this pure coincidence? Why is there a movement to introduce a new!!?? 4/3rds format. This is the old fashioned TV format. Are we all creatures of fashion?
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BJL

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« Reply #12 on: January 17, 2003, 09:18:00 pm »

Ray,

   you seem to draw very different conclusions than me from the same facts!

First a small numerical correction: 67 medium format is actually 56mm by 69.5mm, a ratio very close to 1.25, presumably chosen to fit 8x10 prints.

The two "longest" formats on your list are moving picture formats, a very different issue than still images; and the next longest, 35mm is simply NOT a heavily used format for serious prints even when it is what the camera gives; the overwhelming majority of prints bigger than snapshots are cropped squarer.

The evidence of the choices made by most serious artists in large format and medium camera design, printing paper sizes, and artists' supplies is that 2:3 is not a good compromise, it is off towards one end of the scale.

I repeat, the most common artistic choices are in the range 1.25 to 1.4, and if any one of the common numbers is nicely in the middle of the common range, to minimize average cropping needs, it is 1.33 or 4/3.

Also, 35mm format does not dominate in digital: the overwhelming majority of digital cameras have 3:4 format. Yes, a lot of 35mm and MF based systems have used 2:3, but probably for compatability with 35mm film scans in the commercial marketplace, and note also the recent trend of square and 3:4 formats in MF/LF backs.

Again, I agree that some subjects like panoramas favor wider shapes, and I look forward to digital panorama cameras in a variety of formats (including perhaps Widelux style, with a rotating lens and a linear sensor), but on the subject of cropping, it is rather clear that 35mm leads to more cropping (mostly at the ends) than any other commonly used film format, and formats like 645 and 67 medium format are favored in part for reducing the amount of cropping needed for the sort of photography most often done with such cameras.
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« Reply #13 on: December 16, 2002, 09:24:35 am »

[font color=\'#000000\']Dan,

You're quite right, and I likely sholuldn't ave invoked Moore's Law.

But, conceptually my point is the same. Based on some conversations with thos ein the know I'm pretty confident in saying that some manufactruer's are going to have solid yields from CMOS imaging chip wafers in the years ahead and this is going to bring down the cost of full-frame chips.

Certainly they will always cost more than smaller chips, all other things being equal, but the incremental cost of a complete camera might only be increased by a couple of hundred dollars at most. This isn't enough, in my opinion, to justify a paralell reduced-size line of lenses and cameras.

I could be wrong, but my gut tells me I'm not.

Michael[/font]
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Rainer SLP

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« Reply #14 on: December 17, 2002, 01:32:31 pm »

[font color=\'#000000\']Hi Petru,

somehow what you say will also apply on the smaller chips, because the image circle will be smaller and then you get the same problems of steep angle on the smaller chip.

If you have 16mm wide angle on 35mm full frame and 16mm on 3/4" chip you have the same angle, or am I wrong in my thinking?

Just make a sketch on paper and you will see.

So having said this, there will be the same vignetting on the DX lenses as we have right now on the 35mm full frame lenses.

If the frame covers diagonally the image circle, whatever lens you have, you will have the known problems.

Why should a lens specifiaclly designed for the digital e.g. 3/4" be better than the full frame lens?

I keep thinking that a 35mm full frame lens used on a not full frame chip is far better than those new? calculated DX or whatever lenses? Why, because you are not touching the limits of the image circle an therefore working on the better 66% ( or whatever focal correction factor) image circle of the lens. Just take a look at the MTF charts of the lenses and you see where they are good and where these begin to fall down.

Why do they make the aspherical grindings on the lenses? This specially grinding is always on the outer side of the circumference. Take a look at an image taken with the Canon 17-35mm zoom where you clearly see a nice curve in form of an Hunter's Bow. This is because of the aspherical correction.

The industry makes all as " Good as Necessary" and not as " Good as Possible ". OK there are exceptions like the 50mm f1.0 which for me is only a proove of the capability of a company but does not give nothing better than a well known 50mm f1.4.

Why do not we tell the industry to make as a chip in form of a automatically adjusting concave pan to the focal length of the lens   (this already exists in the mirrors of the astronomical observatories) and then the light rays will all fall at the same distance at a 90° angle onto the corresponding pixel and the lenses can be made cheaper because we will have no chromatic and sharpness aberration  which is the main problem when designing a lens  :D  Please allow me to keep dreaming of my SS-HAA-100MP (SSuper-Hyper-Automatic-Adjusting-100MegaPixel) Chip  :D[/font]
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« Reply #15 on: December 21, 2002, 12:43:18 am »

[font color=\'#000000\']I'm sure there must be some advantage to a larger lens mount, but why would the F mount's diameter make it not possible to "effectively" cover a 24x36mm sensor?  It's the same size as a 35mm frame and they cover that effectively.  Also, Kodak seems to have accomplished the feat with their 14n?[/font]
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bjanes

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« Reply #16 on: December 29, 2002, 11:17:59 am »

[font color=\'#000000\']I too hope that Nikon’s decision to pursue a set of optics for their D series of digital cameras does not detract them from pursuing development of a camera with a full frame sensor.

However, in developing this series of lenses, they can optimize them for the characteristics of the digital sensor. With a digital sensor significant MTF above the Nyquist frequency is undesirable (unless a low pass anti-aliasing filter is used), since it only contributes to aliasing (false image data) The design goal would be to maximize MTF in the usable range of the sensor and have it fall off to less than 10% above this range.

Schneider Optics has a series of lenses specifically designed for digital imaging and they discuss some of their objectives in a white paper posted on their website:
http://www.schneideroptics.com/info....phy.pdf

Norman Koren offers some interesting comments on his web site.
http://www.normankoren.com/Tutorials/MTF7.html

Of course, a sharp cutoff of MTF above the Nyquist frequency cannot be obtained with a lens as is possible with the audio signal of a CD. It is not possible to have good MTF up to the Nyquest frequency and low MTF beyond. This approach implies some degree of over sampling. It will be interesting to see how the upcoming Kodak camera will perform without a low pass filter).[/font]
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bjanes

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« Reply #17 on: December 30, 2002, 06:11:43 pm »

[font color=\'#000000\']Ray,

I'm no expert on CD, but if oversampling were done during the recording phase, there would be incompatabilities between players using 4x, 8x, or more oversampling. Here is a link which might be helpful:

http://www.repairfaq.org/REPAIR/F_cdfaqb.html#CDFAQB_005


I just estimated for the 4 micron; maybe it is actually 6.

When I said that the resolution of the small sensor camera was limited by the lens I was using Norman Koren's chart as a reference. He says that an 11 mm diagonal (3.4 um pixel) sensor such as used on the coolpix 5700 becomes diffraction limited at f4; I guess that's why the aperture range you mentioned is limited. Well corrected lenses are limited by diffraction  when you stop down, rather than abberations--as I'm sure you know.

Thanks for your replies--you've brought up some good points.

Bill[/font]
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Ray

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« Reply #18 on: December 30, 2002, 07:15:34 pm »

Quote
[font color=\'#000000\']When I said that the resolution of the small sensor camera was limited by the lens I was using Norman Koren's chart as a reference. He says that an 11 mm diagonal (3.4 um pixel) sensor such as used on the coolpix 5700 becomes diffraction limited at f4; I guess that's why the aperture range you mentioned is limited. Well corrected lenses are limited by diffraction  when you stop down, rather than abberations--as I'm sure you know.[/font]
[font color=\'#000000\']Bill,
That's a good point. I wonder if I've misunderstood that concept. I've been under the impression that diffraction is a function only of F stop and that any lens at F4 is theoretically capable of resolving (according to Rayleigh's Law) something like 1500/4 or maybe 1000/4 lp/mm. Taking the more conservative figure, that's 250 lp/mm. Not bad for a relatively cheap lens. Now, if only the lens designers/manufacturers could do this with 35mm lenses - ie. optimum performance at F4 instead of the usual F8!!

BTW, the oversampling in the recording stage of the new DVD audio format is just that - a new format. It's not compatible with a normal CD player.[/font]
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Ray

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« Reply #19 on: January 06, 2003, 06:42:38 pm »

Quote
The figures I quote for 35mm pro lenses are for lens resolution, based on "MTF50", the lp/mm at which MTF is 50%, as recommended by Norman Koren and others. For example,
http://www.normankoren.com/Tutorials/MTF1A.html
gives an MTF50 of 61lp/mm for the Canon 28-70mm f/2.8L, one of the sharpest 35mm normal focal length zooms around.

I ignore the far higher lp/mm figures based on "extinction resolution" at which a very high contrast target is barely visible: those numbers correspond to resolving only 2-10% of true subject contrast, and so are of little relevance to human perception of a normal image.
BJL,
Maybe I'm out of my depth here, but isn't there a lot of resolution between the MTF50% level and the MTF2% extinction. Maybe such 'buried' detail is irrelevant for the usual enlargements from 35mm, but I envisage some time in the future when people are making 24"x36" prints (and larger) from 24MP 35mm full frame sensors, they'll want that extra detail however faint. I believe the Rayleigh's diffraction limit applies to a 9% or 10% MTF. I would have thought even detail that's lost 90% of its original contrast can be enhanced and made useful.

But I agree there's a big future for the smaller than 35mm format for the non-photographic enthusiast or the occasional photographer who's not likely to print anything larger than A4 or Super A3.
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