Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

Started Jun 16, 2014 | Discussions
Anders W Forum Pro • Posts: 21,468
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

If you can scale down manufacturing tolerances by a factor 2

Why wouldn't manufacturing tolerances scale?

That is such a ridiculous question, if just you stop to think about it. Every manufacturing process has an associated set of tolerances. So, if you use the same process to produce a smaller product, you are not scaling the tolerances. If on the other hand you develop the tolerances so as to be able to scale them for the smaller product, then that finer tolerance process is available also for the larger product. The exception is only if the smaller size itself allows some change in the process which provides for smaller tolerances.

See my reply to noirdesir here, penultimate section:

http://www.dpreview.com/forums/post/53893177

No connection with the question of scalability of tolerances at all. Linking irrelevant posts, implying that you had made some response to the point already is a most dishonest mode of argumentation.

I pasted the wrong link by mistake. Try this instead:

http://www.dpreview.com/forums/post/53896543

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Anders W Forum Pro • Posts: 21,468
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2
2

Just another Canon shooter wrote:

Anders W wrote:

I hoped you might see the analogy, but apparently I was mistaken. So let me translate: The fact that certain factors are always present does not prevent us from isolating their impact.

The part that you keep ignoring, is that their (diffraction) impact is different for the two cases we discuss.

After a lot of dancing, you are trying to change your statement to something like this: If we can perfectly scale a lens and consider the geometric optics theory only, the projected images scale by the same factor, as well. Duh! Do you really think that we are still discussing whether if you can shrink something, it shrinks?

What I originally said in my first reply to noirdesir is the following:

"What is known based on the laws of optics is that if we take a lens design for a certain format, say a 50/1.8 for FF, and scale it down in all relevant dimensions so as to make 25/1.8 for MFT, the two lenses will deliver the same resolution if we measure per image diagonal (and the MFT lens twice as much as the FF lens if we measure per mm) at the same f-stop as long as resolution is limited by lens aberrations only."

I haven't changed that statement, just substantiated it (see my reply to bobn2 here). And the implication is that the larger sensor has no advantage as far as optical aberrations are concerned. In view of the discussion in this thread, that's hardly a trivial claim.

As to diffraction, the larger format has an advantage when comparing at the same (rather than equivalent) f-stops. At equivalent f-stops, there is no difference at all, and the impact of diffraction is generally trifling at wide apertures.

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bobn2
bobn2 Forum Pro • Posts: 61,123
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2
3

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

If you can scale down manufacturing tolerances by a factor 2

Why wouldn't manufacturing tolerances scale?

That is such a ridiculous question, if just you stop to think about it. Every manufacturing process has an associated set of tolerances. So, if you use the same process to produce a smaller product, you are not scaling the tolerances. If on the other hand you develop the tolerances so as to be able to scale them for the smaller product, then that finer tolerance process is available also for the larger product. The exception is only if the smaller size itself allows some change in the process which provides for smaller tolerances.

See my reply to noirdesir here, penultimate section:

http://www.dpreview.com/forums/post/53893177

No connection with the question of scalability of tolerances at all. Linking irrelevant posts, implying that you had made some response to the point already is a most dishonest mode of argumentation.

I pasted the wrong link by mistake. Try this instead:

http://www.dpreview.com/forums/post/53896543

OK, what you said was

The tolerances at issue in this case are those for producing and fitting glass elements. Suppose we were to fit a lens with a diameter of one centimeter and another with a diameter of one meter to the same precision in absolute terms, say one micrometer difference between the edges. Do you think that could be done with the same ease for the one meter lens as for the one centimeter lens?

That in no way answers the question. It is a 'thought experiment' situated in a fantasy. You have chosen an absurd example to 'prove' your case. There are no 1m elements in commodity photographic elements, and those optical instruments which use them certainly do not use the same production processes either for grinding nor for mounting the lenses - but then they don't have to be produced to the same market costs. Is the technology used to grind, coat and mount mFT lenses, for example, any different to that for FF lenses, so a 2cm vs a 1cm element? Are the mFT lenses half the size of FF lenses? If we're talking about scalability of tolerance (if it actually existed) then you'd have to assume that they are, else the tolerances wouldn't scale.

As I said, the truth is that the tolerance goes with the production process, not the size of thing being produced. If the size allows another production process, then tolerances will change, otherwise they won't.

-- hide signature --

Bob

bobn2
bobn2 Forum Pro • Posts: 61,123
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2
1

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Ulric wrote:

Anders W wrote:

The post of yours that began this exchange in the previous thread was:

http://www.dpreview.com/forums/post/53861976

"Additionally there is one inherit advantage larger formats have over smaller ones: enlargement factor. A large format image needs to be enlarged less than a medium format image, which needs to be enlarged less than FF image which needs to be enlarged less than APS-C image which needs to be enlarged less than m4/3 image which needs to be enlarged less than cell phone image and when less enlargement is needed, the lens is stressed less, thus the lens can be of lesser quality to achieve the same image quality."

Exactly what do you mean by "stressed less" and "lesser quality" here? And in what way does the "lesser quality" actually translate into an "inherent advantage of larger formats"?

The larger format lens does not have to resolve as many lines per millimeter on the image plane, thus it can be (but need not be) optically inferior to achieve the same output image quality compared to a smaller format lens. The reason is in the lesser need for enlargement from the image in the image plane to the output image of arbirtary size.

OTOH, what matters is not resolution per millimeter but per image, and the larger format lens has to perform over a larger image circle. It evens out.

In practice, no it doesn't - the advantage is to the larger image circle.

On what grounds?

On the grounds of that's how it is in practice, never mind any theoretical arguments.

OK. What's the evidence?

Plenty of it out there,

I didn't ask how much of it there was. I asked you which evidence.

the larger image circle generally produces higher resolution (normalised to frame size) in practice on most of the lens tests

Based on what statistical analysis of which lens test data?

Based on observation. Which is what we tend to do around here.

So you have no data and no data analysis to back up your claim.

If you wish to make a counter assertion, do you have a suitable statistical analysis to back that up?

You made an assertion. I didn't. So you carry the burden of proof. But here is an example as a starting point:

http://www.dpreview.com/forums/post/53893177

Well, I considered picking an example like that, but it takes time and doesn't really 'prove' anything at all, does it?

More than the one you refer to below which is systematically biased.

But, if you are interested in bogus 'statistical' analysis, then try looking at DxOmark rankings. So, for instance if we filter the lens test data by MP, as follows:

Then you'll find that lenses ranked 1-368 are FF lenses, then we get the Panasonic Leica DG Nocticron 42.5mm F1.2 ASPH at 369. There is some duplication there down to same lens different camera, but there's little point spending a lot of time cleaning up an 'analysis' like that.

What is the relationship between those lens rankings and the factor we are trying to isolate in this discussion: Lens resolution.

Resolution is a factpr in those rankings.

-- hide signature --

Bob

Anders W Forum Pro • Posts: 21,468
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

If you can scale down manufacturing tolerances by a factor 2

Why wouldn't manufacturing tolerances scale?

That is such a ridiculous question, if just you stop to think about it. Every manufacturing process has an associated set of tolerances. So, if you use the same process to produce a smaller product, you are not scaling the tolerances. If on the other hand you develop the tolerances so as to be able to scale them for the smaller product, then that finer tolerance process is available also for the larger product. The exception is only if the smaller size itself allows some change in the process which provides for smaller tolerances.

See my reply to noirdesir here, penultimate section:

http://www.dpreview.com/forums/post/53893177

No connection with the question of scalability of tolerances at all. Linking irrelevant posts, implying that you had made some response to the point already is a most dishonest mode of argumentation.

I pasted the wrong link by mistake. Try this instead:

http://www.dpreview.com/forums/post/53896543

OK, what you said was

The tolerances at issue in this case are those for producing and fitting glass elements. Suppose we were to fit a lens with a diameter of one centimeter and another with a diameter of one meter to the same precision in absolute terms, say one micrometer difference between the edges. Do you think that could be done with the same ease for the one meter lens as for the one centimeter lens?

That in no way answers the question. It is a 'thought experiment' situated in a fantasy. You have chosen an absurd example to 'prove' your case.

I just chose an example that makes the general point that the ability to reach a certain tolerance target as expressed in absolute terms (e.g., micrometers) rather than relative terms (proportions) depends on the size of the objects we are dealing with.

There are no 1m elements in commodity photographic elements, and those optical instruments which use them certainly do not use the same production processes either for grinding nor for mounting the lenses - but then they don't have to be produced to the same market costs. Is the technology used to grind, coat and mount mFT lenses, for example, any different to that for FF lenses, so a 2cm vs a 1cm element? Are the mFT lenses half the size of FF lenses? If we're talking about scalability of tolerance (if it actually existed) then you'd have to assume that they are, else the tolerances wouldn't scale.

As I said, the truth is that the tolerance goes with the production process, not the size of thing being produced. If the size allows another production process, then tolerances will change, otherwise they won't.

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Anders W Forum Pro • Posts: 21,468
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2
1

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Ulric wrote:

Anders W wrote:

The post of yours that began this exchange in the previous thread was:

http://www.dpreview.com/forums/post/53861976

"Additionally there is one inherit advantage larger formats have over smaller ones: enlargement factor. A large format image needs to be enlarged less than a medium format image, which needs to be enlarged less than FF image which needs to be enlarged less than APS-C image which needs to be enlarged less than m4/3 image which needs to be enlarged less than cell phone image and when less enlargement is needed, the lens is stressed less, thus the lens can be of lesser quality to achieve the same image quality."

Exactly what do you mean by "stressed less" and "lesser quality" here? And in what way does the "lesser quality" actually translate into an "inherent advantage of larger formats"?

The larger format lens does not have to resolve as many lines per millimeter on the image plane, thus it can be (but need not be) optically inferior to achieve the same output image quality compared to a smaller format lens. The reason is in the lesser need for enlargement from the image in the image plane to the output image of arbirtary size.

OTOH, what matters is not resolution per millimeter but per image, and the larger format lens has to perform over a larger image circle. It evens out.

In practice, no it doesn't - the advantage is to the larger image circle.

On what grounds?

On the grounds of that's how it is in practice, never mind any theoretical arguments.

OK. What's the evidence?

Plenty of it out there,

I didn't ask how much of it there was. I asked you which evidence.

the larger image circle generally produces higher resolution (normalised to frame size) in practice on most of the lens tests

Based on what statistical analysis of which lens test data?

Based on observation. Which is what we tend to do around here.

So you have no data and no data analysis to back up your claim.

If you wish to make a counter assertion, do you have a suitable statistical analysis to back that up?

You made an assertion. I didn't. So you carry the burden of proof. But here is an example as a starting point:

http://www.dpreview.com/forums/post/53893177

Well, I considered picking an example like that, but it takes time and doesn't really 'prove' anything at all, does it?

More than the one you refer to below which is systematically biased.

But, if you are interested in bogus 'statistical' analysis, then try looking at DxOmark rankings. So, for instance if we filter the lens test data by MP, as follows:

Then you'll find that lenses ranked 1-368 are FF lenses, then we get the Panasonic Leica DG Nocticron 42.5mm F1.2 ASPH at 369. There is some duplication there down to same lens different camera, but there's little point spending a lot of time cleaning up an 'analysis' like that.

What is the relationship between those lens rankings and the factor we are trying to isolate in this discussion: Lens resolution.

Resolution is a factpr in those rankings.

Yes. But not the only and as already indicated, the others introduce systematic bias.

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Just another Canon shooter
Just another Canon shooter Veteran Member • Posts: 4,691
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

Anders W wrote:

What I originally said in my first reply to noirdesir is the following:

"What is known based on the laws of optics is that if we take a lens design for a certain format, say a 50/1.8 for FF, and scale it down in all relevant dimensions so as to make 25/1.8 for MFT, the two lenses will deliver the same resolution if we measure per image diagonal (and the MFT lens twice as much as the FF lens if we measure per mm) at the same f-stop as long as resolution is limited by lens aberrations only."

This is trivially true because it is a statement about a non-existing situation. Similarly to the statement: "All 100-leg cows can fly".

As to diffraction, the larger format has an advantage when comparing at the same (rather than equivalent) f-stops. At equivalent f-stops, there is no difference at all, and the impact of diffraction is generally trifling at wide apertures.

At equivalent stops, the smaller format lens can NOT be a scaled down version version of the larger one. This is the relevant question, actually.

Here is a 100% crop of a shot I took yesterday, 135/2 on the 5D2. The guy was not staying still, of course. Default sharpening in LR.

And here is his pin, I did not even remove the CA:

Which of your f/1 lenses can do this?

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Anders W Forum Pro • Posts: 21,468
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2
1

Just another Canon shooter wrote:

Anders W wrote:

What I originally said in my first reply to noirdesir is the following:

"What is known based on the laws of optics is that if we take a lens design for a certain format, say a 50/1.8 for FF, and scale it down in all relevant dimensions so as to make 25/1.8 for MFT, the two lenses will deliver the same resolution if we measure per image diagonal (and the MFT lens twice as much as the FF lens if we measure per mm) at the same f-stop as long as resolution is limited by lens aberrations only."

This is trivially true because it is a statement about a non-existing situation. Similarly to the statement: "All 100-leg cows can fly".

You got that wrong. The implication is that two lenses of the kind I describe would for all practical purposes be equally good wide open and a few stops down, since the impact of lens aberrations at those apertures is large and that of diffraction trifling. This in turn explains why results like those I showed you earlier (Panasonic 20/1.7 being roughly on a par with Leica M Summilux 50/1.4) are to be expected.

As to diffraction, the larger format has an advantage when comparing at the same (rather than equivalent) f-stops. At equivalent f-stops, there is no difference at all, and the impact of diffraction is generally trifling at wide apertures.

At equivalent stops, the smaller format lens can NOT be a scaled down version version of the larger one.

Of course it can. For example, the MFT 25/1.8 at f/1.8 would be equivalent to the FF 50/1.8 from which it was scaled down at f/3.6.

This is the relevant question, actually.

I didn't see any question.

Here is a 100% crop of a shot I took yesterday, 135/2 on the 5D2. The guy was not staying still, of course. Default sharpening in LR.

And here is his pin, I did not even remove the CA:

Which of your f/1 lenses can do this?

As I already informed you, I don't use f/1 lenses. My 75/1.8 works nicely in cases like these. The samples below are available at full size for those who want to check them out.

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Just another Canon shooter
Just another Canon shooter Veteran Member • Posts: 4,691
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2
1

Anders W wrote:

As to diffraction, the larger format has an advantage when comparing at the same (rather than equivalent) f-stops. At equivalent f-stops, there is no difference at all, and the impact of diffraction is generally trifling at wide apertures.

At equivalent stops, the smaller format lens can NOT be a scaled down version version of the larger one.

Of course it can. For example, the MFT 25/1.8 at f/1.8 would be equivalent to the FF 50/1.8 from which it was scaled down at f/3.6.

But 25/1.8 is NOT a down scaled version of the 50/3.6! Your scaling argument falls apart at equivalent settings. You need to scale the whole world, wavelength and light density included for that.

The lowly Canon 50/1.4 at f/4 beats the Panasonic 25/1.4 at f/2 by a comfortable margin (PZ) both in the center and at the borders, and I am not even mentioning the new Sigma 50 here which might very well be sharper wide open than anything you own at any aperture.

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Anders W Forum Pro • Posts: 21,468
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2
4

Just another Canon shooter wrote:

Anders W wrote:

As to diffraction, the larger format has an advantage when comparing at the same (rather than equivalent) f-stops. At equivalent f-stops, there is no difference at all, and the impact of diffraction is generally trifling at wide apertures.

At equivalent stops, the smaller format lens can NOT be a scaled down version version of the larger one.

Of course it can. For example, the MFT 25/1.8 at f/1.8 would be equivalent to the FF 50/1.8 from which it was scaled down at f/3.6.

But 25/1.8 is NOT a down scaled version of the 50/3.6! Your scaling argument falls apart at equivalent settings. You need to scale the whole world, wavelength and light density included for that.

I am not arguing that the smaller format can keep up with the larger at equivalent apertures no matter where across the aperture range we compare. It can keep up well enough for my standards in the range I am interested in using, i.e., primes with a max speed somewhere between f/1.7 and f/2 (if it is FLs within the standard range we are talking about) and that's all I care about.

My point is that the "enlargement theory" proposed in the OP of this thread is wrong. Whatever advantages the larger format has, that's not the way it gains them. Rather, the simple truth is that it is easier, regardless of sensor size, to make an f/2.8 normal lens that performs well wide open than to make an f/1.4 normal lens that performs similarly well wide open. The aberrations you have to correct for decent performance are simply smaller at f/2.8 than at f/1.4 and that's it.

The lowly Canon 50/1.4 at f/4 beats the Panasonic 25/1.4 at f/2 by a comfortable margin (PZ) both in the center and at the borders,

Did you see the big sign on PZ's home page saying that their results are not comparable across sensors/platforms? Here is my previous example augmented with the PL 25/1.4 and the Canon 50/1.4 based on reasonably comparable data. Personally, I prefer the 20/1.7 to the 25/1.4. Note that the 20/1.7 at f/1.7 is roughly on a par with the Canon 50/1.4 at f/2.8, and significantly sharper at f/2.8 than the Canon at f/4, in spite of the lower pixel count of the sensor.

The figures are line pairs per image height at MTF-50, center/average, based on unsharpened output from RAW files.

Panasonic 20/1.7 on E-M5 (16 MP)

1.7 870/735

2.8 1050/875

4.0 1075/880

Panasonic 25/1.4 on E-M5 (16 MP)

1.4 690/590

2.8 960/820

4.0 980/850

Leica Summilux 50/1.4 on M9 (18 MP, no AA filter)

1.4 600/530

2.0 950/740

2.8 1025/860

4.0 1110/980

Canon 50/1.4 on 5D2 (21 MP)

1.4 650/530

2.0 790/660

2.8 920/690

4.0 960/890

http://www.lensrentals.com/blog/2012/05/wide-angle-micro-43-imatest-results

http://www.lensrentals.com/blog/2012/01/the-great-50mm-shootout

and I am not even mentioning the new Sigma 50 here which might very well be sharper wide open than anything you own at any aperture.

While the Sigma is a nice lens, I don't think it would be sharper wide open than anything I own at any aperture. I wouldn't be interested in it anyway. As I said, I don't find much need for the shallow DoF that comes with a 50/1.4 wide open on FF and the lens is big and heavy. I'd much rather have the FL control (more lenses in my bag rather than in a drawer back home) that I get with MFT.

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knickerhawk Veteran Member • Posts: 6,023
Re: Feel free ..
1

Sergey_Green wrote:

knickerhawk wrote:

Since this thread was moved to the Photographic Science and Technology forum, I will refrain from replying to your usual bluster, BS and attempts to turn our discussions into some kind of macho thing about who's the better photographer.

Nowhere did I say or hint who the better photographer is. What I did ask you, however, was if you have a camera. So I will repeat it, do you have a camera?

Off topic and irrelevant (although it really shouldn't be that difficult for you to figure out, considering the location of our usual encounters).

However, I will take you up on the t/s bait you dangled above since it at least has a remote chance of leading to something of some relevance to this particular forum. What point are you trying to prove with your "hint"? Dazzle us...

Dazzle "us" or dazzle "you"? It does not matter how far you stop past f/11, except for very small gain it will oftentimes invite unnecessary, and often not pleasing backgrounds. Not a usual composition I am after. And if you really need to have everything in focus, use specialized lens that is designed for it. Or stack the image up in post processing.

As far as that particular image goes, it was only an experimentation; 200mm on FF, at a very close distance, to almost cover the width of a wide flower - not a typical closeups and macro angle. And nowhere did I say this is how it should be normally done.

Why did you link to an article about tilt/shift photography?  That was your "hint".  I'm still not understanding the point you were trying to make.  Please enlighten.

Just another Canon shooter
Just another Canon shooter Veteran Member • Posts: 4,691
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

Anders W wrote:

My point is that the "enlargement theory" proposed in the OP of this thread is wrong. Whatever advantages the larger format has, that's not the way it gains them.

Using wrong arguments to disprove a wrong theory does not make you right. None of the posters here which are still active says that it is a simple matter of more enlargement.

Rather, the simple truth is that it is easier, regardless of sensor size, to make an f/2.8 normal lens that performs well wide open than to make an f/1.4 normal lens that performs similarly well wide open. The aberrations you have to correct for decent performance are simply smaller at f/2.8 than at f/1.4 and that's it.

Right.

The lowly Canon 50/1.4 at f/4 beats the Panasonic 25/1.4 at f/2 by a comfortable margin (PZ) both in the center and at the borders,

Did you see the big sign on PZ's home page saying that their results are not comparable across sensors/platforms?

That is what you actually get in reality.

Panasonic 25/1.4 on E-M5 (16 MP)

1.4 690/590

Canon 50/1.4 on 5D2 (21 MP)

2.8 920/690

See? The 25/1.4 is well behind. BTW, the figures are per picture height. Per diameter, you have to add 8% to the FF format.

As I said, I don't find much need for the shallow DoF that comes with a 50/1.4 wide open on FF and the lens is big and heavy.

And yet, you cannot tell just by looking at a few pictures which DOF is enough for you. Do you find the DOF below too shallow (sorry for the boring photo)?

I'd much rather have the FL control (more lenses in my bag rather than in a drawer back home) that I get with MFT.

One good way to get FL control is to have a capable zoom (with less lenses in the bag). The m43 system has no meaningful answer to the FF f/4 zooms.

EDIT: DXOmark contradicts your claim that the 20/1.4 is sharper than the Canon 50/1.4 (as PZ does), by far, but you knew that, right?

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bobn2
bobn2 Forum Pro • Posts: 61,123
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

If you can scale down manufacturing tolerances by a factor 2

Why wouldn't manufacturing tolerances scale?

That is such a ridiculous question, if just you stop to think about it. Every manufacturing process has an associated set of tolerances. So, if you use the same process to produce a smaller product, you are not scaling the tolerances. If on the other hand you develop the tolerances so as to be able to scale them for the smaller product, then that finer tolerance process is available also for the larger product. The exception is only if the smaller size itself allows some change in the process which provides for smaller tolerances.

See my reply to noirdesir here, penultimate section:

http://www.dpreview.com/forums/post/53893177

No connection with the question of scalability of tolerances at all. Linking irrelevant posts, implying that you had made some response to the point already is a most dishonest mode of argumentation.

I pasted the wrong link by mistake. Try this instead:

http://www.dpreview.com/forums/post/53896543

OK, what you said was

The tolerances at issue in this case are those for producing and fitting glass elements. Suppose we were to fit a lens with a diameter of one centimeter and another with a diameter of one meter to the same precision in absolute terms, say one micrometer difference between the edges. Do you think that could be done with the same ease for the one meter lens as for the one centimeter lens?

That in no way answers the question. It is a 'thought experiment' situated in a fantasy. You have chosen an absurd example to 'prove' your case.

I just chose an example that makes the general point that the ability to reach a certain tolerance target as expressed in absolute terms (e.g., micrometers) rather than relative terms (proportions) depends on the size of the objects we are dealing with.

Shifting your ground again. 'Ability to reach a tolerance target' is a completely different thing that saying that tolerances scale. Sometimes there might be an ability to reach a reduced target, others there might not and the costs might not be in proportion to the effect.

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Bob

bobn2
bobn2 Forum Pro • Posts: 61,123
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2
1

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Ulric wrote:

Anders W wrote:

The post of yours that began this exchange in the previous thread was:

http://www.dpreview.com/forums/post/53861976

"Additionally there is one inherit advantage larger formats have over smaller ones: enlargement factor. A large format image needs to be enlarged less than a medium format image, which needs to be enlarged less than FF image which needs to be enlarged less than APS-C image which needs to be enlarged less than m4/3 image which needs to be enlarged less than cell phone image and when less enlargement is needed, the lens is stressed less, thus the lens can be of lesser quality to achieve the same image quality."

Exactly what do you mean by "stressed less" and "lesser quality" here? And in what way does the "lesser quality" actually translate into an "inherent advantage of larger formats"?

The larger format lens does not have to resolve as many lines per millimeter on the image plane, thus it can be (but need not be) optically inferior to achieve the same output image quality compared to a smaller format lens. The reason is in the lesser need for enlargement from the image in the image plane to the output image of arbirtary size.

OTOH, what matters is not resolution per millimeter but per image, and the larger format lens has to perform over a larger image circle. It evens out.

In practice, no it doesn't - the advantage is to the larger image circle.

On what grounds?

On the grounds of that's how it is in practice, never mind any theoretical arguments.

OK. What's the evidence?

Plenty of it out there,

I didn't ask how much of it there was. I asked you which evidence.

the larger image circle generally produces higher resolution (normalised to frame size) in practice on most of the lens tests

Based on what statistical analysis of which lens test data?

Based on observation. Which is what we tend to do around here.

So you have no data and no data analysis to back up your claim.

If you wish to make a counter assertion, do you have a suitable statistical analysis to back that up?

You made an assertion. I didn't. So you carry the burden of proof. But here is an example as a starting point:

http://www.dpreview.com/forums/post/53893177

Well, I considered picking an example like that, but it takes time and doesn't really 'prove' anything at all, does it?

More than the one you refer to below which is systematically biased.

But, if you are interested in bogus 'statistical' analysis, then try looking at DxOmark rankings. So, for instance if we filter the lens test data by MP, as follows:

Then you'll find that lenses ranked 1-368 are FF lenses, then we get the Panasonic Leica DG Nocticron 42.5mm F1.2 ASPH at 369. There is some duplication there down to same lens different camera, but there's little point spending a lot of time cleaning up an 'analysis' like that.

What is the relationship between those lens rankings and the factor we are trying to isolate in this discussion: Lens resolution.

Resolution is a factpr in those rankings.

Yes. But not the only and as already indicated, the others introduce systematic bias.

That is why there is absolutely no point wasting time producing 'evidence' for you, Anders. Whatever it is it will not be persuasive enough to budge you from endless argument in support of your own concocted theories.

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Bob

OP Truthiness Regular Member • Posts: 122
Cropping an image reduces resolution, isn't it obvious?
1

knickerhawk wrote:

We're talking about cropped sensors, not cropped images.

It does not matter how you crop the image!

If you need to stretch a 1cm image to 100cm output size, the aberrations of the lens will be more visible than if you stretch a 2cm image to 100cm output size. This is obvious so it is a bit odd how someone gets the motivation to argue it.

But it's your own logic. YOU were the one who started this discussion by noting that greater magnification comes with an unavoidable resolution penalty.

I state(ed) the following, nothing more:

  1. With a perfect sensor and a lens with aberrations we will have a limited resolution which can be measured in line pairs per millimiter on the image plane.
  2. What the resolution of the output image is depends on the crop factor and can be measured in line pairs by image height.

Do you agree or disagree?

The problem is that you only applied that penalty from an interim point in the magnification (i.e. the sensor plane) to the output display plane.

Huh! The lens draws an image with finite resolution. The more you have to enlarge it, the more the aberrations will show.

You didn't account for the "penalty" incurred between the lens and the sensor (i.e., the focal length).

Huh!

A Carl Zeiss Jena 35mm f/2.4 Flektogon has 35mm focal length regardless fo the crop factor.

With ideal perfect sensors a cropped sensor will turn a lower resolution output image on perfect output device than what a full frame sensor would do because you need to enlarge the image more, thus enlarge the aberrations more too (after all, there just part of the image).

If you change the lens or the optical configuration, that is your bussiness, but has nothing to do with the point. For example by using the focal reducer you're improving the optical configuration by reducing the aberrations (for example 1µm aberration on the image with a naked lens would reduce to 0.5µm aberration with a perfect 2x focal reducer). High quality focal reducer is certainly a better option in most cases than a conventional adapter.

Jack Hogan Veteran Member • Posts: 6,982
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2
4

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote: Then you'll find that lenses ranked 1-368 are FF lenses, then we get the Panasonic Leica DG Nocticron 42.5mm F1.2 ASPH at 369. There is some duplication there down to same lens different camera, but there's little point spending a lot of time cleaning up an 'analysis' like that.

What is the relationship between those lens rankings and the factor we are trying to isolate in this discussion: Lens resolution.

Resolution is a factpr in those rankings.

Yes. But not the only and as already indicated, the others introduce systematic bias.

That is why there is absolutely no point wasting time producing 'evidence' for you, Anders. Whatever it is it will not be persuasive enough to budge you from endless argument in support of your own concocted theories.

No there isn't, the (shrinking) target is always moving for some folks

As has been said correctly in this and several other threads mFT lenses typically need to be at least twice as 'sharp' in order to match FF linear spatial resolution in equivalent photographs - precisely for the reason mentioned by the OP: even mFT's admittedly state-of-the-art lens design is typically not enough to compensate for the format's size penalty. There are a few exceptions to this rule, but they are just that, exceptional exceptions.

As has also been said correctly in this thread by noirdesir amongst others, although ideally system tolerances would scale perfectly with size, in practice they typically don't. They don't because the difference in size we are discussing here is not orders of magnitude away: if an improved process becomes available to one size it will soon trickle down/up to the other negating its advantage, as Bob mentioned; and because as the system shrinks at these sizes there are more things that get harder than easier to do as far as 'sharpness' is concerned, making it difficult to scale down perfectly as parts get smaller. This is how The_Suede put it recently:

'And then you have optimization theory and deviation statistics in manufacturing that quite accurately predicts that it's hard to halve tolerances in centering, glass surface imperfections and element-to-element distances in the lens just because you halved the scale. Often you get maybe 2/3 tolerances in a 1/2 scale production scenario'

This doubly applies to tolerances necessary to achieve equivalent focus precision in the real world. So where's the beef?

It's very difficult to compare lens performance on different cameras because there typically are too many variables to keep under control, too few tests from too many sources, each with their own methods. Dxomark.com has put together the best effort to date attempting to control the variables, test multiple cameras and provide meaningful 'sharpness' data as perceived by the average photographer as uniformly as they could - in so doing they created one of the largest and well thought out, if obscure, databases in photography. One may disagree with some of their choices or methods but nobody questions the fact that the folks there are doing scientific work.

Their data confirms* the OP's point. As of today mFT cameras are typically not able to make up for their smaller sensing size with better lenses. The pudding is everywhere, all one has to do is open their eyes to see it.

Jack

*Selecting 'sharpness' under Optical Metric Scores as the ranking criterion in Bob's link to their database (limted to sensors between 12-18MP) shows the first mFT camera/lens combo on page 5 (Zeiss 42.5mm f/1.2 on 16MP EM5), a $1500 lens easily bested by its FF equivalent, a $500 lens on a 16MP body (Df+Nikkor 85mmf/1.8G). The Df on the other hand is well represented on page one with a host of lenses across the range.

Sergey_Green
Sergey_Green Forum Pro • Posts: 11,947
Truly ..

knickerhawk wrote:

Sergey_Green wrote:

..So I will repeat it, do you have a camera?

Off topic and irrelevant (although it really shouldn't be that difficult for you to figure out, considering the location of our usual encounters).

Figure out what? Say it .

Why did you link to an article about tilt/shift photography? That was your "hint". I'm still not understanding the point you were trying to make. Please enlighten.

It answers your quest (if there was one),

This effect is one of the more subtle uses of the tilt movement. It can allow you to keep a subject sharp, which would otherwise be impossible even using extremely small apertures.

That is, if you are after everything-in-focus only, use what makes it easy. I tried it with macro lens, and it is barely enough (as you see it) for such framing. Not like it would make difference with mFT camera either. I would not shoot f/45 regularly, or even often enough when photographing insects or flowers. If fact, wide open can work just as pretty,

Here is another one, at f/32. The f/11 does not make much difference here, but I was rather interested in light effect. With wide open (or nearly wide open) lens, you get the whole magnified sun-ball in a frame, stopping the lens down renders it rather differently.

Capisce?

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- sergey

knickerhawk Veteran Member • Posts: 6,023
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2
1

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

Plenty of it out there,

I didn't ask how much of it there was. I asked you which evidence.

the larger image circle generally produces higher resolution (normalised to frame size) in practice on most of the lens tests

Based on what statistical analysis of which lens test data?

Based on observation. Which is what we tend to do around here.

So you have no data and no data analysis to back up your claim.

If you wish to make a counter assertion, do you have a suitable statistical analysis to back that up?

You made an assertion. I didn't. So you carry the burden of proof. But here is an example as a starting point:

http://www.dpreview.com/forums/post/53893177

Well, I considered picking an example like that, but it takes time and doesn't really 'prove' anything at all, does it?

More than the one you refer to below which is systematically biased.

But, if you are interested in bogus 'statistical' analysis, then try looking at DxOmark rankings. So, for instance if we filter the lens test data by MP, as follows:

Then you'll find that lenses ranked 1-368 are FF lenses, then we get the Panasonic Leica DG Nocticron 42.5mm F1.2 ASPH at 369. There is some duplication there down to same lens different camera, but there's little point spending a lot of time cleaning up an 'analysis' like that.

What is the relationship between those lens rankings and the factor we are trying to isolate in this discussion: Lens resolution.

Resolution is a factpr in those rankings.

Yes. But not the only and as already indicated, the others introduce systematic bias.

That is why there is absolutely no point wasting time producing 'evidence' for you, Anders. Whatever it is it will not be persuasive enough to budge you from endless argument in support of your own concocted theories.

Bob, that's a little harsh, considering the misleading nature of the DXO lens ratings, which you seem to accept given your willingness to place "evidence" in quotes.  If the evidence is bad or misleading to begin with, then the amount or scaling of it doesn't really matter, does it?  The fact that 368 lenses appear in the dxo lens rating ahead of the first m43 lens tells us nothing if the scaling is distorted in the first place.  The distortion of the "evidence" is further compounded by the fact that there are far more lens+body combinations tested in the larger formats and - even more fundamentally relevant to the discussion here - you've included in your count many lens+body combos for higher resolution sensors than currently available in the m43 format.

If we throw out the higher resolution sensors and adjust for the many more tested combinations, the number is much smaller than 368, but the problem doesn't end there.  The dxo lens score isn't equivalence based.  For instance, the highest score for the Nikkor 24-70mm f/2.8 on a 16mp Nikon body is 25 and the highest score for the Oly 12-40mm f/2.8 on a 16mp m43 body is 20.  Looks like the Oly lens is inferior to the Nikkor by a significant margin, doesn't it? But look what happens when we set the respective dxo score maps at equivalent aperture settings:

That tells a rather different story than the basic score, doesn't it?

At the end of the day, we don't (yet) have much good "evidence" about how the practical limits of lens design and manufacturing will apply to lenses designed for different formats.  At best we maybe have some indications that might show some correlation, but even there it's hard to separate out the inherent optical design/manufacturing issues from the variable market targeting/placement issues (primarily size, weight and cost of the lenses relative to the markets they're targeted at).

Of all postings in this thread, I think your first one, Bob, where you deflate the importance "magnification" and highlight the size issue was probably the most useful.  It's a shame we've gotten so deep into meaningless weeds that we've lost sight of your original insight.

Just another Canon shooter
Just another Canon shooter Veteran Member • Posts: 4,691
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2
1

Can you tell me what is written here, with the small letters? Nevermind, I can read it now. Even better here.

 Just another Canon shooter's gear list:Just another Canon shooter's gear list
Canon EOS 5D Mark II Canon EF 15mm f/2.8 Fisheye Canon EF 35mm F1.4L USM Canon EF 50mm f/1.2L USM Canon EF 135mm F2L USM +4 more
Sergey_Green
Sergey_Green Forum Pro • Posts: 11,947
I am not sure I read it correctly ..

knickerhawk wrote:


If we throw out the higher resolution sensors and adjust for the many more tested combinations, the number is much smaller than 368, but the problem doesn't end there. The dxo lens score isn't equivalence based. For instance, the highest score for the Nikkor 24-70mm f/2.8 on a 16mp Nikon body is 25 and the highest score for the Oly 12-40mm f/2.8 on a 16mp m43 body is 20. Looks like the Oly lens is inferior to the Nikkor by a significant margin, doesn't it? But look what happens when we set the respective dxo score maps at equivalent aperture settings:

Or if it is clear at all. Are you saying at equivalent (stopped down) aperture 24-70/2.8 will do worse, or that 12-40/2.8 when opened up "more" will perform even better? Can you please clarify what you are saying here?

That tells a rather different story than the basic score, doesn't it?

..
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- sergey

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