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07-15-2015, 12:48 PM   #31
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QuoteOriginally posted by normhead Quote
I wouldn't endorse any description of DoF, that doesn't describe circles of confusion, and the concept of acceptable focus, as different from sharp focus, the effect of contrast and micro contrast on the appearance of sharpness and probably a few other variables I don't even know about. I'll know what they are when I read about them and say "Hey, I didn't know that." I want a couple of those in the explanation.)DoF is way more complex than a a half paragraph explanation. And it can be observed and understood, as opposed to statistically analyzed and understood. Trust me, observation and measurement more than the theory of acceptable focus is the way you want to go. Practical experience of tens characteristics is what makes you a photographer, understand the relationship in photo systems from a theoretical perspective makes you a optical physicist, or possibly a lens designer. Depth of Field is the distance from the nearest to the furthest point in acceptable focus.
You're talking about an expert level of understanding, which is not necessary (and some would argue not helpful) to the act of creating photographs. One can always learn more about any topic in existence. However, it's helpful to have more basic descriptions that can help beginners to intermediate photographers understand what causes their practical experience of depth of field, and what actions they can take to achieve the results they want.

I do think the basic understanding should be something more accurate than "longer lens = shallower depth of field."

A person really doesn't need to have an understanding of circles of confusion to make incredible photographs.

07-15-2015, 01:26 PM   #32
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QuoteOriginally posted by romay Quote
And yes, for a bigger sensor, the total amount of light gathered is higher, which equals more information in the final image. Assuming identical framing and pixel density, the bigger sensor will always be sharper. Assuming equal framing and same pixel count, the larger sensor will always exhibit better S/N ratio.
If an only if, you accept narrower DoF. If you equal the DoF, between APS-c and FF (and I assume other systems) you have to stop the FF down 1 stop to match DoF, which means you have to raise ISO to maintain shutter speed. Meaning the same amount of light is used to create each image, twice the light on half the sensor.

Based on the D750 and K-3 and a lw/ph close to 3000, the advantage to the FF is about 100 lw/ph, about .03 percent, I guarantee you, you can't see the difference.

This is seeming to be a really hard concept for folks to wrap their heads around. I guess it's just repeated so often, people assume there's some truth to it.

People have to realize equivalence describes how systems are the same. People trying to use it to make one system better at something than another system are wasting their time, unless you're talking about narrow DoF, like ƒ1.4. That setting produces the narrowest DoF, of any system available on only FF that's what you're going for. Everywhere else where you are talking about format advantages, you're giving up something to get something. That's because "equivalence" is not about "how do systems differ, and how is one better than the other", it's about "How are these systems equivalent." Why is that such a hard concept to understand? To try and use it to say one format is better than the other is a perversion of the term.

QuoteQuote:
A person really doesn't need to have an understanding of circles of confusion to make incredible photographs.
There is not knowledge necessary to take incredible photographs beside where the shutter release is. But somewhere along the way you learn things to increase your control, and your odds of taking aa great photograph. Accidents do happen. The question is, can you repeat them.

You could construct a series of dictums like

"longer lens = shallower depth of field."
wider aperture means more diffuse out of focus areas
smaller aperture means more DOF.
higher ISO means less noise

There are all kinds of simple explanations that will do, until someone asks "why?" Could you achieve photographic proficiency without ever asking why? You could perhaps, is it a testable theory? Someone should put them together in a field guide with a thorough index.

The school I went to suggested I wouldn't be a proficient photographer if I didn't spend a semester studying lens design, but honestly, how do we know how much we need to know? I can't think of a single time I really needed to know anything about lens design, until this forum came along, and it's mostly used to converse with know it alls making rampant assumptions. But I may have used it a few times. It certainly didn't hurt me. Because of it the first thing I look at in a lens is "how many elements ", and try and understand the trade offs between the IQ , the handling of CA and out of focus areas, weight, and number of elements. I'm guessing you can buy a lens without doing that, but are you getting a lens that is suited to the purpose you are buying it for? You see this all the time on the forum, you see the guys who understand lens design talking to another , one has has bought a Sigma 18-35 ƒ1.8 and the other has bought the DA 20-40, because they understand enough about the design of the lenses and how they apply to the real world to make that decision. it's not that one is smart and one is stupid, it's that they both got what they wanted. They are both smart. But they bought two different lenses. It's an understanding of lens design that makes that possible.

Last edited by normhead; 07-15-2015 at 02:05 PM.
07-15-2015, 01:41 PM   #33
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QuoteOriginally posted by fuent104 Quote
What do you mean when you say you don't print / view at 2/3 the size?
You yourself said in a post above: it also depends on magnification. More magnification reduces sharpness--both real (diffraction limited) and perceived. As regards perceived sharpness, to be acceptably sharp a common criterion is the detail should be on the order of 1/100 inch in the print. If you are enlarging by about an additional 1.5 (due to the smaller sensor), the same 1/100 inch is now about 1/67 inch--noticeably unsharp, thus the need to stop down an additional stop to obtain similar/same DOF.
07-15-2015, 02:16 PM - 1 Like   #34
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QuoteOriginally posted by dms Quote
You yourself said in a post above: it also depends on magnification. More magnification reduces sharpness--both real (diffraction limited) and perceived. As regards perceived sharpness, to be acceptably sharp a common criterion is the detail should be on the order of 1/100 inch in the print. If you are enlarging by about an additional 1.5 (due to the smaller sensor), the same 1/100 inch is now about 1/67 inch--noticeably unsharp, thus the need to stop down an additional stop to obtain similar/same DOF.
Put that in perspective...given that a K-3 produces close to 3000 lw/ph, that's 30 inches wide. Your example makes sense only over 100 lw/ph in your example. Up until that point the smaller sensor is not being reduced, so enlargement factors are irrelevant, or not, depending on if whether people can see the difference between and image printed at 100 distinct lines per inch and one printed at a lower number. And for that there are two approaches, you need to know first if they can see the difference between 100 lines per inch and a higher number, and after you determine they can, you have to show that the picture looks better to them. There is lots of evidence that the threshold for a picture looking good is well less than 100 district lines per inch, possibly as low as 50 distinct lines per inch which would give you line values .02 inches wide as distinct. ( 50 lw/ph would mean your K-3 image could go to 60 inches without suffering from enlargement. and my experience would suggest the limit for a k-3 would be closer to 50 disticnct lines per inch than 100 distinct lines per inch.) I would find a statement like the above somewhat irresponsible. As for stopping down a stop, to equalize for a.33 reduction, stopping down a stop doesn't make anywhere near that much difference. IN fact if you are shooting a kit lens like the 18-55 it's highest value at 2160 lw/ph achieved at ƒ8 compared to a 31 ltd a very sharp lens tops out at 2245 lw/ph that's only 3.7 %. SO changing from an 18-55 to a 31 ltd. could push you up 40 inches to 45 inches, by going from the worst lens to the best... definitely not just by changing ƒ-stops/

Look at some typical charts,


One stop is rarely more than 10-15% one way or the other. IN fact often the difference between the lenses best and worst isn't more than 10-15% for it's whole ƒ-stop range. Using a tripod to ensure sharpness, the difference in DOF is often more a factor in the appearance of sharpness than is the actual sharpness of the lens. The diffraction limited softer ƒ-stop can look sharper, because there is more of the subject in focus, even if it's a stop or two past the diffraction limit. I see that almost every day.


Last edited by normhead; 07-15-2015 at 02:45 PM.
07-15-2015, 02:22 PM   #35
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QuoteOriginally posted by normhead Quote
If an only if, you accept narrower DoF. If you equal the DoF, between APS-c and FF (and I assume other systems) you have to stop the FF down 1 stop to match DoF, which means you have to raise ISO to maintain shutter speed. Meaning the same amount of light is used to create each image, twice the light on half the sensor.

Based on the D750 and K-3 and a lw/ph close to 3000, the advantage to the FF is about 100 lw/ph, about .03 percent, I guarantee you, you can't see the difference.

This is seeming to be a really hard concept for folks to wrap their heads around. I guess it's just repeated so often, people assume there's some truth to it.

People have to realize equivalence describes how systems are the same. People trying to use it to make one system better at something than another system are wasting their time, unless you're talking about narrow DoF, like 1.4. That setting produces the narrowest DoF, of any system available on only FF that's what you're going for. Everywhere else where you are talking about format advantages, you're giving up something to get something. That's because "equivalence" is not about "how do systems differ, and how is one better than the other", it's about "How are these systems equivalent." Why is that such a hard concept to understand? To try and use it to say one format is better than the other is a perversion of the term.



There is not knowledge necessary to take incredible photographs beside where the shutter release is. But somewhere along the way you learn things to increase your control, and your odds of taking aa great photograph. Accidents do happen. The question is, can you repeat them.

You could construct a series of dictums like

"longer lens = shallower depth of field."
wider aperture means more diffuse out of focus areas
smaller aperture means more DOF.
higher ISO means less noise

There are all kinds of simple explanations that will do, until someone asks "why?" Could you achieve photographic proficiency without ever asking why? You could perhaps, is it a testable theory? Someone should put them together in a field guide with a thorough index.

The school I went to suggested I wouldn't be a proficient photographer if I didn't spend a semester studying lens design, but honestly, how do we know how much we need to know? I can't think of a single time I really needed to know anything about lens design, until this forum came along, and it's mostly used to converse with know it alls making rampant assumptions. But I may have used it a few times. It certainly didn't hurt me. Because of it the first thing I look at in a lens is "how many elements ", and try and understand the trade offs between the IQ , the handling of CA and out of focus areas, weight, and number of elements. I'm guessing you can buy a lens without doing that, but are you getting a lens that is suited to the purpose you are buying it for? You see this all the time on the forum, you see the guys who understand lens design talking to another , one has has bought a Sigma 18-35 1.8 and the other has bought the DA 20-40, because they understand enough about the design of the lenses and how they apply to the real world to make that decision. it's not that one is smart and one is stupid, it's that they both got what they wanted. They are both smart. But they bought two different lenses. It's an understanding of lens design that makes that possible.
That's for sure, thanks for bringing that up, Normhead. This is exactly where the equivalence debate starts (which we should probably continue elswhere )
I think you can sum up equivalence very easily: In order to produce the exact same same image with different sensor sizes, one has to capture the exact same photons. At that point, it doesn't matter how big the sensor was that captured those photons (if we leave quantum efficiency out of the equation). If one sensor captures more photons than the other, the images are no longer equivalent because they contain different information. Reasons for the difference in photon count can be shutter time, field of view (equivalent focal length) or entrance pupil size (DOF).
I think the reason why people really don't like to argue on that is that, in a photographer's reality, more photons often *is* better, even though it's no longer equivalent to the lesser system. It allows me things that the "lesser" system can't do. I can get smoother bokeh, better base/high iso performance etc. I also sometimes don't care so much if my DOF is thinner because I actually always wanted it thinner and/or it's never been a limiting factor.
Or because of convenience. Let's say I generally shoot at F8 because I'm used to it and don't wrap my head around equivalence and change my style. Then a bigger sensor gives me better S/N.
Last but not least, in Pentax land, equipment plays a role, too. Sure, the Canikon FF guy with his 50mm 2.8 can't take different pictures than my APS-C Pentax + FA31, but nevertheless I want FF because my FA 31 was built for it and I want to use it to it's fullest.

Last edited by romay; 07-15-2015 at 02:40 PM.
07-15-2015, 02:38 PM   #36
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QuoteOriginally posted by Mattox Quote
Depth of field?...can we close this argument once and for all
Yes, right after we resolve that "chicken or the egg" conundrum.
07-15-2015, 02:57 PM   #37
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QuoteOriginally posted by Parallax Quote
Yes, right after we resolve that "chicken or the egg" conundrum.
the egg came first, there is no requirement that says it had to be produced by a chicken.
07-15-2015, 03:10 PM   #38
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QuoteOriginally posted by promacjoe Quote
the egg came first, there is no requirement that says it had to be produced by a chicken.
Indeed.

07-15-2015, 03:34 PM   #39
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QuoteOriginally posted by dms Quote
You yourself said in a post above: it also depends on magnification. More magnification reduces sharpness--both real (diffraction limited) and perceived. As regards perceived sharpness, to be acceptably sharp a common criterion is the detail should be on the order of 1/100 inch in the print. If you are enlarging by about an additional 1.5 (due to the smaller sensor), the same 1/100 inch is now about 1/67 inch--noticeably unsharp, thus the need to stop down an additional stop to obtain similar/same DOF.
Sorry, I should have been more clear. I was referring to the magnification of the subject as projected onto the sensor by the lens. Or rather, the size of the subject in the frame.
07-15-2015, 05:17 PM   #40
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I think the main thing is to know your format and know how your lenses perform on it. For the most part the discussion about equivalence is academic, misunderstood by a lot of people, and mainly used to "win" my-format-is-better-than-yours arguments. I'd question how much it really helps photographers.
07-15-2015, 06:34 PM   #41
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QuoteQuote:
Let's say I generally shoot at F8 because I'm used to it and don't wrap my head around equivalence and change my style. Then a bigger sensor gives me better S/N.
But the APS-c sensor is giving you one stop more DoF. I have gotten quite used to shooting ƒ5.6 on APS-c. F8 and 11 on macros and close ups where DoF is an issue.
ƒ5.6 on APS_c gives you the same DoF as ƒ8 on FF. That is twice the light, on half the sensor. Your signal to noise should be exactly the same. There is no way to achieve more signal to noise on FF other than giving up DOF. It's equivalence.

I hate to keep harping on this, but the work of the FF propagandsits has been insidious and relentless. It would seem 90% of the photographic world actually believe you get something for nothing when you buy a larger format camera. What you get is the ability to trade DOF for noise shooting wide open, if you want that.

If you are not shooting wide open, you can trade DoF for noise just as effectively on APS-c as you can on FF. Just open up a stop. It's exactly the same as shooting FF. You give up your stop of DoF, you use a lower Aperture number and double your light increasing your signal to noise ratio, you do exactly what you do on FF without changing systems. And you can do that right until you reach maximum aperture, where FF will allow you to trade one more stop of DoF for one more stop of noise. That's it. ON an ƒ 1.4 lens any FF setting down to ƒ1.4 can be matched on APS-c. AT ƒ2.0 FF, you match your signal to noise by shooting the APS-c at 1.4, same for every stop above that.

Once you get to ƒ1.4 APS-c has no where to go. But that's it. Until you hit ƒ1.4 whatever you do with FF, APS-c has an equivalent for shutter speed, DoF, and Signal to Noise.

This is what people are not understanding when they say "Then a bigger sensor gives me better S/N.". It does in one very specific circumstance. Shooting wide open. For all the ƒ-stops from 2-16, there is no FF advantage in Signal to Noise. Yet folks make it sound like they will get the Signal to Noise advantage with every image they take, and they don't.

The fact is it's quite possible that the vast majority of FF users haven't taken one image for which there is no APS-c equivalent. And if they did take one, there's a very good possibility it sucked.

The reasons for FF are... the possibility to buy an FF system with more resolution if and only if the FF system is 36 MP, and not all of them are high res.

The ability to use the more advanced AF systems, if and only if the system you buy has one of those systems, and not all of them do.

Some folks very much like the rendering of FF at wide angle more than an equivalent APS-c lens if an only if you even notice the difference.

The extra stop of S/N performance if and only if you are shooting with ƒ1.4 or faster lenses.

There is not one FF advantage that does not require some pretty serious qualification to make it happen. And if you meet none of those qualifications, you're wasting money on an FF system. You are getting nothing for the extra money you spend. Exactly nothing.

Last edited by normhead; 07-15-2015 at 07:02 PM.
07-15-2015, 07:24 PM - 1 Like   #42
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It's true you don't need to understand circles of confusion to take great photos, and there are tons of calculators out there to give at least a general idea of how DoF is changed with the many variables. However, for the math minded who have an interest it's still worth looking at. Here's a handy derivation of the equations involved with DoF and, for me at least, working through it was far more insightful than trying to understand explanations from photographers who only have working understandings:

The DOF equations

QuoteOriginally posted by normhead Quote
I hate to keep harping on this, but the work of the FF propagandsits has been insidious and relentless. It would seem 90% of the photographic world actually believe you get something for nothing when you buy a larger format camera. What you get is the ability to trade DOF for noise shooting wide open, if you want that.
No need to trade anything for situations where you can keep the iso down with a slower shutter speed + tripod, or by cranking up the lights (turn up the flashes or throw more hydrogen into the sun). I don't consider these to be "serious qualifications" These won't apply to every situation, or even to everyone, but for me this would be most of the time when I'm not being exceedingly lazy.

Be fair or you risk sounding like a propaganda machine in your own right*.


(* and to continue with the policy of fairness, for my own use I'm nowhere near pushing the limits of APS-C, that doesn't mean the rest of the photographic world isn't pushing them, or that they're incapable of making their own rational purchasing decisions)
07-15-2015, 07:34 PM - 1 Like   #43
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QuoteOriginally posted by normhead Quote
But the APS-c sensor is giving you one stop more DoF. I have gotten quite used to shooting ƒ5.6 on APS-c. F8 and 11 on macros
f/8 on crop is well into visible diffraction territory, f/11 on crop is ugly.

so you are losing resolution by shooting at f/8 on crop... f/8 on ff will give you better resolution than f/8 on crop, because there are no visible diffraction errors.

funny how crop apologists don't know the limits of their own format :-)

QuoteOriginally posted by normhead Quote
This is what people are not understanding when they say "Then a bigger sensor gives me better S/N.". It does in one very specific circumstance. Shooting wide open. For all the ƒ-stops from 2-16, there is no FF advantage in Signal to Noise. Yet folks make it sound like they will get the Signal to Noise advantage with every image they take, and they don't.
dxo measurements prove otherwise:

07-15-2015, 07:40 PM   #44
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QuoteOriginally posted by Mattox Quote
Let's discuss this issue and close it to avoid future confusion.
If the previous threads did not do it, this one will not either :-)
07-15-2015, 07:41 PM   #45
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Obviously, we can't close this argument once and for all. Doing so would deprive billions of electrons their purpose in the universe.


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