the meaning of equivalence

[tko]

Just have to set the record straight. I firmly believe that the poster_formally_known_as_Joe's equivalency theory is totally correct. It's very straight forward and I don't understand why people are upset with it.

For example one poster stated : "I have never accepted his "equivalence theory" and never will. It is plain wrong. It contradicts every book on photography that I have ever read; it makes a mockery of my light meter readings."

How does it "make a mockery of light meter readings?" It's just a simple way to compare different sensors on the same footing. Granted, nothing is perfect, but if you insist on comparing systems Joe's theory is the way to go.

My explanation of its opposition is that people take the word "equivalency" much too strongly. In engineering it doesn't mean equal, it's just a useful way to compare things. 10,000 lbs of TNT may be equivalent to one atom bomb, but they are NOT equal. One is a lot heavier, for starters : ) A pound of feathers weighs the same as a pound of lead. That doesn't mean they are the same.

Equivalency just gives you a useful way to help you think about things and make comparisons. It's down and dirty, hands on, practical engineering. Whenever your use "equivalence", you have to use it in the spirit in which it was given. To use my lame example with the TNT, if you were to reply to my statement by saying “10,000 lbs of TNT is NOT equivalent an atom bomb because they are different colors," wouldn't that sound like a stupid reply? Misses the point and is technically correct but totally useless. Equivalence lets us visualize things in terms we understand.

Consider focal length and crop factor. To find the equivalent focal length we multiple by the crop factor. True, the real focal length doesn't change, but it behaves as though it does - for us photographers. That's why it's the EQUIVALENT focal length. It's a very useful concept that allows photographers to quickly visualize how different sensor sizes affect the FOV. If you’re an optical designer you wouldn't use this concept.

Engineering definitions exist because they serve a purpose and are useful. Focal length itself is a definition that some people found useful. So are F-stops and ISO. If you’d never heard of them they’d sound weird. Why the h*ck would you divide the focal length by the diameter of the aperture? The usefulness has to be explained.

Changing sensor size effects DOF for all practical applications. You don't have to write the equations out, any beginning photographer knows that a prosumer has a lot more DOF than their old FF at the same F-stop. You can slice and dice this a dozen different ways, but the presented viewpoint is the most practical way to look at things FOR photographers. Not for physicists.

Lastly, a larger sensor gathers more light for the same lens. How hard is that to grasp? Yes, there are lots of interesting subtleties here, all of which I'm aware of. So? The basic statements are not changed. For example some people will argue that equivalent focal length is really a function of pixel density. That's true, and may represent a higher truth, but is that a useful equivalency for everyday use?

You can put all the equivalencies together and it becomes a nice, simple, unifying theory. Multiple the FL, aperture, and ISO by the sensor crop factor to see how the performance for one sensor compares to the performance of a different crop sensor. For example, if you have a prosumer with a 4.0 crop factor sensor, and are shooting F8, 100MM and ISO 1600, when you change to a FF sensor you'll need about F2, ISO 400, and 25MM. Less noise, more DOF, a wider angle lens. That's not a mathematical statement, or a position of higher physics, it just lets you visualize how the change would work. So why is this so controversial?

Notice that the exposure, angle of view, DOF, and noise stays about the same with the crop factor equivalency applied. That’s exactly why we did this. Not in search of any higher truth, but because it helps us! (I still don’t see how this makes a mockery of a light meter)

You want to argue about this? Then give me a better equivalency by answering this question; given a 4.0 crop factor, F8, 100MM, ISO 1600, what settings would give the most similar photograph if you changed to a full frame sensor? That's all equivalency is about.

You can ignore this equivalency. You don’t have to use other imaginary concepts like F-stop if you don’t think they benefits you. Doesn't affect real life, doesn't affect lens designers, doesn't affect CCD designers, doesn't affect nuclear engineers. Just a simple little equivalency that lets you visualize how, when you change one thing, everything else is effected.

If you got a nice fast prosumer with a F2 lens like a G9, and you want to move up to a dSLR but can only afford a F5.6 lens, equivalency gives you a simple way to compare performance. Will the noise be better when you get the kit dSLR? Will the DOF be more or less? All types of complex questions can be answered very simply by using equivalency.

Now, if you’re a photographer and you've just use one system, and you never plan to use any other system, then you don't even need to think about equivalency. But lets say you borrow your niece's point and shoot, isn't it nice to know that at F4 you'll have the same DOF as F16 on your full frame system? Lets you feel right at home just by modifying the old rules. You can still use your FF intuition, developed over years of use.

I'm not really interested in why you may think the above equivalency is wrong. I don't want to hear why you think the Moon Landing was a fake, or why the Earth is really flat, or why a pound of feathers isn't really a pound of lead. Just not interested, don’t want to play word games, not starting a flame war, not knocking any system.

For the rest of you, I am interested in why and what you think about equivalency is so controversial? Why do people want to fight it so hard?

 

[hbx2004]

Hi,

Nice summary, really. Even I've followed this topic all the time (with big interest), I've never discuss it.... because:
-most of eqivalence was "obvious", and
-it happened, that I couldn't "follow" all the time.

I think, Joe made a great article there... the only thing I'm missing (and many others, maybe) are some graphics inbetween (remember Doug Kerr articles?).

In my opinion, the only mistake Joe made (and got banned) is: in discussions, he "pushed" his article too much.... he almost forced everyone to accept it. People just don't like be pushed, that's all.

So, Joe (if you're reading this), put some graphics into "equivalence" article (so more people could understand how stuff work) and come back soon.

Greetings to all,
Bogdan
--
My pictures are my memories
http://freeweb.siol.net/hrastni3/

 

[devnull]

Just have to set the record straight. I firmly believe that the
poster_formally_known_as_Joe's equivalency theory is totally correct.
It's very straight forward and I don't understand why people are
upset with it.

Ditto.

For example one poster stated : "I have never accepted his
"equivalence theory" and never will. It is plain wrong. It
contradicts every book on photography that I have ever read; it makes
a mockery of my light meter readings."

Heh, reasons i. to v. below

For the rest of you, I am interested in why and what you think about
equivalency is so controversial? Why do people want to fight it so
hard?

You don't want to get there. You'll get unpopular and banned

I think there were quite a lot of reasons for the unpopularity. I'll just name a few.

i. Lots of people who don't care about how optics work joined the forums due to digital camera boom. At most, those know about the ISO/time/aperture triangle, at worst, they know about the green box. And now here comes Joe and says that their expensive camera can be equivalent to a cheap one. Or that their prosumer camera needs EXPENSIVE glass to be as good as a large sensor one. Add some fanboism, and it's world war three.

ii. Joe is an educator. Those are usually unpopular. Also he brought new ideeas to the table - and those weren't written in popular books.

iii. Joe is an efficient debater. He'd prove his point AND request the same from the other argumenteers. "Ain't so" would have not been acceptable.

You have already enough reasons for murder
Add to that:

iv. Natural resistance to new ideeas: string and quantum physics (just fantasy, does not work like this), Goedel and Heisenberg theorem/theory (are you kidding me?), evolution and genetics (I'm not cousin to that monkey) down to the earth is not the universe (heresy, let's burn this Giordano Bruno).

v. Natural resistance to criticism. I'll bring only three examples to the table: smoking is bad for you, and burning fossil fuel is bad for us. And, of course, stuffing your face with junk food is hardly good for you. Look around on the streets

There are other reasons, but in my opinion those are the main. Time is short, maybe I'll come back later with more today.

d/n

 

[mamallama]

Joe's Equivalence Theory may be absolutely correct but no one will ever know it is because of his convoluted way of explaining it. When all you do is spend article after article and paragraph after paragraph just of explain the basic concept as Joe mama has and you just did, it'll never get to a point of a precise engineering or mathematical level definition. Until you do all you are doing is hand waving. Sorry.

--mamallama

 

[natureman]

The last thing we need here is a joe mama clone.

Ya know, when I'm out taking pictures, I NEVER think of "equivalence". NEVER. It has no effect on my photography. In fact, until recently, I had never heard or seen the term, in regard to photography. I hope I never hear or see it again.

 

[Graystar]

So why is this so controversial?

Possibly, the heated arguments might have more to do with relevance than accuracy...like some of the recent discussions on pixel size. Even if everyone agreed that smaller pixels are better (they’re not, but hypothetically speaking... ) it doesn’t matter because you can’t buy a camera with a 160 megapixel full-frame sensor.

So saying that under certain conditions, when viewed a certain way, when factors are carefully adjusted, etc. and so forth makes two different objects “equivalent” might not mean much when it’s not going to affect the way anyone takes pictures.

I have images elsewhere in the forum showing that an image taken using 35 times greater sensor area has considerably reduced noise. So does that mean that from now on every image I produce will be in 6x6 mosaic fashion? Of course not. The information may be interesting, but it doesn’t change how I take pictures. It has no relevance.

 

[sherwoodpete]

Does it have any relevance?

Well, we are used to the concept of 35mm equivalent focal length. I think Joe's ideas attempt to include a fuller understanding, so that for example we understand why sports photographers are lined up at the edge of the field with massive telephoto lenses, when one might otherwise think that a compact ultrazoom 18x camera might do the job.

The problem perhaps is the juggling of so many ideas and variables simultaneously does not come naturally to many people, whereas a single idea such as equivalent focal length can be grasped fairly easily.
Regards,
Peter

 

[Barrie Davis]

For example, if you
have a prosumer with a 4.0 crop factor sensor, and are shooting F8,
100MM and ISO 1600, when you change to a FF sensor you'll need about
F2, ISO 400, and 25MM.

==================================================

Please Note: As the quote above reads to me, I believe the example cameras have been inadvertently swapped over.

In my understanding it would make much more sense if the FF camera, for example, was the one at 1600ISO, not the mini-digi!! ;-)
==================================================

Less noise, more DOF, a wider angle lens.
That's not a mathematical statement, or a position of higher physics,
it just lets you visualize how the change would work. So why is this
so controversial?

Well. I understand the concept, and I didn't need Joe to tell me about it, either. But then, I come from a background of multi-format film shooting....

I used to use 5x4" mostly, but regularly swapped between the large format size to 2+1/4" square (6x6cm), 35mmFF, and, much more rarely, right back up to 10x8" sometimes. I did this format-swapping day by day and on a on a job-to-job basis... and knew how to translate ALL the factors relating to image quality between formats.

So YES.... "equivalency" is NOT just for digital.. It is part and parcel of cross-format considerations, and pretty much always has been.
--
Regards,
Baz

 

[Steen Bay]

You can put all the equivalencies together and it becomes a nice,
simple, unifying theory. Multiple the FL, aperture, and ISO by the
sensor crop factor to see how the performance for one sensor compares
to the performance of a different crop sensor. For example, if you
have a prosumer with a 4.0 crop factor sensor, and are shooting F8,
100MM and ISO 1600, when you change to a FF sensor you'll need about
F2, ISO 400, and 25MM. Less noise, more DOF, a wider angle lens.
That's not a mathematical statement, or a position of higher physics,
it just lets you visualize how the change would work. So why is this
so controversial?

As the former poster pointed out you got things a bit backwards there. A 4x crop camera at f/2, 25mm, ISO 100 and a FF camera at f/8, 100mm ISO 1600 will give you 'equivalent' images. Joe explained it all in this post a few days ago.

http://forums.dpreview.com/forums/read.asp?forum=1018&message=28561393

 

[mamallama]

Does it have any relevance?

Well, we are used to the concept of 35mm equivalent focal length. I
think Joe's ideas attempt to include a fuller understanding, so that
for example we understand why sports photographers are lined up at
the edge of the field with massive telephoto lenses, when one might
otherwise think that a compact ultrazoom 18x camera might do the job.

The concept of 35mm equivalent focal length is FULLY, AND I MEAN FULLY, FULLY understood. No need for any "equivalence" confusion factor that joe mama has tried to explain in his convoluted way. Photography has done well before and will continue to do well without some concocted "equivalence" nonsense. Let move on.

--mamallama

 

[S N G]

The last thing we need here is a joe mama clone.

Ya know, when I'm out taking pictures, I NEVER think of
"equivalence". NEVER. It has no effect on my photography. In fact,
until recently, I had never heard or seen the term, in regard to
photography. I hope I never hear or see it again.

I never think of the currency rates until I travel to another country. Or I never thought of miles/hour, killograms to pounds and Fahrenheit to Celcius till I lived oversees. You see, different names different numbers but in essense mean the same thing (not faster, not heavier, and not warmer). Same goes for equivalnce, as long as you do not compare different formats to the same apparent outputs (when comaparing comparable) the term is just a word to you that has no meaning. I can almost relate to it. What I do not understand is why blame joe for it though. He only tried to explain it, as he understood it himself, and not to invent.

• sergey

 

[natureman]

The last thing we need here is a joe mama clone.

Ya know, when I'm out taking pictures, I NEVER think of
"equivalence". NEVER. It has no effect on my photography. In fact,
until recently, I had never heard or seen the term, in regard to
photography. I hope I never hear or see it again.

I never think of the currency rates until I travel to another
country. Or I never thought of miles/hour, killograms to pounds and
Fahrenheit to Celcius till I lived oversees. You see, different names
different numbers but in essense mean the same thing (not faster, not
heavier, and not warmer). Same goes for equivalnce, as long as you do
not compare different formats to the same apparent outputs (when
comaparing comparable) the term is just a word to you that has no
meaning. I can almost relate to it. What I do not understand is why
blame joe for it though. He only tried to explain it, as he
understood it himself, and not to invent.

• sergey

I'm not blaming anyone for the theory(?) of equivalence. I'm just tired of hearing about it (and joe mama) and it has no relevance to taking pictures. It has been beaten to death on these forums and is more aggravating than useful. To keep bringing it up is a waste of time and will just stir up more contoversy and fighting. Somehow I've managed to take pictures for about 40 years without being interested in or concerned about equivalence.

 

[S N G]

The last thing we need here is a joe mama clone.

Ya know, when I'm out taking pictures, I NEVER think of
"equivalence". NEVER. It has no effect on my photography. In fact,
until recently, I had never heard or seen the term, in regard to
photography. I hope I never hear or see it again.

I never think of the currency rates until I travel to another
country. Or I never thought of miles/hour, killograms to pounds and
Fahrenheit to Celcius till I lived oversees. You see, different names
different numbers but in essense mean the same thing (not faster, not
heavier, and not warmer). Same goes for equivalnce, as long as you do
not compare different formats to the same apparent outputs (when
comaparing comparable) the term is just a word to you that has no
meaning. I can almost relate to it. What I do not understand is why
blame joe for it though. He only tried to explain it, as he
understood it himself, and not to invent.

• sergey

I'm not blaming anyone for the theory(?) of equivalence. I'm just
tired of hearing about it (and joe mama) and it has no relevance to
taking pictures. It has been beaten to death on these forums and is
more aggravating than useful. To keep bringing it up is a waste of
time and will just stir up more contoversy and fighting. Somehow I've
managed to take pictures for about 40 years without being interested
in or concerned about equivalence.

I do not disagree with you that equivalence has almost no direct relevance to taking pictures. But this forums is not about taking pictures only, or if at all, but about the technical aspects of the hardware that is used. And the subject has not been beaten to death any more than Olympus users claiming that their lenses can always give better than from FF results when used wide open, or that smaller sensors have some kind of an advantage when it comes to DoF comparison. I do agree there should be no controversy about it but you would not explain and understand things any better by simply not discussing it.

• sergey

 

[TrapperJohn]

Different formats will respond to similar lens designs in a different manner. For those that have worked with multiple film formats, the same situation arose.

Where JM went wrong was selectively applying this to a narrow range of photographic measurements, in promotion of his personal agenda to prove that 24x36 was the absolute best choice. Which it might have been, for him. He then proceeded to inject that into every conversation he could find, on any forum he could find. It became rather tedious.

Equivalency could also be applied to other areas. Size, weight and cost, to name a few. On a more esoteric level, lost opportunities because the gear was so heavy or unwieldy that it discouraged carrying around. If one is going to challenge photographic constants, challenge all of them, not just the ones that benefit one specific format.

Equivalency was supposed to clarify measurements, but selective application of it merely muddied the waters even more.

 

[iMac therefore iAm]

For the rest of you, I am interested in why and what you think about
equivalency is so controversial? Why do people want to fight it so
hard?

My question is why do people keep harping on it? The ONLY people that need to worry about it are those who shoot multiple sensor sizes.

It doesn't matter if your 200mm lens on your 40D yields a field of view equivalent of 320mm on a full frame - you're not shooting a full frame. You never hear people saying that a 200mm on a full frame yields the equivalent field of view as a 125mm lens on a 1.6 crop!

One more time: Unless you shoot full frame and crop - equivalency is MEANINGLESS!

 

[Martin Frost]

If (1) the Fourthirds mount would be a scaled-down canon mount and
the (2) fourthirds sensor would be a scaled canon-sensor,
and (3) the Fourthirds lenses would be scaled-down canon lenses,+
and (4) all Canon lenses including the primes would have antishake.

Then except the useless lengths of the lenses the theory might be correct.

But these four things are not true.

The truth is

(1) the Fourthirds mount is bigger than a scaled-down canon mount
the (2) fourthirds sensor has no 12-22 MP but has better colors,
and (3) the Fourthirds lenses are better than scaled-down canon lenses,
and (4) all Canon prime lenses have no antishake.

regards
Martin F.

-----------------------
Typing errors are intended to provide a basis for global amusement

 

[S N G]

Different formats will respond to similar lens designs in a different
manner. For those that have worked with multiple film formats, the
same situation arose.

Where JM went wrong was selectively applying this to a narrow range
of photographic measurements, in promotion of his personal agenda to
prove that 24x36 was the absolute best choice. Which it might have
been, for him. He then proceeded to inject that into every
conversation he could find, on any forum he could find. It became
rather tedious.

Equivalency could also be applied to other areas. Size, weight and
cost, to name a few. On a more esoteric level, lost opportunities
because the gear was so heavy or unwieldy that it discouraged
carrying around. If one is going to challenge photographic constants,
challenge all of them, not just the ones that benefit one specific
format.

Equivalency was supposed to clarify measurements, but selective
application of it merely muddied the waters even more.

Yes, it can be applied in many areas, but my intuition tells me that in photography it has something to do with the image. Not?

• sergey

 

[Joesiv]

For the rest of you, I am interested in why and what you think about
equivalency is so controversial? Why do people want to fight it so
hard?

Honestly, for me, I never understood equivalence until your post. I think if Joe Mamma was an "educator" he could do a better job educating in ways that people could understand.

Having said that, I don't think equivalence IS controversial, joe mamma is.

Perhaps that's why he was banned?

What I found from a few threads where joe mamma was posting, is he seemed to have more time than most people to respond to EVERY post, and require that other people put in as much time and effort into each post. Frankly, I don't, and I doubt other people have as much time hitting F5 to respond in such a way.

I guess in the end, it made joe think that he "won", since noone could refute him, or even discuss at the same level as him.

I don't think a public forum mixed with pople with so many ranging skillsets/knowledge is a good person for someone like joe mamma to "educate". I think he just stirred up more controversy than was needed.

but thanks for the summary, it is making sense now. And I can see some benefit to it. For me personally, I would rather look at each aspect individually as there are so many other factors such as sensor qualities that factor in for me.

I'd rather just know that this F-Stop is equivalent to that Fstop in DoF, and know that my light meter gives me this shutter speed for that Fstop.

All else can be compared without equivalences, becuase shutter speeds are just timed exposure, and ISO's are not directly comparible since technologies vary so much (and NR).

--
Cloverdale, B.C., Canada
Olympus e-510 e-330 L1
http://joesiv.smugmug.com

 

[Rriley]

For the rest of you, I am interested in why and what you think about
equivalency is so controversial? Why do people want to fight it so
hard?

The problem with 'equivalence' comes in how it is applied, it is after all just (just) a theory, but it is often taken as an absolute. Where 'absolute' it absolutely is not. The application of this theory has been held to ransom by some, to evaluate over any other cause, that of shallow DoF photography.

People see this theory and begin to apply it, we could call this 'Applied Equivalence Theory'. Taking as gospel an applied theory is an unnaturally dangerous assumption. It is taken that if 'equivalence' theory is right, it is right in every possible way. This is rarely so with so broad a theory, as it does not consider lens performance (vignetting, blooming, fall-off, soft edges/corners) and does not consider sensor performance, it cannot then, be so wholly trusted.

Science, Engineering and Art

There are always those who seek to apply to black and white an absolute reference to 'equivalence' as substantial proof. This is a mistake, for it is then no longer science, engineering or art. The supposition that this is science dismisses the notion that the operant will fail to optimise his/her position which is a nonsense, for the art of the science dictates that the operant will. The engineering of the science then disposes the operant to more latitude that the art of the operant would exploit. Science then takes a back seat to art, and art disposes itself to engineering, and the use of the theory for all practical matters is quaintly disposed of.

The adherents of equivalence dictate limits that impose the same 'equivalent FL', the limits sound worthy b/se everything is 'numerically' the same except the sensor. The adherents superimpose that the same image, same EFL, same DoF, should only be possible where the smaller system can access faster lenses, faster by the size/crop factor it lacks to the larger.

There is probably one major problem with this, almost nobody does it. Its only worth is in some feast of comparison that sees the smaller sensor crippled with one arm behind its back, the need to acquire EFL to achive the same image FoV. If the score were given to deep DoF, no advantage to FF.

In discussion it is more usual that no other proposition is considered in opposition to shallow DoF. Yet at the same time it confines crop systems to FL equivalent to that of FF. Yet IF the object of the argument were to demonstrate shallow DoF, it dismisses with some surprise, that utilising the same FL, indeed the same lens, sees the smaller sensor exhibit even shallower DoF, b/se it seeks to uphold the DoF range that the same image can be taken. Which is the reverse of what the art seeks to navigate, that of acquiring 'that' image, not the same image.

Engineering and Art

The photographer that knows the engineering of the art, applies to imagery 'with the tools at hand' whatever principles are required to achieve the shot required. The photographer/artist, would seek the format tools that best describe the most common usage for that individual. Given a lesser format, the artist would select the FL and shooting position that induces the DoF required for the look that is sought.

Suggesting that there is only one way/one format is simplistic and unreasonable that is why it met such opposition. Even suggesting that a particular format is better disposed for a particular field of photography is fraught with complications that the engineering of the art need to deal with.

Where particular lens performance is sub par (and we all know that condition exists), the artist/photographer needs to deal with this to his/her disadvantage.

The fact that every system has limitations be they s/n or a manufacturers optical incompetence, or a low scope control suite isnt considered by equivalence and highlights the simplistic nature of its origin and its continual improper use.

--
Riley

in my home, the smoke alarm is the dinner bell (just)

 

[mamallama]

Right on, Professor Irwin Corey.