[eyeswideshut]

Oh, how I thank the Lord for Equivalence. I was seriously afraid I'd have to spend a boring evening of bad German Beer and lousy World Cup Football* in a bar :-(
Now I'm saved: Equivalency 101 (remedial section) right here on Pentax Forums :-)

Or perhaps I'll take my laptop with me and chime in around 1:00 am zzzzzzzzzzz

Cheers


*for my American friends: Football = Soccer and World Cup = (World Series + Superbowl)²

[jsherman999]

, "equivalence" is lying by pretending to be physics when it's not. Don't believe it!

The problem with 'not believing it' is that there's a multitude of photographic evidence out there proving it in images - you don't even have to rely on the math. I myself own aps-c and FF, and have taken shots at the same FOV, distance and F-stop on both formats, and have seen it's effects, exactly as described.

The people who have described it in specific mathematical terms (James, Bob Newman, John Sheehy, Lumo, Joseph Wisniewski, Eric Fossum, etc, etc etc) have come to the same conclusion. One that apparently doesn't match your "I don't want to learn anything new" stance.

If you want another PhD source who's dabbled a bit - over 35 years of professional digital imaging experience, beginning with NASA - check out Dr Clark who has written a very nice overview here, which pre-dates J. James summary article.


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[eyeswideshut]

You know, Norm, I've been quoting that article to you for probably over two years now, and I've tried to make probably every one of those bullet points to you at various times. Sometimes it's just easier to hear from another source, huh?

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---------- Post added 06-13-14 at 11:16 PM ----------



It's fully applicable to film cameras as well. The physics is the physics. It never came front n' center as a concept back then because 1) we never really had film cameras with different film sizes sharing mounts/lenses, like we do with aps-c and FF sensor cameras, and 2) There was no internet in the same sense and degree prior to the DSLR age, and the iterations of discussion happened much slower, and comparisons (and questions about what you were seeing) happened in islands, cut off, unlinked and not-reference-able.

The concepts were reportedly known out there, though, just not carrying a catchy single label. (I've noticed naming something always gives it legs, makes it less amorphous, wraps it up in a bow.)

As I said, Joseph Wisniewski has said he was telling people about focal length and f-stop conversion ratios between large, medium and 135mm film formats back in the day. That was equivalence.

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After this and the other recent equivalence debate here I went back and perused Saint Anselm's "The Camera" with an eye towards equivalence and while he never used the word, nor indeed spent much time on the conversion logic, he certainly pointed out all the elements that make it up.

Perhaps that underlines what I have tried to argue at various times, that equivalence, while technically 'true' is overrated and blown out of all proportion by some of it's devotees (not so much you though, you keep a fairly level head about it) - and hence 'loathed' by those who are forced into discussions of aspects of physics they really do not want to discuss.

Anyway, if anyone ever had a practical need of equivalence, it would have been Ansel Adams, who famously shot any format from 35mm on up and recycled lenses from one format to the other as well. After all, thats what large format photographers have been doing forever.

---------- Post added 06-14-14 at 04:27 PM ----------

What you need to know about equivalency...

I've never heard. "It was a really tough shoot last night, I was losing my light, my model was grumpy and I was really having trouble getting my equivalency calculations to work out." No one ever says that.

It's the pet rock of armchair photographers.

Touché

[Pål Jensen]

The problem with 'not believing it' is that there's a multitude of photographic evidence out there proving it in images - you don't even have to rely on the math. I myself own aps-c and FF, and have taken shots at the same FOV, distance and F-stop on both formats, and have seen it's effects, exactly as described.
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If you take the same image at the same angle of view, distance and F:stops with various format you'll get different DOF. Nobody is debating that point.

However, you fail to tell us why DOF wide open is the only parametre thats important in a lens justifying it as a benchmark for equivalence at the expense of everything else.

While at it, the "equivalent" proponents fail to explain why it is that APS lenses need to comply with DOF characteristics of FF lenses but FF lens need not mimick the DOF characteristics of APS lenses in order to be equivalent.

If you apply physics to these subjective and partly incoherent premises you get weird results that do not reflect how people actually buy or use their cameras.

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Last edited by Pål Jensen; 06-14-2014 at 07:43 AM.

[ElJamoquio]

Not unless Optics, Common Sense and I are family.
It's amusing when one is assuming a strong emotional involvement on the other side only, when he himself has an agenda (e.g. to "prove" FF is cheaper)

That's not an agenda. That's a fact (because I (unless I forget) use the qualifier 'for me').

and is emotionally involved in this matter. My only involvement is, however, just a reaction against this "equivalence in any form and circumstances is good" propaganda.

I think you're projecting your emotion on me. I have no dog in this fight. I'd like to use my beautiful Pentax lenses to make beautiful pictures, but honestly they're more valuable used than I paid for them new.

---------- Post added 06-14-14 at 08:08 AM ----------

However, you fail to tell us why DOF wide open is the only parametre thats important in a lens

Life would be easier for people learning about cameras if you would stop mis-characterizing the argument.

The physics behind equivalence show us that any size sensor can take any picture with any DOF. Lens design will have to change (like focal length and f/stop).

[jsherman999]

1) Yes we did. We had APS cameras in the film days. In addition Pentax 645 and 67 lenses could be used on 35mm and Pentax 67 lenses could be used on the Pentax 645 body. There was lots of discussion about this a crop factors. But no equivalency nonsense.
2) We had internet about a decade before digital made a major impact.

I don't think many people shot aps film - not nearly as many as shoot aps-c DSLR, the ratio isn't remotely close. Fewer people, fewer discussions, and all happening largely in non-connected silos.

Re internet - if you count the arpanet and the links between universities and some research companies, we had the internet three decades before the first DSLRs hit, but usenet didn't really take off until maybe the mid eighties and of course dpreview and pentaxforums, etc are a product of the 00's. The point is, the sharing of images and ideas about photography really exploded about the same time DSLRs came on the scene, and that combined with the aps-c sensor being the only thing available in the first DSLRs and people moving from film - the effects that can be described as 'equivalence' began to really be noticed and the medium (ubiquitous internet forums) was there to discuss it.

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[Pål Jensen]

Re internet - if you count the arpanet and the links between universities and some research companies, we had the internet two decades before the first DSLRs hit, but usenet didn't really take off until maybe the mid eighties and of course dpreview and pentaxforums, etc are a product of the 00's. The point is, the sharing of images and ideas about photography really exploded about the same time DSLRs came on the scene, and that combined with the aps-c sensor being the only thing available in the first DSLRs and people moving from film - the effects that can be described as 'equivalence' began to really be noticed and the medium (ubiquitous internet forums) was there to discuss it.

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The point is that there were active and thriving photography forums long before digital. Eg Photo.net and the PDML (Pentax list originally hosted by Pentax: I think I joined in 95). People who used several formats. Nobody proposed the "theory" of equivalence as proposed nowadays. The impact on DOF on larger formats was obvious to anyone and is nothing new.
You won't find the "theory of equivalence" as proposed in any photography text - and I have several. There are good reasons for that.

[jsherman999]

If you take the same image at the same angle of view, distance and F:stops with various format you'll get different DOF. Nobody is debating that point.

However, you fail to tell us why DOF wide open is the only parametre thats important in a lens justifying it as a benchmark for equivalence at the expense of everything else.

No-one is saying that. PLease, read the pertinent articles and at least make an attempt to bring yourself up to speed. Every time you enter the discussion we waste time backtracking and going over things most other folks 'got' a long time ago.

If you apply physics to these subjective and partly incoherent premises you get weird results that do not reflect how people actually buy or use their cameras.

People buy their camera and lens combination based on things like noise control, angle of view, and DOF control, right? If you shoot more than one format - or plan to - you don't do yourself any favors if you don't know the basics of equivalence. You could end up buying something way more expensive than you need, or more commonly buying something that doesn't really give you much advantage because you didn't take the equivalent f-stops into account.

And the biggest shame with that is that it's relatively simple to understand. And it doesn't describe any format being 'better' than any other across the board.


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[Pål Jensen]

No-one is saying that. PLease, read the pertinent articles and at least make an attempt to bring yourself up to speed. Every time you enter the discussion we waste time backtracking and going over things most other folks 'got' a long time ago.



People buy their camera and lens combination based on things like noise control, angle of view, and DOF control, right? If you shoot more than one format - or plan to - you don't do yourself any favors if you don't know the basics of equivalence. You could end up buying something way more expensive than you need, or more commonly buying something that doesn't really give you much advantage because you didn't take the equivalent f-stops into account.

And the biggest shame with that is that it's relatively simple to understand. And it doesn't describe any format being 'better' than any other across the board.
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I have read the pertinent articles and equivalence is based on DOF wide open constancy and nothing else. Nobody is saying that but thats what you are doing; you compare the DOF wide open and ignore the rest incuding DOF range. The lenses claimed to be DOF equivalent are patently not.
Normhead has alreday pointed out what you need to know when using different formats. I shoot three formats and equivalence has no value. I didn't choose three different formats in order for them to be equal; quite the opposite in fact like most people. I know that the larger formats give less DOF at the same aperture and that is fact all I need to know.

We have a equivalency video that claims that manufacturers are lying on their lenses. It is obvious that some proponents of this "theory" has no clue.

[jsherman999]

After this and the other recent equivalence debate here I went back and perused Saint Anselm's "The Camera" with an eye towards equivalence and while he never used the word, nor indeed spent much time on the conversion logic, he certainly pointed out all the elements that make it up.

Yes, and others did as well. People like Pal don't see the word 'equivalence', so they don't apply the concepts - but they were there. And as I said, it mattered less back then because we rarely shared lenses between formats and we didn't typically encounter purchase decisions that overlapped so closely as we do now (between m43, aps-c and FF.)

It's really very logical why the concepts floated to the top after the introduction of DSLRs sporting aps-c sensors that mounted the same lenses hat were used on 135mm film. This "I never personally heard of it before 2004(5,6,7,8,..) , so it must not exist" is the odd viewpoint here.

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---------- Post added 06-14-14 at 10:15 AM ----------

I don't choose three different formats in order for them to be equal.

Making this ^^ statement shows you don't understand the whole parent concept behind equivalence. I don't know how to get through to you.

Equivalence doesn't mean you need to try to make the images equal - it's there to describe the relationship between formats, and it uses the concept of equivalent images as examples to show you these relationships.

(Can anyone else who understands this describe it better so folks like normhead and Pal get it? I might be at my articulation limit.)

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[Pål Jensen]

It's really very logical why the concepts floated to the top after the introduction of DSLRs sporting aps-c sensors that mounted the same lenses hat were sued on 135mm film. This "I never personally heard of it before 2004(5,6,7,8,..) , so it must not exist" is the odd viewpoint here.
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That is not the argument. Equivalency is simply the fact that you use a longer focal lenght for the same angle of view on a larger format and hence you get less DOF at the same aperture. Equivalence is nothing more than that; its no theory or a new thing. Everybody had heard about it but nobody formulated a rigid theory on that based on a subjective choice of one parametre over the others. It simply isn't valid - you could as well develop a shutterspeed equivalency among formats. It is just that back then photography forums where populated by photographers to a larger extent than now, and no photographer I've heard of is concerned about DOF wide open equivalency.

---------- Post added 06-14-14 at 06:24 PM ----------

Yes, and others did as well. A I said, it mattered less back then because we rarely shared lenses between formats and we didn't typically encounter purchase decisions that overlapped so closely as we do now (between m43, aps-c and FF.)

It's really very logical why the concepts floated to the top after the introduction of DSLRs sporting aps-c sensors that mounted the same lenses hat were used on 135mm film. This "I never personally heard of it before 2004(5,6,7,8,..) , so it must not exist" is the odd viewpoint here.

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---------- Post added 06-14-14 at 10:15 AM ----------



Making this ^^ statement shows you don't understand the whole parent concept behind equivalence. I don't know how to get through to you.

Equivalence doesn't mean you need to try to make the images equal - it's there to describe the relationship between formats, and it uses the concept of equivalent images as examples to show you these relationships.

I've already explained the relationship between formats:

"All you do when increasing or decreasing the format while maintaining the angle of view is transposing the DOF scale towards thinner or deeper DOF". Which scale is "correct" is purely a subjective issue. Theres no meaningfull law to be had from this - just preferences.

Aperture - shutterspeed - Sensitivity = exposure

This tells you all you need to know and is the physics behind a photograph.
If you change any of these parametres you'll have change at least one of the other to maintain the exposure. Which one is of course purely subjective and you cannot make any generalized rules from it, let alone a law. When changing format while maintaining angle of view you change focal lenght. Then DOF at the same aperture will be different.

The ruling eqiuvalent law is the law of exposure. It is in every photography book. F:4, 1/250s at ISO 100 will give the equivalent exposure regardless of format.

The above cannot create any confusion, but the equivalency surely has when people don't anylonger the difference between focal lenght and angle of view.
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[Parallax]

(Can anyone else who understands this describe it better so folks like normhead and Pal get it? I might be at my articulation limit.)

I'll give it a shot.
1 cup is the equivalent of 47 teaspoons. That doesn't mean that in any situation it's reasonable to substitute one for the other. If a pie crust recipe calls for one cup of flour, you could measure out 47 teaspoons instead of using a one cup measure, but it's probably not the best choice; just as trying to add sugar and stir your coffee with a one cup measure instead of a teaspoon isn't all that practical.

[Kunzite]

That's not an agenda. That's a fact (because I (unless I forget) use the qualifier 'for me').

That is an agenda. Otherwise you would say it once, maybe twice and be done with it - but no, you have to tell us that FF is cheaper (sometimes adding that it's "for you").

The problem with 'not believing it' is that there's a multitude of photographic evidence out there proving it in images - you don't even have to rely on the math. I myself own aps-c and FF, and have taken shots at the same FOV, distance and F-stop on both formats, and have seen it's effects, exactly as described.

The people who have described it in specific mathematical terms (James, Bob Newman, John Sheehy, Lumo, Joseph Wisniewski, Eric Fossum, etc, etc etc) have come to the same conclusion. One that apparently doesn't match your "I don't want to learn anything new" stance.

If you want another PhD source who's dabbled a bit - over 35 years of professional digital imaging experience, beginning with NASA - check out Dr Clark who has written a very nice overview here, which pre-dates J. James summary article.


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You're mistaken, there is no photographic evidence proving "equivalence". You still don't understand what "equivalence" is, I'm afraid: it's not the act of taking pictures, nor optics - but a parasite feeding on both. In its most rigorous form - which you're supporting - it's just a senseless application of known relations between different notions. In its worst form, however - which you're also supporting - the basic notions are distorted, e.g. by claiming that focal length can be changed on a whim.

Your repeated attempts at asking people to read are amusing. I started reading photography books decades ago - perhaps that's why I have a clearer view on this matter.

After this and the other recent equivalence debate here I went back and perused Saint Anselm's "The Camera" with an eye towards equivalence and while he never used the word, nor indeed spent much time on the conversion logic, he certainly pointed out all the elements that make it up.

That's not because "equivalence" is "true", but because it's using basic optical notions - except when it's not, e.g. when twisting the meaning of focal length.
To give an example, the relation between format, focal length and angle of view is not "equivalence"; it's optics. Using this relation to compute "equivalent" camera systems based on a restricted set of parameters is "equivalence". Claiming that focal length is angle of view is "equivalence" as well.

[ElJamoquio]

We have a equivalency video that claims that manufacturers are lying on their lenses.

They are.

[Pål Jensen]

You still don't understand what "equivalence" is, I'm afraid: it's not the act of taking pictures, nor optics - but a parasite feeding on both. .

Fantastic. Quote of the year!

---------- Post added 06-14-14 at 06:45 PM ----------

They are.

Are you telling that manufacturers are printing the wrong focal lenght on their lenses?