[eyeswideshut]

You guys may argue all you want about how useless it is...but the fact of the matter is that plenty of people do use it because they want their FF lenses to look how they looked on their 35mm cameras, hence Lens Turbos and Metabones. The existence of those products proove that there are MANY people that care enough about getting equivalent pictures across different formats that they are willing to pay hundreds of dollars. So you can stick your fingers in your ears and say "its useless its useless its useless", but the money changing hands prove otherwise.

I wonder if the increased speed is not the bigger motivating factor here?

[Kunzite]

I'm sorry to jump in on a discussion that's way above my head but please stop quoting this! I am a noob and say so without any reservations but, I have never measured the size of a sensor or a piece of film. I do accept that someone might have done that and I accpet that 50mm in FF is normal, that someone else measured an APS-C and said 30mm is normal I have to accept that too. I think however that they just did the math based on one measurement. I don't even know where to find the documented diagonal for a 1/2.3 sensor, or who measured it so I don't even know what's normal there.

Sorry... what? Are you upset because decades ago, people agreed to call a lens "normal" if its focal length is roughly the same as the frame's diagonal? And you'd like to silence me, the others who know this, and burn all the books that were written on the subject?

How could they do the math "based on one measurement"? The Mighty Crop Factor itself is computed using the format's diagonal, so you can't avoid finding out the normal in the process. It doesn't make any sense... sorry, but you're one of the people confused, not helped by "equivalence"

[Aksel]

This is a very interesting topic. It goes sometimes too theoretical (at least for me), but here are also some very practical issues that most of us (I think so ) are probably dealing with our minds. Here is one of these matters, which I also deal in relation to equivalence topic:

...

They can answer the question, for example: "Should I get a FF body and a 28-75 2.8, or stick with my aps-c body and buy a Sigma 18-35 f/1.8? Which would perform better for me and be better bang/buck, knowing what I know about my shooting needs, usual FLs used, etc? If I buy a FF body, what lenses would I want to keep, or sell, based on my most-used FLs on aps-c? Will I even see an advantage in DOF for my FOVs, if I move to FF? Or is there an m43 alternative that would work even better, for me? What exactly would I lose IQ-wise by going m43, or gain?"

...

I understand that photography is not mathematics (or physics). However, photography differs from painting in that it depends to a greater extent the laws of physics.

[Rondec]

Of course not, equivalence can't answer everything about everything, it's simply acts like a calculator solving arithmetic problems - it provides a strong, accurate starting point for you, the decision maker to embark from. You have to decide what matters after you reach the point equivalence brings you to. And again it's not the fault of equivalence if the answers it brings are not to your liking, it's the fault of a manufacturer, or format.



OK. It's not a rationalization thing, either, but I suppose some could use it that way. However it's master is best served.

But all equivalence does is tell you what lens has less depth of field on a given format. That's it. If you aren't particularly interested in less of depth of field, then the equivalence formula makes much less difference. If you shoot landscape, if you use a tripod and low iso, if you shoot macro photography, if you shoot really long lenses, suddenly the equations don't really make much difference. The applications where it seems to be most useful are those where you are shooting portraiture and don't want to include the environment.

Cost is a weird factor too. Because when people want to make a particular format look good, then they start throwing around prices of used gear, manual focus lenses, off brand lenses. If you want to make it look bad, you choose expensive brand lenses. I got a DA 55-300 for 250 dollars (new), I don't even know if there is an 80-450 Nikon lens that is full frame compatible for a similar price, that has similar performance. But I guess it doesn't really matter. In the end, it is really more about photographic skill than it is about gear, however much we say otherwise.

[audiobomber]

Cost is a weird factor too. Because when people want to make a particular format look good, then they start throwing around prices of used gear, manual focus lenses, off brand lenses. If you want to make it look bad, you choose expensive brand lenses. I got a DA 55-300 for 250 dollars (new), I don't even know if there is an 80-450 Nikon lens that is full frame compatible for a similar price, that has similar performance. But I guess it doesn't really matter

Equivalence does matter. Nikon makes an 80-400mm f4-5.6 full-frame lens for $1500, but that is not comparable. Aperture equivalence tells us that a DA 55-300 f/4-5.8 on your Pentax K-5 II is equivalent to an 83-450mm f/6-8.7 on a D800E. Nikon doesn't make one. They do make a directly comparable 55-300mm f/4-5.6 though, for $400, and three 70-300mm f/4-5.6 lenses from $160-1100.

[Rondec]

Equivalence does matter. Nikon makes an 80-400mm f4-5.6 full-frame lens for $1500, but that is not comparable. Aperture equivalence tells us that a DA 55-300 f/4-5.8 on your Pentax K-5 II is equivalent to an 83-450mm f/6-8.7 on a D800E. Nikon doesn't make one. They do make a directly comparable 55-300mm f/4-5.6 though, for $400, and three 70-300mm f/4-5.6 lenses from $160-1100.

I am mostly shooting on a K3 now, meaning that I do have some extra reach over a D800, for what it is worth.

[eyeswideshut]

Aperture equivalence tells us that a DA 55-300 f/4-5.8 on your Pentax K-5 II is equivalent to an 83-450mm f/6-8.7 on a D800E.

Yes and No. Within the strict parameters of equivalism you are right - but does it matter? Only if Rondec wants to contemplate recreating an equivalent image, dof included. Actually, though, using the lens at 300mm he is probably glad that he can benefit from the larger depth of field at equivalent focal lengths ( angle of view, really) and still enjoy a relative aperture of f/5.8 for exposure.

[jsherman999]

But all equivalence does is tell you what lens has less depth of field on a given format. That's it.

Not at all. When applied, when used in conjunction with basic knowledge of sensor efficiency/age, it can be instrumental in answering pre-purchase questions like:

1) If I buy a 1'' sensor camera that includes an 85mm equivalent FL with an f/2 F-stop**, what would it's images look like if I tried to use it for portraiture, and would that be satisfactory to me?
2) I use my 15ltd for indoor, low-light architecture at times - exactly how much noise advantage would a 20mm f/2.8 allow me on the latest FF? ie, what would my wide-open ISO 6400 on aps-c shots look like with the new combo?
3) Should I get a FF body and a 28-75 2.8, or stick with my aps-c body and buy a Sigma 18-35 f/1.8? Which would perform better for me and be better bang/buck, knowing what I know about my shooting needs, usual FLs used, etc?
4) If I buy a FF body, what lenses would I likely want to keep, or sell, based on my most-used FLs on aps-c? (thinking of selling those less-used lenses to fund purchase perhaps)
5) Will I even see an advantage in DOF for my FOVs, if I move to FF? Or is there an m43 alternative that would work even better, for me?
6) What exactly would I lose IQ-wise by going m43, or gain, if I usually shoot FLx and aperture range y-z?
7) etc, etc, etc, etc, ...

You can certainly go into these purchases completely blind instead, but that's a lot of money to spend that way, and disappointment lurks around every corner. On the fora we do sometimes see FF or m43 or 1'' buyers lamenting the negative IQ 'surprises' they encounter.

** "85mm equivalent FL with f/2 F-stop" is probably exactly how that camera would be advertised, too - the manufacturer benefiting from a half-conversion. It would be up to the equivalence-savvy buyer to figure out what they were really getting with regard to IQ, and if hey would like it - pre-purchase.

.
.

[ElJamoquio]

Not at all.

Correct.

Equivalence is about more than DOF. It shows you at which settings, given a similar sensor, that you'll have the same SNR, the same DOF, and the same shutterspeed.

It's a set of very compact equations that are basically indispensable* if you are considering using two different sized sensors/films.


*You could spend 100x as long, of course, purchasing what you think you might want and running your empirical experiments, assuming you don't have experimental error and are somehow averse to multiplying one number by another number.



I really can't understand the consternation regarding equivalence. I wonder if it's just that people make up their minds first about which side of a debate they're going to be on, and later on determine what 'evidence' they're going to use.

[Kunzite]

You can certainly go into these purchases completely blind instead, but that's a lot of money to spend that way, and disappointment lurks around every corner. On the fora we do sometimes see FF or m43 or 1'' buyers lamenting the negative IQ 'surprises' they encounter.

That's one of the false assumptions that "equivalence" supporters would want us to believe, that we either use it or we have nothing. Yeah, right.

As eyeswideshut said - and I agree wholeheartedly - "equivalence" only works if you want "to contemplate recreating an equivalent image, dof included". That's an assumption which must be proved true.

Another assumption, is that you have a baseline. "A 50mm f/1.4 on m4/3 is equivalent to a 100mm f/2.8 on FF" is a pretty much useless information, if you don't have a clue how any of them looks like. You'd end up cluelessly paper-comparing lenses, an equivalent of buying cameras based on DXOMark scores (and since you're there, you can combine the two).

A most annoying assumption, is that "equivalence" is the best way of comparing the included parameters. Point 2) mentions noise, and "equivalence" should give you some computed score about it via "total light". But "equivalence" does not differentiate between any cameras of the same format! The old 5D or the brand new D810, they're all the "same" ("equivalence" works within the assumption that all sensors are the same, which is completely and totally untrue). But what better way could there be? Is it even possible, after all we have those nice formulae which appears scientific and such?
Sure: use your own eyes! There are plenty of review sites with sample images taken in near-identical conditions; you can look at them and observe, which image is noisier, how's the quality of noise and much more than that. Since photography is a visual art, you'll get more information this way (even if you'll get less numbers).

4) is another point where "equivalence" is useless and even dangerous. Don't sell your lenses based on some numeric computations! Try to use them, see by experience if you're OK with their new role - sell them if you're not.
You might discover that you like them better instead of wanting them to be "equivalent lenses", and I know many FA Limited (and other "full frame" K-mount lenses) owners waiting for a Pentax "full frame" camera will agree with me.

5) is debatable, what's a DOF advantage? I guess it's assumed to be the capacity to offer a shallower DOF, but that's not true for every usage.

6) You cannot compute the image quality loss using angle of view and DOF, that's ridiculous.
As above, you will find it by simply looking at image samples. Perhaps with your usage you'll find out nothing compels you to jump from APS-C to "FF". Perhaps you'll get an immediate and significant benefit. There is no single answer.

Seeing is the most powerful tool we have, and it irks me when equivalentionists are equating it to being "completely blind" - trying to teach unsuspecting people to do the same. They're the ones blinded by some silly numbers.

[Rondec]

Not at all. When applied, when used in conjunction with basic knowledge of sensor efficiency/age, it can be instrumental in answering pre-purchase questions like:

1) If I buy a 1'' sensor camera that includes an 85mm equivalent FL with an f/2 F-stop**, what would it's images look like if I tried to use it for portraiture, and would that be satisfactory to me?
2) I use my 15ltd for indoor, low-light architecture at times - exactly how much noise advantage would a 20mm f/2.8 allow me on the latest FF? ie, what would my wide-open ISO 6400 on aps-c shots look like with the new combo?
3) Should I get a FF body and a 28-75 2.8, or stick with my aps-c body and buy a Sigma 18-35 f/1.8? Which would perform better for me and be better bang/buck, knowing what I know about my shooting needs, usual FLs used, etc?
4) If I buy a FF body, what lenses would I likely want to keep, or sell, based on my most-used FLs on aps-c? (thinking of selling those less-used lenses to fund purchase perhaps)
5) Will I even see an advantage in DOF for my FOVs, if I move to FF? Or is there an m43 alternative that would work even better, for me?
6) What exactly would I lose IQ-wise by going m43, or gain, if I usually shoot FLx and aperture range y-z?
7) etc, etc, etc, etc, ...

You can certainly go into these purchases completely blind instead, but that's a lot of money to spend that way, and disappointment lurks around every corner. On the fora we do sometimes see FF or m43 or 1'' buyers lamenting the negative IQ 'surprises' they encounter.

** "85mm equivalent FL with f/2 F-stop" is probably exactly how that camera would be advertised, too - the manufacturer benefiting from a half-conversion. It would be up to the equivalence-savvy buyer to figure out what they were really getting with regard to IQ, and if hey would like it - pre-purchase.

.
.

You are assuming I have used a full frame camera recently, but I haven't. It is something that just doesn't mean much to anybody starting in digital photography. What does it really tell a guy who has only shot an iPhone camera to say this camera has an 85mm f5.6 equivalent lens? Nothing. The only people it makes a difference to are those few folks who own multiple formats and can't remember which lenses are wide or fast on a given format.

[audiobomber]

I am mostly shooting on a K3 now, meaning that I do have some extra reach over a D800, for what it is worth.

True, but not then equivalent, because the more cropped K-3 photo will have more noise, different FOV, and different DOF. Just as though you used a m4/3 or 1" sensor.

Yes and No. Within the strict parameters of equivalism you are right - but does it matter? Only if Rondec wants to contemplate recreating an equivalent image, dof included. Actually, though, using the lens at 300mm he is probably glad that he can benefit from the larger depth of field at equivalent focal lengths ( angle of view, really) and still enjoy a relative aperture of f/5.8 for exposure.

Yes and yes. Equivalence matters. An image shot at the long end of a 55-300mm on a D800E and cropped to same FOV as a K-5 II will have equivalence in FOV, DOF, SNR, diffraction, and resolution.

Kunzite, the word is "equivalent", not "identical".

Bye, I'm off on vacation.

[Kunzite]

Yes and yes. Equivalence matters. An image shot at the long end of a 55-300mm on a D800E and cropped to same FOV as a K-5 II will have equivalence in FOV, DOF, SNR, diffraction, and resolution.

Resolution!!! "Equivalence" doesn't even try to touch resolution!
But wait, you're not applying "equivalence" here, you're just cropping to the same format. It's APS-C vs. APS-C.

Kunzite, the word is "equivalent", not "identical".

And it's a misnomer, because 1. it's not qualified ("AOV and DOF-equivalent") and 2. it's incomplete (important parameters like image resolution, color etc. are left out).

Bye, I'm off on vacation.

Have fun!

[jsherman999]

That's one of the false assumptions that "equivalence" supporters would want us to believe, that we either use it or we have nothing. Yeah, right.

Please don't put words in anyone's mouth. No-one is saying you have 'nothing' if you don't use it, we're saying it's to your benefit to use it if you're considering adding another format or migrating between formats. That's all.

As eyeswideshut said - and I agree wholeheartedly - "equivalence" only works if you want "to contemplate recreating an equivalent image, dof included".

It uses the excersize of creating equivalent images to show the differences between formats. It's a simple, accurate modeling framework that takes physical facts into account towards an end. It can help you make purchase decisions and sometimes even active-shooting decisions.

A few people really, really hate it because they think it:

1) Negates the need for other more hands-on system evaluation (it doesn't), and

2) "Proves" that larger formats are better than smaller (it doesn't,) and

3) Is "different" than what they're used to. I suspect that's because it suggests (to them) the removal of 'Exposure' from the throne of primary photographic concepts in favor of a strange usurper: Total Light. That's just not the way they were taught. It's an abomination.

Another assumption, is that you have a baseline. "A 50mm f/1.4 on m4/3 is equivalent to a 100mm f/2.8 on FF" is a pretty much useless information, if you don't have a clue how any of them looks like.

You're really, really stretching now

Isn't it likely that our equivalence-acolyte has at least some exposure to one format - the one they're thinking of moving from or supplementing? Or are you imagining everyone is starting fresh, no camera in hand? I guess your objection works if it's always the latter.

.

A most annoying assumption ...But "equivalence" does not differentiate between any cameras of the same format! The old 5D or the brand new D810, they're all the "same"

You fault equivalence for not being able to discern between sensor QE and read-noise, now, although you claim to have read JJ and Falk and would know that it can't and never made any such claims. Check.

I have a feeling that if I showed you how to use trigonometry and basic polygonal area equations to help you estimate how much it would cost to re-shingle your roof, you'd get angry and discount the equations involved because they don't encompass material cost or labor. It's those silly 'Trigonometrists', don't they know it's all a fool's errand and they should just give up their infernal maths!?!


.

[Rondec]

Correct.

Equivalence is about more than DOF. It shows you at which settings, given a similar sensor, that you'll have the same SNR, the same DOF, and the same shutterspeed.

It's a set of very compact equations that are basically indispensable* if you are considering using two different sized sensors/films.


*You could spend 100x as long, of course, purchasing what you think you might want and running your empirical experiments, assuming you don't have experimental error and are somehow averse to multiplying one number by another number.



I really can't understand the consternation regarding equivalence. I wonder if it's just that people make up their minds first about which side of a debate they're going to be on, and later on determine what 'evidence' they're going to use.

As far as I can tell, equivalence says that DOF and noise are inextricably linked. The only way to have less noise on any format is to shoot with less depth of field. Therefore, if you are talking about one aspect of the equation, you are talking about the others as well.