[Igor123]

FOV is not a property of the lens - it is a result of lens interacting with sensor.

If I put a FA 50mm lens on a K-1 we get one FOV.
If I put same lens on my KP we get a different FOV
If I put same lens on my Q-7 we get a third FOV
ad nuseum

Yes, that is why I wrote "with a format suffix", most lenses are after all made for a specific format even if they are sometimes adapted to others. But I agree, what you say was the point I want to make, the format matters for the FOV, that's why saying 3-18mm on a compact isn't helpful at all...it has to say something about the sensor size or format too in order for a user to get a feeling for the FOV of those "3-18mm", because the FOV is what were after, not that this piece of glass focuses light X mm behind it...

Now, focal length + format OR FOV + format would both give enough "data" about the lens to know what to expect, but I argue that people mostly use the focal length in order to understand the FOV when using it, and not to consider the physics of the lens, so I think discussing and printing the FOV on the lens would help (and prevent some misunderstandings) in favor of having the focal length, but if I could choose I'd prefer both on there.

(Or in truth, since I'm lazy and already used to FF/APS-C/m43 focal length I wouldn't want that changed really =) ...but if getting into a new format or learning photography all over again, I think that (FOV+format or sensor size) would be a better property to print on lenses and discuss rather than focal length without format, as today)

[Kunzite]

Yes, that is why I wrote "with a format suffix", most lenses are after all made for a specific format even if they are sometimes adapted to others. But I agree, what you say was the point I want to make, the format matters for the FOV,

Actually it's the final crop which matters for the FoV. Sometimes decided before taking the picture, sometimes at post processing - and sometimes you might produce 2 or more images cropped differently.
Now... what should you write on the lens?

[Rondec]

The point is not about replicating something exactly. If you take a photo with a 50mm at f2.8 on a K5 II and with the 77mm at f4 on the a K-1, the photos will look similar with regard to framing and depth of field. Maybe we know this instinctively from shooting different formats, but I don't think it is intrinsically obvious to people who are moving one way or the other.

This is the FA 31 limited shot at f2 on the K3.



This is the DA *55 at f2.8 on the K-1.



Not exactly the same framing, but the big thing to me, is that you can actually take similar photos between formats.

[normhead]

As long as you never consider buying a camera with a different format, use a camera with a different format*, or try to learn aperture-choice techniques or effects from photos taken with a different format, you don't need to worry about equivalence.

Equivalence in those cases is learned as accumulated background information. There's no need to even formally give it a name. It would seem, that folks who favour the formal approach take the position that those who handle equivalence informally are in some way deficient.

Every body uses equivalence. The issue is not who uses it. The issue is who actually uses crop factor in their day to day work?
I carry up to three sensor sizes all the time. I have never once taken an image with my K-3 at 50mm, then thought, I should take this at 70mm with the K-1.
Did you catch that?
It should have been 75mm. The only 75mm lens I own is MF and I don't have an adapter for it.
So even for the math heads, equivalence doesn't get you out of having to try out lenses.
Simple fact. People don't own enough lenses to make equivalence a real thing. The equivalent of my 40XS is 60mm. I think Sigma made one of those once.
IN this situations it simply doesn't work.
Maybe it's time for some real world examples of how you used equivalence out in the real world, as opposed to all these hypotheticals.

MY point would be not that equivalence doesn't exist.
MY point is it's better understood by understanding the different lenses in your lens bag, which you have to do anyway and how they affect images on different formats.
The whole mathematical step is unnecessary except for ball park numbers that have to be adjusted for lens characteristics.
And if you have zooms, it's next to useless. The whole thing about composition is getting the framing you want. One UWA zoom, one standard zoom, and one telephoto zoom and you are covered.What do you need equivalence for?

The "rookies need it" argument is also counter intuitive. Rookies deal with a lot of issues, I'm not at all certain that studying equivalence formally even helps. But I'd be happy to hear any real world experiences that would suggest different.

The funny thing to me is that the guys pushing equivalence theory, are assuming, if you don't buy into the math, you don't know equivalence. My point has been you can understand equivalence without mathematical formulas, and you will have a better understand it, if you simply understand your gear. Because it's small part of the question, if I like 35mm on APS-c what do I shoot on a K-1. There are many factors way more complex than equivalence needed to answer that question, and the design and characteristics, that are much harder to understand are more important than the very simplistic "equivalence" method of looking at the decision.

If you want to tell folks 50mm or 55mm on FF is the same as 35mm on APS_c feel free. But that doesn't mesh with my experience. SO I'd consider it misleading. I love my 55 on FF. I really never liked 35mm on APS_c. Forget equivalence. Learn your gear. You'll learn every thing you need to know about equivalence along the way. IN the end it comes down to, I like this lens on this system, and it's way to simplistic to claim equivalence is more than peripheral information.

I don't like it not because I don't believe it is true, I don't like it because I see it as overly simplistic to the point of being misleading, in many situations. There is simply no situation where I would recommend equivalence as the main point of focus in lens selection. It's one of those things you might want to consider in a ball park kind of way, like a quick calculation in your head, but it's not enough to give you definitive help in lens selection. And in many cases, I have my SMC 50 1.4, My FA 50 1.7, my FA 50 2.8 macro, my DA* 55 1.4, my 18-135, a Tamron 17-50, my 28-105, my FA 35-80 and so on and so forth. The big part of lens selection is not equivalence.

And the corollary to that is I get really tired of people who think they are experts on lens selection because of a very simplistic mathematical formula.

Equivalence is only useful when working across formats to answer the question of which focal length and aperture do you use if you use a different format.

Have you ever used it for that? I frequently carry three formats. I look through the lens and zoom to the framing I want. I look up focal length in the exif. I generally make up my mind which format to use before I pick up the cameras. I've never once though out in the field. Oh look I'm using 50 on APS_c . I'm going to change to FF and then I need 75mm, so I can take this shot not only with the format that best suits it but also with the format which theoretically at best can match it, but will never exceed it."

I don't do that. Do you?

---------- Post added 01-25-19 at 11:04 AM ----------

Not exactly the same framing, but the big thing to me, is that you can actually take similar photos between formats.

That is covered by "All cameras take pictures." I think if there's one thing everyone knows it's that they can take their pictures with a little camera or big camera and for most images, the format will make little difference. You get your snapshot. In the end you won't care what it was taken with.

I'd find it curious if there were people who thought you couldn't take similar pictures on different formats. Is that even thing? What I hear is "I can take that same picture with my cell phone." It's the guy who knows why you shoot what format and when that is knowledgeable. The whole idea of a kit lens is that the camera come with a lens that allows it to take practically the same images as every other camera on the market with it's kit lens. You can figure out mathematically why they are the focal lengths they are, but it won't change anything. The camera companies do it for you. They did the math to save you the trouble. But you can still do the "trouble" thing if you want.

---

Last edited by normhead; 01-25-2019 at 09:30 AM.

[Igor123]

Actually it's the final crop which matters for the FoV. Sometimes decided before taking the picture, sometimes at post processing - and sometimes you might produce 2 or more images cropped differently.
Now... what should you write on the lens?

Well of course, but the crop I can choose (in settings or pp), the format not as much... getting a larger sensor in firmware update would be another thing =)...

(so jokes aside if I express myself badly, no I don't think any crop should be considered on that FOV marking =) )

[BigMackCam]

Equivalence in those cases is learned as accumulated background information. There's no need to even formally give it a name. It would seem, that folks who favour the formal approach take the position that those who handle equivalence informally are in some way deficient.

It's interesting to read that...

I always feel if I mention equivalence, I risk invoking the wrath of the "informal approach" crowd

As it is, I have no problem with any approach someone else uses, so long as it achieves what they want. I would never consider them deficient for making a rational choice that works for them. If there's an easier or quicker method, I might suggest that as an alternative - but otherwise, good luck to them.

As for the naming, I guess it's human nature to attach a name to something. It makes it easier to talk about. "Equivalence" might not be the best word for it, but it's the word that has become associated with the concept. It's easier to discuss "equivalence" than "the relationship between focal length and aperture to achieve the same field of view and depth of field when comparing or switching between sensor formats".

If anyone has a (sensible) suggestion for a better word or words to describe that, I'm all for using it.

[BigMackCam]

MY point would be not that equivalence doesn't exist.
MY point is it's better understood by understanding the different lenses in your lens bag, which you have to do anyway and how they affect images on different formats.
The whole mathematical step is unnecessary except for ball park numbers that have to be adjusted for lens characteristics.

I more or less agree with you here, Norm. The quick (very quick) mathematical step can get you in the ball park. But you'll undoubtedly have to experiment to get the results you actually wanted. In reality, the exact focal length and aperture equivalents aren't available when switching between formats - you might have to go a few mm longer or shorter on focal length, and round up or down the calculated aperture. So it's rarely - if ever - going to be exact. Just ball park

And, certainly, once we become used to switching between formats - whether that's within our kit bag, or applying something we've watched to our own gear - there's no need to keep on with the calculations. We get used to it and that becomes part of our acquired knowledge.

[Kunzite]

Well of course, but the crop I can choose (in settings or pp), the format not as much...

You are choosing the format by cropping. For example, transforming your K-1 into an APS-C camera just by turning a dial. Or on a 24x24mm format camera.

The focal length, aperture (f-number) and shutter speed are wonderfully universal concepts. It makes no sense to break them.

[Rondec]

What's wrong with the concept of equivalence? It lets you figure out why a particular camera might or might not work for you. If you shoot portraits and want a full frame lens 30mm f1.4 equivalent, you probably aren't going to get there with micro four thirds. "Ah, but I could have told you without the formula," the informalist says and that's OK, but there's nothing wrong with looking at what sort of lens it would take to achieve that look on a different size sensor.

I guess the thing that aggravates me the most in all these discussions are the folks who break out the whole "smaller sensor makes my lenses longer" argument. If there is something that isn't true in all these discussions, it is that statement.

[HarisF1]

When I first started looking for lenses when I got my K-3, I was really surprised as there were no older wide angles available at a decent price. The 18-135 was a cool lens but my next widest was my 28mm Takumar. Looking online showed me lenses that were 4 or 5 times more expensive than the Takumar, and the older 'wide angles' were extremely expensive too.

This didn't make sense to me until I realised how formats changed over time. Had I been a rich kid then maybe I would have never needed to understand equivalence. But I wasn't, and the idea of equivalence has been pretty interesting to me. I'm a thinker too, and always curious so that's why I think it's intriguing. Maybe some people don't want to think, maybe others are happy where they are. It doesn't mean I'm wrong in thinking about equivalence to explain why there 'weren't any really wide lenses in the past'.

[Kunzite]

I guess the thing that aggravates me the most in all these discussions are the folks who break out the whole "smaller sensor makes my lenses longer" argument. If there is something that isn't true in all these discussions, it is that statement.

That is a consequence of forced "equivalence" - unsuspecting beginners being "educated" that their lenses are "the same" as lenses with a different focal length, on a format they're not using nor should they care about.
Which got shortened to "your 50mm becomes a 75mm on the one and only standard format".

[normhead]

What's wrong with the concept of equivalence? It lets you figure out why a particular camera might or might not work for you. If you shoot portraits and want a full frame lens 30mm f1.4 equivalent, you probably aren't going to get there with micro four thirds. "Ah, but I could have told you without the formula," the informalist says and that's OK, but there's nothing wrong with looking at what sort of lens it would take to achieve that look on a different size sensor.

I guess the thing that aggravates me the most in all these discussions are the folks who break out the whole "smaller sensor makes my lenses longer" argument. If there is something that isn't true in all these discussions, it is that statement.

Only because it's misstated.
The facts are compared to an 18-36 MP FF camera, in good light a 24 MP APS-c camera provides more subject resolution than the full frame. Cropping full frame image decreases lw/ph. Using an APS-c 24 MP camera will increase lw/ph beyond what the FF with the same lens can, and the cropped subject will be bigger and more detailed on their computer screen.

If people want to condense that really long sentence into "the smaller sensor makes my lenses longer", technically they don't make the lenses longer, but practically they have the same effect as a longer lens. So ya, it's not technically correct, but it's also not entirely wrong either.

Larger subject with more detail is not exactly the same as "longer", but it's the same effect as longer.

[photoptimist]

There is no such thing as equivalence because I tell the difference of two prints from apsc and medium format cameras, no need to even look close, the medium format wins on latitude and tone definition. Medium format is bigger, more expensive and deliver better images, so it's not at all equivalent to other formats.

As BigMackCam said, this aspect of the equivalence debate is driven by the unfortunate reuse of an English word in a new way. When BigMackCam, I, and others talk about making "equivalent" images across different formats with different lenses and different apertures, it's certainly not about strictly identical images at the pixel-level. Clearly, different formats and different sensor have different latitude, noise, and color properties. Clearly, different lenses render differently.

But that doesn't mean that someone with a different format camera and different lenses can't try to make their image as similar as possible to one taken by someone else. And in trying to make the image as similar as possible, the math of equivalence would help them pick the equivalent focal length (to replicate framing and perspective as much as possible) and equivalent aperture (to replicate DoF and bokeh size as much as possible). Their picture won't be identical, but it will be a similar as possible.

Maybe "equivalence" should be renamed "similarity."

[Dartmoor Dave]

If anyone has a (sensible) suggestion for a better word or words to describe that, I'm all for using it.

How about "parity" rather than "equivalence"? On the basis that parity means using different formats as if they are the same, without claiming that they can ever actually be the same?

(Always knew that First Class degree in English would come in handy someday.)

(Although I did manage to mis-spell "non-existent" earlier in the thread.)

[Rondec]

That is a consequence of forced "equivalence" - unsuspecting beginners being "educated" that their lenses are "the same" as lenses with a different focal length, on a format they're not using nor should they care about.
Which got shortened to "your 50mm becomes a 75mm on the one and only standard format".

I think it is the consequence of "half" equivalence, where people convert focal lengths based on angle of view, but not based on aperture. A 50-135 f2.8 on crop will behave like a 70-200 f4 on full frame, not a 70-200 f2.8. I own the DA *50-135 and the *70-200 and they are very different lenses, but based on half equivalence, they are the same, it is just that the 50-135 is smaller and easier to handle.

If you are going to say "don't worry about this equivalence thing at all," I am fine with that, but people bring it up all the time to explain that smaller formats are better because your lenses are smaller and longer by decreasing the sensor size.

I don't think it is a big problem on the Forum, because of course, Pentaxians understand all of this intuitively, but it is a common theme elsewhere.