[Fogel70]

You can already pick up any camera and produce artistic images. (Well, YOU maybe, not so much me...)

Anyway, the equivalence you're looking for is field of view. Focal length does not translate to field of view directly, even on the same format camera. Case-in-point, at 17mm, the 10-17 zoom is 100 degrees, compared to the DA Limited 15mm which is 86 degrees. The relationship between focal length and field of view should be considered a "rule of thumb" instead of an immutable physical constant.

That's just because fisheye lenses are not distortion corrected, so they show wider FOV with same focal length as reclinear wide angle lenses.
IMO FOV is better way of specify a lens as you can see that a 17mm fisheye lens has a wider FOV than a 15mm reclinear wide angle lens.

[Aristophanes]

1. No
2. Sentence makes no sense
3. Not related to equivalence

Aristophanes, at some moment in time, you decided to read something into the term equivalence which isn't there. Stop it please for your on sake. You are missing the ball.

A law of physics is completely neutral. We live (or at least, most of us live) in the Age of Enlightenment and such things cannot be turned into belief anymore.

If at all, equivalence can be used to explain in a scientific manner to full frame addicts that cameras with a smaller sensor often produce indistinguishable results. A bit different from your (possibly selective) perception.

I think you missed my point about the Orwellian doublespeak.

Equivalence may be the law of physics, optical and sensor-related, but it's not the law of marketing. So, yes, I did read something in, because, quite frankly, equivalence does nothing to sell cameras or justify the K-3 being FF. In fact, equivalence gets in the way. Or Nikon uses the spectre of it as a weapon.

We're dealing product here. There is no neutrality. Otherwise that amazing Leica glass on that awful sensor would have no market

Equivalence becomes impossible to see in real terms between internet-sharing conspirators when every file is about 1 MB in size. Photoshop lies. So does Flickr.

In practical terms, what the equivalence argument makes clear is that an FF camera with an economically affordable lens can go into a dark bar and is going to be a little better at getting the shot, will take up more room on the table displacing a beer, costs more, and you'll be wrestling with a 50MB file size after.

[Kunzite]

Falk, you've been a valuable contributor to this forum for as long as I can remember. I don't visit as often as i used to, but I hope that you don't leave entirely.

I also appreciate Falk's contribution on this forum, his knowledge and experience and I hope he will keep posting.

So maybe, all of us must calm down a bit

Below, I explain the rationale behind calling equivalence "beautiful". There is no reason anybody must share my opinion, but maybe I should explain at least.



I do agree entirely.

And now about beauty in science.

I am interested in photography, science and women because I find beauty in all of them. It may be less obvious for science.

I give you one example:

When Dirac in 1928 looked at his equations, he noticed that things are more symmetrical (read beautiful) if he gave ALL possible mathematical solutions a physical meaning. Which led him to predict anti matter. Which actually exists as has been verified years later.

Group theory in mathematics would be another example.

It is a surprising attitude of nature that, if its laws can be made more beautiful, it obeys.

An extremely simple yet very known example is F-Stop, the ratio of aperture and focal length. Because it turns out that a correct exposure (for a given sensitivity of an emulsion) only depends on this ratio, not both focal length and aperture diameter. Which is a simplification and makes the "laws" of photography more beautiful. Nobody today would complain that fstop isn't a lens' real aperture (which is to be measured in mm or inch, like it still is for scopes).

A more recent example now is equivalence. Just like fstop replaces aperture by the ratio of aperture and focal, equivalence replaces image circle, focal, fstop and iso by scaled values, aka "equivalent" focal, fstop and iso. Because it turns out (somewhat hard to prove why I wrote a paper about) that ALL image properties only depend on "equivalent" focal, fstop, iso (and exposure time). And not on sensor size or real focal, fstop, iso. This is a massive simplification of the "laws" of photography. A much bigger break-through than fstop was. And makes the "laws" of photography a lot more beautiful. Something to write home about.

Therefore, somebody saying "equivalence destroys real fstop" is making the biggest joke he can actually make

That's my personal opinion.

Which may explain why I am so passionate about it.

Maybe I should explain myself as well, at least partially? (I must admit I'm not very confident in my writing)
Why do I think it's ugly? There are several reasons for that:
- it messes with basic definition, e.g. the focal length is clearly defined, as one the most basics optics notion. It's also expressed in meters, which as we know is a standard measuring units. Trying to change it in the name of "equivalence" is, IMO, a big no-no and (I know you disagree) unscientific.
We can use equivalence by being very careful what we claim, e.g. "lens X on format Y has the same angle of view as lens Z on format W".
- it solves no problem. Really. We don't need to know what's the angle of view and DOF on a foreign format, but on the one we're using; and for this, the old ways simply works.
- it introduces new problems. If we use the "equivalent"(BS) focal length and "equivalent" (BS) aperture, oops, the exposure equation fails. Then, we have to also compute an "equivalent" sensitivity (bye-bye, ISO 5800:1987); and this is only the beginning. You say we're removing the sensor size from the equation, but on the contrary: we're putting it everywhere, even where we shouldn't (bye-bye, optics).
And then, we'll have lenses that can be relabelled, and lenses which cannot (those usable on several formats). And lenses which aren't, extension tubes... what a mess!
- it's a concept which cannot function when the lens is unmounted. How can we claim the lens doesn't have a focal length if it's not mounted on a camera?
- it's incomplete. The format is nothing but a crop from the lens' image circle; but we are often cropping in post. Equivalence is completely ignoring this.
- I saw its ugly face, over and over again; people thinking that a 50mm has a different focal length than another 50mm, people thinking the focal length actually changes etc.
I will say again, this shouldn't be compared with the f-stop which is indeed an elegant simplification; the equivalence thing complicates things.

[gazonk]

- it solves no problem. Really. We don't need to know what's the angle of view and DOF on a foreign format, but on the one we're using; and for this, the old ways simply works.

Really? To take an example from a few posts above: when I see the focal length of a Q lens, I have absolutely no idea what FOV that translates to on the Q system.

[Kunzite]

Except that Pentax gives the "equivalent" focal length for the Q
But please answer this: I'm using APS-C, and only APS-C. Why should I ever bother to compute the lens-on-35mm-equivalent, when what I care about is how my lenses are behaving, on my cameras?
After several times, I can't even remember how's an e.g. 50mm on a 35mm camera (but I know how's on APS-C). And to answer your question, I would have to "convert" the Q 35mm equivalent figures to APS-C equivalent figures, i.e. to a system familiar to me. If I were a Q user, I would rather adapt to the format.

[Fogel70]

- it's incomplete. The format is nothing but a crop from the lens' image circle; but we are often cropping in post. Equivalence is completely ignoring this.

It doesn't ignore this, it does not matter if you crop by using a smaller sensor or make the same crop in post from a larger sensor, the image will be the same on both. FOV and DOF change if you crop in post too, and if you want you can calculate the equivalent focal length and DOF on all crops too. You also get the same image if using a 1.5x TC on a FF, as if using the same lens without TC on a APS-C camera. Crop is crop.

[jatrax]

You folks are making my brain hurt with all of this technical argument stuff.

Pentax: PLEASE release a new camera so we can complain about it instead of arguing about esoteric photographic properties.

[tclausen]

You folks are making my brain hurt with all of this technical argument stuff.

Pentax: PLEASE release a new camera so we can complain about it instead of arguing about esoteric photographic properties.

And when they do, let's hope that they release a new series of lenses with the focal length given in attoparsec's, rather than millimeters....

[IchabodCrane]

Except that Pentax gives the "equivalent" focal length for the Q
But please answer this: I'm using APS-C, and only APS-C. Why should I ever bother to compute the lens-on-35mm-equivalent, when what I care about is how my lenses are behaving, on my cameras?
After several times, I can't even remember how's an e.g. 50mm on a 35mm camera (but I know how's on APS-C). And to answer your question, I would have to "convert" the Q 35mm equivalent figures to APS-C equivalent figures, i.e. to a system familiar to me. If I were a Q user, I would rather adapt to the format.

Maybe this will change some day but 35mm is a reference point that many people are familiar with -- more so than any other single reference point, IMHO.

[jatrax]

series of lenses with the focal length given in attoparsec's, rather than millimeters....

Owh, stop. The pain is too much........ I think I need to go take some pictures.

[Kunzite]

It doesn't ignore this, it does not matter if you crop by using a smaller sensor or make the same crop in post from a larger sensor, the image will be the same on both. FOV and DOF change if you crop in post too, and if you want you can calculate the equivalent focal length and DOF on all crops too.

But I don't see equivalence advocates talking about final crops. I don't see photographers calculating the precise BS focal length for a crop, either - they're using aesthetic reasons to choose a crop instead.

Maybe this will change some day but 35mm is a reference point that many people are familiar with -- more so than any other single reference point, IMHO.

More familiar than looking through the viewfinder and find out what's the angle of view? IMHO you'll find out that "many people" actually have to convert back to the system they're actually using, to find out what that BS focal length translates to.
The reference point is the camera in your hands.

Owh, stop. The pain is too much........ I think I need to go take some pictures.

By all means!
Please don't be mad at us, since there's no new information about the K-3 (leaked) there's nothing to discuss on the subject. Don't forget to come back in few months.

[jatrax]

By all means! Please don't be mad at us, since there's no new information about the K-3 (leaked) there's nothing to discuss on the subject. Don't forget to come back in few months.

Oh, I'm not mad! I might even be learning something. But it's still painful.

[Kunzite]

My apologies; any pain induced was completely unintentional.

[jatrax]

My apologies; any pain induced was completely unintentional.

LOL! No apology needed, any pain is entirely my fault! Or maybe it is Pentax's fault for not providing us more rumors to dissect.

[ElJamoquio]

In practical terms, what the equivalence argument makes clear is that an FF camera with an economically affordable lens can go into a dark bar and is going to be a little better at getting the shot, will take up more room on the table displacing a beer, costs more, and you'll be wrestling with a 50MB file size after.

Really? FF costs more, is bigger, and has larger file sizes?