[Rondec]

What if we made equivalence be based on an APS-C sensor and redrew all of the focal lengths based on that, rather than an arbitrary 35mm film size that 98 percent of the new shooters out there have no connection to and will never shoot? I haven't shot film or a full frame digital SLR in nearly 10 years.

It is awfully nice to have some way to compare angle of view of lenses, but it does seem arbitrary at this point to choose a format that isn't even the preferred format of most photographers.

[normhead]

An FF costs more initially, but after that you can spend less for lenses and get more resolution for your money. A $250 lens on an FF in a recent example I posted will give you 20% more resolution than the equivalent $1500 lens on an APS-c camera, so if resolution is your goal, then FF is cheaper. If maxing out the potential of your camera is your goal then FF is a lot more expensive. A Canon 6D FF is outperformed by a Nikon D3200 APS-c so as I always say, it's a D800 vs the world kind fo argument, not an FF vs APS-c, argument, some folks are strangely resistent to that logic.

The problem is if you aren't using the resolution than a cheap APS-c lens might be just as good as an expensive FF lens, for your purposes. The whole issue is so mind boggling I don't know why people analyze it. My theory is, if you don't like what you have, buy something better. Not very technical, but it works for me. Some people get really frustrated though when I like what I have, and they don't.

[northcoastgreg]

But I get frustrated when people use equivalence as a weapon, declaring larger sensors as "better" than smaller sensors, thus implying that better cameras with bigger sensors are capable of better photographs.

I think this hits the nail on the head, and explains the frustration that people are expressing here with equivalence. Photography is essentially an aesthetic discipline. Equivalence is a technical considertion, perhaps useful as a means of attaining a specific aesthetic end, but of no importance to photography outside of that. Debates about sensor size ultimately are about aesthetic preferences. Equivalence is not only use (or misused) as a weapon, but as a screen or a cloak to hide what is essentially an aesthetic preference with the trappings of science and mathematics. Photographers, many of whom are mere poets of lights, rather than technicians or gearheads, are then baited into arguments over obscure and often irrelevant technical considerations, when the debate all along is over aesthetic values and subjective preferences.

There is a practical side to this issue that gets obscured by equivalence as well. Equivalence sometimes fosters a mindset that stubbornly insists on attaining a specific DOF at a specific aperture and focal length. But of course there are many more ways to skin the narrow DOF cat then running up one's credit cards to buy an FF camera. You can adopt a longer focal length, increase the distance between the subject and the background, choose an artificial background, add blur in post, etc. etc. Many photographers, indeed the majority of us, must make due with such practical compromises, because if there is one thing that equivalence does establish is that attaining narrow DOF at normal and wide focal lengths can be an expensive undertaking, regardless of sensor size.

[Aristophanes]

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.

Exactly. Most shooters care about what they can capture within the frame, whether the AF got, and if it cannot, they are likely in low light and are cursing. HOw many mm was the lens? Was that much of a factor? Hmmm..

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

So what they really care about is whether the "system" they bought can perform a specific photographic task at a certain price without massive external overhead (Mac Pro and 5 external hard drives).

After all that, you get to the esoteric of equivalence. I rant against the Q because I have tried in low light to get CDAF focus (and failed) when a same price 1" system is much better simply because the sensor is larger. More consumers are going to be concerned about sensor size impact on AF than DOF, bokeh, OOF, etc. Cameras with larger sensor will have some advantages, but for the market, it's going to be different thatn many of the optical characteristics discussed here. Low light capabilities and sensor AF are the killer apps.

Now, I am approaching it from a Devil's Advocate, consumerist perspective. The designer of the "system" is going to be well-versed in the equivalence arguments. These same folks invented 126, 110, and APS film...they know and have always known. It's been around long before digital.

And when it comes to digital, the great homogenizer is web-viewing. It used to be printing. Flickr obviates much of this discussion from a market perspective which is why we are not seeing a huge rush to close the sensor size/price ratio.

[falconeye]

What a discussion ... but maybe, it has to happen some time. So, why not here while waiting for K-3 news

I don't have much to add anymore. Just a few remarks ...

1. Equivalence is ugly if used inconsistently. Otherwise, it is an elegant simplification. Focal length and 35mm-equivalent focal length are two separate terms. And using 35mm-equivalent focal length but NOT 35mm-equivalent fstop or NOT 35mm-equivalent iso is inconsistent too. I do not oppose to discard 35mm equivalency (or any equivalency). I only oppose to use it inconsistently, i.e., to apply it to focal but not fstop and iso. Which is what the mobile phone industry does to hide their mediocre equivalent fstop and equivalent iso specs. I strongly oppose a mobile phone be labelled e.g. 2.8/28mm (equiv.) rather than 14/28mm (equiv.) or its iso be labelled 100 when it is 2400 (equiv.). The latter gives us an immediate artistic understanding of what photos it will take.

2. Post-processing crop or digital zoom or panorama stitching: equivalence is very important here as it allows us to understand what is going on. E.g., Nokia 808 pureview uses its 41 MP to digitally zoom. Equivalence let's us understand how this makes the equivalent fstop slow at the tele end. While Nokia marketing tried to make us think otherwise like it had a constant aperture. Digital zoom creates a constant aperture zoom, but no constant equivalent-aperture zoom. And it is the equivalent-aperture which matters photographically.

3. Sensor size is NOT introduced everywhere when using equivalence. The elegance is that 3 simple normalizations remove it everwhere and it won't pop up elsewhere. Yes, it does stop there.

4. It is correct that lenses which can be mount for different sensor sizes can't be labeled in an equivalent way. So what?

5. Lenses of the kind we expect to emerge in the future, i.e., with an embedded sensor (digital lens cap, GXR style), are best labelled in an equivalent notation only. As we may mix a dozen sensor sizes with a single body. Which is the ultimate reason why I am convinced that equivalent labelling of lenses and cameras will become the norm. Maybe not tomorrow, but within 20 years.

6. Angle as FoV... I don't like it. Focal in mm describes better than an angle how perspective becomes strange as we approach a 0mm focal. Moreover, 35mm-equivalent terms can be used just like we are used to, like in DoF calculators, exposure meters etc. If angles were more practical, they would have replaced the focal length already.

[Aristophanes]

6. Angle as FoV... I don't like it. Focal in mm describes better than an angle how perspective becomes strange as we approach a 0mm focal. Moreover, 35mm-equivalent terms can be used just like we are used to, like in DoF calculators, exposure meters etc. If angles were more practical, they would have replaced the focal length already.

Nikon | Imaging Products | Digital SLR Camera Basics | Focal Length and Angle of view

[Uluru]

5. Lenses of the kind we expect to emerge in the future, i.e., with an embedded sensor (digital lens cap, GXR style), are best labelled in an equivalent notation only. . .

So we talk about P&S cameras, and GR-lookalikes then. They are disposable compacts, with lenses specifically designed for a sensor.

However, if you want more sensible approach in a system camera, the GXR is, to me, a totally failed concept because it devalues the whole system camera concept and throws equipment out of use at a much faster pace than a conventional (D)SLR approach. You cannot weld sensor to a lens without immediate repercussions. The GR has 2 years expiry date, and Ricoh told that publicly; next GR will come in 2015. Because that's for how long it can stretch its appeal before it becomes too obsolete.

But DSLRs, well, it's a different story — they hold value longer because the lens is not welded to a sensor. You must separate them. I think that for a environmentally-conscious society (are we?) we must have more lasting approaches, not pursue only what's currently best for the imaging vanity's sake. If DSLRs deliver less sharp images, but lenses can hold value for decades, well, that is the compromise one is willing to take to keep things in balance.

The GXR system camera approach is not only limiting us from that perspective, but it's both photographically (in artistic value sense) and environmentally atrocious.

[rawr]

If equivalence is good enough for Pentax to use on their P&S bodies, I guess it must be a useful and widely understood metric.

Notice they avoid entirely the actual focal length and aperture specs normally seen around the lens:

[gazonk]

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?

I agree, I also no longer think in 35-mm equivalent terms since I haven't used my film DSLRs for a while. Except the other day when I tried my old 24mm/2.8 Vivitar lens, which I hadn't used since the film days (because of a broken focus ring), I had to adjust to the fact that it was only a moderate wide.

When you get to know your lenses, the exact physical properties are no longer important. But when shopping for new equipment, equivalence is important if you e.g. want to know to what extent a Nikon 1 camera can replace your current APS-c camera.

[Uluru]

There could be relatively simple solution for it
For example: DA15 — 15mm/f4 [22.5mm/f5.6]

So with that, a lens stands in its own sensor format (first measure), and [in brackets] what it means in 135 format equivalent.

Same thing we have in engineering and everywhere else, when there are two measures that must address imperial and metric systems for public and individuals that use either:
— a measure in ft and [the metric in m],
— a measure in oz and [the metric in ml].
— etc.

And there's another 'problem' with lenses — for example, Pentax's own playing between commitments. For DA*55 lens, for example, it is confusing because DA*55/1.4 means 55mm/f1.4 in 135 terms, despite the fact that Pentax still doesn't have a digital 135 format camera, and Pentax does not make any 135 format film camera anymore.

But in that case, nothing goes in brackets.

[Jan67]

Rawr> Well, focal lenght is well described on this Pentax P&S. But generally, missing information about equivalent f stop on lenses (I mean lenses dedicated for smaller sensors than FF) causes, that buyers either don´t care (majority) or are misleaded.

I guess that some of those not experienced and educated buyers would also like to make once a photo (portrait e.g.) with background isolation (as they saw somewhere on web). And they have no idea, why it is difficult or not possible with their new P&S camera. The main reason is, that market (vendors, shops) does not educate them at all. Of course nobody from vendors will inform: "be carefull, with this type of camera you are limited to larger DoF only". The main selling argument for DSLR, as I often see in advertisement is: "DSLR enables professional photos". Funny, isn't it? Marketing world loves shortcuts. No explanations, no real arguments.

gazonk> it's a mater of habbit. Many people just think in FF scale. They have in mind that 35mm focal (on FF) is fine for street and something around 85mm (on FF) is fine for portraits. Old dogs don't like to change their habbits.

[Kunzite]

What a discussion ... but maybe, it has to happen some time. So, why not here while waiting for K-3 news

I don't have much to add anymore. Just a few remarks ...

1. Equivalence is ugly if used inconsistently. Otherwise, it is an elegant simplification. Focal length and 35mm-equivalent focal length are two separate terms. And using 35mm-equivalent focal length but NOT 35mm-equivalent fstop or NOT 35mm-equivalent iso is inconsistent too. I do not oppose to discard 35mm equivalency (or any equivalency). I only oppose to use it inconsistently, i.e., to apply it to focal but not fstop and iso. Which is what the mobile phone industry does to hide their mediocre equivalent fstop and equivalent iso specs. I strongly oppose a mobile phone be labelled e.g. 2.8/28mm (equiv.) rather than 14/28mm (equiv.) or its iso be labelled 100 when it is 2400 (equiv.). The latter gives us an immediate artistic understanding of what photos it will take.

2. Post-processing crop or digital zoom or panorama stitching: equivalence is very important here as it allows us to understand what is going on. E.g., Nokia 808 pureview uses its 41 MP to digitally zoom. Equivalence let's us understand how this makes the equivalent fstop slow at the tele end. While Nokia marketing tried to make us think otherwise like it had a constant aperture. Digital zoom creates a constant aperture zoom, but no constant equivalent-aperture zoom. And it is the equivalent-aperture which matters photographically.

3. Sensor size is NOT introduced everywhere when using equivalence. The elegance is that 3 simple normalizations remove it everwhere and it won't pop up elsewhere. Yes, it does stop there.

4. It is correct that lenses which can be mount for different sensor sizes can't be labeled in an equivalent way. So what?

5. Lenses of the kind we expect to emerge in the future, i.e., with an embedded sensor (digital lens cap, GXR style), are best labelled in an equivalent notation only. As we may mix a dozen sensor sizes with a single body. Which is the ultimate reason why I am convinced that equivalent labelling of lenses and cameras will become the norm. Maybe not tomorrow, but within 20 years.

6. Angle as FoV... I don't like it. Focal in mm describes better than an angle how perspective becomes strange as we approach a 0mm focal. Moreover, 35mm-equivalent terms can be used just like we are used to, like in DoF calculators, exposure meters etc. If angles were more practical, they would have replaced the focal length already.

1. You can insist it's elegant, and I will still think it's ugly.
I'll say again, you're opposing the manufacturers using a standard (ISO) way of computing the sensitivity, instead of making up some fake numbers, and you are opposed.to the metric system and the basic optics notions... a thing I will never agree with.

2. Who cares, when one can simply look through the screen and see what happens? You want to force them to think about equivalent sensitivities and apertures, but people just don't care about it. What they care about is just how much of the scenery fits into the frame.

3. Oh, but it is. Everywhere. The focal length would be normalized with the crop factor, the aperture and ISO, normalized as well. You would be unable to tell (unless you can revert the equivalence calculations) anything about the image as projected on the sensor's/film's plane.

4. You have no problem with such inconsistencies?

5. With point&shoots and fixed lens+sensor modules, it sort of makes sense (because they're too limited anyway). But try to use a lens on multiple formats... and watch your theory failing. Behold, the prime lens whose focal length changes in an instant! (and the funniest part, you'd be able to do it in post). An extension tube would magically change length in the same manner, defying physics and the metric system.

6. You don't like the angle of view concept? It never was intended as an alternative to the focal length, and I don't get it why you think it's competing with it.
Perspective is only influenced by your position in relation to the subject; not by focal length.

By the way, what's the "equivalent" focal length of a 50mm lens which is unmounted, sitting on your desk? (please note that I'm not telling the format for which the lens was designed, nor on which camera(s) it was used in the past).

[falconeye]

kunzite, please quote me correctly or not at all. For one thing, I talk about equivalent cameras, not equivalent lenses. I do so for a reason ... And for another thing, I made it clear that e.g., "focal length" and "equivalent focal length" are two separate terms. You confuse both terms to make an argument which I consider poor style.

[Kunzite]

I don't think I've made any mistake quoting you. I believe such concepts must work (or be scrapped) with the ILCs - and your concept doesn't.

[Aristophanes]

The use of "stops" as a generic benchmark is widely entrenched. Such as when people say you "lose a stop" with a handheld camera. Or gain with a tripod. Or with SR on.

Not really impacting equivalence, but demonstrating just how useful the "stop" is at broad stroke discussing a technical issue.

The Ricoh GR lens makes no attempt at 135 comparison: