[Rondec]

I don't get how equivalence is confusing anyone (it's just a bit of maths, ffs!)...

My

58mm f/1.2 lens[1] used on my Fuji X-E1 (exposing for 1/X seconds on a 23.6*15.6mm (28.29mm diagonal) sensor[2] with a sensitivity of ISO Y)

will make the same[3] picture that a

88.7mm f/1.84 lens[1] used on a 135 format camera (exposing for 1/X seconds on a 36*24mm (43.27mm diagonal) sensor[2] with a sensitivity of ISO Y*2.34)

would make when pointed from the same position in the same direction.

[1]: Assuming idealised lenses and that those specs are precise
[2]: Assuming equal quantum efficiency for both sensors and equal resolution
[3]: Same perspective, same perspective distortion, same field of view, same depth-of-field, same amount of motion blur and same image-level signal-to-noise ratio


That isn't confusing, is it?

It just mean:
A ~58/1.2 lens on APS-C can serve the same purpose a ~90/1.8 lens on 135. For roughly contemporary cameras, the APS-C camera will be roughly 1 stop worse in terms of image noise.

It is not confusing to me. It is confusing to people who are completely unfamiliar with photography and to whom terms like aperture and focal length are pretty foreign. And those are most of the people buying cameras.

I know a number of pretty good photographers (that is to say they take nice photos) who I start talking about gear stuff, DXO Mark scores, and equivalence and they immediately glaze over. They just know that if they want to take x photo, they will use y lens. All of them started with APS-C digital cameras and none are familiar with full frame focal lengths.

I can't imagine if equivalence was all related to large format cameras. Sure, mathematically it would all make sense, but it wouldn't mean anything to the majority of folks out there.

[Boris_Akunin]

we don't see medium format cameras advertising 35mm equivalents.

Well, for formats smaller than 135, lenses sound better than they are that way: "28-300mm (equivalent) f/2.8!!!"(example: Olympus Stylus 1, actually 6-64.3/2.8).
"93-186mm (equivalent) f/5.6!!!" on the other hand doesn't sound any more impressive than "150-300mm f/5.6" (example: Pentax-FA 645 150-300mm F5.6).

So even if medium format users were all complete morons, there would be no advantage.

[carpents]

this entire thread simply confirms something that has been known for a long, long tome.

In the bad old days, focal length was focal length, and each format's users knwe what was wide, normal and long for each format they used. My folding KodaK #3 camera didn't have a 4x5 or 8x10 equivelent. the lens just said F=127mm F4.5 or something like that.

however, the world's population was much smaller when the kodak #3 was made.

here is the point,

Intelligence is a constant, the population is growing!

I think at times this is really really true. the longer the human race exists, the dumber we get. there was no need for the first 150 years of photography to have equivalences. they are unnecessary unless it is proof we really are getting dumber

You weren't using your Kodak #3 *on* a 4x5 camera, or else you would have used equivalence.

That's why we do and should use it now. Because the economic decision made 15 years ago to get more sensors out of a waffle of silicon while keeping the same lens mounts has us here.

And it is beyond silly to just use wide, normal, or long (etc.) to describe lenses.

[lytrytyr]

we don't see medium format cameras advertising 35mm equivalents.

"This ultra-wide-angle lens has a field of view that corresponds roughly to that of a 13mm lens mounted on a Pentax APS-C DSLR or a 20mm lens mounted on a full-frame 35mm SLR" is right up front in this forum's description of the SMC Pentax-D FA 645 25mm F4 AL [IF] SDM AW Reviews - 645 Wide-Angle Primes - Pentax Lens Reviews & Lens Database

We don't see these sort of marketing for point and shoot cameras, where f stops and focal lengths produce entirely different results from model to model.

We do, and precisely for the reason you mention:

Amazon, who know a thing or two about marketing and reaching consumers,
include this description of the Canon S120 with its 5.2mm-26mm lens:

"Bright f/1.8 lens with 5x optical zoom and 24mm wide angle view."

Amazon.com : Canon PowerShot S120 12.1 MP CMOS Digital Camera with 5x Optical Zoom and 1080p Full-HD Video : Point And Shoot Digital Cameras : Camera & Photo

[stevebrot]

the APS-C camera will be roughly 1 stop worse in terms of image noise.

I see. In the world of equivalence:

• millimeters equivalent focal length is a measure of FOV
• stops is the unit for noise

OK, now that I have swallowed that Kool Aid, I have to ask. Has anybody uploaded a spreadsheet for this? That way we can create extensive tables. Better yet, a phone app would be just the thing. The app could provide equivalence information and/or suggest a fully equivalent digital optical system (combination of sensor, focal length, taking aperture, and format).

What it would take as input (two sets, one per system):

• Average sensel size
• Total sensels*
• Sensor width
• Sensor height
• Lens focal length
• Taking aperture

With a few tweaks, this might even be able to determine equivalence between digital sensors and photographic film.

Ooooops! Did I say that?


Steve

* Sensel density and average sensel size are required to calculate a mean inter-sensel distance.

---------- Post added 11-13-14 at 05:52 PM ----------

I blame Canon for this.

I blame Kodak and the APS consortium for this.


Steve

---------- Post added 11-13-14 at 05:54 PM ----------

and the quantum efficiency of the sensor by 125% will get you the same arbitrary picture.

Factoring in quantum efficiency is simply brain-dead. Quantum effects are negligible for macro systems.


Steve

---------- Post added 11-13-14 at 05:55 PM ----------

It is not confusing to me.

The whole discourse was tongue-in-cheek


Steve

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

This ultra-wide-angle lens has a field of view that corresponds roughly to that of a 13mm lens mounted on a Pentax APS-C DSLR or a 20mm lens mounted on a full-frame 35mm SLR" is right up front in this forum's description

I guess that shows the silliness. At some point you have to provide equivalence numbers for all possible systems on which the lens may be mounted and for which there is a significant user base.

Steve

---------- Post added 11-13-14 at 06:09 PM ----------

You weren't using your Kodak #3 *on* a 4x5 camera, or else you would have used equivalence.

I noted a few dozen comments back that equivalence is not a concern for large format photographers or for users of vintage gear. If I were to post something to the LF Forum using that term or the term crop-factor, they would probably ban me.

People who know their gear don't think that way.


Steve

[Lowell Goudge]

You weren't using your Kodak #3 *on* a 4x5 camera, or else you would have used equivalence.

That's why we do and should use it now. Because the economic decision made 15 years ago to get more sensors out of a waffle of silicon while keeping the same lens mounts has us here.

And it is beyond silly to just use wide, normal, or long (etc.) to describe lenses.

No , but you had 120 roll film 2 1/2 x 3 1/2 mini speed graphics, 4 x5 and 8x10 all using the same shutter/lens combos. This lasted for years. It is only now in digital we discuss equivelents. 110 cameras didn't give FF equivelents. Neither did the pentax 110 camera.

[Boris_Akunin]

I see. In the world of equivalence:

• millimeters equivalent focal length is a measure of FOV
• stops is the unit for noise

OK, now that I have swallowed that Kool Aid, I have to ask. Has anybody uploaded a spreadsheet for this? That way we can create extensive tables. Better yet, a phone app would be just the thing. The app could provide equivalence information and/or suggest a fully equivalent digital optical system (combination of sensor, focal length, taking aperture, and format).

What it would take as input (two sets, one per system):

• Average sensel size
• Total sensels*
• Sensor width
• Sensor height
• Lens focal length
• Taking aperture

equiv.xls.zip

Factoring in quantum efficiency is simply brain-dead. Quantum effects are negligible for macro systems.

Before you call anyone brain-dead: Do your [EXPLETIVE DELETED]ing research!
Quantum efficiency - Wikipedia, the free encyclopedia

[stevebrot]

Before you call anyone brain-dead: Do your [EXPLETIVE DELETED]ing research!
Quantum efficiency - Wikipedia, the free encyclopedia

It was a joke, though poorly executed. I thought you were still working with trimmed paper equivalence where a trimmed sheet of 20# paper is equivalent to a full sheet of 16#...or something like that...


Steve

---------- Post added 11-13-14 at 07:03 PM ----------

110 cameras didn't give FF equivelents. Neither did the pentax 110 camera.

And neither did the APS film cameras. It may be that it would have eventually come to that, but APS flopped as a film format.


Steve

---------- Post added 11-13-14 at 07:12 PM ----------

The whole discourse was tongue-in-cheek

I guess not...

...I am soooo confused


Steve

[kh1234567890]

What it would take as input (two sets, one per system):

• Average sensel size
• Total sensels*
• Sensor width
• Sensor height
• Lens focal length
• Taking aperture

With a few tweaks, this might even be able to determine equivalence between digital sensors and photographic film.

Don't forget flange distance ...

[carpents]

Steve,

People who know their gear use equivalence all the time.

Sean

PS - I shoot APSC, FF (135), 645 (film, not digital), and 6x7.

---------- Post added 11-14-14 at 10:14 AM ----------

No , but you had 120 roll film 2 1/2 x 3 1/2 mini speed graphics, 4 x5 and 8x10 all using the same shutter/lens combos. This lasted for years.

Ah but you did and still do talk about equivalence. You had to have some frame of reference for what a single lens was going to produce with different film behind it. That's all we are doing today, it wasn't invented by the internet.

[Boris_Akunin]

(...)it wasn't invented by the internet.

Yes but the internet DID invent (or at least enable) de-territorialized and de-temporal complaining about it...

[Lowell Goudge]

Ah but you did and still do talk about equivalence. You had to have some frame of reference for what a single lens was going to produce with different film behind it. That's all we are doing today, it wasn't invented by the internet.

i don't disagree you need to look at equivalence, what i disagree with is marking lenses with anything other than physical properties, i.e. focal length and aperture. you could perhaps add a 3rd property, Image circle diameter. since many lenses do have a limit either due to the rear barrel dimensions or the front end filter ring (or hood if integral to the lens), but lets not add a reference to a format, whether it be 35mm or what, because every sensor is slightly different any way, like the Q vs Q7, so there is no way to mark lenses with multiple equivalent focal lengths or fields of view any way.

It is up to the photographer to know his gear.

We are adding a whole level of complexity for nothing in an attempt to dumb down the issue.

[stevebrot]

Steve,

People who know their gear use equivalence all the time.

Sean

PS - I shoot APSC, FF (135), 645 (film, not digital), and 6x7.

To each his own Sean. I have three lenses for the Chamonix and know what each will do for both 4x5 and 6x7 formats without having to do a single bit of calculation. For APS-C the only time I do the arithmetic is when answering a specific question from former film users on this site.

A good analogy might be driving a Smart vs. a F-250. Yes, it is possible to calculate the required parking space size for both based on the Camry standard, but it is much easier to just simply eyeball it.

Steve