The fallacy of 35mm "equivalent focal lengths"

Started 5 months ago | Discussions
tcg550 Veteran Member • Posts: 8,835
Re: Here's what I do

kiwi2 wrote:

I have a camera with a 35mm lens on it...

If I want a wider field of view then I put a lens with a shorter focal length on it. Any number less than 35 will give me a wider field of view.

Or if I wanted a narrower field of view then I would put a longer focal length on it. Any number greater than 35mm will give a me narrower field of view.

Likewise do you think someone using a Fuji GFX 50 needs to know the equivalence to a FF camera or some other sized MF camera? Does their f/speed suddenly change depending what other sized sensor they compare against?

I thought I was the only one.

tcg550 Veteran Member • Posts: 8,835
Re: Here's what I do

pforsell wrote:

kiwi2 wrote:

I have a camera with a 35mm lens on it...

If I want a wider field of view then I put a lens with a shorter focal length on it. Any number less than 35 will give me a wider field of view.

Or if I wanted a narrower field of view then I would put a longer focal length on it. Any number greater than 35mm will give a me narrower field of view.

Likewise do you think someone using a Fuji GFX 50 needs to know the equivalence to a FF camera or some other sized MF camera? Does their f/speed suddenly change depending what other sized sensor they compare against?

I have three cameras with FourThirds sensor (Oly E-1, Leica DIgilux 3 and Leica D-Lux Typ 109), I also have 7 cameras with APS-C sensor and 6 cameras with a full frame sensor. I also have 50+ lenses I use with the cameras. Equivalence is a useful and an indispensable tool for me every day.

I can see that a user of a single camera and one lens feels no need for equivalence, but it doesn't mean that it still isn't very real and very important for some of us.

The fun thing about facts is that they remain true whether or not you can understand them. You should broaden your horizons and do less navel gazing. Your navel isn't the pivot of the universe.

Because you're the average DPR member.

So what do you do? Sit down with a calculator and all your lenses and camera bodies before photographing something to decide which lens and which body to use on that particular scene?

Seriously, how does it work?

bobn2
bobn2 Forum Pro • Posts: 61,707
Re: Here's what I do
2

kiwi2 wrote:

Forgottenbutnotgone wrote:

gary0319 wrote:

… we banned this equivalence crap on the MFT forum.

Funny thing you feel that way, seeing that now you have to search for it in other forums rather than whatever "crap" piques your interest.

Most people who claim to hate equivalence don't hate it enough to stay away from it, but they think it's equivalence that is stupid.

Perhaps there is a better explanation.

I have a camera with a 35mm lens on it...

If I want a wider field of view then I put a lens with a shorter focal length on it. Any number less than 35 will give me a wider field of view.

Or if I wanted a narrower field of view then I would put a longer focal length on it. Any number greater than 35mm will give a me narrower field of view.

Likewise do you think someone using a Fuji GFX 50 needs to know the equivalence to a FF camera or some other sized MF camera? Does their f/speed suddenly change depending what other sized sensor they compare against?

Someone doesn't 'need' to. Some people find it 'easier' to do so. It's much the same as there is no 'need' to have an aperture description which equalises exposure between different formats. Some people are in a conceptual box, and find it easier to stay in it. This particular conceptual box is that angles of view are described by a number, which happens to be originated in the focal length that gave that angle of view on a 35mm full-frame camera.

-- hide signature --

Ride easy, William.
Bob

bobn2
bobn2 Forum Pro • Posts: 61,707
Re: Here's what I do
5

tcg550 wrote:

pforsell wrote:

kiwi2 wrote:

I have a camera with a 35mm lens on it...

If I want a wider field of view then I put a lens with a shorter focal length on it. Any number less than 35 will give me a wider field of view.

Or if I wanted a narrower field of view then I would put a longer focal length on it. Any number greater than 35mm will give a me narrower field of view.

Likewise do you think someone using a Fuji GFX 50 needs to know the equivalence to a FF camera or some other sized MF camera? Does their f/speed suddenly change depending what other sized sensor they compare against?

I have three cameras with FourThirds sensor (Oly E-1, Leica DIgilux 3 and Leica D-Lux Typ 109), I also have 7 cameras with APS-C sensor and 6 cameras with a full frame sensor. I also have 50+ lenses I use with the cameras. Equivalence is a useful and an indispensable tool for me every day.

I can see that a user of a single camera and one lens feels no need for equivalence, but it doesn't mean that it still isn't very real and very important for some of us.

The fun thing about facts is that they remain true whether or not you can understand them. You should broaden your horizons and do less navel gazing. Your navel isn't the pivot of the universe.

Because you're the average DPR member.

So what do you do? Sit down with a calculator and all your lenses and camera bodies before photographing something to decide which lens and which body to use on that particular scene?

Seriously, how does it work?

If you need a calculator you could do with some arithmetic refresher classes.

-- hide signature --

Ride easy, William.
Bob

gardenersassistant Veteran Member • Posts: 6,111
Re: I think the average person

Aaron801 wrote:

The fact that larger formats are going to produce better quality kind of goes without saying

Now there's a can of worms!

New Day Rising
New Day Rising Senior Member • Posts: 2,536
Re: Here's what I do

kiwi2 wrote:

Forgottenbutnotgone wrote:

gary0319 wrote:

… we banned this equivalence crap on the MFT forum.

Funny thing you feel that way, seeing that now you have to search for it in other forums rather than whatever "crap" piques your interest.

Most people who claim to hate equivalence don't hate it enough to stay away from it, but they think it's equivalence that is stupid.

Perhaps there is a better explanation.

I have a camera with a 35mm lens on it...

If I want a wider field of view then I put a lens with a shorter focal length on it. Any number less than 35 will give me a wider field of view.

Or if I wanted a narrower field of view then I would put a longer focal length on it. Any number greater than 35mm will give a me narrower field of view.

Likewise do you think someone using a Fuji GFX 50 needs to know the equivalence to a FF camera or some other sized MF camera? Does their f/speed suddenly change depending what other sized sensor they compare against?

See, that's not fair. I look at that photo and really, really want that camera and lens. So gorgeous.

Then I go to your Flickr album and look at the photos you've taken with it and I want it even more.

And I want to go to New Zealand again.

Not fair.

 New Day Rising's gear list:New Day Rising's gear list
Fujifilm FinePix S1 Pro Nikon D50 Canon EOS 500D Olympus OM-D E-M5 Fujifilm X-T1 +5 more
tcg550 Veteran Member • Posts: 8,835
Re: Here's what I do
1

bobn2 wrote:

tcg550 wrote:

pforsell wrote:

kiwi2 wrote:

I have a camera with a 35mm lens on it...

If I want a wider field of view then I put a lens with a shorter focal length on it. Any number less than 35 will give me a wider field of view.

Or if I wanted a narrower field of view then I would put a longer focal length on it. Any number greater than 35mm will give a me narrower field of view.

Likewise do you think someone using a Fuji GFX 50 needs to know the equivalence to a FF camera or some other sized MF camera? Does their f/speed suddenly change depending what other sized sensor they compare against?

I have three cameras with FourThirds sensor (Oly E-1, Leica DIgilux 3 and Leica D-Lux Typ 109), I also have 7 cameras with APS-C sensor and 6 cameras with a full frame sensor. I also have 50+ lenses I use with the cameras. Equivalence is a useful and an indispensable tool for me every day.

I can see that a user of a single camera and one lens feels no need for equivalence, but it doesn't mean that it still isn't very real and very important for some of us.

The fun thing about facts is that they remain true whether or not you can understand them. You should broaden your horizons and do less navel gazing. Your navel isn't the pivot of the universe.

Because you're the average DPR member.

So what do you do? Sit down with a calculator and all your lenses and camera bodies before photographing something to decide which lens and which body to use on that particular scene?

Seriously, how does it work?

If you need a calculator you could do with some arithmetic refresher classes.

I don't need a calculator because I just put a lens on the front of my camera and go take pictures.

SirPeepsalot Contributing Member • Posts: 550
Re: Even though you're right, you're actually wrong

Lee Jay wrote:

Tony Beach wrote:

Lee Jay wrote:

When I crop, my 35mm-equivalent FOV

Even a lens used on 35mm format can have its equivalent FOV changed. The issue then becomes how much latitude you have in doing that. Compared to my S95, my 50mm f/1.8D lens just became a 50mm-150mm equivalent lens.

No way. You'll lose 8/9ths of your pixel count if you crop that much.

This is not directly relevant, in principle you can have a single-pixel image equivalent to a 50mp one, format equivalence is just not meaningful under limit conditions of which diffraction is just one.

SirPeepsalot Contributing Member • Posts: 550
Re: Even though you're right, you're actually wrong

Tony Beach wrote:

Lee Jay wrote:

Tony Beach wrote:

Lee Jay wrote:

Tony Beach wrote:

Lee Jay wrote:

When I crop, my 35mm-equivalent FOV

Even a lens used on 35mm format can have its equivalent FOV changed. The issue then becomes how much latitude you have in doing that. Compared to my S95, my 50mm f/1.8D lens just became a 50mm-150mm equivalent lens.

No way.

This is the previously shown crop from the S95 taken at 22.5mm ("105mm focal length equivalent") next to a crop from the the NIKKOR 50/1.8D using my D800; both at 100%.

You've done something wrong. You've got 4.6MP vs 12MP and they are the same size. Can't be.

You missed the relationship between pixel density and focal length. The S95 has 2.4x as much pixel density as the D800, so 22.5mm on the S95 will result in a 100% crop equal to a 100% crop from a D800 using a 54mm lens.

215mm at 16MP but with 5.6x crop on the left, 600mm at 20MP but with 1.6x crop on the right. So, that's 16MP at 1200mm equivalent vs 20MP at 960mm equivalent, and the size and resolving power are similar even if the tone and contrast are a bit different because of the different rendering engines.

It's not a bad result.

We should probably factor the age of the bison into it somehow as well.

Mngnt New Member • Posts: 1
Re: The fallacy of 35mm "equivalent focal lengths"

I can apply whatever AOV I want after the shot is taken. Resolution will be a big determinant in whether its useful or not; so no, not one pixel, but enough to match the S95.

No, you cannot.

Your examples are all on the long end, where the differences in angle are small.

Try cropping a nice wide angle shot of a face at on your full frame with one at 80mm+ on the S95.

https://upload.wikimedia.org/wikipedia/commons/d/d3/Camera_focal_length_distance_house_animation.gif

You can't get around this by cropping. In addition, the 'equivalence' you aim to define is essentially undefinable, as there are far too many other uncontrollable factors, not the least of which is glass resolving power etc. The only way to attempt it is to perform an array of tests with your specific gear in multiple settings and get close - by that point, you've long lost anyone who'll be 'fooled' by your perceived fallacy.

Mark Scott Abeln
Mark Scott Abeln Forum Pro • Posts: 13,632
Re: Equivalence does...

Great Bustard wrote:

...take them all into account:

http://www.josephjamesphotography.com/equivalence/#introduction

But why these six properties and not others, such as noise, detail, dynamic range, color, bokeh, distortion, etc., etc., etc.? The reason is that these six properties are independent of the technology. However, with proper assumptions about the technology, these other attributes can be added in to the equation, and this essay goes into great depth on those points (with special attention being paid to noise, detail, and dynamic range).

Yes, they can be added to the equation, as the OP is attempting to do (in an awkward way).  I've seen someone try to reformulate equivalence by using the thick lens equation, for example.

As with all things, the more specific one wants to be, the more factors that need to be accounted for.

And that requires special information which may be hard to come by. On the other hand, sensor size, focal length, aperture, shutter speed, and ISO are readily and nearly universally available.

 Mark Scott Abeln's gear list:Mark Scott Abeln's gear list
Nikon D200 Nikon D7000 Nikon D750 Nikon AF-S DX Nikkor 35mm F1.8G Nikon AF Nikkor 50mm f/1.8D +2 more
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