I’m confused about telephoto lens meaning

[Prampaj]

I’ve recently discovered, that “A telephoto lens (...) is a specific type of long-focus lens in which the physical length of the lens is shorter than the focal length” (Wikipedia). Before that, I just thought telephoto means longer FL than standard.

Now, where I’m confused - let’s look at Lumix 42.5mm lens (85mm equivalent). The lens is 55mm long, so it’s longer than its focal length. Does that mean that it’s not a telephoto lens? Pretty much every reviewer, site selling them or even Panasonic calls it a telephoto lens - is that wrong?

 

[FrancoD]

Go into any photo shop and ask anyone there to show you a telephoto lens for your camera. I can guarantee that in every case you will be shown one that has a focal length greater than the one on your standard lens. (greater than 25mm in your case)

In fact, ask any pro photographer or keen amateur to show you their telephoto lens, same result....

(the 3 exceptions are all here...)

If you have the time...



take a look at those telephoto lenses, find one that it does not correspond to the way I described or the types in the manufacturers links I posted.

(ever wondered what the tele in teleconverters does mean ?)

 

[pannumon]

I was unclear. By photography I actually meant the common

Common to whom? If you are suggesting that there is a jargon common to many hobby photographers, distinct from both technically correct terminology and the terminology of the general public, I'd agree.

Yes.. In this case anyone who has an idea what a telephoto lens is but is not into the technicals.

non-technical language photographers use let's say when they are discussing in a photo exhibition.

I'd suggest the photographers talking about photography may employ a sort of jargon that differs from both the technical vocabulary and the vocabulary non-photographers might use. For instance, the non-technical photographic jargon may employ "telephoto" and "overexposed" when neither someone speaking technically nor a member of the general public would.

Yes.

I strongly support the idea that in common language the meaning of terms is how they are commonly understood,

I think that is mistaken.

Imagine a photo of an urban scene from the eastern USA. The photo shows an African-American man carrying a weapon, walking by a car near an intersection. The man is wearing a multi-coloured anorak. The car has obviously had some body parts replaced from vehicles with different paint jobs. There is a street sign on the corner and both street names are visible to the viewer. Somebody looks at the photo and says "The hood is black."

What does "hood" mean?

a) the panel over the engine compartment of the car
b) the part of the anorak that covers the wearer's head
c) the armed thug
d) the neighbourhood

The meaning of the word "hood" in this instance doesn't depend on how a listener understood it. The listener's understanding may easily be wrong. The meaning depends on what the speaker intended.

A person using a word needs to have some understanding what the word means. This is what I meant by common understanding. In specific cases what the person means is of course more important than how it is being interpret.

not how they are defined in a dictionary.

How they are defined in the dictionary is how people have used the word when transmitting, not receiving, communication. Most dictionaries are nothing more than collected and summarised documentation of past usage. The are descriptive, not prescriptive.

Yes, I was also thinking about the transmitting and receiving aspect, but being quite tired and English not being my native language, I had difficulties wording it. I also realized this is not important related to the point I was trying to make.

This means dictionaries are merely representations of the actual language, and because language evolves rather quickly, they are constantly out-of-date.

Any document that tries to describe the present is always out of date.

After accepting this there's less need to think that people are ignorant or lazy with their wording.

petrochemist didn't say that people who now use "telephoto" are necessarily lazy. He was talking about how the term first came to be used in its current jargon sense. So past people, those who developed the jargon term were either lazy or ignroant or both. Now there are some other options.

Thanks for opening that up, I did not realize that.

That said, there are times when being precise is extremely important.

And those times include technical discussions in this forum.

Totally, when the topic is lens construction.

P.S. What is the proper way to call a lens with a small F-number? A bright lens? A lens with a large aperture to focal length ratio?

 

[FrancoD]

"P.S. What is the proper way to call a lens with a small F-number? A bright lens? A lens with a large aperture to focal length ratio?'

Fast lens is probably the commonest term. Also called wide aperture lens.

 

[alfn]

Thanks for all the answers.

Looks like no one has referenced the second part yet:

Now, where I’m confused - let’s look at Lumix 42.5mm lens (85mm equivalent). The lens is 55mm long, so it’s longer than its focal length. Does that mean that it’s not a telephoto lens? Pretty much every reviewer, site selling them or even Panasonic calls it a telephoto lens - is that wrong?

One correction to that - said lens is actually 50mm long (that’s still greater than 42.5). And there’s also an even longer (~77mm body) Panasonic Leica 42.5 (also - 85mm equiv.) which is called a “telephoto lens” everywhere.

One thing I thought about: maybe it is the 85mm equivalence being longer than the lens’ body which warrants the use of “telephoto” in this case? Is there any source that even references the equivalent focal length in the telephoto definition? Or are these just long lenses that are described/reviewed/marketed with the “common” telephoto meaning?

Yes, this is a case of the lenses simply having a longer focal length than what is considered standard for the format, which is about 25mm in this case. The equivalent focal length does not come into it - at least not directly. ;-)

 

[Bob]

"Focal length" is not the same thing as the length of the lens.

Please see this:

https://ehabphotography.com/what-is-focal-length/

 

[JohnSil]

That wikipedia article cites a single, obscure book as the source of that definition, which honestly I don't agree with.

It is, however, the traditional definition.

An ordinary 150mm lens, for example, would be a standard lens for a 5x4 inch camera. You could also attach such a lens to a bellows and use it on a 35mm camera, or even an M4/3 camera.

But for use on a 35mm or smaller format, one wants the lens to be as compact as possible. The telephoto design gives you a lens that is shorter than usual for that focal length.

I personally (and many others) call "telephoto" pretty much anything over 80-85mm (FF eq).

Strictly speaking, that is incorrect. "Telephoto" is an optical design, not any particular focal length. Put a 135mm enlarger lens on a bellows, and compare that to a 135mm camera lens. You will see that the front of the enlarger lens is further away from the camera body (when both lenses are focussed on infinity).

There's short, mid, and long telephoto lenses, depending on FL, but referencing the size of the lens is just dumb, I could, in theory, make a physically long 35mm lens, would that now be a telephoto? No.

It's a pity that "Photographic Optics" by Cox is so expensive, as that book explains all these things very clearly.

Don

I'm not a lens designer but to many times people want to invent their own definitions to things which might make sense to the assigner but it can have technical people scratching their heads to understand what is being asked.

A telephoto lens, as far as I know IS a lens that contains a TELEPHOTO grouping of elements. And that grouping will make a lens shorter than the actual focal length of any given lens.

It's just my guess but telephoto groupings are not used, design-wise in short lenses. Probably just doesn't lend itself well to short designs.

BUT I will admit most of us call ANY type of lens, probably certainly longer than 15mm a telephoto regardless of design. I guess that a longer lens without a telephoto design is merely a telescope on a camera!?

John

 

[bobn2]

A telephoto lens, as far as I know IS a lens that contains a TELEPHOTO grouping of elements. And that grouping will make a lens shorter than the actual focal length of any given lens.

It's just my guess but telephoto groupings are not used, design-wise in short lenses. Probably just doesn't lend itself well to short designs.

John

It depends on where you group the groupings. Most wide lenses have a negative element or elements at the back to act as a 'field flattener'. In a strict sense a telephoto is just a negative element or group at the back, so that makes them telephotos.

For instance, Sigma 20mm f/2




The last two elements are negative. Consider them as a group, it's telephoto. The first five elements (including a doublet) are negative, making it reverse telephoto or retrofocal.



Also, these days most fast standard lenses are retrofocal or 'reverse telephoto', which is why they end up big. They have the negative group at the front, and some even have a concave front element. The telephoto configurations, both reverse and normal, help tackle some aberrations by balancing positive and negative lens power (technically the Petzval sum ).

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[jackwelch]

Probably related to my thread how they used a macro lens inverted and bellows to create a telephoto lens.

Notice the length of the physical lens is shorter than it's focal length here.

https://www.dpreview.com/forums/thread/4696172

 

[Tom Axford]

Probably related to my thread how they used a macro lens inverted and bellows to create a telephoto lens.

Notice the length of the physical lens is shorter than it's focal length here.

https://www.dpreview.com/forums/thread/4696172

That does not create a true telephoto lens in the technical sense. The relevant length is the overall length of the lens + the bellows, which will be approximately equal to the focal length when focussed on something at infinity.

If you used it in conjunction with a teleconverter, then you could create your own telephoto lens with the overall length of the lens and bellows being less than the focal length.

 

[Ellis Vener]

TLR version: think about angle of view on a format, not the size of the lens..

You are better off to think of the distinction between fisheye, wide-angle, normal, and telephoto lenses by thinking about the angle of view the lens projects to a specified size format, and not the physical dimensions of the lens.

As someone already pointed out a 150mm on a 4x5 inch /9x12cm negative is considered a normal focal length while the same lens it is undisputedly a telephoto on the 24x36cm (35mm /full-frame) format. The difference being the angle of view project d into that format.

By th same token, a 50mm lens is a normal lens on the 35mm / full-frame format but would be a very wide angle lens on the 4x5 inch / 9x12cm format.

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[FrancoD]

TLR version: think about angle of view on a format, not the size of the lens..

The problem here, and that is why the OP is confused, are those two or three people that insist the term has to do with the lens design rather than function ( narrower angle of view than standard).

No matter how many links to manufacturers one will post (links that as you mention show lenses in categories like fisheye,wide angle, standard and TELEPHOTO...) , those will be always here to confuse the rest.

 

[petrochemist]

TLR version: think about angle of view on a format, not the size of the lens..

The problem here, and that is why the OP is confused, are those two or three people that insist the term has to do with the lens design rather than function ( narrower angle of view than standard).

No matter how many links to manufacturers one will post (links that as you mention show lenses in categories like fisheye,wide angle, standard and TELEPHOTO...) , those will be always here to confuse the rest.

The problem is actually that it has two uses. The technical definition which IS based on lens design & the common usage which is function based.

The function based definition does not stand up well if using lenses on different formats.

I can take a 35mm full frame SLR lens (designed as a moderate wide angle with a retrofocus design, requiring extra rear focal distance to clear the cameras mirror in it's designed role) and mount it on one of my Pentax Q bodies with crop factors around 5.7 the function based usage now makes these 'telephotos' (~200mm equivalent) while their actual design is quite the opposite. Adapters for mounting lenses like this are readily available for under £20. The same would hold true with my 10-17mm fisheye lens, though I'm unlikely to mount that on the Q.

 

[Ellis Vener]

That’s true: there are telephoto formulas, inverse telephoto formulas (generally used for wide angle lenses, especially for SLR and DSLR cameras, and many lenses for mirrorless digital cameras), etc.

But rather than get caught in the technical weeds of lens formula designations stick to functionality.

 

[petrochemist]

That’s true: there are telephoto formulas, inverse telephoto formulas (generally used for wide angle lenses, especially for SLR and DSLR cameras, and many lenses for mirrorless digital cameras), etc.

But rather than get caught in the technical weeds of lens formula designations stick to functionality.

There are no weeds in the technical definition, but functionality is not constant for a lens as can be seen with the 35mm example I gave. It's very easy to have multiple functions if you use more than one format I currently use crops between 0.2 & 5.7 (that's pentax Q to 5x4"). Taking my 5x4 wide angle lenses (90mm focal length) & somehow sticking them on full frame would make them 'functional telephotos'. IIRC both my 5x4 wideangles are fairly symmetrical designs that are technically neither telephoto or retrofocus.

I'm not overly bothered by long focal length lenses being called telephotos even when they technically are not, but please don't try & pretend functionality for a lens is fixed. The functionality can often vary depending on what it's mounted to (and how).

It might be possible to get a reasonable approximation to a true telephoto by considering the maximum angle of view a lens can give, but that's ne easier than sticking with the existing technical definition. A lens with a 30 degree max angle of view will always give a narrower FOV than a normal lens & changing the sensor size to try to get more will only give vignetting. Narrow FOV lenses like these made for fixed body cameras are usually true telephotos to make them more compact.

 

[bobn2]

TLR version: think about angle of view on a format, not the size of the lens..

The problem here, and that is why the OP is confused, are those two or three people that insist the term has to do with the lens design rather than function ( narrower angle of view than standard).

No matter how many links to manufacturers one will post (links that as you mention show lenses in categories like fisheye,wide angle, standard and TELEPHOTO...) , those will be always here to confuse the rest.

The problem is actually that it has two uses. The technical definition which IS based on lens design & the common usage which is function based.

The function based definition does not stand up well if using lenses on different formats.

The point is in this case that the difference between the two is of in interest in a purely technical sense, but unlikely to cause any real confusion to anyone, since the internal construction of the lens, while of interest, won't make any difference to your photography or your understanding of photographic technique. If you're using a lens with a narrow angle of view it really doesn't matter at all whether you call it a 'telephoto lens' (even if that's strictly incorrect) or a 'long lens'. It matters a bit if you wrongly call it a 'zoom lens', because that has a different meaning which can confuse your choice of lenses.

I suspect there's a bit of spin going on here, the line being that since this confusion doesn't matter very much, nor do any other common confusions - even if they are of the basic terminology of photography and very much do impact practice and understanding.

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for one to have the hots for
Comrade Kim Yo Jong?