whats the difference between a telephoto zoom lens and a zoom lens

donkeymusic

donkeymusic

Messages
2,524
Name
Carlo
Edit My Images
Yes
Hello bascially just wondering whats the difference between a telephoto zoom lens and a zoom lens?

cheers
 
Could be the same thing :)

A zoom lens changes its focal length, eg 18-55mm. A prime lens is fixed, eg 50mm

A wide angle zoom will be shorter than 18mm or so, eg 10-20mm.

A telephoto zoom will be longer than 50mm or so, eg 55-250mm.
 
so a telephoto zoom lens just has a longer focal length than a zoom lens?
 
anything below 35mm is classed as wide angle, anything above 35mm is classed as telephoto. As its been said above, prime is a lens at a fixed focal length- zoom won't be fixed.
 
donkeymusic said:
surely a zoom lens allows that option as well?
Click to expand...

Yes, but telephoto means shorter than its focal length. Could be zoom or fixed.

In its most basic form, a 1000mm lens would be a +1 dioptre single element placed 1000mm forward of the film or sensor giving a lens 1 metre long.

That wouldn't be very practical so extra elements are introduced to shorten it (and do other clever stuff).


Steve.
 
You can't actually compare the two terms because they are referring to different things. A zoom lens, as said before, is a lens that changes its focal length. So, both the Sigma 10-20mm and the Sigma 300-800mm, are zoom lens.

Telephoto, is a term used for larger focal length lenses, that are constructed in such a way that they are physically shorter than they would be without the telephoto-design; ie, a short telephoto might be a 100mm lens, and a 500mm is a super telephoto lens, and even though the whole lens is less than 50cm, it still produces 500mm focal length, so the optical centre is not within the lens itself. Now, a telephoto zoom, is a lens with long variable focal length. So, a 300mm is a telephoto lens, and the 120-300mm is a telephoto zoom.

People seem to use the term 'zoom' in a wrong way. Those that are used to P&S cameras, when they see photos of small birds and wildlife, say "you must have used a zoom lens to take this one". So, long telephoto primes, because of their magnification of the subject or object, they are said to have a "big zoom", which is just wrong.
 
Ask a simple question LOL

What about inverted-telephoto wide-angles haha :D
 
HoppyUK said:
Ask a simple question LOL

What about inverted-telephoto wide-angles haha :D
Click to expand...

OK, what's that? Inverted telephoto sounds like it should be a lens longer than its focal length. Can't imagine why you would want one.
 
First, determine what the "standard" focal length is for a particular sensor. For most formats, this is equal to the diagonal measurement of the active part of the sensor or film. For 35mm film (36mm x 24mm) this is 43mm and for the Nikon Dx sensor (24mm x 16mm [rounded up]) this is 29mm. A lens shorter than this is generally reckoned to be a wide angle and longer than this is generally reckoned to be a telephoto (see above for a more accurate meaning of telephoto).

Now to what makes a zoom lens a zoom. Well, a zoom is a lens that has a variable focal length while a prime has a fixed focal length, so if a lens is marked 18-55 (for example), it's a zoom. If this range of focal lengths sits roughly evenly around the standard length for the senso, it's called a standard zoom - the 18-55 mentionned above fits this description well for most crop sensor bodies while 28-70 is more appropriate for FF/35mm film. If the longest length of the zoom is under (or even just over) the standard length, it'll be called a wide angle zoom (for example, the Sigma 10-20mm) while if the shortest length is over (or just under) the standard length, it'll be called a telephoto zoom (eg a 55-200mm).
 
trapper501 said:
OK, what's that? Inverted telephoto sounds like it should be a lens longer than its focal length. Can't imagine why you would want one.
Click to expand...

To improve the angle of incidence of the light falling on the sensor, some wide angle zooms are longer than their longest focal legth - look at a Sigma 10-20 or 12-24. Even some faster standard zooms are like that - measure a 24-70 f/2.8. Primes aren't exempt either - my 8mm fisheye is almost 10 times it's focal length from flange to front element!
 
Nod said:
To improve the angle of incidence of the light falling on the sensor, some wide angle zooms are longer than their longest focal legth - look at a Sigma 10-20 or 12-24. Even some faster standard zooms are like that - measure a 24-70 f/2.8. Primes aren't exempt either - my 8mm fisheye is almost 10 times it's focal length from flange to front element!
Click to expand...

Ah, so UWAs tend to be inverted telephoto?
 
Yes.

For more, look HERE.

(Inverted Telephoto lenses are also sometimes called Retrofocus.)
 
trapper501 said:
Ah, so UWAs tend to be inverted telephoto?
Click to expand...

All wide angles on a DSLR are inverted-telephoto/retrofocus designs. They have to be, to clear the mirror. The back focus on Canon is 44mm from lens flange to sensor.

Only cameras without a mirror can be true wide angles, eg Leica, all compacts, and also the new Olympus and Panasonics with interchanegable lenses. This is a big design advantage for them, smaller lenses and theoretically sharper, too, though there are some digital problems when you get very short due to the acute angle that light hits the pixels so it's not all roses (as Leica has found out to its extreme cost).
 
You must log in or register to reply here.
Back
Top