telephoto prime and normal prime

[kylebybee]

<p>I searched for the answer in other posts and couldn't find it. I'm curious to the difference between say a 50mm "telephoto" prime and a 50mm "normal" prime. A prime telephoto doesn't make sense to me. Please explain, I need educated.</p>

 

[steve_levine]

<p>Prime, simply refers to a fixed focal length lens.(a non-zoom)<br>

The definition of a telephoto lens is one where the optical center of the lens, is ahead of the front element. A 50mm telephoto lens, would likely be made for a format smaller than 35mm.</p>

[rodeo_joe1]

<p>At one time - before around 1959 - there were only "prime" lenses. A prime lens is one whose focal length is fixed, unlike a zoom lens that covers a range of focal length. Being "prime" has nothing to do with a lens being telephoto, normal or wideangle.</p>

<p>The strict meaning of the word "telephoto" is a lens where the back focus is shorter than its focal length. In fact the entire lens and camera body may be shorter than the focal length. It's a type of optical design that enables compact lenses with a long focal length. So yes, you could have a 50mm telephoto lens for a four-thirds format camera. Likewise you could have a 50mm wideangle for a medium format rollfilm camera, or a 90mm wideangle for a large format camera taking sheet film. A "standard" lens for a 5"x4" sheet film camera is around 180mm in focal length.</p>

<p>BTW there's also an optical design type called "retrofocus", where the back focus of the lens is longer than its focal length. Most wideangle and some standard lenses for SLR cameras are of this type.</p>

[Peter_in_PA]

<p>In more useful terms, a "normal" lens basically renders a scene at the same size you see it, a "wide" lens renders everything smaller, and a "telephoto" lens enlarges things. That's overly simple, but perhaps more useful than the literal definitions.</p>

<p>50mm is "normal" on a FX camera (there are some who quibble it's not, but for the most part, it is).</p>

<p>50mm is a "short telephoto" on a DX camera.</p>

<p>I think this is where your confusion is coming from.</p>

[Andrew Garrard]

Just to clarify the different answers, telephoto designs are typically used for longer-than-normal focal lengths, hence

"telephoto" is a colloquial term for "long". Just don't use it in the large format forum, because the literal definition matters

there. Peter's "same size as you see it" comment for normal lenses might need elaboration - it's about the field of view you

typically get for comfortable viewing of a reasonable print size. Stand near a poster and you'll see the field of view of a wide

lens; peer at a postage stamp and your view will match a long lens. Hth.

[JDMvW]

<ul>

<li>As my daughter said when her mother suggested that she ask Dad about "how elevators work":</li>

<li>"I don't want to know <em>that much</em> about how they work."</li>

</ul>

<p>To repeat:<br>

Common usage these days is that a "prime" lens is one with a fixed (not zoom) focal length.<br /> As for what a "telephoto" lens is, well, despite the technicalities, it is in common usage any lens that is longer in focal length than a "normal" lens. The difference these days between "telephoto" and "long" focal length is no longer critical.<br /> A "normal" lens is one that approximates the field of view of the human eye - that is to say about a 28-35mm focal length on a "crop" body camera, and about 40-50mm lenses on a so-called "full format" camera.</p>

[eric_arnold]

<p>a crop sensor body, like the d90 or other APS-C cameras, has a 1.5x multiplier on focal length. so... that means a 50mm lens has an equivalent FL of 75mm. a 50mm lens on 35mm or Full Frame sensor is a "normal" lens as, like Andrew says, it approximates the field of view to the human eye. anything longer than that is "telephoto." but on a crop sensor body, the equivalent FL is 50% longer. so your 50mm lens is still a "normal" lens, but because you're using it on a DX body, it essentially becomes a short telephoto. what that means in practical terms is that if you wanted a "normal" FL on a DX body, you'd have to use a shorter lens, such as a 28mm or 35mm. </p>

<p>btw there are lots of telephoto primes out there: 85mm, 90mm, 100mm, 105mm, 135mm, all the way up to the "exotics" -- 200mm and beyond. remember that prime just means fixed focal length, i.e., no zoom.</p>

[ariel_s1]

<p>Prime means non-zooming, so the lens is only a single focal length. Telephoto means that the lens is designed so that it isn't as long as the focal length, so a 50mm lens doesn't have to be 50mm long. Those two things have nothing to do with each other, so it is easy to see how they both exist. Just like how a car can have a V6 diesel engine. Both terms describe something different about the engine.</p>

<p>As others mention, 50mm is only a normal lens on a full frame FX camera. On a DX camera, it is a telephoto lens, and a normal lens for DX is more like 30mm or 35mm. This is because of the crop factor, so the lens has a different EQUIVALENT focal length on DX cameras. Emphasis added to make your realize that the lens doesn't actually change focal length, but mounting it on different cameras, you get a different field of view. If you don't understand any of these terms, a combination of Wikipedia and Google, plus a few creative search terms, will do wonders.</p>

[kylebybee]

<p>Thanks people, I understand prime and telephoto, just didn't understand them put together. I guess it would be like a V6 engine trying to be a V8? So if someone is trying to sell a 50mm prime telephoto, what is are they selling? Ocean front property in Arizona? :)</p>

[ariel_s1]

<p>Read my analogy again. Yours is incorrect. You are confusing "telephoto prime." The oxymoron like you describe would be if it's "prime zoom," or "telephoto retrofocal." Telephoto and prime are not mutually exclusive; both can exist. Reread all of the posts here, and then read these:<br>

http://en.wikipedia.org/wiki/Prime_lens<br>

http://en.wikipedia.org/wiki/Telephoto_lens<br>

If it still doesn't make sense, I really don't know what to tell you. A lens CAN be both a telephoto lens, which describes its design and colloquially refers to a lens being the opposite of wide angle, whereas a prime just means that the lens is ONLY 50mm, so it doesn't zoom.</p>

[john_narsuitus]

<blockquote>

<p>“I'm curious to the difference between say a 50mm "telephoto" prime and a 50mm "normal" prime. A prime telephoto doesn't make sense to me. Please explain, I need educated.”</p>

</blockquote>

 

<blockquote>

<p>“I guess it would be like a V6 engine trying to be a V8?”</p>

</blockquote>

<p>How you describe the performance of a lens can depend on the camera body used with the lens.</p>

<p>For example, a 50mm lens is a prime lens (that is, it is not a zoom lens).</p>

<p>However, if you mount the 50mm lens on a 35mm film camera, the lens will perform like a “normal” lens. Therefore, the lens could be described as a “normal prime.”</p>

<p>If you mount a 50mm lens on a medium format camera, it is still a prime lens but mounted on a medium format camera it will perform like a wide-angle lens not a normal lens. Therefore, the lens could be described as a “wide-angle prime.”</p>

<p>If you mount a 50mm lens on a micro 4/3 camera body, it is still a prime lens but mounted on this smaller format camera, it will perform like a telephoto lens not a normal lens or a wide-angle lens. Therefore, the lens could be described as a “telephoto prime.”</p>

<p>As another example, I have a 50mm f/1.4 Takumar lens that I can use on my 35mm film camera or my micro 4/3 camera. This lens is a prime lens (not a zoom lens).</p>

<p>When I mount the lens on my 35mm camera, it performs like a normal lens (not wide-angle; not telephoto) and can therefore be described as a “normal prime.”</p>

<p>When I mount the lens on my micro 4/3 camera, it performs like a telephoto lens (not a wide-angle; not a normal) and can therefore be described as a “telephoto prime.”</p>

<p>Using your engine analogy, it would be more like a V6 engine mounted in a go-cart or mounted in a panel truck. The engine is still a V6, however, in one case you could describe it as a racing engine and in the other as a gas efficient engine.</p>

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