kinda newbie question about lenses

[X-SOFT]

i've seen that there are zoom lenses and prime.
as i understood, zoom are the X-Y renge.
the prime are Xmm.

what is the difference?
i mean, how much can the prime, lets say 300mm, can zoom and from what range?

is the quality different from "zoom" lenses, lets say 70-300 mm?

any other info you may add will be welcomed

[coldrain]

zoom lenses are more difficult to design, but it is hard to say anything about quality differences nowadays. That very much depends on the exact lens, some primes are rubbish, zome zooms are great.

www.photozone.de

You can read about a lot of lenses there, primes and zoom lenses.

[regP]

thanks for that link, the Technology tab has some really good & understandable information.

[DonSchap]

A PRIME lens is a fixed focal length lens. It cannot ZOOM, per se ... you put it on the front of your camera and it is what it is ... fixed at 50mm. You can have no other focal length unless you add some kind of optic to the lens to alter it.

Canon EF 50mm f/1.0 USM
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A ZOOM lens is a variable focal length between the widest setting to the longest. Let's take a 200-500mm ... as you zoom out (that means as you go toward the widest focal length available with this lens) it stops at 200mm. As you zoom in ... going to the longest focal length, it stops at 500mm.

TAMRON SP AF200-500mm f/5-6.3 Di LD
21836

As you can see ... there can be considerable differences in these different lenses.

[AlexMonro]

As others have said, a prime lens is designed for a single fixed focal length, whereas a zoom lens allows you to change the focal length between the design limits. So at first glance, why would anyone want prime lenses?

Well, a prime lens can have seveal advantages over a zoom lens set to the same focal length. It may have better image quality, although with modern lenses, some zooms are getting so good that you couldn't tell the difference. A prime lens is probably a lot lighter than a zoom lens of the same maximum focal length and aperture.

Also, you're likely to be able to find prime lenses with wider maximum apertures than most zoom lenses - there are very few zooms with max aperture wider than f/2.8, and many zooms have a smaller maximum aperture at maximum focal length than they do at shorter focsal lengths. There are quite a few prime lenses from several makers with maximum apertures of f/2 or wider - some up to f/1.2.

[r3g]

but because the focus length is fixed doesnt that mean you can only shoot a subject properly from a certain distance, and if that subject happens to move further or something the lens wont be able to capture it optimally?

[DonSchap]

but because the focus length is fixed doesnt that mean you can only shoot a subject properly from a certain distance, and if that subject happens to move further or something the lens wont be able to capture it optimally?

Nah ... it not the "focus length is fixed" ... it's the focal length (the actual distance between elements). If the subject moves ... you recenter and either get a smaller, the same or larger subject, depending on whether the subject changed the distance between you and it. There is an adjustable focusing element which adjusts either automatically or manually to sharpen the focus on your subject.

For example ... your subject (a car) is driving at 3 mph along a dirt road. You train your camera with a 50mm lens on it, center your graticule on the subject, press the shutter release, the camera autofocuses, the focus locks and the shutter trips. The image is captured.

Next ... the subject has moved closer, it looks larger in your viewfinder, you again press the shutter release, the camera refocuses, the focus locks, the shutter trips and wellah, another great shot.

Finally the car has passed and is now moving away from you. It looks smaller in the viewfinder ... you want to zoom in on it, but alas ... you have a 50mm PRIME lens on your camera. Not a ZOOM ... tough luck.

Your choices? Use MANUAL ZOOM METHODOLOGY --> Run at 5 mph and catch up to the subject ... to get that a larger image. My personal favorite ... just forget MANUAL ZOOM and snap with what you have and get what you can ... a smaller subject image in the viewfinder.
Wait until the subject returns down the dirt road, in the opposite direction.
Get rid of that darn PRIME and buy a decent zoom lens ... such as a TAMRON SP AF 28-75mm f/2.8 XR Di LD Aspherical (IF) or similar. ;)

All images were properly taken, because the camera constantly refocuses with every press of the shutter (except on a SONY A100, where the camera is constantly refocusing on the subject lined up with gracticule center with your eye close to the viewfinder).


MACRO lenses might have different issues with this. :cool:

If you want to talk about a fixed focus lens ... let's talk PINHOLE or an Instamatic prepackaged camera. LOL :D

[r3g]

OH i get it! i was under the impression that the focus was locked to a certain distance. thx for that.. i wont be using manual zoom very much

<_<
>_>

[X-SOFT]

correct me if i understood wrong DonSchap:

in example, i have 300mm prime lense, and if the car passes near me , lets say in lens perspectives- 100 mm, it can be focused, and the image will be fine.
but if the car moves beyond the limit of the prime lens, lets say 400mm, it wont focus on the max focus because the max focus is 300 mm?

[DonSchap]

correct me if i understood wrong DonSchap:

in example, i have 300mm prime lense, and if the car passes near me , lets say in lens perspectives- 100 mm, it can be focused, and the image will be fine.
but if the car moves beyond the limit of the prime lens, lets say 400mm, it wont focus on the max focus because the max focus is 300 mm?


Let me put it this way: Focal length has nothing to do with focus ... except minimum focus distance (MFD).

Every lens has physical MINIMUM distance that a subject has to be away to be able to acheive a focus. In many of the lenses ... this was roughly 5-feet. If a subject was closer than 5-feet, you could NOT adjust the focus enough to get it sharp. This distance is usually stamped somewhere on the side of the lens.

That being said ... your lens' focal length determines the "field of view" that your lens has available to it and has NOTHING to do with the distance it can see. It should be able to see into infinity ... but not beyond.

If you have a 50mm lens on the front of a camera (forget DCF for the moment), the field of view is approximately 46° and the magnification is roughly that of the human eye. Whatever fits in that 46° of view is what you get ... however big the subject is. If you walk closer to the subject, it gets larger ... walk the other way ... it tends to decrease in size. The lens still sees 46° of field, no matter which way you walk.

If you remove the 50mm lens and replace it with a 100mm lens, your field of view is reduced to 24° of field, or about half and the subject is magnified to about twice its size.

As you may suspect, by this ... if we place a 300mm lens on the front of the camera, the field of view is further cut down to 8° 15' ... which is getting tight. The image you see through this 300mm lens is also magnified six-times (6x) what it looked like when viewed through the 50mm lens.

Once again, other than the minimum focus distance that you have to keep in mind, you can focus any of these lenses on your subject and adjust for sharpness. It really doesn't matter how far beyond the MFD the subject is ... you should be able to focus on it.

Is this a clear enough explanation?

[zmikers]

With fixed lenses, it doesn't mater how far or close a subject is (unless it's too close like within a few feet of you). A fixed lens can take a picture of any subject whether it's 20 ft or 300 ft from you. Just think of it in this way. When you look at a person 20 ft away from you and then look at that person after he has walked to 300 ft away, he looks smaller at 300 ft. You can still see him but he looks smaller. The same is going to happen with a fixed lens. Your lens will "focus" on your desired subject at any distance (again as long as its not too close) Its just how large or small your subject will look in your photo that matters. Hope this helped!:D

[X-SOFT]

yeap it's clear- thanx and sorry for crazing you.

[zmikers]

yeap it's clear- thanx and sorry for crazing you.

No worries, that's why this forum is here:)

[DonSchap]

yeap it's clear- thanx and sorry for crazing you.

Just to help ... here are a couple illustrative explanations. I'm sure some others will appreciate some clarity with it, also.

Consider what you see through this lens as a 1:1 proportion (or no Apparent Magnification of subject)
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Consider what you see through this lens as a 1:2 proportion (or Apparent Magnification of subject 2 times)
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Consider what you see through this lens as a 1:6 proportion (or Apparent Magnification of subject 6 times)
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[T06]

Nice to see the colour of mud in black & white:D :D

[DonSchap]

Nice to see the colour of mud in black & white:D :D

I figure since no one else was going to offer any insight ... FIRE ONE! ;)