Camera Labs

I've been looking through some other forums and people seem to rave about primes. Correct me if I'm wrong, but a prime is just one fixed focal length isn't it and you can't zoom in or out at all?

Doesn't sound so great to me, what's all the fuss about? Is this something I should be thinking about in deciding what camera to buy?

Thanks,
Mark

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Mark
Nikon D300 / Sigma 10-20mm / Nikkor 17-55 f2.8 / Nikkor 18-200mm VR / Nikkor 50mm f1.8 / SB600 Speedlight
Mark Amy Photography
My Squidoo lens - Images of China

A zoom lens has to be capable of producing images at a variety of focal lengths. Sometimes this can lead to compromises in image quality. This is particularly true of lens that have a large zoom range. Take a look at the geometry test in Gordon's group test of Nikon's kit lenses. You will see that the lenses with a larger zoom range have a greater level of barrel distortion at 18mm. They also have a greater pincushion distortion at maximum zoom level.

If you were to perform a similar test on an 18mm prime or a 200mm prime you would get much better results than any of the zoom lenses. This is because the prime lenses are designed to operate at just one focal length. This means the lens designers don't have to make any compromises to get the lens to perform over a large operating range.

Another benefit of prime lenses is that they typically offer a much wider aperture than the corresponding zoom does at the same focal length. I can't remember of hand what the aperture of my 18-70mm zoom is at 500mm but I think it is around f/4. My 50mm Nikkor prime has a maximum aperture of f/1.8. That's 3 full stops of extra light I can get with my prime lens compared with my zoom at the same focal length.

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Nikon D80, Nikkor lenses: 35mm f1.8 G AF-S DX, 50mm f/1.8 AF D, 18-70mm f/3.5-4.5G ED-IF AF-S DX, 70-300mm f/4.5-5.6G IF-ED AF-S VR, SB800 flash
My photos on SmugMug

Thanks for answering Phil. If you don't mind me asking, what do you mostly use a 50mm prime for? I can understand now why people would want a prime for the wide end and the zoom end so as to avoid the things you mentioned, but why 50mm? Is it just for the wider aperture so that you can keep the ISO down in low light?

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Mark
Nikon D300 / Sigma 10-20mm / Nikkor 17-55 f2.8 / Nikkor 18-200mm VR / Nikkor 50mm f1.8 / SB600 Speedlight
Mark Amy Photography
My Squidoo lens - Images of China

I also own a 50mm prime but it's purely because of availability, it's an used lens. I have really no idea why 50mm is popular but if I try with a 35mm (about the same as 50mm on film SLR) on my DSLR with the zoom lens I must admit it's a good distance to subjects I wonder if there is some kind of rule about 50mm?

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Minolta primes: 2.8/20 2.8/24 1.7/50 2.8/135
Minolta zooms: 28-135 35-70 70-210(beercan) kit
Minolta cameras: Dynax 5D 7000
M42: Pentax Asahi S-M-C Takumar 1.4/50 and 2.8/105 Carl Zeiss Jena Flektogon 2.4/35 Industar-61L/Z Kiron 2.8/105 Macro

Hi Mark,

I also bought a "prime"-lens, but this being a 105mm macro
The motivation in my case was clear: my 18-200mm could barely touch 5:1 without visible loss in pic quality. And as I love little things the power to go to 1:1 was the reason.

As to the more normal primes, I think people go for them because of the extra light those lenses can capture for available light photos of good quality. But this is only (partially) true for people without anti-shake-lens or with a anti-shake cam-body, as no prime that I know of has built in anti-shake. So in my situation you would lose the lens-based anti-shake of the 18-200mm VR and gain 3EV light. That is almost a wash...

The other thing is the very limited depth of field. If you love it: go for a prime-lens with F/1.4-F/2.0. And the longer the focal length the smaller the d.o.f becomes. So for the fans of this effect certainly a 135m/F2.0 or 85mm/F1.4 is the dream-lens.

Others that are more into "street-photography" at available light coul dbe interested in the Sigma 30mm/F1.4, see the article here: http://www.cameralabs.com/forum/viewtopic.php?t=483

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses

Hi - the reason 50mm became a standard was because it delivered roughly the same magnification as the human eye - albeit with much smaller peripheral coverage.

Of course this 'rule' was with 50mm lenses mounted on 35mm film cameras so in the digital world only applies to full-frame bodies. If you mount a 50mm lens on a typical DSLR, its field of view effectively becomes reduced by 1.5 times, so it acts like a 75mm lens - ie a short telephoto, more suited to close-range portraiture.

To match the old 50mm coverage on a non full-frame DSLR, you'd need something closer to 35mm (or 25mm on a Four Thirds body).

One of the great things about 50mm lenses though is they're relatively easy to make, so you could get yourself an optically-fast, well-corrected, small and light lens at a low price.

It's funny though to think 20 years ago the first lens almost everyone got with their SLR was a 50mm, whereas today the first lens tends to be an 18-55mm zoom, equivalent to 27-82mm.

The zoom seems like a better choice, but the quality of these budget kit models rarely measures up. Zooms also tend to encourage people to stand still and just zoom in and out, whereas a fixed focal length encourages you to move around and explore different angles.

I reckon some of my best photos were taken with my older collection of primes on a 35mm body, but the combination of cropped DSLR sensors and the problem of dust has encouraged me to go down the zoom route today...

Gordon

Sorry, I just realised I didn't thank you all for your feedback. You gave me a lot of helpful info about primes and I get it now!

Gordon, you mentioned some of your best pics were taken with primes, where can we have a look at some of your pics????

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Mark
Nikon D300 / Sigma 10-20mm / Nikkor 17-55 f2.8 / Nikkor 18-200mm VR / Nikkor 50mm f1.8 / SB600 Speedlight
Mark Amy Photography
My Squidoo lens - Images of China

Most of my prime days were back with a film SLR, so there's no cameralabs galleries I can link to! I do have some scans though, so perhaps I should do a flickr gallery sometime...

If dust wasn't such an issue for DSLRs, I think I'd go back to primes...

It's funny that with zoom lenses I almost always just zoom them all the way in or all the way out and generally wish they got a bit closer or a bit wider. I very rarely seem to use them in the middle of their range. I wonder how many others are like that? I feel a poll coming up!

Gordon

I second that, I also find myself using the extremes the most on my kit lens an now my telezoom.
I'm new to primes but I'm really starting to like it a lot, and when you think about it it's quite versatile in the sense that you can use it both in bright and low light situations. And it's also really fun to play with, you really have to move a lot to fill the frame and you have great control of DOF.

Let's have a poll

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Minolta primes: 2.8/20 2.8/24 1.7/50 2.8/135
Minolta zooms: 28-135 35-70 70-210(beercan) kit
Minolta cameras: Dynax 5D 7000
M42: Pentax Asahi S-M-C Takumar 1.4/50 and 2.8/105 Carl Zeiss Jena Flektogon 2.4/35 Industar-61L/Z Kiron 2.8/105 Macro

Yeah, extremes! Depends on your zoom...
With a lens like the 18-200 or the super-zoom compacts you'll be really using many focal lengths.

But zooms make you lazy. If you see an object of your desire, you tend to just point, zoom and shoot. Whereas with a prime you have to go back and forth to fix the right crop and that has an influence on the perspective too.
So I've to constantly remind me when I have the 18-200mm mounted (almost all the time ) that I first fix the perspective (close=more depth, far away=flat) that I'd like and then use the zoom to do the cropping.

But if you're into reproducing a faithful real-life perspective, then you should use the 30mm prime, because when reproducing the picture at a 21" monitor or A3-printout at normal viewing distances, that should render the "viewport" almost lifelike...

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses