whats a prime lens and why is fixed 50mm good?

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shaggy

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i have been reading a lot lately about lens's but am getting more confused
firstly i dont understand what a prime lens is:shrug:
and also people talk about a nifty 50 and how good a fixed 50mm is but why is it better than my stock 18-55 that cam with my 400d.
i am looking for a macro lens also but can't afford £300.
 
A prime lens has a fixed focal length, ie is not a zoom.

The main virtue of primes is that they have very low f/numbers that zooms cannot get near, eg nifty-fifty is 50mm f/1.8 whereas your kit zoom is around f/5.6 at 50mm, which is over three stops difference - that's a factor of 8x.

So the prime lens will be much better in low light, and you also get much shallower depth of field at low f/numbers, which is a great creative technique. However, if you take pictures with your kit lens at f/5.6 or f/8, and compare them with the same shot taken with the fifty-fifty at the same f/number, they will be identical. Maybe the prime shot will be sharper at the edges of the picture, but that's mainly because you have the earlier version of the 18-55 lens - the newer IS version is completerly redesigned and quite a bit sharper.

The main thing about the nifty-fifty is that it can do f/1.8, and is cheap. It's good for portaits on a crop camera like your 400D, but not a lot else IMHO.
 
Lol there was just another thread about this

Primes are lenses that have a fixed focal length, they don't zoom. To normals this may seem silly but to those who know about lenses it's a well known fact that primes give better IQ, basically because its optimized for the one and only focal length that it achieves. In other words it's not like a zoom lens which is a Jack of all trades but a master of none. They're also shorter, lighter (because of less glass elements again because it doesn't zoom) and usually have crazy wide apertures. The Canon nifty fifty (f1.8 version) for instance costs under a hundred quid. To get zooms of that aperture is a) nearly impossible and b) would cost an arm and a leg.

Personally I think primes are the way to go, I will soon have two.

Also, the IQ of the 18-55 kit lens isn't bad but it's not exactly great either so to be honest most offerings from Canon or the other manufacturers can improve upon it. For the price of the Canon 50mm f/1.8 it's really a no brainer.

Hoppy's comment about it being good for portraits and not much else is interesting, personally I think if you're creative you can do anything with it. But oh well.
 
trencheel303 said:
<snip>

Hoppy's comment about it being good for portraits and not much else is interesting, personally I think if you're creative you can do anything with it. But oh well.
Click to expand...

I should have qualified that. Most people find that 50mm is no-man's land on a crop format camera. It's neither 'standard' - around 30mm, or 'wide' - say 15mm and below, or telephoto - 70mm-plus.

Easy enough to see how useful it might be to you by checking the exif data on the pics you have taken with your kit zoom, and see how many were shot at 50mm or so.
 
wow thanks guys a lot to digest there for my fragile little mind :eek:
is mine a crop camera?
what is a crop camera?
 
There was a time when you'd have struggled to buy a 35mm SLR without a 50mm standard lens. It was considered the basic essential lens. The reason mainly was that 50mm on a 35mm neg gives the closest view when looking through the viewfinder, to what you see with your own eyes in terms of relative sizes of objects and perspective, For this reason it was considered an essential lens to cut your photographic teeth on. In addition they tend to be fast lenses with a max aperture of f2.8 or often larger, so they are great for low light photography and taking shots with shallow DOF.

All these advantages still hold true on a full frame digital sensor, but the biggest bugbear when using a 50mm lens on a crop sensnr is the restricted field of view, particularly in cramped interiors. For all that, I still wouldn't want to be without a 50mm lens in my bag- my 50mm 1.2 means I can take hand held shots in virtually any light.
 
shaggy said:
wow thanks guys a lot to digest there for my fragile little mind :eek:
is mine a crop camera?
what is a crop camera?
Click to expand...

Yes, it has a smaller sensor than, for example, full-frame format film cameras from which it was derived - the sensor is 'cropped' to a smaller size.

Because the senor is smaller, it records less of the image projected by the lens, so it needs a shorter focal length to compensate, which takes in a wider field of view in the first place.

In that way, you end up with the same view in the final picture. To compare crop format and full frame, you mulitply the focal length by the crop factor to arrive at equivalents. Canon use a 1.6x crop factor, which means that a 30mm lens on your 400D has the same field of view as a 48mm lens on full-frame (30 x 1.6 = 48).

Only top-end pro spec camera use full-frame sensors these days, costing £2k plus.

Edit: crossed post with CT. Just to clarify full-frame film is known as 35mm, but that is just the width of the film, nothing to do with lenses at all.
 
Primes are for the anally fixated.................;)
 
I made a crop checker....

wtshe.jpg
 
Basically...

A prime is a fixed length lens, by asking the lens to only do one length means they can be made to do that one thing to a much higher standard. The 'nifty' fifty is classic because they've been making them for years and are relatively simple designs; ergo, cheap and good. However, the 50mm length is a little 'wrong' for a crop body camera.

A crop body sensor is a sensor that is smaller than a full frame sensor. It's all a little archaic but 'full frame' comes from the days of 35mm film cameras and the modern references to it are, to be honest, a little daft but that is what's done.

So, in the 'olden days' a 50mm lens gave you a certain level of magnification when you looked through the viewfinder, you would see the same level of magnification on a modern 'full frame' digital camera.

On a cropped sensor camera the same 50mm lens would look closer to the subject when you look through the view finder than on the full fram equivalent. The amount closer it would seem is known as the crop factor, for my Nikon I believe it's 1.6.

So 50mm on a cropped sensor would look like a 80mm (50x1.6) lens on a FF camera.

The advantage of the cropped sensor is that you don't need to buy as long (and therefore, expensive) lenses for when you want to get close to little birdies.

The disadvantages (amongst others) is that for wide angle shots you need silly wide lenses which are difficult (and expensive) to make.
 
The trouble with that is there are a large number of lenses and combinations with cameras although it would be lovely to see what each camera/lens can do.

Plus it doesn't matter what camera and lens you have it's how it's used...
 
P.S.

So why's the 50mm a little wrong on a cropped sensor? On a full frame (i.e. when they were invented) 50mm gives essentially the same field of view as a human naturally sees which makes it ideal for taking photos. When you put this on a cropped body it becomes the equivalent of 80mm (1.6x50) which is a little too long to give a nice natural field of view and a little too short to be any good at telephoto...
 
To get down to basics. The 50mm lens is good because it is easier to make. See how many elements there are in a 50mm then see how many there are on a 18mm prime lens. So much correction needed. The longer the focal length the fewer elements needed.
 
I have the "Nifty Fifty" - which is an excellent lens and very cheap - despite what a lot of people say.

To start with it's extremely sharp compared with most zoom lenses.

And if you want to try Macro photography then it's also excellent used with extension tubes.

I also like photographing kids and the low light capabilities of it mean that you can catch pics that you'ld lose with a zoom - and it's excellent for portraits.

All round a great lens and I'd say ideal for a beginner.
 
I think that if you want a fast medium telephoto on a cropped sensor then a 50mm is the only way to go. There are 60mm lens out there (giving a slightly longer 90mm equivalent) but these are typically F2.8 (i.e. believe that Tamrom or Tokina have brought out a F2 version) and F2.8 isn't really that fast on a cropped sensor - i.e the effective f stop for depth of field purposes is around F4. Consequently, if you want to have a blurred background for portraits then a 50mm 1.8 or 1.4 are the only lenses that can do that.
 
i have just bought a 50mm/F1.8 my first lens apart from the standard 18-55.

I have quickly fallen in love with it, great little lens for the price.
 
HoppyUK said:
It's good for portaits on a crop camera like your 400D, but not a lot else IMHO.
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I'd agree with this, my 50 1.4 is a fantastic lens but it's been pretty much redundant since I bought it as the Sigma 30 1.4 gets all the use. The 50 comes out when I want to do some head shots but not a lot else.
 
well
i have just ordered a 50mm from Kerso.
i will try the extension tube i have to see if i can do close ups of my watches and if not i will buy the Raynox dcr-250 as once i have done what i want to do it may well be redundant:thinking:

i am very very new and confused with all these numbers etc and believe i can learn a lot from you guys here and although im not interested in being a pro i would like to learn how to do it right
so thank you folks for all your help past present and future for sure

the problem i have at the moment is too many people in the house and cant get any room on the table to do it
 
fracster said:
Primes are for the anally fixated.................;)
Click to expand...

Like it ! Is that for pictures taken of bums or for pictures taken by bums :)

I think I fall into the later catagory Ahhhemm......:)
 
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