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Why buy a 50mm prime if I have got an 18-55 mm standard kit lens?

Sorry if it sounds like a dumb question. I am going to get my first DSLR in a few days. I have read a lot many experienced photographers recommending everyone to buy a 50 mm fixed focal length prime lens, besides standard lenses.

Now what I don't understand is, if I have a kit lens of 18-55 mm, why should I spend more on buying a 50mm prime, as my kit lens is capable of shooting at 50 mm, right?

As I have already said above, I have less technical info about such stuff and would love to get wise.

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Those who say this speak from only their area of photography, so I will speak from mine. The main advantage is a fixed lens is it is going to be faster, f/1.something as opposed to f/3.5 or slower. For me, I rarely shoot below f/11 in landscape imaging, so such a feature is a total waste of cash. There will be those who say the fixed is sharper, but Popular Photography tests showed the Nikkor 18-55 mm image results were A+ across the f/stop range for images up to 8x10. If you are happy with it stay with it. Depending on your interests, maybee the 55-200 is a good option, if you want an additional lens. For me, I'm having a great time playing with a huge depth of field on my 10-20mm.

Thanx, Greg, for your detailed info. I wish you can help me again on a few things:

1. How does the crop factor of a particular sensor make an effect on the size of focal length of a lens?

2. You said you rarely shoot below f/11 for landscapes, while I have read that landscape shots are better at widest aperture, i.e. f/1.something.


changing your reading source would help Nishant, "F:1. some thing or widest lens aperture" is not really suitable for landscape on the whole because of the narrow focus plane.

On landscape F11 need not be a starting point, it all depends on the 'in focus' elements you want included in your scene and the distance you are away from them.

Camera Clicker if i remember has a link to an online depth of field chart which may be helpful in explaining

how it works.

He's also good at explaining about the crop factor which you asked for, meanwhile i'll point you to a link here for reference:

Thanx, Gary,

I guess I got mixed up as the 'small F number is the wider aperture' and not the otherwise:)

& thanx for the link about crop factor.

Wishing you a very happy new year 2012.

They are likely speaking of a standard 50mm lens which can be had for relatively little money.. but that can have great benefits.(usually around $100 US - 50mm f/1.8)  A lot depends on your preferred subjects and shooting style.  

The best arguments for this lens (aside from price) are the ability to shoot in low light without having to raise the ISO and the ability to isolate a subject from the background (controlled/shallow depth of field). This type of lens is typically going to be useful for wide portraits/subjects in natural light. 

a great deal of information on depth of field can be found here: 

Have fun with your new camera!

Why purchase a 50 mm prime lens?  For the large aperture, which gives shallow depth of field and low light hand-held photography without having to increase ISO to unacceptably noisy levels.

For the same reason, I have a 24 mm, f/1.4 lens which I actually use more than the 50 mm because I find the 50 mm a little long for a crop sensor body, sometimes.

The 50 mm f/1.8 lens for either Canon or Nikon is quite inexpensive relative to the other lenses being offered.

If you are only going to shoot certain subjects or you always want a specific look that can be achieved with the kit lens, then you can get away with just that lens.  If you want to photograph more diverse subjects, you may end up with a number of lenses.  Wide aperture lenses for portraits/street photography at night; macro lenses; telephoto lenses; tilt/shift lenses if you get into a lot of architecture, it really depends what you want to shoot and which is the best tool for the circumstances.

So far, my experiments with a full frame body and crop sensor bodies have led me to the conclusion that crop factor does not affect the focal length of a lens as is so often stated by others.  Crop factor affects the width/height of the view but a 100 mm lens is always a 100 mm lens regardless of the sensor you put behind it.  That goes for any other focal length as well.  I see Papa Rotzzi provided the link to, the explanations at that link are interesting but the calculator has a problem.  The calculator suggests DOF changes if you move from a full frame body to a crop sensor body, changing from a 5D to a 7 D for instance.  My experiments indicate DOF through the same lens at the same aperture results in the same DOF regardless of sensor size, at least within reasonable limits.  This stands to reason -  if I take a photo with a full frame camera or even a medium format camera, then print the image and get out scissors to crop it, the DOF does not change because I cut the edges off.  By the same token, cutting the edges off does not make objects in the photo larger, so cropping does not make a lens magically change from 100 mm to 150 mm.  That is not the whole story though because a sensor can have more or less pixels on it and if you have two APS-C sized sensors with different numbers of pixels, the one with more pixels will give you a larger image and at 100% objects from the sensor with more pixels will appear larger.  However, the number of pixels on the sensor does not affect DOF either.   There are some more words and some photos here:

You are right about the depth of field.  If you chart the depth of field using a 50mm lens on a 1.6 crop camera, 35mm camera, Hasselblad 2 1/4 camera and 4x5 view camera DOF will be the same in each case provided the aperture number and image size remain constant.  DOF is governed by the laws of physics and optics and don't change, which we all should be glad about.

^^ that ^^

I am a relative novice at photography, but a 50mm prime is definitely the next lens I plan to purchase, I have done some research on my own, and much of what I have read echos what was said above, 50-mm prime lens are inexpensive relative to other lenses, but they are extremely versatile.  Some photographers even use it as their go-to lens, and prefer it over the 18-55 mm standard.  Below are a few links that might be of interest to you (don't worry, these are just informational link - I am not selling anything here):

One of the most compelling aspect of 50-mm prime lenses to me is that they tend to have higher quality optics than other lenses.  Because they lack auto-focus, zoom, etc, the money to manufacture them goes primarily into the glass. Intuitively, that makes sense to me.  Enjoy your nifty fifty!


I also like the prime lenses for the fact that will make you have to move to get the shots you want.  With a zoom lens you may find yourself getting the same angles because you just zoom in and out.  The aperture would be the other big thing with the prime lens, it is cheaper to buy a prime with a big aperture then get a zoom with a similar aperture.  I just purchased the 50mm Nikon 1.8F and really like it alot.  I also bought the Tamron 17-55mm 2.8F and love the versatility of that lens as well.

This is a great question. The 50mm will produce far better results than a kit lense. Kit lenses are usualy of the poorest quality and contain no glass elements. If you generally shoot party photo's or birthday shot's, they are ok. I would without question go for a nice price lens vs a kit lense every time..

Just to be clear, the 50 mm f/1.8 lens and the 18-55 mm kit lens probably have the same amount of glass in them based on their weight.  Both are actually pretty good, optically.  I still take that kit lens with me if I take a crop sensor body because it is inexpensive insurance and it weighs very little.  It is the only lens I ship in my suitcase.  The only real advantage the fixed lens has is a much larger aperture, so you can shoot at higher shutter speeds with shallow depth of field if you are so inclined.

For walking around, I like the Rebel T2i (550D) with a Sigma 18-250 mm zoom, and a Sigma 10-20 mm zoom for really wide angle shots.  Typically I also carry the 50 mm f/1.8 because it is small and light, so in the city I can forgo a tripod even at night.  To be honest, though, the T2i takes a clean enough photo at ISO 3200 and the stabilization in the Sigma 18-250 is good enough that I can shoot at night with that combination and no tripod; the 50 mm is rarely used unless I want shallow depth of field. 

I can't speak for other brands but Canon offers their EF-S 18-200 mm as a kit lens bundled with the 60D and the 5D Mk III kit lens is a 24-105 f/4 IS USM L lens which is a better lens than many prime lenses.


Until Midnight!

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