How to use Primes

M

mspics

Member
I've used mostly single lens cameras (HVX, DVX, EX-1) and I'm getting my hands on a 5d Mark II with several lenses. I'd like to do some test shooting.

I know the basics of lenses - as in, I know that a zoom well, zooms. I know that a prime doesn't. I know that a macro lens is for really close shots.

What I want to know is what's the purpose of different primes, specifically? Why would I switch from a 50mm to a 24mm prime in a shoot? Any specific purpose? I want to test that all out but it'd help to have some background.

Thanks!
 
The difference is in the angle of view. Just like zooming out on a zoom lens, you can substitute a 24mm instead of a 50mm and you'll have a much wider-angle field of view.
 
So a 200mm prime starts to get distorted on the outside by being so wide? Or am I thinking the wrong direction?
 
Way wrong direction. 200mm is a long telephoto, that magnifies the image, like a telescope. You're probably thinking of a fisheye or barrel distortion on wide-angle lenses.
 
Okay, gotcha.

So, the real differences between a zoom and a prime (aside from the ability to zoom) are f stops?
 
No, the only difference between a zoom and a prime is the ability to zoom.

It is that zoom capability that makes zoom lenses more complex to build, needing lots more glass elements, and usually dictates that they are softer and slower than a properly-engineered prime lens.
 
Barry just answered your question above - Primes are easier to make with low F-stops (or T-stops). That is probably why you noticed the differences. Also, cheaper zooms have 'moving F-stops'. That is to say, when you zoom in, the lens automatically stops down.

One other difference is that even cheap primes tend to be a little sharper than moderately priced zooms, unless compared to a top of the line zoom.


Jason
 
And the weight. A good prime can be heavy, but odds are a good zoom will outweigh a single prime lens within the range of its focal distance. The notable exceptions might be extreme telephoto lenses, like the 180 f/2.8 Zeiss Sonnar I have which makes my 28-70 f/2.8 Canon f/2.8 zoom look like a tonka toy.

And, since you mention the 5D, I am going to assume you are talking about still photo lenses, not cinema style lenses.

My advice is to get a few prime lenses across the normal shooting spectrum (18, 24, 28, 35, 50, 85, 135) and get to know them, become comfortable with the field of view, light loss, space requirements, shallow DOF, weight, and you will have a better idea of when/why/how to use them.
 
The purpose of having primes versus using a zoom lense is the quality of the lenses. Can most of us tell the difference? Probably not. Can cinematographers worth their salt tell the different...yes! But the reason of when to use them comes down to what do you want in each shot? What exposure, what depth of field, what lighting set-up are you using, what do you want to capture in each shot? What does each shot represent in your film? What shot wil come before and what shot will come after the shot you are shooting? What impact do you want that shot to have on the audience? Learn why you would use a certain focal length lens versus another lens?

Check out a few cinematography books like:
5 C's of Cinematography or ????
...and of course I hate to do it, but you forced me...I have to plug my own book "Just Shoot It!" which has a great cinematography section explaining what decisions you need to make for each and every shot.
 
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