Prime vs Zoom - Numpty Question!

Lynton

Lynton

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Lynton (yes really!)
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Sorry, for what is probably a really really stupid question to more accomplished photographers.......

Why is a "prime" lens considered so much better (and much more expensive) than a zoom with similar max range.......... just that i am thinking if you are shooting towards the upper end of the magnification range, maybe 450 fits the frame better than 500 but if yoou had a 500 prime, (i dunno, imagine a plane coming straight at you........then possibly cannot move in relation to the object you are trying to shoot, quick enough relevant to the moving object)

However, for my K-m, a siggy 150-500 is about £600-£700, whilst a 500 prime is around £4500. Diffence between f-stops is 5-6.3,compared with 4.


Sorry for a numpty Q! :(
 
it's not a numpty question at all.

as far as i can tell Primes are built for the job and zooms are a compromise.
it does of course depend on what the job is :D
 
guess i will always have to compromise then.......... just don't get the price differential, given there has to be some clever stuff inside a zoom (i.e. moving elements/lens) which happens automatically with a right thumb push..... yet the prime also weighs twice as much........and as far as i can see is a fixed focal length.......

I am obviously missing something key here.......
 
primes usually provide better IQ and hence demand a better price. zooms are a convenience and fast optically good zooms are expensive, but will never match the quality of primes.
 
The prime lens has much fewer moving parts, so the image quality when compared to a zoom of similar length will almost always be better! The zoom will always have to compromise a little, whereas the prime does not.

You can also make lenses much faster this way, for example if you want anything faster than f/2.8, there are no zooms on the market (as far as I'm aware?). If you want f/1.8, f/1.2 etc it has to be prime, I guess because it would be too hard/expensive/complex to produce a zoom that would do it!

The faster the lens is, the larger the aperture, and hence more glass is needed. More glass = more weight, so the simpler, faster lenses weigh more!

Edit: Really have got to learn to type faster!
 
There is a stupendous difference between f/6.3 and f/4 @ 500mm, that's where the money goes.
 
joxby said:
There is a stupendous difference between f/6.3 and f/4 @ 500mm, that's where the money goes.
Click to expand...

Absolutely right. The other small detail is that the 500 4 will be superbly sharp, whereas the Sigma zoom will not. Canon doesn't make a zoom longer than the 100-400L - you just can't make them with a low f/number, or sharp enough.
 
HoppyUK said:
Absolutely right. The other small detail is that the 500 4 will be superbly sharp, whereas the Sigma zoom will not. Canon doesn't make a zoom longer than the 100-400L - you just can't make them with a low f/number, or sharp enough.
Click to expand...

what about the 300-800 f2.8 :D


edit I know its not canon
 
ok thanks but say i had a 150-500 sigma or a 500 sigma prime, just how much difference would i see in image quality given the prices (according to sigma are £900 and £4700)
 
dunno which I meant but it was massive and green and defo f2.8 - looked like a rocket launcher and had its own battery - didn't pay too much attention as its a bit beyond my budget :D
 
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